.9. H nfi . . s A .. mflnri . ... .rtuwfinhi. Kevan; rid. a. i... guiflflf Pt.)- . | 3’- ti calf. . s5 . x . ”1.1-, .,. ; s. .y if... : . {kn . .8 3...! 31:345.... V rialeuwéza. “hm-n13 I .3 (”51‘ . 15L)??? . xfi L- .. {lag . 2 i Lag. grow, g. i .3, x7, ... 9b» “firm-”Q.“ ya- ...31 n 9m g 1%.? mm. W t 3!...» I. flirt.” . glint no... 33,. _ . i . {ant 33.5 '2 . 5.: )5}: 13.2.?! . {firs-Offiwmia‘l “I . .fifniii‘s . r.f...i...u1. €373“: Qaflikfli ‘1'" l ’4 E7 . .23, ; :1; .9. is: z. .r. .4 ~ ‘D'I, ”h. .W.‘5¢o5\(-‘a 319.3“. a 353i rat!“ blush. vi . 900‘} This is to certify that the dissertation entitled THE ENTHALPY OF FROMATION AND OUADRUOLE MOMENTS OF ACETYLENE AND DOUBLY SUBSTITUTED ACETYLENES AND ACETYLIDES, INTERMOLECULAR INTERACTIONS, AND COLLISION-INDUCED MOLECULAR FRAME DISTORTIONS presented by Dorothy J. Gearhart has been accepted towards fulfillment of the requirements for the Doctoral degree in Chemistry ZamJ/sA/mwa Major Professor’s Signature 3W4 l7, ZOflé Date MSU is an Affinnative Action/Equal Opportunity Institution LIBRARY Michigan State . University "'— -.-.-._.-.-.-.-.-.-.-.-y-.— PLACE IN RETURN BOX to remove this checkout from your record. To AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE 2/05 p:IClRC/DateDue.indd«p.1 THE ENTHALPY OF FORMATION AND QUADRUPOLE MOMENTS OF ACETYLENE AND DOUBLY SUBSTITUTED ACETYLENES AND ACETYLIDES, INTERMOLECULAR INTERACTIONS, AND COLLISION-INDUCED MOLECULAR FRAME DISTORTIONS By Dorothy J. Gearhart A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 2006 ABSTRACT TI-IE ENTHALPY OF FORMATION AND QUADRUPOLE MOMENTS OF ACETYLENE AND DOUBLY SUBSTITUTED ACETYLENES AND ACETYLIDES, INTERMOLECULAR INTERACTIONS, AND COLLISION -INDUCED MOLECULAR FRAME DISTORTION S By Dorothy J. Gearhart This thesis is broken into five chapters. The first chapter is a short summary of the calculations for this report. The second chapter concerns the calculation of CCSD(T) heats of formation at the complete basis set limit for HCCH, FCCF, ClCCCl, linear LizCz, planar LizCz, linear NazCz, and planar Na2C2. CCSD(T) optimized geometries and CCSD(T) vibrational frequencies are calculated to aid in the calculation of the heats of formation. Core-valence, spin-orbit coupling, and relativistic corrections are made to the calculated heats of formation. Calculated values are compared to experimental and theoretical values with success. The third chapter concerns the calculation of SCF, DFI‘(B3LYP), and CCSD(T) molecular quadrupole moments of HCCH, FCCF, ClCCCl, linear Li2C2 planar Li2C2, linear Na2C2, and planar N aZCZ. The linear molecules have one unique component of the quadrupole moment whereas the planar molecules have two. The quadrupole moments of HCCH, FCCF, and ClCCCl are compared to experimental and theoretical results of other researchers with success. Molecular quadrupoles are broken into partition of charges to compare algebraic charges of terminal atoms. The fourth chapter concerns the development of the third—order two-body interaction energies of molecules. The second-order two-body and the third-order two-body interaction energies are derived and developed using the Unsold Theorem. Numerical estimates are made for the two-body second- and third-order interaction energies for two— and three- body configurations as a function of internuclear separation. The fifth chapter concerns the frame distortion of CH4 in CH4+X pairs where X is N2, H2, or He. The methane molecule is approached by each molecule or atom, and the frame distortion is calculated. Additional energy calculations are made to determine energy influences in the methane pairs. To my mother, Marjory Acknowledgments I would like to take this opportunity to thank both my advisers Dr. Katherine Hunt and Dr. James Harrison for their academic support and friendly guidance during my years as a student at Michigan State University. I would also like to thank my guidance committee, Dr. Ned Jackson and Dr. Gary Blanchard for their advise and gentle incentives along my path to graduation. I would like to acknowledge the faculty and staff of Michigan State University’s Department of Chemistry. Special thanks to Lisa Dillingham and Janet Haun for their constant encouragement. Special thanks also to Paul Reed, Dr. Tom Carter, and Dr. T om Atkinson for maintaining the departmental computers and for their technical advise. I would like to thank the many friends I have gathered while attending Michigan State University, especially those of the computational chemistry research groups. Without their support, I would not have completed my studies. Finally, I would like to thank all the members of my family for their inspiration and support. TABLE OF CONTENTS List of Tables .................................................................................. x List of Figures ................................................................................. xx CHAPTER 1 INTRODUCTION ............................................................................ 1 CHAPTER 2 THE ENTHALPY OF FORMATION OF DOUBLY HALOGENATED ACETYLENES AND ALKALI ACETYLIDES ......................................... 5 2. 1 Introduction .................................................................. 6 2.1.1 Method ...................................................... 7 2. l .2 Computational Details .................................... 9 2.1.3 Corrections ................................................. 9 2.1.4 Extrapolations to CBS Limit ............................ 13 2.2 HCCH ........................................................................ 16 2.3 FCCF ......................................................................... 23 2.4 ClCCCl ....................................................................... 31 2.5 Linear LizCz .................................................................. 37 2.6 Planar LizCz .................................................................. 43 2.7 Linear Na2C2 ................................................................. 49 2.8 Planar NazCz ................................................................. 55 2.9 Discussion .................................................................... 6O 2. 10 References .................................................................... 62 CHAPTER 3 QUADRUPOLE MOMENTS OF HCCH, FCCF, CICCCI, LizCz, and NazCz ........................................................................................... 64 3. 1 Introduction ................................................................... 65 vi 3.1.1 Computational Details .................................... 67 3.1.2 Multipole Expansion ...................................... 68 3.1.3 Method ...................................................... 70 3.2 HCCH ........................................................................ 72 3.3 FCCF .......................................................................... 74 3.4 CICCCI ........................................................................ 76 3.5 Li2C2 ........................................................................... 78 3.5.1 Molecular Quadrupole Moment ......................... 78 3.5.2 Linear ....................................................... 79 3.5.3 Planar ....................................................... 80 3.6 Na2C2 ......................................................................... 82 3.6.1 Linear ....................................................... 82 3.6.2 Planar ....................................................... 83 3.7 Partition Quadrupole Moment into Point Charges ..................... 84 3.8 Discussion .................................................................... 85 3.9 References ................................................................... 95 CHAPTER 4 HIGHER-ORDER VAN DER WAALS INTERACTIONS AND NONLINEAR RESPONSE TEN SORS .................................................... 97 4. 1 Introduction ................................................................... 98 4.1.1 Interaction Energy ......................................... 98 4.1.2 Perturbation Theory ....................................... 102 4.2 Second-Order Energy Correction ......................................... 104 4.3 Third-Order Correction to the Energy .................................... 109 vii 4.3.1 Third-Order Terms in the Static Dipole oonrB .......................................... 111 4.3.2 First-Order Terms in the Dipole of Both A and B ..................................................... 114 4.3.3 First-Order Terms in the Static Dipole of System A or B, But Not Both ........................ 120 4.3.4 Zero-Order Term in the Static Dipole Moments of Systems A and B .................. 134 4.4 Numerical Estimates ........................................................ 138 4.4.1 HCl Dimer .................................................. 143 4.4. 1.1 Second-Order Two-Body Terms .............................................. 147 4.4.1.2 Third-Order Two-Body Terms .............................................. 148 4.4.2 HCl Trimer ................................................. 150 4.4.2.1 Third-Order Three-Body Terms .............................................. 153 4.4.2.2 Third-Order Two-Body Terms ............................................. 155 4.5 References ................................................................... 156 CHAPTER 5 MOLECULAR FRAME DISTORTIONS IN CH4+X PAIRS, WITH X=He, N2, OR H2 ............................................................................. 157 5.1 Introduction .................................................................. 158 5.1.1 Approaches ................................................ 159 5.1.2 Methods .................................................... 163 5.1.3 Computational Details .................................... 163 5.2 CH4-N2 ....................................................................... 163 viii 5.2.1 Linear Approach .......................................... 164 5.2.2 Perpendicular Approach ................................. 170 5.3 CH4-H2 ....................................................................... 176 5.3.1 Linear Approach .......................................... 176 5.3.2 Perpendicular Approach ................................. 178 5.4 CH4-He ....................................................................... 179 5.5 Discussion .................................................................... 180 5.6 References .................................................................... 1 82 APPENDIX A RAW DATA FOR CHAPTER 2 ............................................................. 184 APPENDIX B RAW DATA FOR CHAPTER 3 ............................................................ 209 APPENDIX C RAW DATA FOR CHAPTER 5 ........................................................... 219 ix LIST OF TABLES Table Page CHAPTER 2 2-1. Optimized Geometries of HCCH as a Function of Basis Set .................. 17 2-2. Vibrational Frequencies of HCCH ................................................. 18 2-3. Calculated Dissociation Energies and Heats of Formation for HCCH as a Function of Basis Set ............................................. 18 2-4. Heats of Formation for HCCH Extrapolated to the Complete Basis Set Limit ........................................................................ 19 2-5. Core-Valence Correction for HCCH as a Function of Basis Set ...................................................................................... 20 2-6. Core-Valence Correction for HCCH at the Complete Basis Set Limit ........................................................................................................ 20 2-7. AH; Values Corrected for Core-Valence Correlation, Spin- Orbit Coupling, and Relativistic Effects for HCCH at the Complete Basis Set Limit for each Method ...................................... 22 2-8. Comparison of Heats of Formation of HCCH ................................. 23 2-9. Optimized Geometries of FCCF as a Function of Basis Set ................... 24 2-10. Vibrational Frequencies of FCCF .................................................. 25 2-11. Calculated Dissociation Energies and Heats of Formation for FCCF as a Function of Basis Set .............................................. 25 2-12. Heats of Formation for FCCF Extrapolated to the Complete Basis Set Limit ....................................................................... 27 2-13. Core-Valence Correction for FCCF as a Function of Basis Set ...................................................................................... 28 2-14. Core-Valence Correction for FCCF at the Complete Basis Set Limit .............................................................................. 28 2-15. 2-16. 2-17. 2-18. 2-19. 2-20. 2-21. 2-22. 2-23. 2-24. 2-25. 2-26. 2-27. 2-28. 2-29. 2-30. AHf Values Corrected for Core-Valence Correlation, Spin- Orbit Coupling, and Relativistic Effects for FCCF at the Complete Basis Set Limit for each Method ...................................... 29 Comparison of Heats of Formation of FCCF ..................................... 30 Optimized Geometries of ClCCCl as a Function of Basis Set ................. 31 Vibrational Frequencies of ClCCCl ............................................... 32 Calculated Dissociation Energies and Heats of Formation for ClCCCl as a Function of Basis Set ............................................ 32 Heats of Formation for ClCCCl Extrapolated to the Complete Basis Set Limit ........................................................................ 33 Core-Valence Correction for ClCCCl as a Function of Basis Set ...................................................................................... 34 Core—Valence Correction for ClCCCl at the Complete Basis Set Limit .............................................................................. 35 AHf Values Corrected for Core-Valence Correlation, Spin- Orbit Coupling, and Relativistic Effects for ClCCCl at the Complete Basis Set Limit for each Method ...................................... 36 Comparison of Heats of Formation of ClCCCl .................................. 37 Added Diffuse Function Exponents to Create Li AUG-CC PVXZ Basis Sets ..................................................................... 38 Optimized Geometries of Linear Li2C2 as a Function of Basis Set ............................................................................... 38 Vibrational Frequencies of Linear Li2C2 .......................................... 39 Calculated Dissociation Energies and Heats of Formation for Linear Li2C2 as a Function of Basis Set ....................................... 40 Heats of Formation for Linear Li2C2 Extrapolated to the Complete Basis Set Limit ........................................................... 41 Core-Valence Correction for Linear Li2C2 as a Function of Basis Set ............................................................................... 41 xi 2-31. 2-32. 2-33. 2-34. 2-35. 2-36. 2—37. 2-38. 2-39. 240. 2-41. 2—42. 2-43. 2-44. 2-45. 2-46. Core-Valence Correction for Linear Li2C2 at the Complete Basis Set Limit ....................................................................... 42 AHf Values Corrected for Core-Valence Correlation, Spin- Orbit Coupling, and Relativistic Effects for Linear Li2C2 at the Complete Basis Set Limit for each Method ....................................... 42 Comparison of Heats of Formation of Linear Li2C2 ............................. 43 Optimized Geometries of Planar Li2C2 as a Function of Basis Set ............................................................................... 44 Vibrational Frequencies of Planar Li2C2 .......................................... 44 Calculated Dissociation Energies and Heats of Formation for Planar Li2C2 as a Function of Basis Set ....................................... 46 Heats of Formation for Planar Li2C2 Extrapolated to the Complete Basis Set Limit ........................................................... 46 Core-Valence Correction for Planar Li2C2 as a Function of Basis Set ............................................................................... 47 Core-Valence Correction for Planar Li2C2 at the Complete Basis Set Limit ........................................................................ 47 AH; Values Corrected for Core-Valence Correlation, Spin- Orbit Coupling, and Relativistic Effects for Planar Li2C2 at the Complete Basis Set Limit for each Method ...................................... 48 Comparison of Heats of Formation of Planar Li2C2 ............................. 48 Energy Difference Between Linear and Planar Li2C2 ........................... 49 Added Diffuse Function Exponents to Create Na AUG-CC PVXZ Basis Sets ..................................................................... 49 Optimized Geometries of Linear Na2C2 as a Function of Basis Set .............................................................................. 50 Vibrational Frequencies of Linear Na 2C2 ........................................ 50 Calculated Dissociation Energies and Heats of Formation for Linear Na 2C2 as a Function of Basis Set ..................................... 52 xii 2-47. Heats of Formation for Linear Na 2C2 Extrapolated to the Complete Basis Set Limit ........................................................... 52 2—48. Core-Valence Correction for Linear Na 2C2 as a Function of Basis Set ............................................................................... 53 2-49. Core-Valence Correction for Linear Na 2C2 at the Complete Basis Set Limit ........................................................................ 53 2-50. AHf Values Corrected for Core-Valence Correlation, Spin- Orbit Coupling, and Relativistic Effects for Linear Na 2C2 at the Complete Basis Set Limit for each Method ....................................... 54 2-51. Comparison of Heats of Formation of Linear Na 2C2 ........................... 54 2-52. Optimized Geometries of Planar Na 2C2 as a Function of Basis Set ............................................................................... 55 2-53. Vibrational Frequencies of Planar Na 2C2 ......................................... 56 2-54. Calculated Dissociation Energies and Heats of Formation for Planar Na2C2 as a Function of Basis Set ...................................... 57 2-55. Heats of Formation for Planar N a2C2 Extrapolated to the Complete Basis Set Limit ........................................................... 57 2-56. Core—Valence Correction for Planar Na2C2 as a Function of Basis Set ............... ' ................................................................ 58 2-57. Core-Valence Correction for Planar Na2C2 at the Complete Basis Set Limit ........................................................................ 58 2-58. AHf Values Corrected for Core-Valence Correlation, Spin- Orbit Coupling, and Relativistic Effects for Planar Na2C2 at the Complete Basis Set Limit for each Method ....................................... 59 2-59. Comparison of Heats of Formation of Planar Na2C2 ............................ 59 2-60. Energy Difference Between Linear and Planar Na2C2 .......................... 60 2-61. Dissociation Energies and Heats of Atomization for All Molecules .......... 61 CHAPTER 3 3-1. Quadrupole Moment, 9 (eafi ),of HCCH ......................................... 73 xiii 3-2. HCCH Quadrupole Moments ...................................................... 74 3-3. Quadrupole Moment, 9 (e33 ),of FCCF .......................................... 75 3-4. FCCF Quadrupole Moments ........................................................ 76 3-5. Quadrupole Moment, (9 (eafi ),of CICCCI ........................................ 77 3-6. ClCCCl Quadrupole Moments ...................................................... 78 3-7. Quadrupole Moment, (9 (ea?) ),of Linear Li2C2 .................................. 79 3-8. Quadrupole Moment, (922 (eafi ),of Planar Li2C2 ................................. 80 3-9. Quadrupole Moment, (9,, (eafi ),of Planar Li2C2 ................................. 81 3-10. Quadrupole Moment, (9 (e33 ),cf Linear Na2C2 ................................. 82 3-11. Quadrupole Moment, 922 (ea?) ),of Planar N a2C2 ................................ 83 3-12. Quadrupole Moment, (9,, (ea?) ),of Planar Na2C2 ............................... 84 3-13. Linear Molecules (XCCX) Partitioned into Point Charges ..................... 86 3-14. Planar Molecules (X2C2) Partitioned into Point Charges ....................... 93 CHAPTER 4 4-1. Values for Use in Approximations ................................................ 149 CHAPTER 5 5-1. CH4-N2 Linear Approach ............................................................ 169 5-2. Dipole and Potential from Molecular Distortion in the CH4-N2 Linear Approach ............................................................ 170 5-3. CH4-N2 Perpendicular Approach ................................................... 175 5-4. Dipole and Potential from Molecular Distortion in the CPL-N2 Perpendicular Approach ................................................... 176 xiv 5-5. CH4-H2 Linear Approach ............................................................ 177 5-6. Dipole and Potential from Molecular Distortion in CH4-H2 Linear Approach ............................................................ 177 5-7. CH4-H2 Perpendicular Approach ................................................... 178 5-8. Dipole and Potential from Molecular distortion in the CH4-H2 Perpendicular Approach ................................................... 178 5-9. CH4-He Approach .................................................................... 179 5-10. Dipole and Potential from Molecular Distortion in CI-I4-He Approach .................................................................... 180 APPENDIX A A-l. Heats of Formation of Atoms and Molecules ....................................... 185 A-2. HCCH Energies, De, and Do Values ................................................. 186 A-3. Extrapolated HCCH Energies, De, Do Values ...................................... 187 A-4. Core-Valence and Extrapolated Core-Valence HCCH Energies, De, Do, Values with Unfrozen Core ...................................................... 188 A-5. Core-Valence and Extrapolated Core-Valence HCCH Energies, De, Do, Values with Frozen Core ......................................................... 188 A-6. Optimized Geometries for FCCF ............................................ , .......... 189 A-7. FCCF Energies, De, and Do Values .................................................. 189 A-8. Extrapolated FCCF Energies, De, and Do Values .................................. 190 A-9. Core-Valence and Extrapolated Core-Valence FCCF Energies, De, Do, Values with Unfrozen Core ...................................................... 191 A-10. Core-Valence and Extrapolated Core-Valence FCCF Energies, De, Do, Values with Frozen Core ....................................................... 192 A-1 1. Optimized Geometries for ClCCCl ................................................. 193 A-12. ClCCCl Energies, De, and Do Values .............................................. 193 A-l3. Extrapolated ClCCCl Energies, De, and Do Values .............................. 194 XV A-l4. Core-Valence and Extrapolated Core-Valence ClCCCl Energies, De, Do, Values with Unfrozen Core .................................................... 195 A-15. Core-Valence and Extrapolated Core-Valence ClCCCl Energies, De, Do, Values with Frozen Core ...................................................... 195 A-l6. Optimized Geometries for Linear Li2C2 .......................................................... 196 A-l7. Extrapolated Geometries of Linear Li2C2 ........................................................ 196 A-18. Linear Li2C2 Energies, De, and Do Values ......................................... 197 A-19. Extrapolated Linear Li2C2 Energies, De, and Do Values ........................ 197 A-20. Core-Valence and Extrapolated Core-Valence Linear Li2C2 Energies, De, Do, Values with Unfrozen Core ............................................... 198 A-21. Core-Valence and Extrapolated Core-Valence Linear Li2C2 Energies, De, Do, Values with Frozen Core .................................................. 198 A-22. Optimized Geometries for Planar Li 2C2 ............................................ 199 A-23. Extrapolated Geometries of Planar Li2C2 .......................................... 199 A—24. Planar Li2C2 Energies, De, and Do Values ......................................... 200 A-25. Extrapolated Planar Li2C2 Energies, De, and Do Values ........................ 200 A-26. Core-Valence and Extrapolated Core-Valence Planar Li2C2 Energies, De, Do, Values with Unfrozen Core ............................................... 201 A-27. Core-Valence and Extrapolated Core-Valence Planar Li2C2 Energies, De, Do, Values with Frozen Core .................................................. 201 A-28. Optimized Geometries for Linear Na 2C2 .......................................... 202 A-29. Extrapolated Geometries of Linear Na 2C2 ......................................... 202 A-30. Linear Na 2C2 Energies, De, and Do Values ....................................... 203 A-31. Extrapolated Linear Na 2C2 Energies, De, and Do Values ....................... 203 A-32. Core-Valence and Extrapolated Core-Valence Linear Na 2C2 Energies, De, Do, Values with Unfrozen Core ............................................... 204 xvi A-33. Core-Valence and Extrapolated Core-Valence Linear Na 2C2 Energies, De, Dc, Values with Frozen Core .................................................. 205 A-34. Optimized Geometries for Planar N a2C2 ........................................... 206 A-35. Extrapolated Geometries of Planar N a2C2 .......................................... 206 A-36. Planar N a2C2 Energies, De, and Do Values ........................................ 207 A-37. Extrapolated Planar Na2C2 Energies, De, and Do Values ........................ 207 A—38. Core—Valence and Extrapolated Core-Valence Planar Na2C2 Energies, De, Do, Values with Unfrozen Core ............................................... 208 A-39. Core-Valence and Extrapolated Core-Valence Planar N a2C2 Energies, De, Do, Values with Frozen Core .................................................. 208 APPENDIX B B-l. SCF Quadrupoles of HCCH ........................................................... 210 8—2. CCSD(T) Quadrupoles of HCCH ..................................................... 210 B-3. DFT(B3LYP) Quadrupoles of HCCH ................................................ 210 8-4. Quadrupoles of FCCF .................................................................. 212 8-5. Quadrupoles of ClCCCl ................................................................ 212 B6 Quadrupoles of Linear Li2C2 .......................................................... 213 B—7. 6),; Component of Planar Li2C2 Quadrupole ........................................ 214 B-8. (9,, Component of Planar Li2C2 Quadrupole ........................................ 215 B—9. Quadrupoles of Linear Na2C2 ......................................................... 216 8-10. (92, Component of Planar N a2C2 Quadrupole ...................................... 217 B-1 1. (9,, Component of Planar N a2C2 Quadrupole ...................................... 218 APPENDIX C C-l. CH4-N 2 Perpendicular Approach using aug-cc-pvtz basis set for 5.0 and 4.0 Angstrom Separations ................................................. 220 xvii C-2. CH4-N2 Perpendicular Approach using aug-cc-pvtz basis set for 3.5 and 3.25 Angstrom Separations ................................................ 220 C-3. CPL-N2 Perpendicular Approach using aug—cc-pvtz basis set for 3.0 Angstrom Separations ........................................................... 221 C-4. CH4-N2 Linear Approach using aug-cc-pvtz basis set for 5.0 and 4.0 Angstrom Separations ........................................................... 221 C-5. CHu-N2 Linear Approach using aug-cc-pvtz basis set for 3.5 and 3.25 Angstrom Separations ......................................................... 222 C-6. CH4-N2 Linear Approach using aug-cc-pvtz basis set for 3.0 Angstrom Separations ............................................................... 223 C-7. CH4-H2 Perpendicular Approach using aug-cc-pvtz basis set for 4.0 and 3.5 Angstrom Separations ................................................. 223 C-8. CH4-H2 Perpendicular Approach using aug-cc-pvtz basis set for 3.25 and 3.0 Angstrom Separations ................................................ 224 C-9. CH4-H2 Perpendicular Approach using aug-cc-pvtz basis set for 2.75 and 2.5 Angstrom Separations ................................................ 224 010. CH4-H2 Perpendicular Approach using aug—cc-pvtz basis set for 2.25 Angstrom Separations ......................................................... 225 C-1 1. CH4-H2 Linear Approach using aug-cc—pvtz basis set for 4.0 and 3.5 Angstrom Separations ........................................................... 225 C-l2. CH4-H2 Linear Approach using aug-cc-pvtz basis set for 3.25 and 3.0 Angstrom Separations ........................................................... 226 C-13. CH4-H2 Linear Approach using aug-cc-pvtz basis set for 2.75 and 2.5 Angstrom Separations ........................................................... 226 014. CH4-H2 Linear Approach using aug-cc-pvtz basis set for 2.25 Angstrom Separations ............................................................... 227 015. CH4-He Approach using aug-cc-pvtz basis set for 4.0 and 3.5 Angstrom Separations ............................................................... 227 016. CH4- He Approach using aug-cc-pvtz basis set for 3.25 and 3.0 Angstrom Separations ............................................................... 228 xviii C-17. CH4-He Approach using aug-cc-pvtz basis set for 2.75 and 2.5 Angstrom Separations ............................................................... 228 C-18. CPL-He Approach using aug-cc-pvtz basis set for 2.25 Angstrom Separations ............................................................................ 229 xix LIST OF FIGURES Figure Page CHAPTER 2 2-1. Vibrational Modes of Linear Li2C2 ................................................ 39 2-2. Vibrational Modes of Planar Li2C2 ................................................ 45 2-3. Vibrational Modes of Linear Na2C2 ................................................ 51 2-4. Vibrational Modes of Planar N a2C2 ................................................ 56 CHAPTER 3 3-1. Diagram of Point Charge not located at Origin .................................. 68 3-2. HCCH Density Difference Plot .................................................... 87 3-3. FCCF Density Difference Plot ...................................................... 88 3-4. CICCCI Density Difference Plot ................................................... 90 3-5. Linear LiCCLi Density Difference Plot ........................................... 92 3-6. Planar Li2C2 Density Difference Plot ............................................. 94 CHAPTER 4 4-1. Representation of the 3-0 term ...................................................... 114 4-2. Representation of the 1-1 terms .................................................... 120 4-3. Representation of the 1-0 term in the Third-Order Energy. . . . . . . . . . . . . . .........134 4-4. Representation of the Third—Order Pure Dispersion Energy .................... 137 4-5. First Configuration of the HCI Dimer ............................................. 144 4-6. Second Configuration of the HCl Dimer .......................................... 144 4-7. Third Configuration of the HCl Dimer ............................................ 146 4-8. First Trimer Configuration .......................................................... 150 XX 4-9. Second T rimer Confi guration ...................................................... 150 4-10. Third Trimer Configuration (the triangle formation) ........................... 151 CHAPTER 5 5-1. Reflection Planes in CH4 ............................................................ 160 5-2. Diagram of Linear Approach, Viewed Locking Down on Plane A ........... 161 5-3. Diagram of Linear Approach, Viewed Looking Down on Plane B ............ 161 5-4. Diagram of Perpendicular Approach, Viewed Looking Down on Plane A... 162 5-5. Diagram of Perpendicular Approach, Viewed Looking Down on Plane B... 162 5-6. Energy as a Function of Bond Angle at 5.0 A Separation for Methane-Nitrogen: Linear Approach .......................................... 165 5-7. Energy as a Function of Bond Angle at 4.0 A Separation for Methane-Nitrogen: Linear Approach .......................................... 166 5-8. Energy as a Function of Bond Angle at 3.5 A Separation for Methane-Nitrogen: Linear Approach .......................................... 167 59 Energy as a Function of Bond Angle at 3.25 A Separation for Methane-Nitrogen: Linear Approach .......................................... 168 5-10. Energy as a Function of Bond Angle at 3.0 A Separation for Methane-Nitrogen: Linear Approach .......................................... 169 5-11. Energy as a Function of Bond Angle at 5.0 A Separation for Methane-Nitrogen: Perpendicular Approach ................................. 171 5-12. Energy as a Function of Bond Angle at 4.0 A Separation for Methane-Nitrogen: Perpendicular Approach ................................. 172 5-13. Energy as a Function of Bond Angle at 3.5 A Separation for Methane-Nitrogen: Perpendicular Approach ................................. 173 5-14. Energy as a Function of Bond Angle at 3.25 A Separation for Methane-Nitrogen: Perpendicular Approach ................................. 174 5-15. Energy as a Function of Bond Angle at 3.0 A Separation for Methane-Nitrogen: Perpendicular Approach ................................. 175 xxi CHAPTER 1 INTRODUCTION 1.1 Introduction The purpose of Chapter 2 of this thesis is to report the most accurate heats of formation data for dilithium and disodium acetylide. Accurate enthalpies of formation values are important for thermodynamic study of molecules. In general, chemical theory can calculate the heat of formation to within 2 kcal/mol of experimentally determined heats of formation. In order to calculate the heat of formation, accurate vibrational frequencies are needed. For the dilithium and disodium acetylides, this information is not available. Optimized geometries, vibrational frequencies and the heats of formation are calculated. The HCCH, FCCF, CICCCI geometries, vibrational frequencies, and heats of formation are calculated as reference points to check accuracy. The optimized geometries and heats of formation for all molecules discussed are extrapolated to the complete basis set limit using four extrapolation equations. A comparison of the results for each extrapolation method was made. Core-valence, spin-orbit coupling, and relativistic corrections are added to attempt to determine the most accurate heats of formation. In Chapter 3, the quadrupole moments of HCCH, FCCF, CICCCI, Li2C2, and Na2C2 are calculated. For these molecules, the quadrupole moment is the first non- vanishing multipole moment, and as the dipole moment provides information about the electron distribution in a dipolar molecule, the quadrupole moment provides information about the electron distribution for these doubly substituted acetylenes and acetylides. For HCCH, FCCF, CICCCI, and the linear acetylides, there is only one unique component for the quadrupole moment, but for the planar acetylides, the quadrupole moment has two unique components. After calculating the quadrupole moment for each molecule, the quadrupole moment is broken down into its various components. Discussions are made concerning inferences that can be made between the quadrupole moment components and the electron distribution in the molecule. The quadrupoles are then partitioned into algebraic charges and compared in an attempt to draw conclusions about the nature of the bonding in the disubstituted acetylides. The shortcomings of the theory are discussed. Chapter 4 and Chapter 5 concern van der Waals forces and the influences of those interactions. Van der Waals forces explain the boiling points of noble gases and collision induced absorption of compressed gases. In Chapter 4, the two body second order and two body third order interaction energies are derived. The interaction energies are broken into categories and physical explanations for each type of interaction are given. Using the Unsold’s Theorem, numerical estimates are made including estimates for newly developed terms in the third-order interaction energy. Using HCI as an example, the two body second- and third-order interaction energies are compared for two configurations. The three and two body third-order interaction energies are compared for three HCl configurations. Finally, Chapter 5 deals with the effects of two body interactions. CH4+X compressed gases, where X=N2, H2, or He, are studied due to their intriguing behavior when examined using IR. Each pair exhibits unusual absorption in the far- infrared region of their spectrum. There is belief that some of this absorption is due to induced dipoles from distortion of the molecular frame of CH4. This distortion is due to the collision of CH4 with N2, H2, or He. Two collision paths are defined and calculations to determine the distortion of the methane molecule caused by these approaching molecules are made. Electrostatic interactions within the CH4+X pairs are discussed. In addition, the dipole moment and potential difference due to distortion are calculated as are the interaction energies within the pairs. Chapter 2 The Enthalpy of Formation of Doubly Halogenated Acetylenes and Alkali Acetylides 2.1 Introduction Gas phase Li2C2 and Na2C2 are intriguing compounds for which there is no experimental thermochemical or geometric data available and little to no theoretical information available. During an investigation into the electronic properties of these doubly alkalized acetylides, the two geometry configurations of these acetylides were shown to be viable minima on the potential energy surface]. Although a linear configuration is the form of acetylene and many substituted acetylenes, the lowest energy arrangement for Li2C2 and N a2C2 is a doubly bridged molecule. In this report, the geometries for Li2C2 and Na2C2 at both the linear and doubly bridged configurations are tabulated, and the respective enthalpy of formation for each species is calculated. Because there is a lack of experimental and theoretical data available for these two metal acetylides, we calibrated our calculations by determining the geometry and the enthalpy of forrnaticn for acetylenez‘3 and the two doubly substituted halogenated acetylenes, ClCCCl3 and FCCF“, and then compared those results to those found by previous researchers. There have been several experimental studies for HCCH, CICCCI, and FCCF. Acetylene, due to its commonality, is well documented theoretically and experimentally, and its properties have been used in comparative studies to determine the accuracy of theoretical methods. CICCCI and FCCF, on the other hand, are very reactive molecules making such extensive study harder. Although the equilibrium geometry and the enthalpy of formation for CICCCl are known, the experimental heat of formation for dichloroethyne has error bars which are approximately a fifth of the experimental value. Due to its wider range of experimental values, FCCF is even more intriguing. There are two experimental heats of formation available, which describe the enthalpy of formation of difluoroacetylene as both an endothermic or exothermic process. 2.1.1 Method For the general reaction, Y2X2(g) —-> 2X(g) + 2Y(g) , the first step taken in determining the enthalpy of formation for Y2X2 was to determine the energy change after the reaction moves from reactant to products. The total energy of the reactants and products are a sum of the electronic energies, as well as translational, vibrational, and rotational contributions. Since the products are atoms, only the reactant has rotational and vibrational contributions. Assuming that Y2X2 is linear, as in the case of HCCH, FCCF, CICCCI, linear Li 2C2, and linear Na2C2, the reactant only has two rotational degrees of freedom. Eproducts=2Ex+ 333 +2Ey+ 313$ . (1) translations translations K \ 3n-5 3 hv- hv' Emma“, =EYXXY+ —RT + RT +NAZ —J-+ J .(2) 2 “'7‘ _ 2 hv- HE rotations J ex J _ translations . \ "bT 1. vibragns In the case of doubly bridged Li2C2 and Na2C2, the reactant has three rotational degrees of freedom. f \ 3n-6 3 3 hv- hv- Ereactant = EYZXZ + ERT + ERT +NA 2 21+ th .(3) U ‘V‘.’ W" i exp[—J]—l anslatrons rotations k T . K b 2. vibrations The difference in the initial and final states gives the energy change, and Equation (5) shows the generic relation between the energy change and the enthalpy of atomization. AB = Eproducts ‘ Ereactants' (4) AH am, = AE + AnRT . (5) Shown in Equation (6) is the relation between the energy change and the enthalpy of atomization for the reactions described in this manuscript. AHaltm = AE + 3RT . (6) In any reaction, the enthalpy of reaction is related to the heat of formation of the products and reactants through Equation (7). AHrxn = Z AHf (products)- 2 AHf (reactants). (7) For the specific case of Y2X2 , the heat of reaction is described by Equation (8). Ana", = 2m, (x(g))+ 2qu (Y(g))— AHf (Y2x2(g)). (8) Equation (8) can be rearranged to express the enthalpy of formation of Y2X2 as a sum of the heats of formation of the constituent atoms and the enthalpy of atomization. AHf (Y2x2(g))= 2AHf (x(g))+ 2AHf (Y(g))— AHatm . (9) The enthalpies of formation for the atoms are nonzero because the atoms are not the standard state of the elements. A table of the standard enthalpy of formation for the atoms is in the appendix. Using experimental heats of formation for the atoms and the calculated heat of atomization, the enthalpy of formation for the reactant, Y2X2 , was determined. 2.1.2 Computational Details Using the MOLPRO 20005 and Gaussian 986 software packages, we calculated geometry optimization, fundamental vibrational frequency, and single point energy. Dunning ccrvxz. AUG-CC-PVXZ, and D-AUG-CC-PVXZ basis sets7'8‘9‘m were used, as well as augmented basis sets which were constructed on site by augmenting the Li and Na Dunning CC-PVXZ basis sets with even-tempered diffuse functions. X is the cardinal index of the basis set. Therefore, the CC-PVXZ basis set where X equals 2 refers to the CC-PVDZ basis set. Since the core-valence correlation was not captured using the suite of Dunning polarized valence basis sets, Dunning’s CC—PCVXZ and AUG-CC-PVXZ basis sets were used to determine core-valence correlation corrections. The standard enthalpy of formation and optimized geometries for each of the aforementioned molecules were calculated as a function of basis set at the CCSD(T) level and then extrapolated to the complete basis set limit. After extrapolation, the thermochemical values were corrected for spin-orbit coupling, core-valence correlation, and mass dependent relativistic effects. The atomic spin-orbit effects were computed using atomic energy levels tabulated by Charlotte Moore”. Core-valence correlation was determined as a function of basis set from CCSD(T) single point energy calculations and extrapolated to the basis set limit. The mass dependent relativistic energy corrections were determined from a Hartree-Fock calculation using the Cowan-Griffin approach from expectation values of the mass-velocity and Darwin terms using a CC-PVDZ basis set. 2.1.3 Corrections The non-relativistic Hamiltonian commonly used in quantum calculations only accounts for the kinetic energy of the electrons and the electrostatic potential energy due to nuclear-nuclear, nuclear-electron, and electron-electron interactions. Since there is no consideration of spin or relativistic effects, any consideration of the mass-velocity correction, Darwin term, or spin-orbit coupling corrections is considered relativistic. The only non-relativistic correction made to the enthalpy of formation in this manuscript was the addition of core-valence correlation. The dissociation energy (De) for these acetylene and doubly substituted acetylene molecules was calculated from CCSD(T) energy calculations in which the non-valence shell electrons were frozen. In addition to this inability of the core electrons to be excited to unoccupied molecular orbitals, the Dunning basis sets used were not designed to pick up core-valence correlation. To include core-valence correlation absent from the CCSD(T) single point energy calculations, a core-valence correction was determined using the Dunning CC-PCVXZ and AUG-CC-PCVXZ basis sets. These polarized core- valence basis sets are different from polarized valence basis sets because of additional gaussian functions, which have been added to the polarized valence basis sets. These added gaussian functions have exponents, which place them in the electron shell directly below the valence shell. Because these new basis functions are located in the “core” of the atom or molecule, additional information concerning the core-valence interactions can be extracted. The additional functions were added to the carbon, lithium, and fluorine ls orbital and the sodium and chlorine 2s and 2p orbitals. We calculated the D2 for each molecule twice using the polarized core-valence basis sets. The first calculation was done using a set of CCSD(T) single point energy calculations where the atomic and molecular electronic cores were frozen, and the second was made from a set of CCSD(T) calculations in which the core electrons were unfrozen. 10 The energy difference between the two dissociation energies is representative of the core- valence correlation, and this energy difference is considered the core—valence correction. Often with lighter atoms and molecules during quantum calculations, the relativistic effects within the atom or molecule are ignored. In general, this approximation is valid because for light species the energy differences for relativistic effects between energy states or geometric orientations are negligible. Even though this approximation tends to diminish the importance of the relativistic effects, the contribution of relativistic effects to the total energy of an atom or molecule is significant. Therefore, we made two corrections. The first correction is for the change in the mass of the electrons and the resulting change in the velocity due to the mass change. The second correction is for the “Zitterbewegung” or “trembling” of the electrons, which is the relativistic smearing of an electron’s charge. In the Dirac theory, this correction is often referred to as the Darwin term. The Darwin term correction can be thought of as a correction for the “size” of the electrons. As stated above, the mass-velocity and the Darwin term relativistic energy contributions were determined using a Hartree-Fock wavefunction consisting of CC- PVDZ basis functions. We added the mass—velocity and Darwin term operators to the non-relativistic Hamiltonian as a perturbation, and the first-order energy correction was computed. Having determined these corrections for the atoms and the molecule of interest, a correction to the De was calculated producing the mass-dependent relativistic energy correction. The remaining relativistic energy correction is spin-orbit coupling. Resulting from the interaction between the magnetic moments created by an electron’s spin and 11 orbital angular momentum, this splitting in the energy levels is generally referred to as the fine structure, and it is the cause for the unique optical spectra of atoms. A carbon atom in its ground electronic state is 3P. Due to the spin-orbit interaction, this 3P state divides into sets of one 3 P0 state, three 3 PI states, and five 3P2 states. For halogens such as chlorine and fluorine, the ground state is a 2 P state, which divides into four 2Py and 2 two 2 P}, states. For hydrogen, lithium, sodium, acetylene, and the doubly substituted 2 acetylene molecules, the ground state does not split. The multiple energy levels created by this splitting are not degenerate, and since the possibility that a ground state atom can be in one of these ground state energy levels, the distribution must be taken into account. The single point energy calculations for the atoms and molecules used in this study are run at zero degrees Kelvin (0 K), and only the lowest lying state is taken into consideration. At this temperature, the probability of an atom being in any of the higher energy levels is equal to a Boltzmann distribution. Therefore, the average energy of the ground-state atoms is described by Equation (10). (E) = _9;_ng where, q = 2.:gie-giB . (10) After completing the derivative, the average energy takes the form of Equation (11). Zgiei i =—___, (11) Zgic—SIB i (E) Since the temperature is 0 K, the average energy is equal to the mean energy as seen in Equation (12). 12 Zgiei (E) = lZgi ° (12) Because the De values are calculated for the lowest lying energy states of the molecule and its constituent atoms, the spin-orbit correction for HCCH, Li2C2, and Na2C2 is the difference between the energy of the lowest lying state of carbon and the average energy of the carbon atom. Equation (13) shows this relation. AB.-. = 2(Ecarbon)-2Ewbo- (13) The spin-orbit correction for ClCCCl and FCCF is equal to the spin-orbit correction for acetylene and the doubly substituted acetylides plus the difference between the energy of the lowest lying state of the halogen and the average energy of the halogen atom. Equation (14) expresses this relation. ABs-o = 2(Ecarbon) - 2Ecarbon + 2 — 25 halogen . (14) The tables of atomic energy levels that Charlotte Moorell published list the energy of these spin-orbit states. Using these values, the correction for average energy of the atoms (the spin-orbit correction) was subtracted from the dissociation energy. 2.1.4 Extrapolations to CBS limit Extrapolated values are done using two extrapolation techniques: extrapolating only the property to the basis set limit, P(oo) , and calculating the property from extrapolated energies of the molecule and its constituent atoms at the basis set limit, P(E(oo)). For example, in order to determine the DC of a molecule at the basis set limit, first the molecular and atomic energies are calculated as a function of basis set. From these single point calculations, the De is calculated as a function of basis set. To 13 extrapolate to the basis set limit, one could either extrapolate the property (De) to the basis set limit, or one could individually extrapolate the single point molecular and atcrnic energies to the basis set limit and calculate the De from those extrapolated energies. This concept of extrapolating a property to the basis set limit is dependent on a property of the variational theorem. For the non-relativistic time-independent Hamiltonian operator, there is a lowest energy eigenvalue. In quantum mechanics, the wavefunction of an atom or molecule is approximated. As the wavefunction becomes more accurate for the system in question, the resulting eigenvalue approaches this lowest value. The point where an infinite basis set is used is referred to as the basis set limit, and it is the limit of accuracy for the particular method used. Since the energy converges in this manner, this same methodology is applied to the calculation of properties by extrapolating to the basis set limit. Many researchers have investigated the relation between basis set size and the convergence of the energy of a system. The Feller equation, as Martin calls it, originates from an empirical development. There is no quantitative development made to reach that nonlinear equation except to note how well the equation models the behavior of the system. The Schwartz equations originate from a quantitative derivation of how the energy converges as higher order angular momentum functions are added to the basis set. The Martin'3 paper compares the behavior of each extrapolation equation for small molecules. 14 For each of the extrapolation techniques, the CCSD(T) values were fit to four different nonlinear equations. Dunning and associates use an exponential equation originated by Feller12 where X is again the cardinal index and Otis a variable power. P(X)= P(oo)+Ae‘°‘X. (Feller) (15) In a recent paper, Martinl3 offers three alternative polynomial equations for nonlinear fitting referred to as Schwartz-type formulas derived from the works of Schwartz”, Kutzelnigg's’w, Morgan”, and Hill”. P(X)= P(oo)+—A—. (Schwartza) (16) (met P(X)=P(oo)+ A + B 6.(Schwartz6) (17) (x+i)“ (mi) A (Schwartz4) (18) Both P(oo) and P(E(oo)) methods should not necessarily produce the same value. For the Schwartz4 and Schwartz6 methods, the P(oo) and P(E(oo)) results are more likely to be equivalent because the extrapolation equations for the atoms and molecules are consistent. If the error in the complete basis set (CBS) limit is consistent for all the extrapolated properties and energies, then the results produced will be consistent. Feller and Schwartzor equations allow more freedom for the extrapolation equation because of the variable a. exponent. This freedom provides an Opportunity for the fit for the atoms to be tighter than the fit for the molecule, and this inconsistency will cause differences between the P(oo) and P(E(oo)) results. 15 Removing the data points from calculations in which smaller basis sets were used is another option in extrapolating to CBS limit. Using the most accurate data points for extrapolation can aid in producing a more accurate extrapolated value. For this report, many smaller data sets were created from each complete data set collected. For example, the energy of the carbon atom was calculated using a spectrum of basis sets ranging from CC-PVDZ to CC-PV6Z. The original set contained all the data points calculated. Then, subsequent sets were created by systematically removing the data calculated at smaller basis sets such as the CC-PVDZ and CC-PVTZ basis sets. By removing carbon atom energies calculated at smaller basis sets, the only values remaining are the most accurate values. Extrapolations were done for each of these data sets and listed to show the change in the extrapolated values as the less accurate values were removed. The extrapolated core-valence correction was extrapolated using only the results from the larger basis sets. 2.2 HCCH Table 1 lists calculated CCSD(T) optimized geometries for HCCH as a function of the Dunning unaugmented and augmented CC-PVXZ basis sets. Table 1 also tabulates HCCH extrapolated bond distances and an experimental geometry provided by Strey and Mills”. The notation for each extrapolation designates both the nonlinear fitting equation and the cardinal indices of the basis sets included in the extrapolation. Therefore, a Schwartz4(Q56) value is an extrapolated value using Equation (18) or the Schwartz4 equation from extrapolated properties calculated using basis sets where the cardinal index X is equal to the set {Q,5,6}. l6 Table 1. Optimized Geometries of HCCH as a Function of Basis Set . RCC RCH . RCC RCH Basrs Basrs (arts) (ang) (ang) (ans) CC-PVDZ 1.22877 1.07899 AUG-CC-PVDZ 1.22998 1.07866 CC-PVTZ 1.20973 1.06372 AUG-CC-PVTZ 1.21016 1.06387 CC-PVQZ 1.20634 1.06337 AUG-CC-PVQZ 1.20686 1.06355 CC-PVSZ 1.20557 1.06303 AUG-CC-PVSZ 1.20587 1.06314 CC-PV6Z 1.20534 1.06300 AUG-CC-PV6Z 1.20556 1.06312 Feller(DTQ56) 1.2054 1.0631 Feller(DTQ56) 1.2057 1.0633 Feller(TQ56) 1.2053 1.0628 Feller(TQ56) 1.2054 1.0628 Feller(Q56) 1 .2052 1.0630 Feller(Q56) 1.2054 1.0631 Schwartza(DTQ56) 1.2051 1.0631 Schwartza(DTQ56) 1.2053 1.0632 SchwartzuCTQ56) 1.2052 1.0626 SchwartzaCT Q56) 1.2052 1.0623 Schwartza(Q56) 1.2052 1.0630 Schwartza(Q56) 1.2053 1.0631 Schwartz4(DTQ56) 1.2042 1.0617 Schwartz4(DTQ56) 1.2045 1.0618 Schwartz4(TQ56) 1.2048 1.0630 Schwartz4(TQ56) 1.2051 1.0631 Schwartz4(Q56) 1.2050 1.0629 Schwartz4(Q56) 1.2051 1.0629 Schwartz4(56) 1.2051 1.0630 Schwartz4(56) 1.2052 1.0631 Schwartz6(DTQ56) 1.2050 1.0634 Schwartz6(DTQ56) 1.2052 1.0635 Schwartz6(TQ56) 1.2052 1.0628 Schwartz6(TQ56) 1.2052 1.0629 Schwartz6(Q56) 1.2052 1.0631 Schwartz6(Q56) 1.2053 1.0632 Schwartz6(56) 1.2051 1.0630 Schwartz6(56) 1.2052 1.0631 ‘gexperi mental 1 .2033 1.0605 In Table 1, the augmented and unaugmented basis sets carbon-carbon bond length has converged to three decimal places by the 5-zeta basis set, and the carbon-hydrogen bond length has converged to three decimal places by the Q-zeta basis set. The extrapolated bond lengths confirm that at the 6-zeta basis set both the augmented and unaugmented basis sets are very close to the basis set limit. There is no general trend in the extrapolated values as optimized geometries calculated at smaller basis sets are removed. Compared to the experimental geometry, the basis sets are not converging towards the Strey and Mills experimental geometry. Although the geometry at the basis set limit is not the true HCCH geometry, the CCSD(T) method limit is within three thousandths of an angstrom, which is a small deviation and will have no effect on the calculated heat of formation. Using the Strey and Mills experimental geometry listed in Table 1, we completed single point CCSD(T) calculations for the acetylene molecule. Taking advantage of experimental vibrational frequencies provided by Schimanouchi19 listed in Table 2, and using standard heats of formation for the constituent atoms provided by Chase2 listed in the appendix, we calculated the enthalpy of formation of HCCH as a function basis set. Table 2. Vibrational Frequencies of HCCH Symmetry Frequency (cm'l) Cis-bend (11“) 730 Trans-bend (Hg) 612 CC stretch(2g) 1974 s-CH stretch (2g) 3374 a-CH stretch (21,) 3289 Shown in Table 3 are dissociation energies of HCCH at 0 K and heats of formation for HCCH at 298K for the unaugmented and augmented CC-PVXZ Dunning basis sets. Table 3. Calculated Dissociation Energies and Heats of Formation for HCCH as a Function of Basis Set . De AHf Basrs Set (kcal/mol) (kcal/mol) CC—PVDZ 370.20 89.23 CC-PVTZ 393.35 66.08 CC-PVQZ 399.59 59.84 CC-PVSZ 401.47 57.96 CC-PV6Z 402. 19 57.24 AUG-CC-PVDZ 371.09 88.34 AUG-CC-PVTZ 394.56 64.87 AUG-CC-PVQZ 400.09 59.35 AUG-CC-PVSZ 401.73 57.70 AUG-CC-PV6Z 402.33 57.1 1 Augmentation of the CC-PVXZ basis set does not alter the magnitude of either the De or the heat of formation greatly, and the enthalpy of formation is near convergence for both basis sets. Note that as the De increases, the enthalpy of formation decreases. l8 This behavior is due to the mathematical nature of the relation between the two values. Equation (9) shows the inverse dependence of the enthalpy of formation on the enthalpy of atomization in which the enthalpy of atomization is merely the Dc with thermal corrections. Table 4 lists the dissociation energies and enthalpies of formation at the complete basis set limit for each nonlinear extrapolation equation for both P(oo) and P(E(oo)) methods. Table 4. Heats of Formation for HCCH Extrapolated to the Complete Basis Set Limit Basis sets AHf (°°) AHf (E(°°» CC-PVXZ (kcal/mol) (kcal/mol) Feller(DTQ56) 57.18 57.18 Feller(Q56) 56.79 56.82 Schwartza(DTQ56) 56.03 56.03 Schwartzor(Q56) 56.51 56.57 Schwartz4(DTQ56) 56.81 56.81 Schwartz4(56) 56.48 56.48 Schwartz6(DTQ56) 56.25 56.25 Schwartz6(56) 56.48 56.48 AUG-CC-PVXZ Feller(DTQ56) 57.16 57.18 Feller(Q56) 56.77 56.78 Schwartza(DTQ56) 56.29 56.34 Schwartzor(Q56) 56.57 56.59 Schwartz4(DTQ56) 56.39 56.39 Schwartz4(56) 56.48 56.48 Schwartz6(DTQ56) 56.30 56.30 Schwartz6(56) 56.48 56.48 Table 4 has two columns of data. The rightmost column contains the enthalpy of formation calculated using extrapolated energies for the constituent atoms and the acetylene molecule. The left data column contains the heat of formation where values for the enthalpy of formation were extrapolated to the complete basis set limit. As required, the Schwartz4 and the Schwartz6 results are consistent for each method at both suites of 19 basis sets, and when only the two best points are used for extrapolation, the Schwartz4 and Schwartz6 results are equal to each other. Looking at the Feller and Schwartza results, the differences between the two methods for each equation is minute. For all the extrapolation methods and fitting equations, the extrapolated value was within 1 kcal/mol of the enthalpy of formation computed at the AUG-C C -PV6Z basis set. To correct for missing core-valence correlation, we used the Dunning unaugmented CC-PCVXZ basis sets, and the results are shown as a function of basis set and tabulated in Table 5. Table 5. Core-Valence Correction for HCCH as a Function of Basis Set Basis Sets Core-Valence Correction (kcal/mol) CC-PCVDZ _ 1.13 CC-PCVTZ _ 1.88 CC-PCVQZ -2.28 CC-PCVSZ 4.41 Using the data in Table 5, we extrapolated the core-valence correction to a complete basis set for both P(oo) and P(E(oo)) extrapolation techniques. Table 6 lists the corrections. Table 6. Core-Valence Correction for HCCH at the Complete Basis Set Limit Basis sets ACV(°°) ACV(E(°°» CC-PCVXZ (kcal/mol) (kcal/mol) Feller(T Q5) -2.46 -2.47 Schwartza(TQ5) -2.50 -2.51 Schwartz4(Q5) -2.51 -2.51 Schwartz6(Q5) -2.51 -2.51 As mentioned before, not all data points were included in the extrapolations. Only corrections calculated with the larger basis sets were kept for extrapolation, and those extrapolated corrections were used as core-valence corrections. Table 6 illustrates the core-valence corrections at the basis set limit. From the table we can see, the core- 20 valence correction extrapolations are consistent between methods and differ only slightly between extrapolation equations. In Table 7, we collected enthalpy of formation values corrected for relativistic effects (0.25 kcal/mol), spin-orbit coupling (0.17 kcal/mol), and the core-valence corrections from Table 6. As we can now see, the relativistic corrections to the energy were not negligible. We added the core-valence corrections to the enthalpy of formation values from Table 4. We calculated the Feller(TQS) core-valence correction using the P(oo) method and combined it with the Feller(DTQ56) and Feller (Q56) heat of formation values calculated using the P(oo) method. This methodology was used for all extrapolation equations and methods. Table 7 includes also the difference between the calculated enthalpy of formation and the excepted experimental value of 54.19 i019 kcal/mol provided by Chasez. 21 Table 7. AH; Values Corrected for Core-Valence Correlation Spin-Orbit Coupling and Relativistic Effects for HCCH at the Complete Basis Set Limit for each Method Difference from Difference Basis sets Corrected experimental Corrected from AHf (co) value AHf (E(oo)) experimental value CC-PVXZ (kcallmol) (kcallmol) (kcallmol) (kcallmol) Feller(DTQ56) 55.14 0.95 55.14 0.95 Feller(Q56) 54.74 0.55 54.77 0.58 Schwartza(DTQ56) 53.95 -0.24 53.94 ~0.25 Schwartza(Q56) 54.43 0.24 54.48 0.29 Schwartz4(DTQ56) 54.72 0.53 54.72 0.53 Schwartz4(56) 54.39 0.20 54.39 0.20 Schwartz6(DTQ56) 54. 16 -0.03 54. 16 -0.03 Schwartz6(56) 54.39 0.20 54.39 0.20 AUG-CC-PVXZ Feller(DTQ56) 55.12 0.93 55.14 0.95 Feller(Q56) 54.73 0.54 54.74 0.55 Schwartza(DTQ56) 54.21 0.02 54.25 0.06 Schwartzor(Q56) 54.49 0.30 54.50 0.3 1 Schwartz4(DTQ56) 54.30 0.1 1 54.30 0.1 1 Schwartz4(56) 54.39 0.20 54.39 0.20 Schwartz6(DTQ56) 54.22 0.03 54.22 0.03 Schwartz6(56) 54.39 0.20 54.39 0.20 The first thing to note is the loss of accuracy with the removal of points calculated at smaller basis sets. When only the best data points were used, the error increased by at least 0.1 kcallmol; however, regardless of the basis sets used, the resulting enthalpy of formation is within 1 kcallmol of the experimental value. In addition, the difference between the two extrapolation methods is very small, presumably due to the high convergence of the values before extrapolation. The more accurately the fitted equation matches the true convergence curve, the less discrepancy exists between the two extrapolation methods, P(oo) and P(E(oo)). Of the four extrapolation equations, the best performing equations are the Schwartz-type equations. These three equations yield results, which fall within the experimental error bars. However, the Feller equation does 22 not provide such accuracy. These general trends are consistent with Martin’sl3 findings in his study of the DC of HCCH. In Table 8, we collect the best-extrapolated heats of formation from the AUG-CC-PVXZ basis sets from this work, as well as experimental and select theoretical results from the literature. Table 8. Comparison of Heats of Formation of HCCH AHf EI‘I‘OI' kcallmol kcallmol ”This work 54.73 0.54 brhis work 54.21 0.02 ”This work 54.30 0.11 “This work 54.22 0.03 3Parthiban(W1) 54.41 0.22 31>arthiban(wz) 54.48 0.29 2experiment 54.19 $0.19 alFeller(Q56) extrapolation of augmented basis set values with P(oo) method bSchwartza(DTQ56) extrapolation of augmented basis set values with P(oo) method cSchwartz4(DTQ56) extrapolation of augmented basis set values with P(oo) method dSchwartz6(DTQ56) extrapolation of augmented basis set values with P(oo) method The acknowledged values for the enthalpies of formation are the experimental values provided by Chasez. As mentioned earlier, most of the results from this work are within the error bars associated with Chase's work. The Parthiban3 values are calculated in a similar manner as this report using the Schwartz4, 6, and or equations, but the initial geometries and vibrational frequencies for HCCH were calculated using ab initio and DFT methods. In this study, the experimental geometries and fundamental vibrational frequencies from the literature were used. 2.3 FCCF Experimental values for FCCF are difficult to determine as stated by Parthiban3 et al. , 23 “. . .there remains no direct determination of the heat of formation of any haloacetylene-these species are simply too unstable and/or reactive to allow for such measurements.” Because FCCF is so reactive, there are no reliable experimental data to use for comparison. Therefore, we used the equilibrium geometry and vibrational frequencies from theoretical work done by Breidung20 et al. Table 9 and Table 10 list these values. Calculated CCSD(T) optimized geometries as a function of the CC-PVXZ and AUG-CC- PVXZ basis sets are listed in Table 9 along with the extrapolated geometries and the reference geometry provided by Breidung.20 Table 9. Omimized Geometries of FCCF as a Function of Basis Set Basis Sets RCC RCF Basis RCC RCF (ang) (ang) (ang) (ans) CC-PVDZ 1.20969 1.30039 AUG-CC—PVDZ 1.21 157 1.30594 CC-PVTZ 1.19277 1.28859 AUG-CC-PVTZ 1.19280 1.28948 CC-PVQZ 1.18918 1.28586 AUG-CC-PVQZ 1.18951 1.28613 CC-PVSZ 1.18857 1.28512 AUG-CC-PVSZ 1.18868 1.28524 Feller(DTQS) 1.1883 1.2850 Feller(DTQS) 1.1886 1.2851 Feller(TQS) 1.1884 1.2849 Feller(TQS) 1.1884 1.2849 Schwartza(DTQ5) 1.1878 1.2844 Schwartza(DTQ5) 1.1881 1.2845 Schwartza(TQ5) 1.1884 1.2847 Schwartza(TQ5) 1.1882 1.2847 Schwartz4(DTQ5) 1.1872 1.2844 Schwartz4(DT Q5) 1 . 1872 1.2841 Schwartz4(TQ5) 1.1875 1.2844 Schwartz4(TQ5) 1 . 1878 1.2845 Schwartz4(Q5) 1.1881 1.2845 Schwartz4(Q5) 1.1880 1.2845 Schwartz6(DTQ5) 1.1877 1.2844 Schwartz6(DTQ5) 1 . 1880 1.2844 Schwartz6(TQ5) 1 . 1884 1.2846 Schwartz6(TQ5) 1 . 1882 1.2846 Schwartz6(Q5) l . 1881 1.2845 Schwartz6(Q5) 1 . 1880 1.2845 20reference 1.186 1.2835 The optimized geometries in Table 9 show that the augmentation of CC-PVXZ basis set does not affect the convergence of the basis set. Like the HCCH geometries, the carbon-carbon and carbon-fluorine bonds, if rounded, converges to three decimal places by the 5-zeta basis set. Note the extrapolated geometries differ by less than a thousandth of an A from the 5-zeta result for both the unaugmented and augmented basis sets. Also, 24 note the CCSD(T) optimized geometries are converging to a value that differs only 0.002A from the reference value. We used the unaugmented, augmented, and doubly augmented Dunning basis sets to make single point CCSD(T) calculations at the reference geometry provided in Table 9. We used vibrational frequencies provided by Breidung20 et al listed in Table 10 and the heats of formation for the fluorine and carbon atoms provided by Chase2 to determine the enthalpy of formation for FCCF. Table 10. Vibrational Frequencies of FCCF Symmetry Frequencies (cm'l) Cis-bend (1'1“) 276 Trans-bend (l'Ig) 284 s-CF stretch (22g) 792 a-CF stretch (2“) 1375 CC stretch (22) 2527 Table 11 lists the calculated standard enthalpy of formation values at 298 K and dissociation energies at 0 K as a function of basis set. Table 11. Calculated Dissociation Energies and Heats of Formation for FCCF as a Function of Basis Set - Dc AHf Basrs sets (kcallmol) (kcallmol) CC-PVDZ 343.01 43.15 CC-PVTZ 370.27 15.89 CC-PVQZ 378.47 7.70 CC-PVSZ 381.10 5.06 AUG-CC-PVDZ 344.37 41.80 AUG-CC-PVTZ 372.44 13.73 AUG-CC-PVQZ 379.67 6.50 AUG-CC-PVSZ 381.65 4.51 D-AUG-CC-PVDZ 346.83 39.33 D-AUG-CC-PVTZ 373.75 12.42 D-AUG-CC-PVQZ 380.36 5.80 D-AUG-CC-PVSZ 38 1 .87 4.29 25 Unlike HCCH, the dissociation energies of FCCF are not as closely converged at these basis set levels. The heats of formation show that the difference between the Q-zeta and 5-zeta results is a large percentage of the calculated value. The level of augmentation seems to aid in the rate of convergence, but the differences between unaugmented, augmented, and doubly augmented values are small but significant in comparison to the magnitude of the reported 5-zeta value. Therefore, the addition of higher angular momentum functions to the wave function influences the enthalpy of formation of FCCF greatly. Table 12 illustrates heats of formation values extrapolated to the basis set limit. 26 Table 12. Heats of Formation for FCCF Extrapolated to the Complete Basis Set Limit Basis sets AHf (co) AHf (E(°o)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ5) 4.00 4.08 Feller(TQ5) 3.81 3.87 Schwartza(DTQ5) 1.55 1.76 Schwartzon(TQ5) 2.88 3.01 Schwartz4(DTQ5) 4.24 4.24 Schwartz4(Q5) 2.92 2.92 Schwartz6(DTQ5) 2.52 2.52 Schwartz6(Q5) 2.92 2.92 AUG-CC-PVXZ Feller(DTQ5) 3.88 4.08 Feller(TQ5) 3.76 3.93 Schwartza(DTQ5) 2.23 2.71 Schwartzoc(TQ5) 3.22 3.57 Schwartz4(DTQ5) 3.05 3.05 Schwartz4(Q5) 2.90 2.90 Schwartz6(DTQ5) 2.44 2.44 Schwartz6(Q5) 2.90 2.90 D-AUG-CC-PVXZ Feller(DTQ5) 3.75 4.03 Feller(TQ5) 3.84 3.10 Schwartzo.(DTQ5) 2.42 3.08 Schwartzoc(TQ5) 3.52 4.04 Schwartz4(DTQ5) 2.61 2.61 Schwartz4(Q5) 3.06 3.06 Schwartz6(DTQ5) 2.44 2.44 Schwartz6(Q5) 3.07 3.07 Varying from around 1 kcallmol to over 3 kcallmol between extrapolation equations and from 0.06 kcallmol to 0.8 kcallmol between methods, the results in Table 12 seem erratic. This behavior is true only because all the extrapolated results describe the heat of formation of FCCF as only a few kcallmol above zero. Due to the relative magnitude of the calculated enthalpy of formation, the difference in extrapolated values is a large percentage of the heat of formation. 27 In all the single point calculations on FCCF and its component atoms, the Is core on carbon and fluorine was frozen. Table 13 reports the calculated core-valence corrections tabulated as a function of basis set for the unaugmented and augmented polarized core-valence basis sets. Table 13. Core-Valence Correction for FCCF as a Function of Basis Set Core-Valence Basis Sets Correction (kcallmol) CC-PCVDZ -1.40 CC-PCVTZ -2.29 CC-PCVQZ -2.7l CC-PCVSZ -2.85 AUG-CC-PCVDZ -1.99 AUG-CC-PCV'IZ -2.48 AUG-CC-PCVQZ -2.75 AUG-CC-PCVSZ -2.86 As seen in Table 13, the level of augmentation has little effect on the core-valence correction. In Table 14, the values of the core-valence correction are extrapolated to the basis set limit using the same procedure as previously discussed. Table 14. Core-Valence Correction for FCCF at the Complete Basis Set Limit Basis sets ACV(oo) ACV(E(oo)) CC-PCVXZ (kcallmol) (kcallmol) Feller(TQ5) -2.90 -2.90 Schwartzoc(TQ5) -2.95 -2.94 Schwartz4(Q5) -2.95 -2.95 Schwartz6(Q5) -2.95 -2.95 AUG-CC-PCVXZ Feller(TQ5) -2.93 -2.93 Schwartzoc(TQ5) -2.98 -2.99 Schwartz4(Q5) -2.94 -2.94 Schwartz6(Q5) -2.94 -2.94 Between the two extrapolation methods, the difference between the core-valence corrections is negligible; and amongst extrapolation equations, the difference in the correction is less than 0.1 kcallmol. Table 15 lists heat of formation values corrected for 28 the core-valence correlation, spin-orbit coupling (0.94 kcanol), and the relativistic effects (0.70 kcallmol) not originally included in the values in Table 11. Table 15. AHf Values Corrected for Core-Valance Correlation, Spin-Orbit Coupling, and Relativistic Effects for FCCF at the Complete Basis Set Limit for each Method Basis sets Corrected AHf (co) Corrected AHf (E(°°)) CC-PVXZ I (kcallmol) (kcallmol) Feller(DTQ5) 2.7 l 2.79 Feller(TQ5) 2.52 2.58 Schwartzor(DTQ5) 0.21 0.41 Schwartza(TQ5) 1.54 1.67 Schwartz4(DTQ5) 2.94 2.94 Schwartz4(Q5) 1.62 1.62 Schwartz6(DTQ5) 1.21 1.21 Schwartz6(Q5) 1.62 1.62 AUG-CC-PVXZ Feller(DTQ5) 2.59 2.79 Feller(TQ5) 2.47 2.64 Schwartzct(DTQ5) 0.88 1.37 Schwartzct(TQ5) 1.88 2.23 Schwartz4(DTQ5) 1.75 1.75 Schwartz4(Q5) 1.60 1.60 Schwartz6(DTQ5) 1.14 1.14 Schwartz6(Q5) 1.60 1.60 D-AUG-CC-PVXZ Feller(DTQ5) 2.46 2.74 Feller(TQ5) 2.56 1.81 Schwartzor(DTQ5) 1.08 1.73 Schwartzct(TQ5) 2.18 2.69 Schwartz4(DTQ5) 1.31 1.31 Schwartz4(Q5) 1.76 1.76 Schwartz6(DTQ5) 1.14 1.14 Schwartz6(Q5) 1.76 1 .76 Even though the results in Table 15 show that the heat of formation values between methods change by substantial percentages, the results describe the enthalpy of formation for FCCF as an endothermic process. We used the D—AUG-CCPVXZ basis set extrapolations performed using the P(oo) method to produce a list of calculated and 29 experimental heats of formation. The results are presented in Table 16. Theoretical contributions by Bauschlicher4 and Parthiban3 and experimental results provided by Chase2 and Ehlert2| are also listed in Table 16. Table 16. Comparison of Heats of Formation of FCCF AHr kcallmol 3’This work 2.46 l”This work 1.08 cThis work 1.31 “This work 1.14 3r>arthiban(wr) 0.48 3l>arthiban(w2) 1.38 4Bauschlicher 1.433 2experiment 5.00 $5.00 21experiment -45 16.00 aFeller(DTQ5) extrapolation of doubly augmented basis set values with P(oo) method bSchwartzaCDTQS) extrapolation of doubly augmented basis set values with P(oo) method cSchwartz4(DTQ5) extrapolation of doubly augmented basis set values with P(oo) method dSchwartz6(DTQ5) extrapolation of doubly augmented basis set values with P(oo) method The computational work done by Baushlicher4 and Parthiban3 is a mixture of CCSD(T), DF'T, and other ab initio calculations. The discrepancies between theoretical values produced in this research and other computational methods are due mainly to a use of different starting geometries and vibrational frequencies and a different core-valence correction. Because we calculated the heat of formation values using many similar techniques, it is not surprising that the values are within a kcallmol of each other. Since the experimental values are inconsistent and the error bars broad, all of the calculated heats of formation fall within experimental accuracy. 30 2.4 CICCCI Table 17 is a collection of CCSD(T) optimized geometries as a function of augmented and unaugmented basis sets, the experimental geometry of ClCCClzz, and geometries extrapolated to the complete basis set limit. Table 17. Optimized Geometries of CICCCI as a Function of Basis Set . RCC RCC] . RCC RCCl Basrs Basrs (ang) (ang) (ang) (ang) CC-PVDZ 1.22442 1.66458 AUG-CC-PVDZ 1.22560 1.66890 CC-PVTZ 1.20872 1.64891 AUG-CC-PVTZ 1.20889 1.64883 CC-PVQZ 1.20530 1.64339 AUG-CC-PVQZ 1.20551 1.64339 CC-PVSZ 1.20506 1.63965 AUG-CC-PVSZ 1.20533 1.63970 Feller(DTQ5) 1.2048 1.6379 Feller(DTQ5) 1.2050 1.6390 Feller(TQ5) 1.2050 1.6318 Feller(TQ5) 1.2053 1.6319 Schwartza(DTQ5) 1.2043 1.6339 Schwartza(DTQ5) 1.2046 1.6365 Schwartzot(TQ5) 1.2050 1.6162 SchwartzaCTQS) 1.2053 1.6162 Schwartz4(DTQ5) 1.2037 1.6406 Schwartz4(DTQ5) 1.2037 1.6400 Schwartz4(TQ5) 1.2040 1.6386 Schwartz4(TQ5) 1.2043 1.6387 Schwartz4(Q5) 1.2049 1.6366 Schwartz4(Q5) 1.2052 1.6367 Schwartz6(DTQ5) 1.2042 1.6379 Schwartz6(DTQ5) 1.2045 1.6382 Schwartz6(TQ5) 1.2054 1.6353 Schwartz6(TQ5) 1.2057 1.6354 Schwartz6(Q5) 1.2049 1.6366 Schwartz6(Q5) 1.2052 1.6367 22experimental 1.205 1.635 The augmentation of the CC-PVXZ basis set lends little to the accuracy and speed of convergence of the optimized geometries listed in Table 17. The optimized geometries are slower to converge than HCCH and FCCF, but the carbon-carbon bond distance has converged to within three decimal places by the 5-zeta basis set, and the carbon-chlorine bond has converged to within two decimal places by the Q-zeta. Interestingly, it seems the optimized geometries are converging to within 0.001A of the experimental geometry and the converged geometry is within 0.004A of the 5-zeta optimized geometry. 31 Table 18. Vibrational Frequencies of ClCCCl Symmetry Frequency (cm’l) Cis-bend (1'1“) 172 Trans-bend (Hg) 333 s-CCl stretch (2g) 477 a-CCI stretch (2,.) 988 CC stretch (2g) 2234 We used the experimental geometry provided in Table 17, the Schimanouchil9 vibrational frequencies provided in Table 18, and the standard heats of formation for the carbon and chlorine atoms provided by Chase2 to compute the heat of formation at 298K and dissociation energy at 0 K for ClCCCl. We compiled these results as a function of the suite of Dunning unaugmented, augmented, and doubly augmented basis sets. Table 19 reports our results. Table 19. Calculated Dissociation Energies and Heats of Formation for ClCCCl as a Function of Basis Set . De Mi Basrs sets (kcallmol) (kcallmol) CC-PVDZ 306.97 97.89 CC-PVTZ 332.28 72.58 CC-PVQZ 341.61 63.24 CC-PVSZ 345.74 59.12 AUG-CC-PVDZ 306.89 97.97 AUG-CC-PVTZ 334.55 70.31 AUG-CC-PVQZ 342.76 62.10 AUG-CC-PVSZ 346.32 58.54 D-AUG-CC-PVDZ 308.71 96.14 D-AUG-CC-PVTZ 335.61 69.25 D-AUG-CC-PVQZ 343.35 61.51 D-AUG-CC-PVSZ 346.62 58.24 If we compare the calculations in Table 19 to the corresponding tables for HCCH and FCCF, we notice a general trend. Regardless of basis set, the heats of formation calculations seem to be essentially independent of the level of augmentation. Similar to FCCF, for ClCCCl neither the dissociation energy at 0 K nor the heat of formation at 298 32 K converges, but the change in values between the Q- and 5-zeta basis sets is only 10 percent of the computed value for ClCCCl compared to 40 percent for FCCF. We made extrapolations of the heat of formation to the complete basis set limit. Table 20 reports our results. Table 20. Heats of Formation for CICCCI Extrapolated to the Complete Basis Set Limit Basis sets AH, (co) AH, (E(oo)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ5) 56.91 57.33 Feller(TQ5) 55.86 56.39 Schwartzor(DTQ5) 52.26 53.31 Schwartzoc(TQ5) 53.08 54.29 Schwartz4(DTQ5) 59.60 59.60 Schwartz4(Q5) 55.77 55.77 Schwartz6(DTQ5) 55.99 55.99 Schwartz6(Q5) 55.78 55.78 AUG-CC-PVXZ Feller(DTQ5) 57.45 57.49 Feller(TQ5) 55.81 56.22 Schwartzor(DTQ5) 54.53 54.62 Schwartzoc(TQ5) 53.51 54.43 Schwartz4(DTQ5) 58.19 58.19 Schwartz4(Q5) 55.65 55.65 Schwartz6(DTQ5) 56.03 56.03 Schwartz6(Q5) 55.65 55.65 D-AUG-CC—PVXZ Feller(DTQ5) 57.31 57.33 Feller(TQ5) 55.84 55.12 Schwartza(DTQ5) 54.72 54.75 Schwartzor(TQ5) 53.86 54.45 Schwartz4(DTQ5) 57.75 57.75 Schwartz4(Q5) 55.58 55.58 Schwartz6(DTQ5) 55.91 55.91 Schwartz6(Q5) 55.59 55.59 Table 20 shows that the Feller, Schwartz4, and Schwartz6 extrapolation equations consistently extrapolate to a higher value than the Schwartza equation. Using only the values from larger basis sets, the resultant enthalpy drops. There is little difference 33 within methods, but there are differences of up to several kcallmol between extrapolation equations. To be physically viable, the extrapolated values for the enthalpy of formation can not be higher than the best unextrapolated value. In Table 20, the Schwartz4(DTQ5) extrapolated value exceeds the unextrapolated CC-PVSZ heat of formation. This result is in italics and is the first example of how these extrapolation equations are fallible. Although that value is the only result higher than the unextrapolated value in Table 20, other values do lie very close to the unextrapolated values. These results in bold italics, and they occur when data points calculated at smaller basis sets are included in the extrapolation. This problem does seem to 1i ght itself once the smaller data points are removed from involvement in the extrapolations. Table 21 contains the core-valence correction to the values in Table 14 due to the frozen 1s, 28, and 2p core on chlorine and frozen ls core on carbon in the atomic and molecular CCSD(T) energy calculations. Table 21. Core-Valence Correction for ClCCCl as a Function of Basis Set Core-Valence Basis Sets Correction (kcallmol) CC-PCVDZ -2.09 CC-PCVTZ -2.61 CC-PCVQZ -2.81 The core-valence correction is close to convergence. Table 22 contains the core-valence correction at the basis set limit. 34 Table 22. Core-Valence Correction for ClCCCl at the Complete Basis Set Limit Basis sets ACV(°°) ACV(E(°°)) CC-PCVXZ (kcallmol) (kcallmol) Feller(DTQ) -2. 93 -I.23 Schwartza(DTQ) -3.06 2.09 Schwartz4(TQ) -2.92 -2.92 Schwartz6(TQ) -2.92 -2.92 Notice in Table 22 that between methods for the Feller extrapolations, the energy difference is 1.7 kcallmol, and the value for the core-valence correction changes sign between methods for the Schwartza extrapolations. The cause for this sign change, an unusual result, depends, most likely, on how closely the data had converged before fitting of nonlinear equations to the data points. Notice that the ACV(oo) value for the Feller and Schwartza fitting equations is approximately equal to the results for Schwartz4 and Schwartz6. As mentioned earlier, since the Feller and Schwartza fitting equations have variable exponents, there is a chance that the relative consistency in how tightly the atomic and molecular data was fit could cause inconsistency in the extrapolated result. This discrepancy between the two methods for the Schwartz and Feller equations would have a tremendous impact on their respective corrected AH, (E(oo)) values in Table 23. As stated earlier, instead of calculating the corrected AH, values by combining the enthalpy of formation and core-valence corrections from like methods and extrapolation equations, we added a constant -2.92 kcallmol core-valence correction to all the extrapolated AH, values. Table 23 contains the enthalpy of formation values for ClCCCl after we added the core-valence correction, spin-orbit coupling correction (1.85 kcallmol), and the correction due to relativistic effects (0.99 kcallmol). 35 Table 23. AH, Values Corrected for Core-Valance Correlation, Spin-Orbit Coupling, and Relativistic Effects for ClCCCl at the Complete Basis Set Limit for each Method Basis sets Corrected AH, (co) Corrected AH, (E(oo)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ5) 56.83 57.25 Feller(TQ5) 55.7 8 56.31 Schwartzor(DTQ5) 52.18 53.23 Schwartzor(TQ5) 53.00 54.21 Schwartz4(DTQ5) 59.52 59.52 Schwartz4(Q5) 55.70 55.70 Schwartz6(DTQ5) 55.91 55.91 Schwartz6(Q5) 55.70 55.70 AUG-CC-PVXZ Feller(DTQ5) 57.37 57.41 Feller(TQ5) 55.73 56.14 Schwartzor(DTQ5) 54.45 54.54 Schwartza(TQ5) 53.43 54.35 Schwartz4(DTQ5) 58.1 1 58.1 1 Schwartz4(Q5) 55.57 55.57 Schwartz6(DTQ5) 55.95 55.95 Schwartz6(Q5) 55.57 55.57 D-AUG-CC-PVXZ Feller(DTQ5) 57.23 57.25 Feller(TQ5) 55.76 55.04 Schwartzoc(DTQ5) 54.64 54.67 Schwartzor(TQ5) 53.78 54.37 Schwartz4(DTQ5) 57.67 57.67 Schwartz4(Q5) 55.50 55.50 Schwartz6(DTQ5) 55.83 55.83 Schwartz6(Q5) 55.51 55.51 Table 24 presents a few values from Table 23 along with results from the works of Parthiban3 and Chase2 for comparison. 36 Table 24. Com arison of Heats of Formation of CICCCI AHf EITOI‘ kcallmol kcallmol “This work 57.23 7.13 l*rhis work 54.64 4.54 cThis work 57.67 7.57 this work 55.83 5.73 3Parthiban(w1) 56.46 6.36 3Parthiban(W2) 56.21 6.11 2experiment 50.1 :10 alFeller(DTQ5) extrapolation of doubly augmented basis set values with P(°°) method bSchwartzot(DTQ5) extrapolation of doubly augmented basis set values with P(°o) method °Schwartz4(DTQ5) extrapolation of doubly augmented basis set values with P(oo) method dSchwartz6(DTQ5) extrapolation of doubly augmented basis set values with P(oo) method All the heat of formation values in Table 24 are within the experimental error bars. The calculated values from this manuscript differ from Parthiban’s work due to Parthiban’s use of calculated DFT geometries and frequencies. Having completed the three molecules for which there is experimental data available, it is evident that the procedure used for evaluation is adequate for determining the enthalpy of formation for HCCH and the halogenated acetylenes. Almost all values fall very near the experimental result, and most fall within experimental error bars. 2.5 Linear L12C2 We generated augmented lithium CC-PVXZ basis sets for CCSD(T) calculations single point, geometry optimization, and vibrational frequency calculations by adding even—tempered basis functions to the Dunning lithium CC-PVXZ basis sets. Table 25 lists the added gaussian function exponents for the constructed AUG-CC-PVDZ, AUG- CC-PVTZ, and AUG-CC-PVQZ basis sets. 37 Table 25. Added Diffuse Function Exponents to Create Li AUG-CC- PVXZ Basis Sets AUG-CC-PVDZ AUG-CC-PVTZ AUG-CC-PVQZ S 0.01122 0.01104 0.01067 P 0.01047 0.007649 0.007978 D 0.04765 0.03560 0.03207 F --- 0.08627 0.07383 G --- --- 0.1253 To calculate the heat of formation, we used the equilibrium geometry and fundamental vibrational frequencies. Table 26 lists CCSD(T) optimized geometries, extrapolated geometries, other theoretical geometeries, and the geometry used for the heat of formation calculations. Table 26. Optimized Geometries of Linear Li2C2 as a Function of Basis Set Basis RCC (ang) RCLi (ang) CC-PVDZ 1.2765 1.9255 CC-PVTZ 1.2577 1.8939 CC-PVQZ 1.2540 1.8939 Feller(DTQ) 1.2531 1.8939 Schwartza(DTQ) 1.2522 1.8939 Schwartz4(DTQ) 1.2515 1.8876 Schwartz4(TQ) 1.2519 1.8939 Schwartz6(DTQ) 1.2520 1.8963 Schwartz6(TQ) 1.2519 1.8939 23MP2 1.267 1.883 74RHF 1.2314 1.8845 USED 1.2531 1.8943 Table 26 demonstrates that the optimized geometries are close to convergence. The extrapolated values are within 0.002A of the optimized geometry calculated at the highest basis set and are within a few thousandths of an angstrom of the value used in the heat of formation calculations. The results of other researchers are within 0.01A for the carbon lithium bond and 0.03A of the carbon-carbon bond. We calculated the vibrational frequencies using the CC-PVTZ and AUG-CC-PVTZ basis sets wherein the basis sets 38 had all the higher angular momentum functions intact. These values are shown in Table 27. Table 27. Vibrational Frequencies for Linear L12C2 Basis Sets Symmetry CC-PVTZ AUG-CC-PVTZ (D) Cis-bend (11“) 86 86 (E) Trans-bend (fig) 147 157 (A) s-CLi stretch (2g) 582 577 (C) a-CLi stretch (21,) 737 733 (B) CC stretch (2g) 1943 1937 Figure 1 provides a visual description of the vibrational modes. Each of these vibrations is the same type of vibration for linear four atom molecules. The A vibration is normally referred to as the symmetric carbon-lithium stretches, and the vibration C is the asymmetric carbon-lithium stretch. The B stretch is the carbon-carbon stretch, and the D and E vibrations are doubly degenerate cis and trans-bends, respectively. Because there are no imaginary frequencies, the linear configuration is a viable geometric minimum on the Li2C2 potential energy surface. <—> <——b <——§ _,4_‘__. Li—C—C—Li Li—C—C—Li Li—C—C—Li A B C LTi_T:i—l i Li—A—q—Iti Figure l: Vibrational Modes of Linear Li2C2 Using the CCSD(T) vibrational frequencies calculated at the AUG-CC-PVTZ basis set described in Table 27, the geometry RCC = 1.2531 A, RCLi = 1.8943 A from 39 Table 26, and the heats of formation of atomic carbon and lithium provided by Chase2 from the appendix, we calculated dissociation energy at 0 K and heat of formation at 298 K for linear Li2C2. Table 28 shows our results. Table 28. Calculated Dissociation Energies and Heats of Formation for Linear Li2C2 as a Function of Basis Set Basis sets De AHr (kcallmol) (kcallmol) CC-PVDZ 291.44 130.69 CC-PVTZ 315.98 106.16 CC-PVQZ 323.21 98.92 aCC-PV(QZ-SZ) 325.12 97.01 bCC-PV(QZ-6Z) 326.04 96.10 AUG-CC-PVDZ 298.01 124.12 AUG-CC-PVTZ 318.99 103.14 AUG-CC-PVQZ 324.20 97.93 °AUG~CC-PV(QZ-SZ) 325.80 96.33 dAUG-CC-PV(QZ-6Z) 326.43 95.71 atLi CC-PVQZ basis set with C CC-PVSZ basis set bLi CC-PVQZ basis set with c CC-PV6Z basis set cLi AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dLi AUG-CC-PVQZ basis set with C AUG-CC-PV6Z basis set The enthalpy of formation is not converged by the Q-zeta basis set for the unaugmented and augmented basis sets. Table 28 shows also results from mixed basis set calculations. In these calculations, we allowed the carbon basis set to progress beyond the Q-zeta level, but the lithium basis set did not progress pass the Q-zeta level. These basis sets are unusual, so the extrapolations in Table 29 do not include those values. We did not attempt extrapolation of the augmented basis sets. Since the constructed basis sets were not optimized, the extrapolation behavior would be unlike that of the Dunning optimized basis sets. We used the data from the unaugmented basis sets, excluding the mixed basis set calculations, to extrapolate to the complete basis set limit. Table 29 reports the extrapolations. 40 Table 29. Heats of Formation for Linear Li2C2 Extrapolated to the Complete Basis Set Limit Basis sets AHf (°°) AHf (E(°°)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ) 95.90 95.94 Schwartza(DTQ) 92.78 92.87 Schwartz4(DTQ) 96.33 96.33 Schwartz4(TQ) 94.75 94.75 Schwartz6(DTQ) 94.16 94.16 Schwartz6(TQ) 94.77 94.77 The extrapolated enthalpies of formation in Table 29 range from around 93 to around 97 kcallmol. Again, any extrapolated heat of formation that is higher than the best-unextrapolated value is not physically viable and highlighted in red. Keep in mind that we determined the highlighted values in Table 29 from extrapolations of the pure basis sets. The extrapolated value is higher than the value from unextrapolated mixed basis set values. Previously for HCCH, FCCF, and ClCCCl by the 5-zeta basis set, the enthalpy of formation was near convergence. It seems that the same may be true for Li. Without the 5-zeta basis set, the extrapolations are not as precise as previous examples. To correct for the core-valence correlation of the 1s shell on carbon and lithium, we made core-valence corrections. Table 30 presents those results as a function of basis set. Table 30. Core-Valence Correction for Linear L12C2 as a Function of Basis Set Basis Sets Core-Valence Correction (kcallmol) CC-PCVDZ -1 . 15 CC-PCVTZ -2.09 CC-PCVQZ -2.62 aCC-PCV(QZ-SZ) -2.74 aLi with CC-PCVQZ basis set C with cc-pCVSZ basis set The core-valence correction did not converge, but the magnitude of the correction is approximately the same as for the halogenated molecules. Table 31 reports complete 41 basis set extrapolation values that we calculated using the results calculated using the three unmixed basis sets. Table 31. Core-Valence Correction for Linear Li2C2 at the Complete Basis Set Limit Basis sets ACV(oo) ACV(E(oo)) CC-PCVXZ (kcallmol) (kcallmol) Schwartzor(DTQ) -4.65 1.07 Schwartz4(TQ) -2.93 -2.93 Schwartz6(TQ) -2.93 -2.93 Similar to CICCCI, the differences between the methods and extrapolation equations are large. These discrepancies may be due to differences among the nonlinear fit equations and the fitting methods created by inconsistencies in how accurate the fit for each equation and the method is to the data. In previous core-valence calculations, such as, HCCH and FCCF, we used a 5-zeta basis set. Similar to the ClCCCl molecule, we set the ACV correction for all the extrapolated linear Li2C2 heat of formation values to —2.93 kcallmol. Table 32 shows the values of the enthalpy of formation that we added after the missing core-valence correlation (-2.93 kcallmol), spin-orbit coupling (0.17 kcallmol) and relativistic effect (0.19 kcallmol) corrections. Table 32. AH, Values Corrected for Core-Valance Correlation, Spin-Orbit Coupling, and Relativistic Effects for Linear Li2C2 at the Complete Basis Set Limit for each Method Basis sets Corrected AH, (co) Corrected AH, (E(°°)) CC-PVXZ (kcallmol) (kcallmol) Schwartzor(DTQ) 90.21 90.28 Schwartz4(TQ) 92.18 92.18 Schwartz6(DTQ) 91.59 91.59 Schwartz6(TQ) 92.20 92.20 The enthalpy of formation of linear Li2C2 seems to be substantially larger than the enthalpy of formation of the previous acetylenes. The largest inconsistency between extrapolation equations is the range of 2 kcallmol between the Schwartza and Schwartz6 42 extrapolation equations. Table 33 presents selected values from Table 32, the value for the enthalpy of formation calculated from the unextrapolated enthalpy of formation in Table 28, and core-valence correction at the largest basis set. Table 33. Comparison of Heats of Formation of Linear L12C2 Basis Set AH, (co) kcallmol 2”This work 90.21 l*rhis work 92.18 cThis work 91.59 dUnextraEflated value 93.30 aSchwartzcr(DTQ) extrapolation of unaugmented basis set values with P(°°) method bSchwartz4(TQ) extrapolation of unaugmented basis set values with P(oo) method cSchwartz6(DTQ) extrapolation of unaugmented basis set values with P(°o) method dAH, from AUG-CC-PV(QZ-6Z) using ACV from CC-PCV(QZ-SZ) basis set Table 33 shows that the unextrapolated result from the AUG-CC-PV(QZ-6Z) heat of formation and the CC-PCV(QZ-6Z) core-valence correction is the largest heat of formation. The enthalpy values from Table 33 are generally around 92 kcallmol, but the Schwartzor result is closer to 90 kcallmol. 2.6 Planar L12C2 The doubly bridged or planar Li2C2 complex is the lowest energy configuration for the Li2C2 species with a 7.3 kcallmol (11.7 millihartree) energy difference between the linear and doubly bridged geometries. To find the equilibrium geometry, we calculated CCSD(T) optimized geometries for the planar Li2C2 species. These optimized geometries are extrapolated to the complete basis set and compared to previously determined theoretical geometries. Table 34 lists the geometry used in the heat of formation calculations. 43 Table 34. Optimized Geometries of Planar Li2C2 as a Function of Basis Set Basis RCC (ang) RCLi (ang) CC-PVDZ 1.2932 2.0406 CC-PVTZ 1.2730 2.0072 CC-PVQZ 1.2686 2.0049 Feller(DTQ) 1.2673 2.0047 Schwartza(DTQ) 1.2661 2.0045 Schwartz4(DTQ) 1.2660 1.9989 Schwartz4(TQ) 1.2660 2.0036 Schwartz6(DTQ) 1.2661 2.0053 Schwartz6(TQ) 1.2660 2.0053 24MBPT(2) 1.2808 1.9954 23MP2 1.282 2.017 USED 1.2673 2.0086 The optimized geometries in Table 34 are close to converging, and the extrapolated geometries are within 0.003A of the best-unextrapolated geometry and within 0.001A of the geometry used to calculate the heat of formation. The literature values from previous studies differ by 0.02A for the carbon-carbon bond and 0.002A for the carbon-lithium bond. Table 35 lists the vibrational frequencies of planar Li2C2 at the CC-PVTZ and AUG-CC-PVTZ basis sets. To conserve computation time, we removed the d and f gaussian functions from the lithium AUG-CC-PVTZ basis set, but we retained them for the carbon AUG-CC-PVTZ basis set. Table 35. Vibrational Frequencies for Planar Li2C2 Basis Sets Symmetry CCePVTZ AUG-CC-PVTZ vibration A (B3,,) 66 64 vibration B (B2,) 199 193 vibration C (83g) 306 302 vibration D (Ag) 564 557 vibration E (Blu) 685 681 vibration F (Ag) 1799 1793 Again, there are no imaginary frequencies to indicate that the planar complex is not a minimum. Figure 2 is a visual representation of the vibrational frequencies of planar Li2C2. Vibration A is a side view of the doubly bridged molecule. The second carbon atom is located directly behind the labeled carbon. Note that the vibration C resembles the type of motion which might move the planar species towards the formation of the linear species. Ll-> Li-> Li-p A <-C <—C-<—C C—C L1-> Li» «L1 X --------- -> Z --------- -> Z --------- -> A B C A L1 Li L1 C C C—C COC i Li Li L1 Z --------- 9 Z --------- -> Z --------- -> D E F Figure 2: Vibrational Modes for Planar Li2C2 Using the geometry RCC = 1.2673 A, RLic = 2.0086 A, ACCLi = 71.6 from Table 34 and vibrational frequencies calculated at the CCSD(T) level using the mixed AUG- CC-PVTZ basis set, we calculated dissociation energies at 0 K and heat of formation values at 298 K for the doubly bridged species. Table 36 shows our results. 45 Table 36. Calculated Dissociation Energies and Heats of Formation for Planar Li2C2 as a Function of Basis Set Basis Set De AH, kcallmol kcallmol cc-onz 300.86 119.87 CC-PVTZ 324.15 96.57 CC-PVQZ 330.84 89.89 aCC-PV(SZ-QZ) 332.62 88.11 bCC-PV(6Z-QZ) 333.47 87.26 AUG-CC-PVDZ 304.54 116.19 AUG-CC-PVTZ 326.28 94.45 AUG-CC-PVQZ 331.52 89.21 °AUG-CC-PV(SZ-QZ) 333.12 87.61 dAUG-CC-PV(6Z-QZ) 333.77 86.96 aLi CC-PVQZ basis set with C CC-PVSZ basis set bLi CC-PVQZ basis set with C CC-PV6Z basis set cLi AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dLi AUG-CC-PVQZ basis set with C AUG—CC-PV6Z basis set The unaugmented and augmented basis sets are not converged by the Q-zeta basis set. We extrapolated the data from the unaugmented basis sets, excluding the mixed basis set calculations, to the complete basis set limit. Table 37 shows the results of this investigation. Table 37. Heats of Formation for Planar L12C2 Extrapolated to the Complete Basis Set Limit Basis sets AH, (co) A501...» CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ) 87.19 87.23 Schwartzor(DTQ) 84.43 84.50 Schwartz4(DTQ) 87.36 87.36 Schwartz4(TQ) 86.03 86.03 Schwartz6(DTQ) 85.52 85.52 Schwartz6(TQ) 86.05 86.05 Again, the Schwartz4(DTQ) and Feller extrapolation results in an unphysical value higher than the unextrapolated values. 46 To correct for the frozen ls core on lithium and carbon, we calculated core- valence corrections using the Dunning CC-PCVXZ basis sets. Table 38 reports the results of these calculations. Table 38. Core-Valence Correction for Planar Li2C2 as a Function of Basis Set Basis Sets Core-Valence Correction (kcal/mol) CC-PCVDZ -1.31 CC-PCVTZ -2.19 CC-PCVQZ -2.68 aCC--PCV(QZ-SZ) -2.79 aLi with CC-PCVQZ basis set C with CC-PCVSZ basis set Similar to the linear species, the core-valence correction for planar Li2C2 has not converged. Yet, the core-valence correction for the planar molecule differs by less than 0.1 kcallmol from the linear core-valence correction. Table 39 reports the core-valence correction extrapolated to an infinite basis set. Table 39. Core-Valence Correction for Planar L12C2 at the Complete Basis Set Limit Basis sets ACV(°°) ACV(E(°°)) CC-PCVXZ (kcallmol) (kcallmol) Feller(DTQ) -3.30 ~2.95 Schwartza(DTQ) —4.43 1.14 Schwartz4(TQ) -2.96 -2.96 Schwartz6(TQ) -2.96 -2.96 Similar to the linear species, the extrapolated values for the variable exponent equations are erratic, so the core-valence correction used for the planar molecule is -2.96 kcallmol. Table 40 reports the enthalpy of formation for the planar species after we added the core-valence corrections (-2.96 kcallmol), spin-orbit coupling (0.17 kcallmol), and relativistic corrections (0.15 kcallmol). 47 Table 40. AH, Values Corrected for Core-Valance Correlation, Spin-Orbit Coupling, and Relativistic Effects for Planar Li2C2 at the Complete Basis Set Limit for each Method Basis sets Corrected AH, (co) Corrected AH, (E(°°)) CC-PVXZ (kcallmol) (kcallmol) Schwartzor(DTQ) 81.79 81.87 Schwartz4(TQ) 83.39 83.39 Schwartz6(DTQ) 82.89 82.89 Schwartz6(TQ) 83.41 83.41 The heat of formation results reported in Table 40 span a range of 2 kcallmol. Table 41 reports the better values from Table 40 and the combination of the heat of formation calculated with the AUG-CC-PV(QZ-6Z) basis set and the core-valence correction calculated using the CC-PCV(QZ-5Z) basis set. Table 41. Comparison of Heats of Formation of Planar Li2C2 Basis Set AH, kcallmol aThis work 81.79 brhis work 82.89 cThis work 83.41 dUnextrapolated value 84.49 aSchwartza(DTQ) extrapolation of unaugmented basis set values with P(°°) method bSchwartz4(T Q) extrapolation of unaugmented basis set values with P(oo) method cSchwartz6(DTQ) extrapolation of unaugmented basis set values with P(oo) method dAH, from AUG-CC-PV(QZ-6Z) using ACV from CC-PCV(QZ-SZ) basis set Table 41 shows that the extrapolated heats of formation are a kcallmol smaller than the unextrapolated heat of formation using larger basis sets. Table 42 shows a comparison of the enthalpy of formation for Li2C2 at its two ground-state geometries. 48 Table 42. Energy Difference between Linear and Planar Li2C2 Planar Li2C2 Linear Li2C2 Difference Basis Set AH, AH, kcallmol “This work 81.79 90.21 8.42 ”This work 83.39 92.18 8.79 cThis work 83.41 92.20 8.79 ‘Unextrapolated value 84.49 93.30 8.81 aSchwartzr1(DTQ) extrapolation of unaugmented basis set values with P(oo) method bSchwartz4(TQ) extrapolation of unaugmented basis set values with P(oo) method cSchwartz6(TQ) extrapolation of unaugmented basis set values with P(°o) method “AH, from AUG-CC-PV(QZ-6Z) using ACV from CC-PCV(QZ-SZ) basis set We compared the enthalpy of formation for both the linear and planar species and found the energy difference between the two configurations to be 8 kcallmol. We found the energy difference between the two configurations using De values with no thermal corrections to be 7 .3 kcallmol. 2.7 Linear Na2C2 Using the same process followed for calculating the properties of the Li2C2 molecules, we calculated the molecular geometries, vibrational frequencies, and enthalpy of formation of both Na2C2 species. We generated augmented CC-PVXZ basis sets by adding even-tempered basis functions to the sodium Dunning CC-PVXZ basis sets. Table 43 lists the gaussian function exponents added for augmentation of the CC-PVDZ, CC-PVTZ, and CC-PVQZ basis sets. Table 43. Added Diffuse Function Exponents to Create Na AUG-CC-PVXZ Basis Sets AUG-CC-PVDZ AUG-CC-PVTZ AUG-CC-PVQZ 8 0.00995 0.00942 0.00790 P 0.00648 0.00602 0.00323 D 0.0228 0.0296 0.02740 F --— 0.05588 0.0560 G --- --- 0.0861 49 We calculated CCSD(T) single point energy, geometry optimization, and vibrational frequency using these generated basis sets. Table 44 reports the calculations. Table 44. Optimized Geometries of Linear Na2C2 as a Function of Basis Set Basis RCC (ang) RCN a (ang) CC-PVDZ 1.2777 2.2427 CC-PVTZ 1.2592 2.2373 CC-PVQZ 1.2560 2.2378 Feller(DTQ) 1.2553 2.2376 Schwartz0t(DTQ) 1.2546 2.2376 Schwartz4(DTQ) 1.2533 2.2366 Schwartz4(TQ) 1.2541 2.2382 Schwartz6(DTQ) 1.2544 2.2387 Schwartz6(T Q) 1.2541 2.2382 USED 1.2549 2.2341 Table 44 shows that both the carbon-carbon and carbon-sodium bond length are converged to within 0.004A by the Q-zeta basis set. The extrapolated values differ less than 0.003A from the unextrapolated geometries, but the carbon-sodium bond length differs by 0.004A from the geometry used to calculate the enthalpy of formation. We calculated CCSD(T) vibrational frequencies at the CC-PVTZ and AUG-CC-PVTZ basis sets where the sodium basis set is void of any higher order angular momentum functions above a p orbital. Table 45 lists these frequencies. Table 45. Vibrational Frequencies of Linear Na 2C2 Basis Sets Symmetry CC-PVTZ AUG-CC-PVTZ (D) Cis-bend (nu) 45cml 51 cm" m) Trans-bend (rig) 85i cm" 69 cm'1 (A) s-CNa stretch (23g) 278 cm" 275 cm" (C) a-CNa stretch (2,) 475 cm'1 473 cm" (B) CC stretch (2,) 1922 cm'I 1907 cm" Figure 3 illustrates the motion of atoms during each of the vibrations. Table 45 shows that the trans-bend or vibration E is imaginary at the CC-PVTZ basis set, but it is real 50 when the basis set is augmented. Therefore, there is a question as to the whether the linear Na2C2 is a viable minimum. The vibration E diagram, Figure 3 shows that the trans-bend vibration is similar to the motion the linear molecule might take to form the planar configuration. Maybe the potential energy surface calculated using the CC-PVTZ basis set does not accurately describe the shallow well that is the linear Na2C2 minimum. Na—C—C—Na Na—C—C—Na Na—C—C—Na A B C t Na—T:i—l$a Nf—$:i—Ila Figure 3: Vibrational Modes of Linear Na2C2 Using the optimized geometry obtained in previous work', RCC = 1.255 A, RCNa = 2.234 A, and CCSD(T) vibrational frequencies from Table 45, we calculated the enthalpy of formation. Table 46 presents the heats of formation at 273 K and dissociation energies at 0 K for linear Na2C2 as a function of basis set. 51 Table 46. Calculated Dissociation Energies and Heats of Formation for Linear Na 2C2 as a Function of Basis Set Basis sets De AHf (kcallmol) (kcallmol) CC-PVDZ 258.94 137.70 CC-PVTZ 280.18 1 16.46 CC-PVQZ 287.59 109.05 aCC-PV(QZ-5Z) 289.62 107.02 bCC-PV(QZ-6Z) 290.57 106.07 AUG-CC-PVDZ 265.19 131.45 AUG-CC-PVTZ 283.78 1 12.86 AUG-CC-PVQZ 288.92 107.73 cAUG-CC-PV(QZ—5Z) 290.53 106.1 1 dAUG-CC-PV(QZ-6Z) 291.23 105.41 aNa CC-PVQZ basis set with C CC-PVSZ basis set bNa CC-PVQZ basis set with c CC-PV6Z basis set cNa AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dNa AUG-CC-PVQZ basis set with c AUG-CC-PV6Z basis set The enthalpy of formation is not converged by the Q-zeta basis set for either the unaugmented or augmented basis sets. The extrapolations shown in Table 47 do not include the larger basis sets above the unaugmented Q-zeta basis set. Table 47. Heats of Formation for Linear Na 2C2 Extrapolated to the Complete Basis Set Limit Basis sets AHf (°°) AHf (E(°°)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ) 105.09 105.65 Schwartzct(DTQ) 100.79 102.13 Schwartz4(DTQ) 107.1 7 107.1 7 Schwartz4(TQ) 104.78 104.78 Schwartz6(DTQ) 103.88 103.88 Schwartz6(TQ) 104.80 104.80 The extrapolated enthalpies of formation in Table 47 range from about 100 to about 107 kcallmol. Most of the extrapolated enthalpies of formation are very close to the 105.41 kcallmol value that we found using the AUG-CC-PV(QZ-6Z) basis set. 52 To correct for the core-valence correlation of the 2s and 2p shells on sodium and the frozen 1s orbital on carbon, we made core-valence corrections. Table 48 presents those results as a function of basis set. Table 48. Core-Valence Correction for Linear Na2C2 as a Function of Basis Set Basis Sets Core-Valence Correction (kcallmol) CC-PCVDZ -1.14 CC-PCVTZ -0.74 CC-PCVQZ -0.74 aCC-PCV(QZ-SZ) -0.97 “Na with CC-PCVQZ basis set C with CC-PCVSZ basis set The core—valence correction converges, and the magnitude of the correction is much smaller than that of the halogenated molecules and the two lithium complexes. The mixed basis set calculation provides a correction that is larger than the unmixed basis set. This result is unusual, but the mixing of basis sets does not insure a proper convergence to the basis set limit. Table 49 reports the complete basis set extrapolation values using the results that we calculated using the three unmixed basis sets. Table 49. Core-Valence Correction for Linear Na2C2 at the Complete Basis Set Limit Basis sets ACV(oo) ACV(E(oo)) CC-PCVXZ (kcallmol) (kcallmol) Feller(DTQ) -0.74 _--- Schwartzor(DTQ) -0.74 ---- Schwartz4(TQ) -0.73 -0.73 Schwartz6(TQ) -0.73 -073 The core-valence correction for the Feller(DTQ) and Schwartza equations using the P(E(oo)) method are not reported because the resulting values are not realistic. Similar to the lithium species, the differences between the methods for Schwartza and Feller extrapolation equations are large. As done previously in the ClCCCl and the lithium species, the ACV correction for all the extrapolated AH, we set values to -0.73 53 kcallmol. Table 50 shows the values of the enthalpy of formation after we added the missing core-valence correlation (-0.73 kcallmol), spin-orbit coupling (0.17 kcallmol), and relativistic effect (0.21 kcallmol) corrections. Table 50. AH, Values Corrected for Core-Valance Correlation, Spin-Orbit Coupling, and Relativistic Effects for Linear Na 2C2 at the Complete Basis Set Limit for each Method Basis sets Corrected AH, (co) Corrected AH, (E(oo)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ) 104.74 ---- Schwartzor(DTQ) 100.44 101.78 Schwartz4(TQ) 104.43 104.43 Schwartz6(DTQ) 103.53 103.53 Schwartz6(T Q) 104.45 104.45 The enthalpy of formation of linear Na2C2 seems to be about 10 kcallmol larger than the enthalpy of formation of linear Li2C2. The largest inconsistency between extrapolation techniques is a 7 kcallmol difference between Schwartza and Schwartz4 extrapolation results. Table 51 presents selected values from Table 50 and the value for the enthalpy of formation calculated from the enthalpy of formation and core-valence correction at the largest basis set. Table 51. Comparison of Heats of Formation of Linear Na2C2 Basis Set AH, (00) kcallmol 21This work 104.74 bThis work 100.44 °This work 104.43 “This work 104.45 °Unextrapolated value 104.82 method alFeller(DTQ) extrapolation of unaugmented basis set values with P(oo) method bSchwartzrr(DTQ) extrapolation of unaugmented basis set values with P(oo) °Schwartz4(T Q) extrapolation of unaugmented basis set values with P(oo) method dSchwartz6(T Q) extrapolation of unaugmented basis set values with P(oo) method °AH, from AUG-CC-PV(QZ-6Z) using ACV from CC-PCV(QZ-5Z) basis set 54 Table 51 shows the unextrapolated result from the AUG-CC-PV(QZ-6Z) heat of formation and the CC-PCV(QZ-5Z) core-valence correction to be closer to the fixed exponent extrapolations. 2.8 Planar Na2C2 The doubly bridged or planar N a2C2 complex is the lowest energy configuration for the Na2C2 species with a 11.2 kcallmol (17.8 millihartree) energy difference between the linear and doubly bridged geometries. Table 52 lists CCSD(T) optimized geometries as a function of basis set. Table 52 lists also the optimized geometries, extrapolated geometries to the basis set limit, and the geometry that we used to calculate the enthalpy of formation for planar Na2C2. Table 52. Optimized Geometries of Planar Na 2C2 as a Function of Basis Set Basis RCC (ang) RCNa (ang) CC-PVDZ 1.2958 2.3612 CC-PVTZ 1.2761 2.3543 CC-PVQZ 1 .27 16 2.3497 Feller(DTQ) 1.2703 2.3394 Schwartza(DTQ) 1.2689 2.2883 Schwartz4(DTQ) 1.2691 2.3498 Schwartz4(TQ) 1 .2690 2.3470 Schwartz6(DTQ) 1.2690 2.3459 Schwartz6(TQ) 1 .2690 2.3470 USED 1 .2704 2.3427 Both the carbon-carbon bond length and the carbon-sodium bond length have converged to two decimal places by the Q-zeta basis set. The extrapolated geometries vary only 0.001A from the carbon-carbon bond length we used to calculate the heat of formation, but the sodium-carbon bond length differs by as much as 0.008A from the bond length that we used to calculate the heat of formation. Even a geometry difference of this size will not affect the enthalpy of formation to any substantial amount. Table 53 lists the CCSD(T) vibrational frequencies for the planar sodium species. Similar to our 55 investigation of linear Na2C2, we removed the d and f gaussian functions from the sodium CC-PVTZ and AUG-CC-PVTZ basis set for the frequency calculations. Table 53. Vibrational Frequencies of Planar Na 2C2 Basis sets Symmetry CC-PVTZ AUG-CC-PVTZ vibration A (B3,) 42 cm" 48 cm'1 vibration B (B2u) 122 cm'l 119 cm ' vibration C (ng) 297 cm'l 296 cm ' vibration D (Ag) 276 cm'1 275 cm”1 vibration E (Blu) 462 cm'1 460 cm ' vibration F (Ag) 1790 cm'1 1782 cm'1 The vibrational frequencies listed in Table 53 are not imaginary. This data leads to the conclusion that both the linear and planar configurations are rrrinima on the potential energy surface. Figure 4 is a visual representation for the planar Na2C2, vibrational frequencies. Na» Na» Na» A 4-C +C+C E—C Na» Na-> «Na X --------- -> Z --------- + Z --------- -> A B C Na Na Na C~I~C C—C C0 C i Na I‘Ia Na 2 --------- -> Z --------- -> Z --------- -> D E F Figure 4: Vibrational Frequencies of Planar Na2C2 Using the geometry, RCC=1.2704 A, RNaC=2.3427 A, ACCNa=74.31 from Table 52 and vibrational frequencies calculated at the CCSD(T) level using the AUG-CC- 56 PVTZ basis set from Table 53, we calculated dissociation energies at 0 K and heat of formation values at 298 K for the doubly bridged species. Table 54 reports the results. Table 54. Calculated Dissociation Energies and Heats of Formation for Planar Na2C2 as a Function of Basis Set Basis Set De AH, kcallmol kcallmol CC-PVDZ 271.95 123.412 CC-PVTZ 292.44 102.921 CC-PVQZ 299.14 96.226 aCC-PV(SZ-QZ) 301.03 94.33 bCC-PV(6Z-QZ) 301.97 93.39 AUG-CC-PVDZ 275.87 119.50 AUG-CC-PVTZ 295.01 100.35 AUG-CC-PVQZ 300.09 95.28 °AUG-CC-PV(SZ-QZ) 301.71 93.65 dAUG-CC-PV(6Z-QZ) 302.40 92.96 a‘Na CC-PVQZ basis set with C CC-PVSZ basis set bNa CC-PVQZ basis set with C CC-PV6Z basis set cNa AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dNa AUG-CC-PVQZ basis set with C AUG-CC-PV6Z basis set Table 55 presents extrapolations to the complete basis set limit for the enthalpy of formation using the unaugmented unmixed basis set results. Table 55. Heats of Formation for Planar Na2C2 Extrapolated to the Complete Basis Set Limit Basis sets AHf (°°) AHf (E(°°)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ) 92.98 93.39 Schwartztx(DTQ) 89.54 90.49 Schwartz4(DTQ) 94.27 94.27 Schwartz4(TQ) 92.36 92.36 Schwartz6(DTQ) 91.65 91.65 Schwartz6(TQ) 92.38 92.38 The difference between the heat of formation between the linear and planar Na2C2 species is approximately 11 kcal/mol. 57 To correct for the frozen 2s and 2p core on sodium and ls core on carbon, we calculated core-valence corrections using the Dunning CC-PCVXZ basis sets. Table 56 reports the results of these calculations. Table 56. Core-Valence Correction for Planar Na2C2 as a Function of Basis Set Basis Sets Core-Valence Correction (kcallmol) CC-PCVDZ -l.09 CC-PCVTZ -0.57 CC-PCVQZ -0.7 1 aCC-PCV(QZ-SZ) -0.97 aNa with CC-PCVQZ basis set C with CC-PCVSZ basis set Like the linear species, the core-valence correction for planar Na2C2 has not converged, but more importantly, the core-valence correction for the planar molecule differs from the linear molecule at the T-zeta basis set. Otherwise, the core-valence correction for both the linear and planar species is approximately the same. Table 57 reports the core—valence correction extrapolated to an infinite basis set. Table 57. Core-Valence Correction for Planar Na2C2 at the Complete Basis Set Limit Basis sets ACV(°°) ACV(E(°°)) CC-PCVXZ (kcallmol) (kcallmol) Feller(DTQ) -0.64 ---- Schwartzor(DTQ) -0.64 ---- Schwartz4(TQ) -0.80 -0.80 Schwartz6(TQ) -0.80 -0.80 Similar to the linear species, the extrapolated values for the variable exponent equations are erratic or non-physical. For the planar molecule, we used the core-valence correction of -0.73 kcallmol. Table 58 reports the enthalpy of formation for the planar species after we added the core-valence correction (-0.73 kcal/mol), spin-orbit coupling (0.17 kcallmol), and relativistic corrections (0.21 kcallmol). 58 Table 58. AH, Values Corrected for Core-Valance Correlation, Spin-Orbit Coupling, and Relativistic Effects for Planar Na2C2 at the Complete Basis Set Limit for each Method Basis sets Corrected AH, (0°) Corrected AH, (E(oo)) CC-PVXZ (kcallmol) (kcallmol) Feller(DTQ) 92.63 93.04 Schwartzor(DTQ) 89.19 90.14 Schwartz4(TQ) 92.01 92.01 Schwartz6(DTQ) 91.30 91.30 Schwartz6(TQ) 92.03 92.03 The heat of formation results reported in Table 58 span a range of 5 kcallmol. Table 59 reports the better values from Table 58 and the combination of the heat of formation calculated with the AUG-CC-PV(QZ—6Z) basis set and the core-valence correction calculated using the CC-PCV(QZ-6Z) basis set. Table 59. Comparison of Heats of Formation of Planar Nang Basis Set AH, kcallmol aThis work 92.63 I’rhis work 89.19 °This work 92.01 “This work 92.03 °Unextmolated value 92.37 aFeller(DTQ) extrapolation of unaugmented basis set values with P(°o) method bSchwartzo.(DTQ) extrapolation of unaugmented basis set values with P(oo) method cSchwartz4(T Q) extrapolation of unaugmented basis set values with P(oo) method dSchwartz6(TQ) extrapolation of unaugmented basis set values with P(oo) method eAH, from AUG-CC-PV(QZ-6Z) using ACV from CC-PCV(QZ-SZ) basis set Table 60 lists the difference in the enthalpy of formation between the linear and planar Na2C2 species. 59 Table 60. EnergLDifference Between Linear and Planar Na2C2 Planar Li 2C2 Linear Li2C2 Difference Basis Set AH, AH, kcallmol alFeller(DTQ) 92.63 104.74 12.1 1 aSchwartzt3t(DTQ) 89.19 100.44 1 1.25 aSchwartz4(TQ) 92.01 104.43 12.42 aSchwartz6(TQ) 92.03 104.45 12.42 bUnextrapolated value 92.37 104.82 12.45 aExtrapolations of CC-PVXZ basis set values using P(oo) method I’AH, from AUG-CC-PV(QZ-6Z) using ACV from CC-PCV(QZ-SZ) basis set Similar to the lithium molecules, the energy difference between the heats of formation for the linear and planar sodium species is a kcallmol larger than the differences between the D, values where there is no correction for thermal effects. 2.9 Discussion The heats of atomization at zero Kelvin (0 K) for ClCCCl, FCCF, and HCCH are very similar values. The dissociation energy difference between HCCH and ClCCCl is approximately 60 kcallmol, whereas the difference between the enthalpies of formation is closer to 4 kcallmol. The difference between the FCCF and ClCCCl dissociation energies is approximately 35 kcallmol, but the difference between the enthalpies of formation are around 40 kcallmol. This behavior is primarily due to differences in the enthalpy of formation of the constituent atoms and the size of the zero point energy. 60 Table 61. Dissociation Enegies and Heats of Atomization for All Molecules Linear Planar Linear Planar HCCH FCCF ClCCCl Li2C2 Li2C2 Na2C2 Na2C2 Dc (kcallmol) 408° 388b 355° 335d 342d 300° 310° Do (kcallmol) 392° 379b 348° 331d 337d 296° 305° AHam (kcallmol) 393° 380b 348° 330d 338d 296° 306° method method method method a'Schwartzot(Q56) extrapolation of augmented basis set values with P(oo) method bSchwartzot(T Q5) extrapolation of doubly augmented basis set values with P(oo) cSchwartzchI‘ Q5) extrapolation of doubly augmented basis set values with P(°°) dSchwartzoi(DTQ) extrapolation of unaugmented basis set values with P(oo) °Schwartza(DTQ) extrapolation of unaugmented basis set values with P(oo) All the substituted acetylenes and acetylene itself have dissociation energies of the same magnitude and very different heats of formation. This behavior is primarily due to the contributions from the vibrational frequencies of the molecule discussed and the heats of formation of its constituent atoms. The core-valence corrections for all the molecules, except the sodium molecule, are comparable. 61 2.10 References 1. D. Gearhart, J. F. Harrison, K. L. C. Hunt ( In preparation) 2. Chase, M.W., Jr., NIST-JANAF Therrnochemical Tables, Fourth Edition, J. Phys. Chem. Ref. Data, Monograph 9, 1998, 1-1951. 3. S. Parthiban, J. M. Martin, J. F. Liebman, Mol. Phys, 100, 453 (2002). 4. C. W. Jr. Baushlicher,A. Ricca, J. Phys. Chem. A, 104, 4581 (2000). 5. Werner, H. J.; Knowles, P. J .; Almof, J.; Amos, R. D.; Deegan, M. J. 0.; Elbert, S. T.; Hampel, C.; Meyer, W.; Peterson, K.; Pitzer, R.; Stone, A. J .; Taylor, P. R.; Lindh, R.; Mura, M. E.; Thorsteinsson, T. Molpro, a package of ab initio programs. 6. Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, 0.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, 1.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.6; Gaussian, Inc., Pittsburgh, PA, 1998. 7. TH. Dunning, Jr., J. Chem. Phys, 90, 1007 (1989). 8. DE. Woon and TH. Dunning, Jr., J. Chem. Phys, 98, 1358 (1993). 9. R. A. Kendall, T. H. Dunning, R. J. Harrison, J. Chem. Phys, 96, 6796 (1992). 10. D. E. Woon, K. A. Peterson, T. H. Dunning, Unpublished. 11. Moore, C. B. Atomic energy levels; Natl. Bur. Stand. (US); 1949,circ. 467. 12. D. Feller, D., J Chem Phys, 96, 6104 (1992). 13. J. M. L. Martin, Chem. Phys. Lett. 259, 669 (1996). 14. C. Schwartz, in: Methods in computational physics, ed. 3.]. Alder (Academic Press, New York, 1963). 15. w. Kutzclnigg. Theor. Chim. Acta 68, 445 (1985). 62 16. W. Kutzelnigg and J .D. Morgan 111, J. Chem. Phys. 96, 4484 (1992); 97, 8821 (1992) (E)- 17. RN. Hill, J. Chem. Phys. 83, 1173 (1985). 18. G. Strey, I. M. Mills, J Mol Spec, 59, 103 (1976). 19. Shimanouchi, T., Tables of Molecular Vibrational Frequencies Consolidated Volume II, J. Phys. Chem. Ref. Data, 1972, 6, 3, 993-1102. 20. J. Briedung, T. Hansen; W. Thiel, J Mol Spec, 179, 73 (1996). 21. T. C. Ehlert, J. Phys. Chem., 73, 949 (1969). 22. Tables of interatomic distances and configuration in molecules and ions; The Chemical Society: London, 1958. 23. P. Schleyer, J. Phys. Chem, 94, 5560 (1990). 24. Jaworski, A., Person, W., Adamowicz, L., Bartlett, R., International Journal of Quantum Chemistry Symposium, 1987, 21, 613. 63 Chapter 3 Quadrupole Moments of HCCH, FCCF, CICCCI, Li2C2, and Na2C2 3.1 Introduction An important facet of intermolecular interactions and key in understanding intermolecular interactions is the permanent electronic moment of a molecule. For the HCCH, FCCF, CICCCI, Li2C2, and Na2C2 molecules, the first permanent non—vanishing electric moment is the quadrupole moment, and since quadrupole moments have been shown to play an important role in chemistryLz'z‘IA's'“:7 , the quadrupole moments of these molecules influences the interactions of these molecules with others. Although quadrupole moments of molecules are difficult to determine experimentally, they are very simple to calculate. Unfortunately, the composition of and chemical implications of quadrupole moments and the basis set and electron correlation dependence of quadrupole moment calculations are still under investigation. From the work of Lawson and Harrisons, it was shown for the 13202;) molecule, the quadrupole moment was heavily influenced by the level of correlation in the calculation. Using a T-AUG-CC-PVSZ basis set, the quadrupole moment at the MRCI level was 0.4759 ea?) , whereas the RHF result reported a value of 1.055 eag . It was later shown that this large difference was due to the insufficient description of it bonding in the P2 molecule within the SCF calculation. The Lawson prediction of the quadrupole moment of the C12 (12; ) molecule showed the differences between the SCF (2.2846 eag ) and MRCI (2.2998 eag ) calculated values were minute which is due to the lack of 7: bonding in C12. From the same work, the size of the basis set used in calculations greatly influenced the magnitude and sometimes the sign of the calculated quadrupole moments. 65 For all the addressed molecules, the convergence of the quadrupole moments with unaugmented basis sets was considerably slower than that of the augmented basis sets. For P2(12; ) the difference between the MRCI quadrupole moment calculated at the CC- PVDZ and CC-PVSZ basis set was 0.6822 ea?) , whereas the difference between the AUG-CC-PVDZ and AUG-CC-PVSZ quadrupole moments was only 0.1888 atomic units. The difference between the AUG-CC-PVSZ and CC-PVSZ quadrupole moments was 0.0978 atomic units. From this data, it was determined that the addition of diffuse s, p, and d functions upon augmentation not only allowed the quadrupole to converge faster, but the augmentation of the basis sets was necessary for a proper description of the quadrupole moment of diatomics. In this manuscript we studied seven molecules. Two of those molecules have two different geometry types, a linear and a doubly bridged! geometry. For the linear I molecules—acetylene, the doubly halogenated acetylenes, and the linear doubly alkalized acetylides—there is only one unique quadrupole making the description of the quadrupole simple, but during our investigation of the quadrupole moments of the doubly alkalized acetylides, the existence of a second geometric minimum on the potential energy surface was reaffirmed. The second geometry, a doubly bridged geometry, has two unique quadrupole moments, making the interpretation slightly more complicated. Therefore, we hope that further investigation of the quadrupole moments of these alkalized acetylides, as well as the doubly halogenated acetylenes, will provide additional enlightenment about the relationship between the magnitude and the sign of the quadrupole moment, as well as the molecule’s electronic structure. The intention of this discussion is to investigate the basis set dependence of the quadrupole moments for the 66 aforementioned molecules and the influence of different correlation methods on the calculated results. Although there has been at least one theoretical study on the FCCF and ClCCCl quadrupole moments, experimental quadrupole moments of the doubly halogenated acetylenes have yet to be determined due to the high reactivity of these molecules. The metal acetylides have neither experimental nor calculated quadrupole moment results with which to compare our results. Therefore, similar to Chapter 2, because of the limited information for the Li2C2, Na2C2, FCCF, and ClCCCl quadrupole moments, we calculated the quadrupole moment of a heavily studied molecule, HCCH, as a gauge for the accuracy of the calculated quadrupole moments in this manuscript. 3.1.1 Computational Details Using Molpro2000, we determined all CCSD(T), DFT(B3LYP) and SCF single point and geometry optimization calculations. We used the Dunning CC-PVXZ, AUG- CC-PVXZ, and D-AUG-CC-PVXZ basis sets, as well as AUG-CC—PVXZ basis sets constructed on site from Dunning CC-PVXZ basis sets in our calculations. We used a field gradient of 0.0001 atomic unit to make field gradient calculations. We determined quadrupole densities using locally written codes. We used the Z-axis as the internuclear axis for the linear molecules. For the linear molecules, the quadrupole moment defined is the traceless quadrupole moment so 1 . . that (9 xx = (9 y, = -2- (922 , and by convention the (9,; component is taken as the quadrupole moment. For the nonlinear molecules, the metal atoms lie on the Z-axis while the carbon atoms lie on the Y-axis. The quadrupole moment of the planar molecules is traceless so 67 that®xx + (9yy + (9n = 0 , but since (9,, 7E (9,0,, both of the two quadrupole moment components, (922 and (9,,, are needed for a full description of the molecular quadrupole moment. 3.1.2 Multipole Expansion The definition of the quadrupole moment stems from an expansion of the electrostatic potential. Figure 1 illustrates a charged particle Q located at a distance 5 from the origin with a potential at a point P equal to the magnitude of Q divided by the distance between Q and the point P. Equation (1) gives the mathematical representation of the relationship. C2 r Origin Figure 1: Diagram of Point Charge not located at Origin ) Q Q (1) <1)R=—=—:—. ( |'r‘| 'R-El Expanding the potential around 8'" = 0 results in the expression in equation (2), ,,,,|\il)=ea,,. (11) 7O A l N A A A2 INK A A A2 (9,1,3 =§Zl3rairl3i —r, +§KZBraKrI3K —r,(. (12) i= =1 Although the expectation value of the quadrupole moment is the most accurate method, at the time of these calculations, there was no software to allow this type of calculation to be done at the CCSD(T) level. Instead we calculated the CCSD(T) quadrupole moments using a finite field calculation. If the energy of a system is expanded as a function of the field gradient, the expression for the energy takes the form of equation (13). dB 1 82E E F' E F ——F' F' ( ): “ii—FEB “B 2311,3811,” 78 (13) 1 03B PEBFifiFE9+ +58 wary, 81:; The derivatives of the energy with respect to the field gradient are assigned physical interpretations. Equation (14) reflects the quadrupole moment as the leading term in the expansion of the energy as a function of the field gradient. Equation (14) includes a few of the trailing terms. We interpret these trailing terms as the change in the quadrupole as a function of the field gradient. BE 1 _-—e 817,, 3 “‘3 32E __13®mi_ 1 ——C . . 14 arises”, 3 or“, 3 “5'75 ( ) 83B _ _1 a__®__a[i _1 G argflasaargg 3 85,811,, 3 “3:75;” 71 If we substitute the results of equation (14) into equation (13) (which is the energy of a molecule as a function of the field gradient), the quadrupole moment and other terms take the form of equation (15). E(F')= 130 -—1- l l 39aBFEB-gcaawsf‘3fi6‘fiGaaweSxJEBPisFEcp-m - (15) If we calculate the energy of a molecule with a positive and negative field gradient, the difference between the two energies takes the form of equation (16). l l l E(- FI) : EO + 3 aaflFdfi - g CaB;78FdBF;6 + EGanlethdBFyéFEo l l l — 15(17): 130 + 3 9011311313 + g (3115;751:3355 + 15 Ga3;y5;e¢pF&sP§aFE«p (16) 2 l E(F')- 13(- 17) = 3911135113 + gGaa;ya;e¢F&aP§5Fé¢- Examination of equation (16): By choosing a field gradient small enough to cause the contributions of the trailing terms to be minute, the quadrupole moment is isolated. A comparison of the results of both the expectation value of the quadrupole moment and the finite field quadrupole moment shows that not only is there an ability to select a gradient small enough to minimize the contribution of the higher order terms, but there is also a quick check of both methods. 3.2 HCCH We calculated the CCSD(T), DFT(B3LYP), and SCF quadrupole moments for the nonvibrating HCCH molecule at the Strey and Mills9 experimental geometry, RCC = 1.2033 A and RCH = 1.0605 A. Table 1 lists each result as a function of basis set. 72 Table 1. Quadrupole Moment, 9 (eafi ),of HCCH SCF CCSD(T) DFT(B3LYP) Basis Set Field Field Field <9 3 ) Gradient Gradient <9 “ ) Gradient CC-PVDZ 5.2112 5.2112 4.5078 4.6171 4.6172 CC-PVTZ 5.4186 5.4187 4.8010 4.9014 4.9014 CC-PVQZ 5.4345 5.4345 4.8428 4.8981 4.8981 CC-PVSZ 5.4444 5.4444 4.8608 4.9090 4.9092 CC-PV6Z 5.4442 5.4442 4.8652 4.9079 4.91 15 AUG-CC-PVDZ 5.4689 5.4689 4.7721 4.8739 4.8739 AUG-CC-PVTZ 5.4577 5.4577 4.8451 4.9173 4.9171 AUG-CC-PVQZ 5.4456 5.4455 4.8570 4.8722 4.8723 AUG-CC-PVSZ 5.4445 5 .4445 4.8634 4.9078 4.9068 AUG-CC-PV6Z 5.4435 5.4435 4.8661 4.8903 4.8901 D-AUG-CC-PVDZ 5.4557 5 .4557 4.7584 4.8650 4.8643 D—AUG-CC-PVTZ 5.4456 5.4456 4.8333 4.8934 4.8940 D-AUG-CC-PVQZ 5.4441 5.4441 4.8359 4.8907 4.8896 Table 1 compares the two computational methods that we used to calculate the SCF and DFT quadrupole moments. The results of the two methods should be equal, but the difference between the results for the SCF quadrupole moments at each basis set is slight and only affects the quadrupole moment at the fourth decimal place. We found that the difference between some SCF quadrupole moments was zero. The DFT results differ between the two methods at the third decimal place. The SCF quadrupole moment converges to two decimal places by the 52 basis set and is unaffected by augmentation by the QZ basis set. By the 52 basis set the CCSD(T) quadrupole moment has converged to two decimal places. The two correlated methods converge and agree to one decimal place, while the DFT(B3LYP) method converges to a larger value than that of the CCSD(T) method. The difference between the correlated and uncorrelated quadrupole moment is less than 1 eag. Table 2 is a tabulation of experimental and calculated values for the quadrupole of HCCH. 73 Table 2. HCCH madrupole Moments 9(eag ) Method Reference 5.366 SCF 10 5.443 SCF l 1 5.460 SCF 12 5.426 SCF 13 5.05, 5.24 SCF 14 5.444 SCF This work 4.703 BLYP l 1 4.890 DFT(B3LYP) This work 4.925 CC 13 4.88 MP4 15 4.787, 4.795,4.806 MP4, QCISD, BD(T) 11 4.717 MRCI 16 4.866 CCSD(T) This work 4.71 10.14 Field gradient-induced birefringence 17 5.65 $0.07 Cotton-Mouton effect 18 4.03 10.30 Collision-induced far-infrared absorption 19 The range in experimental values for the quadrupole moment of HCCH is as wide as the range in theoretical values. Although the SCF calculated results of other researchers are comparable to the SCF quadrupole moment calculated in this work, the correlated quadrupole moments vary within methods and even between methods. The correlated quadrupole moments differ from the experimental values, but these values are not corrected for molecular vibrations. By correcting the CCSD(T) quadrupole moment for vibrational contributions”, the CCSD(T) quadrupole moment falls within experimental error of the field gradient-induced birefringence quadrupole”. 3.3 FCCF We examine FCCF as one of two doubly halogenated acetylenes in this chapter. The doubly halogenated acetylenes are very reactive, making the calculation of the quadrupole moment possibly the only route available for determining the quadrupole. We used the equilibrium geometry provided by Briedung et alz', RCC = 1.186 A and 74 ch=1.2835 A, to calculate the SCF, CCSD(T), and DFT(B3LYP) quadrupole moments as a function of basis set. Table 3 reports the results. Table 3. Quadrupole Moment, (9 (eafi ),of FCCF SCF CCSD(T) DFT(B3LYP) Basis Set Field Field Field <9 ‘2 > Gradient Gradient (9 a) Gradient CC-PVDZ 0.9726 0.9726 0.4090 0.0534 0.0534 CC-PV'IZ 0.8457 -0.8457 0.4569 0.2783 0.2783 CC-PVQZ 0.8986 0.8986 0.5825 0.4419 0.4419 cc—vaz 0.9225 0.9225 0.6343 0.5104 0.5108 AUG-CC-PVDZ -1.0335 4.0335 0.7860 0.6003 0.6004 AUG-CC-PVTZ 0.9430 0.9429 -0.6485 0.5404 0.5391 AUG-CC-PVQZ 0.9130 0.9130 0.6357 0.5163 -0.5180 AUG-CC-PVSZ 0.9168 -0.9168 0.6400 0.5218 0.5245 D-AUG-CC-PVDZ 0.8547 0.8547 0.6367 -0.5128 0.5126 D-AUG-CC-PVTZ 0.9067 0.9067 0.6156 0.5060 0.5069 D—AUG-CC-PVQZ 0.9119 0.9119 -0.6331 0.5141 0.5152 D-AUG-CC-PVSZ 0.9157 0.9157 -0.6389 0.5182 0.5193 Interestingly, the substitution of fluoride for hydrogen in acetylene causes a change in the sign of the quadrupole moment and lowers the magnitude greatly. We discuss this result later. The change in sign is attributed to the size of the fluorine atom quadrupole moment and the electronegativity of the fluoride atom. The quadrupole expectation value for the SCF reproduces an equivalent to the quadrupole that the field gradient method produces, as expected. Again, there is some discrepancy in the DFT values, but in general they are consistent to the second decimal place. Table 3 shows that the convergence is slow for all three methods. All the calculated quadrupoles are dependent on the level of augmentation of the basis set, especially the DFT(B3LYP) quadrupoles. The SCF quadrupoles have only converged to one decimal place by the augmented 52 basis set, whereas the correlated methods have converged to two decimal places by the augmented QZ basis set. The two correlated 75 quadrupoles are within 0.1 atomic unit of each other, and the uncorrelated quadrupole is within 0.4 atomic units of the two correlated methods. Table 4 lists the results of this work with other calculated results for the quadrupole of FCCF. Table 4. FCCF Quadrupole Moments 6(ea3 ) Method Reference -0.9085 SCF 22 -0.9157 SCF This work -0.6524 MP2 22 -O.5193 DFT(B3LYP) This work -0.6389 CCSD(T) This work The results of this work and the results of Maroulis are equivalent to one decimal place for the SCF quadrupole and are within 0.1 atomic unit of each other for the correlated calculations. The FCCF calculated quadrupole moments were not corrected for vibration. 3.4 CICCCI We calculated SCF, CCSD(T), and DFT(B3LYP) quadrupoles for the second doubly halogenated acetylene, CICCCI, at the experimental geometry, Rcc=l .205 A and RCIC=1.635 A, as a function of the Dunning basis sets. Table 5 lists these results. 76 Table 5. Quadrupole Moment, 6 (ea?) ),of CICCCI CCSD(T) DFT(B3LYP) Basis Set Field Field Field <9 a ) Gradient Gradient (8a) Gradient CC-PVDZ 3.9317 3.9316 3.7337 4.1042 4.1037 CC-PVTZ 3.9343 3.9342 3.8524 3.9956 3.9960 CC-PVQZ 3.9253 3.9252 3.7892 3.9157 3.9167 CC-PVSZ 3.9353 3.9352 3.8054 3.8977 3.8949 AUG-CC-PVDZ 4.0586 4.0586 3.7755 3.8246 3.8236 AUG-CC-PVTZ 3.8568 3.8568 3.7970 3.7688 3.7674 AUG-CC-PVQZ 3.8783 3.8782 3.7595 3.7787 3.7787 AUG-CC-PVSZ 3.8988 3.8987 3.7672 3.7909 3.7905 D-AUG-CC—PVDZ 3.9381 3.9379 3.6686 3.7565 3.7563 D-AUG-CC-PVTZ 3.8219 3.8217 3.7492 3.7387 3.7384 D-AUG-CC-PVQZ 3.8685 3.8684 3.7478 3.77 12 3.7674 D-AUG-CC-PVSZ 3.9006 3.9005 3.7683 3.7918 3.7952 Remarkably, the quadrupole moment of the chlorinated acetylene has the same sign and close to the same magnitude as that of HCCH. This similarity comes as a surprise when compared to the quadrupole of FCCF. Therefore, the negative quadrupole of FCCF is not solely due to electronegativity. The differences in quadrupoles calculated by expectation value and field gradient are slight. We detected most differences in the fourth decimal place within the SCF calculations. Again, the DFT results are not equivalent, but still comparable. The results for all calculations are slow to converge beyond the second decimal place, but they are comparably close in magnitude. All the quadrupoles have converged to one decimal place by the Q2 basis set. The SCF is converging to a higher value than the correlated methods, and the difference between the correlated methods is less than 0.04 atomic units. The relative difference between the DFT and CCSD(T) results may be an indication of the level of covalent bonding in the CICCCI molecule. Table 6 lists other calculated results for the quadrupole moment of CICCCI. 77 Table 6. ClCCCl Quadrglole Moments 9(ea3) Method Reference 3.9140 SCF 22 3.9006 SCF This work 3.6612 MP2 22 3.7952 DFT(B3LYP) This work 3.7683 CCSD(T) This work The SCF results of this work are equivalent to one decimal place with the SCF result provided by Maroulis, and the correlated results are within 0.2 ea?) of the result provided by Maroulis. Again, the quadrupole moment of ClCCCl was not corrected for vibration. 3.5 LizCz Since there is no experimental geometric information provided for dilithium acetylide in the literature, we calculated an equilibrium geometry. In Chapter 2, we explain the process used to calculate the equilibrium geometries and reaffirm that the metal acetylides have two equilibrium geometries. First, the linear molecule geometry of RCC = 12531134 . RCLi = 1.8943A , and the doubly bridged molecule geometry of RCC = 1.2673A , RCLi = 2.0086A , and 4 CCLi = 71.6° , seem to locate the lithium atoms very far from the carbon atoms, so that the atoms seem to be hanging off a C2 species. 3.5.] Molecular Quadrupole Moment Each geometry has its own quadrupole moment. The linear molecule, like the other linear species discussed in this paper, has one unique component to the quadrupole moment, which lies along the internuclear line, while the doubly bridged or planar molecule has two unique quadrupole moment components, one parallel to the carbon atoms and one parallel to the Li atoms. 78 3.5.2 Linear We used the geometry, RCC = 1.531A , RCLi = 1.8943A, to calculate the quadrupole moment of linear dilithium acetylide. Table 7 lists the results. Table 7. Quadrupole Moment, (9 (ea?) ),of Linear LizCz SCF CCSD(T) DFT(B3LYP) Basis Set Field Field Field (9“) Gradient Gradient <9“) Gradient CC-PVDZ 35.921 1 35.9209 34.7707 34.2305 34.2295 CC-PV'IZ 36.1191 36.1189 35.1960 34.5417 34.5412 CC-PVQZ 36.3687 36.3685 35.4927 34.7938 34.7934 aCC-(SZ-QZ) 36.4222 36.4221 35.5717 34.8403 34.8388 bCC-(6Z-QZ) 36.4878 36.4877 35.6443 34.8973 34.8978 AUG-CC-PVDZ 36.6568 36.6566 35.7495 35.0863 35.0855 AUG-CC-PVTZ 36.5193 36.5191 35.6585 34.9204 34.9184 AUG-CC-PVQZ 36.5094 36.5093 35.6662 34.9233 34.9228 °AUG-CC-(SZ-QZ) 36.5083 36.5082 35.6749 34.9248 34.9241 dAUG-CC-(6Z-QZ) 36.5078 36.5077 35.6787 -- -- alLi CC-PVQZ basis set with C CC-PVSZ basis set bLi cc-onz basis set with C CC-PV6Z basis set cLi AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dLi AUG-CC-PVQZ basis set with c AUG-CC-PV6Z basis set One of the most interesting aspects of the Li2C2 quadrupole moment is the magnitude. The magnitude of linear LizCz is nearly 10 times the magnitude of the ClCCCl quadrupole moment. The quadrupole is so large that the differences in the quadrupole moment between the unaugmented and augmented basis sets is minute. The differences are only 2% of the total value at the DZ basis set and 0.05% at the largest basis set. Again, the difference between the expectation value and field gradient methods is minute for the SCF quadrupoles; however, the DFT results show the field gradient has some strong influence beyond the first decimal place. Also note that the CCSD(T) results are sandwiched between the DFT and SCF results as the SCF results are converging to 79 the higher value. The difference between the DFT and SCF results is less than 2 atomic units which is around 6% of the total quadrupole moment. 3.5.3 Planar Since there are two unique quadrupole moment components for the planar quadrupole, a unique property of doubly bridged molecules with D21I symmetry, we calculate the Z2 and YY components. By calculating two components, the third is known since the quadrupole moment is traceless. For these calculations, keep in mind that the carbon atoms lie on the Y axis and that the Li atoms lie on the Z axis. We used the geometry provided in Chapter 2, RCC = 1.2673A, RCLi = 2.0086A, and A CCLi = 716°, to calculate the SCF, CCSD(T), and DFT @n for planar dilithium acetylide. Table 8 reports the results as a function of basis set. Table 8. Quadrupole Moment, 9,, (ea?) ),of Planar Li2C2 SCF CCSD(T) DFT(BBLYP) Basis Set Field Field Field <9 3’: > Gradient Gradient (9 u ) Gradient CC-PVDZ 26.4236 26.4235 25.8323 25.3724 25.3720 CC-PVTZ 26.2621 26.2619 25.8399 25.2043 25.2023 CC-PVQZ 26.2875 26.2874 25.9046 25.2641 25.2632 aCC-(5Z-QZ) 26.3001 26.2999 25.9366 25.2872 25.287 1 bCC-(6Z-QZ) 26.3076 26.3074 25.9538 25.3017 25.2999 AUG-CC-PVDZ 26.4269 26.4267 26.0478 25.4179 25.4198 AUG-CC-PVTZ 26.3124 26.3123 25.9502 25.2977 25.2967 AUG-CC-PVQZ 26.31 15 26.31 14 25.9538 25.3068 25.3067 cAUG-CC-(SZ-QZ) 26.3094 26.3092 25.9564 25.3070 25.3054 dAUG-CC-(6Z-QZ) 26.3089 26.3088 25.9578 25.3064 25.3051 aLi CC-PVQZ basis set with C CC-PVSZ basis set bLi CC-PVQZ basis set with C CC-PV6Z basis set cLi AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dLi AUG-CC-PVQZ basis set with C AUG-CC-PV6Z basis set Note the magnitude and sign of the quadrupole component. Like the linear species it is large, but it is not as positive. We compared the unaugmented and 80 augmented quadrupoles and found no need for augmentation in order to calculate the quadrupole component to three significant figures. The unaugmented and augmented suites of basis sets are equivalent to the units place when rounded. The differences between the two calculation methods are consistent with previous results in this study. Also note, the SCF and CCSD(T) quadrupole moments are close in magnitude while the DFT result is a slight outlier. We used the same geometry to calculate the SCF, CCSD(T), and DFT results for the YY component of the planar molecule’s quadrupole moment. Table 9 lists the results. Table 9. Quadrupole Moment, 3,, (ea% ),of Planar Li2C2 SCF CCSD(T) DFT(B3LYP) Basis Set Field Field Field <9 W > Gradient Gradient (9” > Gradient CC-PVDZ 46.0693 46.0693 -15.8702 45.4046 45.4047 CC-PVTZ 46.1829 -16.1829 46.1661 45.6996 45.6995 CC-PVQZ 46.2317 -16.2317 46.2694 45.8119 -15.8110 ‘CC-(SZ-QZ) 46.2663 46.2663 46.3300 45.8685 45.8674 bCC-(6Z-QZ) -l6.283l 46.2831 46.3687 45.9055 45.9046 AUG-CC-PVDZ 46.1994 46.1995 46.3309 45.8374 45.8384 AUG-CC-PVTZ 46.2843 46.2843 46.3798 45.9184 45.9165 AUG-CC-PVQZ 46.2761 46.2761 46.3706 45.9114 45.9088 “AUG-CC-(SZ-QZ) 46.2739 46.2739 46.3697 45.9099 45.9107 dAUG-CC-(6Z-QZ) 46.2736 46.2737 46.3699 45.9095 45.9112 a‘Li CC-PVQZ basis set with C CC-PVSZ basis set bLi cc-onz basis set with c CC-PV6Z basis set cLi AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dLi AUG-CC-PVQZ basis set with c AUG-CC-PV6Z basis set Again, due to the magnitude of the quadrupole, we determined little need for the augmentation of the basis set. The two methods are consistent with the remainder of the study. The SCF behaves well, while the DFT results differ in the second decimal place. The YY component quadrupoles are nearly equivalent. The CCSD(T) and SCF YY component are closer to each other than they are to the DFT result. 81 3.6 Na2C2 Similar to Li2C2, there are two viable minima on the potential surface. The linear geometry is RCC = 1.2549A, RCNa = 2.2341A, and the planar geometry is RCC = 1.2704A, RCNa = 2.3427A, A CCNa = 74.3°. Again, the large separations between the Na atoms and carbon atoms seem to describe two sodium ions attached to a C2 molecule. 3.6.1 Linear Table 10 lists SCF, DFT, CCSD(T) quadrupole calculations at the aforementioned linear geometry as a function of the Dunning basis sets. Table 10. Quadrupole Moment, (9 (ea?) ),of Linear Na2C2 SCF CCSD(T) DFT(B3LYP) Basis Set Field Field Field <9 ZZ > Gradient Gradient <9 a) Gradient CC-PVDZ 47.5156 47.5143 44.4711 42.4321 42.4258 CC-PVTZ 48.4753 48.4741 46.0046 43.2959 43.2893 CC-PVQZ 48.6964 48.6953 46.4453 43.5136 43.5060 aCC-(SZ-QZ) 48.6933 48.6922 46.5153 43.5297 43.5241 bCC-(6Z-QZ) 48.7012 48.7001 46.5590 43.5392 43.5260 AUG-CC-PVDZ 49.0474 49.0462 46.4530 43.8956 43.8890 AUG-CC-PVTZ 48.8505 48.8494 46.5903 43.6743 43.6638 AUG-CC-PVQZ 48.7065 48.7054 46.5634 43.5591 43.5563 cAUG-CC-(SZ-QZ) 48.6725 48.6714 46.5663 -- -- dAUG-CC-(6Z-QZ) 48.6368 48.6357 46.5490 -- -- “Na CC-PVQZ basis set with C CC-PVSZ basis set bNa CC-PVQZ basis set with c CC-PV6Z basis set cNa AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dNa AUG-CC-PVQZ basis set with c AUG-CC-PV6Z basis set Again, due to the magnitude of the quadrupole moment, the level of augmentation has a small influence. The magnitude of the calculated quadrupole is larger than the magnitude in the Li case. The SCF and CCSD(T) results are not nearly as equivalent as they were in the Li case. The SCF converges to a higher value than the CCSD(T) results, and the DFT quadrupole converges to the lowest value which is the same as in the Li case. The two 82 computation methods behave differently than previously in this study with the SCF values deviating as much as the DFT values. 3.6.2 Planar We used the calculated planar geometry for N a2C2, RCC = 1.2704A, RCNa = 2.342721, 2 CCNa = 743°, to calculate SCF, CCSD(T), and DFT quadrupoles at various basis sets for the ZZ component of the quadrupole moment. Table 11 lists the results. Table 11. Quadrupole Moment, on (eaf, ),of Planar Na2C2 SCF CCSD(T) DFT(B3LYP) Basis Set Field Field Field <6 32) Gradient Gradient (6 7“) Gradient CC-PVDZ 36.3662 36.3655 35.3337 33.4682 33.4645 CC-PVTZ 36.4226 36.4218 35.7632 33.5028 33.4990 CC-PVQZ 36.4039 36.4032 35.8558 33.5168 33.5159 aCC-(SZ-QZ) 36.3964 36.3957 35.8854 33.5276 33.5265 bCC-(6Z-QZ) 36.3738 36.3732 35.8846 33.5310 33.5298 AUG-CC-PVDZ 36.7047 36.7040 36.0321 33.8974 33.8914 AUG-CC-PVTZ 36.4725 36.4719 35.9317 33.6177 33.6135 AUG-CC-PVQZ 36.3394 36.3745 35.8768 33.4561 33.4506 cAUG-CC-(SZ-QZ) 36.3619 36.3612 35.8777 33.5289 33.5323 dAUG—CC-(6Z—QZ) 36.3448 36.3441 35.8669 33.5225 33.5247 aNa CC-PVQZ basis set with C CC-PVSZ basis set l’Na CC-PVQZ basis set with c CC-PV6Z basis set cNa AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dNa AUG-CC-PVQZ basis set with C AUG-CC-PV6Z basis Set The magnitude of the Z2 component is, again, smaller than that of the linear species, and again the level of augmentation seems unimportant with such a large property. The two computational methods are behaving well while DFT still differs in the second decimal place. The SCF and CCSD(T) results for the ZZ component are close. DFT reports results with the lowest magnitude. We used the same geometry to calculate the YY component at the SCF, CCSD(T), and DFT levels. Table 12 shows the results. 83 Table 12. Quadrupole Moment, 9,, (ea?) ),of Planar Na2C2 SCF CCSD(T) DFT(B3LYP) Basis Set Field Field Field (9” > Gradient Gradient <9”) Gradient CC-PVDZ -21.3517 -21.3515 -20.8689 -l9.6638 -l9.6634 CC-PVTZ -21.5251 -21.5249 -21.4l47 -20.0101 -20.0093 CC-PVQZ -21.5899 -21.5898 -21.6085 -20. 1510 -20. 1498 aCC-(SZ-QZ) -21.6039 -21.6039 -21.6500 -20. 1775 -20.1760 bCC-(6Z—QZ) -21.5957 -21.5957 -21.6660 -20. 1939 -20. 1977 AUG-CC-PVDZ -21.6850 ~21.6851 -21.7050 -20.31 14 -20.3091 AUG-CC-PVTZ -21.6563 -21.6564 -21.7 172 -20.2745 -20.2722 AUG-CC-PVQZ -21.57 14 -21.5898 -21.6713 -20. 1717 -20.2101 cAUG-CC-(SZ-QZ) -21.5844 -21.5844 -21.6729 -20.2068 -20.2082 dAUG-CC-(6Z-QZ) -21.5757 -21.5758 -21.6668 -20.2048 -20.2050 aNa CC-PVQZ basis set with C CC-PVSZ basis set bNa CC-PVQZ basis set with C CC-PV6Z basis set cNa AUG-CC-PVQZ basis set with C AUG-CC-PVSZ basis set dNa AUG-CC-PVQZ basis set with C AUG-CC-PV6Z basis set Again, due to the magnitude of the quadrupole moment, there is little need for the augmentation of the basis set. The behavior of the two methods is consistent with the remainder of the study. The SCF behaves well, while the DFT results differ in the second decimal place. Note the quadrupoles are nearly equivalent with the magnitude of the CCSD(T) and SCF YY component closer to each other than to the DFT result. Overall, the YY component to the planar Na molecule quadrupole moment is larger in magnitude than the YY components of the planar Li molecule. 3.7 Partition Quadrupole Moment into Point Charges We used the algebraic definition of the quadrupole moment to partition the quadrupole moments of the aforementioned molecules into a collection of charges. When conceptualizing the dipole moment, the general argument made is that the dipole consists of two charges that are opposite in sign, but equal in magnitude, and separated by a distance R. The LiF dipole, for example, is discussed as having a positive charge located at Li and a negative charge of equal magnitude located at F. The value of the 84 dipole is expressed as the magnitude of the charge times the internuclear separation. Based on the principle that a dipole moment of a molecule is a collection of two charges separated by a distance such that the total system has no charge, the quadrupole moment of a molecule is broken up in much the same manner as four charges arranged such that the system has no dipole. We partitioned the quadrupole moment of each molecule into a collection of four charges, and we used equation (3) to calculate the magnitude of those charges. Equation (3) shows that the quadrupole moment equals the contribution of each charge in the system in the manner described in equation (17). )J. (17) cr 4 l 2 2 2 965 =Zqi(5(3faifpi—5up(xi +yi +Zi) i=1 So, for linear molecules like HCCH, equation (18) describes the 9‘; component of the quadrupole moment, (92; =2<1H(Rcc +RCH)RCH- (18) where, RCC is the carbon-carbon bond length and RCH is the carbon-hydrogen bond length. For the nonlinear molecules like Li2C2, equation (19) describes the 6);; component of the quadrupole moment, and equation (20) describes the 6),, component, 9;; = 9Li(2R12..iC “iRécj (19) where, RCC is the carbon-carbon bond length and Rue is the carbon-lithium bond length. ®§ry = QLi(R12.iC +fiRéc] (20) 3.8 Discussion Recall that the molecular quadrupole moment consists of contributions from the atomic quadrupoles and the contribution from charge redistribution upon molecular 85 formation. To determine the atomic contributions, we calculated the atomic quadrupoles of C(3Po), F(ZPO), and Cl(2Po), and we used these calculated atomic quadrupoles to determine the molecular quadrupole due to charge redistribution. Table 13 lists the results from determining the partitioning of each of the charge redistribution quadrupole moments of the titled linear molecules into a collection of point charges. Table 13. Linear Molecules (XCCX) Partitioned into Point Charges ®zz( 30% ) ®(zz)atomsa( €03 ) Ger( 308 ) QX(®zz) HCCH 4.8558 2.8406 2.0152 +0104 FCCF 0.6389 4.1976 -3.5587 0.214 CICCCI 3.7685 5.8730 2.1045 0.063 Linear Li2C2 35.6787 2.8406 32.8381 +0771 ““6” 46.5490 2.8406 43.7084 +0.785 N32C2 “Atomic quadrupoles C(l.4203 gag ), F(0.6785 gag ), Cl(l.5162 eag ) Beginning with HCCH, Table 13 lists the 22 component to the molecular quadrupole moment that we calculated at the CCSD(T) level with an AUG-PV6Z basis set. By subtracting out the contribution due to the atomic quadrupoles, the remaining portion of the quadrupole moment is due to the redistribution of charge on the formation of the molecule. Partitioning that quantity into algebraic charges shows the terminal hydrogen atoms to be slightly positive. Positive hydrogen atoms are consistent with the basic understanding of molecular bond formation. Electron density moves from occupying, in this case, four individual atoms to surrounding one molecule in which some of the electron density occupies the newly created bonds. It is evident that upon molecular formation the electron density around the hydrogen atoms shifts toward the carbon atoms. Figure 2 is a graphical representation of this redistribution of charge. 86 HCCH density difference —8 . . . . . . . , . . . . . -8 0 Molecular axis Figure 2: HCCH Density Difference Plot. Images in this dissertation are presented in color. Figure 2 shows a plot with blue and red regions. The blue regions are descriptive of areas that are electron deficient in comparison with the atomic electron distribution, and the red regions are descriptive of electron rich areas. The electronegativity argument holds in this example. Carbon is more electronegative which pulls electron density away from the hydrogen atoms. This distribution of charge removes some of the shielding 87 from the hydrogen nucleus which results in a positive charge on hydrogen and an overall positive quadrupole moment. It is important to note the magnitude of the atomic quadrupoles of FCCF. After removal of the atomic quadrupoles, the quadrupole moment due to redistribution is more negative. When partitioned into charges, the fluorine atom has a negative charge twice that of hydrogen. The density difference between the atomic and molecular densities is plotted in Figure 3. FCCF Molecular axis Figure 3: FCCF Density Difference Plot Images in this dissertation are presented in color. 88 Figure 3 makes the electronegativity of fluorine obvious. In HCCH the electron density is pulled from the hydrogen atom leaving the nucleus slightly unshielded; however, in FCCF the electron density moves toward the fluorine atoms creating two islands of negative charge at the terminus of the molecule. Islands of negative charge at the terminus of the molecule are not present in the plot of HCCH. The charge distribution shows clearly the negative quadrupole moment of the molecule and the negative charge of the fluorine atoms. ClCCCl is the second case of a doubly halogenated acetylene. Table 13 shows the magnitude of the atomic quadrupoles to be larger than in the case of FCCF. This discrepancy is not unusual if one considers that the atomic radii of chlorine are larger than the radii of fluorine and that the quadrupole moment has a square dependence on distance. The atomic quadrupoles are large enough that when removed from the molecular quadrupole the quadrupole moment due to charge redistribution is negative. Therefore, when the redistribution quadrupole is partitioned into point charges, the charge on the chlorine atom is negative, which gives credence to the following electronegativity arguments: Fluorine is the most electronegative element on the periodic table followed by chlorine, and hydrogen has a small electronegativity in comparison to chlorine and fluorine. The charge redistribution of the CICCCI molecule on molecular formation is plotted in Figure 4. 89 ClCCCl 10 ....,fi...,-.... 04 0 10 Molecular axis Figure 4: CICCCI Density Difference Plot Images in this dissertation are presented in color. Chlorine is very electronegative, and it is pulling electron density toward it. The molecular quadrupole of ClCCCl is positive, but this is true only because the quadrupole moments of the constituent atoms are positive, and they compensate for the negative quadrupole created during charge redistribution. 90 The last of the linear molecules that we discuss are the metal acetylides. Note the enormous magnitude of the partitioned charges on the metal atoms. This type of magnitude lends itself to the interpretation that the metal complexes are ionic in nature. Also note that the partitioned charge on Na is larger than that on Li. This phenomenon is explained by electronegativity arguments which state that sodium is easier to ionize into positively charged particles than lithium. Figure 5 is a plot of the density difference for the linear Li2C2 molecule. 91 Linear Li2C2 0- -8 . . . . . - . . . . . . . . . _8 0 8 Molecular axis Figure 5: Linear LiCCLi Density Difference Plot Images in this dissertation are presented in color. The most noticeable feature of Figure 5 is the highly positive Li atoms. Most of the electron density has moved to the carbon atoms leaving the Li nucleus unshielded. Most of the electron density is surrounding the carbon atoms making the center of the molecule very negatively charged. The density difference for the Na complex behaves 92 the same way; however, the positive regions will be more electron deficient and farther reaching. Table 14 contains the partitioned charges of the titled planar molecules. Table 14. Planar Molecules (X2C2) Partioned into Point Chagg ®zz ®(zz)atomsa ®(zz)cr Clx(®zz) Li2C2 25.958 2.841 23.117 0.844 Na2C2 35.867 2.841 33.026 0.870 @1717 ®(yy)at_or_n_sb ®(zz)cr (11491717) Li2C2 - 16.370 -1.420 -l4.950 0.944 Na2C2 -21.667 -1 .420 -20.247 0.958 Again, the partitioned charges are large, but the partitioned charges are not equal between the two components. This discrepancy, which has been shown by other research in the laboratory, is due to induced dipoles in the molecule. Therefore, the model which illustrates that the molecules can be partitioned into point charges does not adequately describe the planar molecules. Figure 6 shows the density difference for the LiZC2 planar complex. 93 Planar L12C2 8 I v v I l 1 1 999 - .l ’ . .2 - >7 \‘y l O— I i ’ > I J.- ; a . 2x -- ‘ .7." . —3 . . . . . . . , . . . . . . . —s 0 8 Li-Li axis Figure 6: Planar L12C2 Density Difference Plot Images in this dissertation are presented in color. Figure 6 shows the planar molecule as what seems to be a collection of four charged species with positively charged Li atoms and negatively charged carbon atoms. 94 3.9 References 1. A. D. Buckingham, Adv Chem Phys, 12, 107 (1967). 2. D. E. Stogryn; A. P. Stogryn, Mal Phys, 11, 371 (1966). 3. A. Krishnaji; B. Prakash; C. Vinod, Rev Mod Phys, 38, 690 (1966). 4. Bogaard, M. P.; Orr, B. J. MTP International Review of Science; Physical Chemistry Series 2; edited by Buckingham, A. D.; Butterworths: London, 1975; Page 144. 5. Buckingham, A. D. Intermolecular Interactions: From Diatomics to Biopolymers; edited by Pullman, B.; Wiley: New York, 1978; Page 1. 6. Maitland, G. C.; Rigby, M.; Smith, E. B.; Wakeham, W. A. Intermolecular Forces; Oxford University Press: Oxford, 1981. 7. Gray, C. G.; Gubbins, K. E. Theory of Molecular Fluids, Volume 1: Fundamentals; Claredon Press: Oxford, 1984. 8. D. B. Lawson; J. F. Harrison, Mol Phys, 93, 519 (1998). 9. G. Strey, M. J. Mills, J Mol Spec, 59, 103 (1976). 10. P. Biindgen; F. Grein; A. J. Thakhar, J Mol Structure, 334, 7 (1995). 11. A. J. Russell; M. A. Spackman, Mol Phys, 88, 1109 (1996). 12. G. Maroulis; A. J. Thakhar, J Chem Phys, 93, 652 (1990). 13. C. E. Dykstra, S. Y. Liu; D. J. Malik, Adv Chem Phys, 75, 37 (1989). 14. G. deLuca, N. Russo; E. Sicilia; M. Toscano, J Chem Phys, 105, 3206 (1996). 15. G. Maroulis, J Phys B, 26, 775 (1993). 16. J. Briedung; T. Hansen; W. Thiel, J Mol Spec, 179, 73 (1996). 17. Watson, J. N. Ph.D Thesis, University of New England, Arrnidale NSW, Australia, 1995. 18. H. King; H. Gerschka; W. Huttner, Chem Phys Lett, 96, 631 (1983). 19. I. R. Dagg, A. Anderson; W. Smith; M. Missio; C. G. Joslin; L. A. A. Read, Can J Phys, 66, 453 (1988). 95 20. D. J. Gearhart; J. F. Harrison; K. L. C. Hunt, Int J Quan Chem, 95, 697 (2003). 21. Briedung, J.; Hansen, T.; Thiel, W. J Mol Spec 1996, 179, 73. 22. G. Maroulis; D. Xenides, Electric Moments and (hyper) polarizability of X - C E C — X, X = F, Cl, Br, and I (preprint). 96 Chapter 4 Hi gher-order van der Waals Interactions and Nonlinear Response Tensors 97 4.1 Introduction Van der Waals forces are the intermolecular forces that arise from electrostatic interactions, induction, and fluctuations in the charge distribution within each molecule'. Van der Waals interactions also affect the dipoles and polarizabilities of the interacting moleculesz. In this chapter we derive the van der Waals interaction energy between two molecules to third order. Our analytical results at second order are identical to known results. Our results at third order are consistent with those of Piecuch, but we provide new equations for the third-order two-body van der Waals interaction energy: We express the fluctuation effects in terms of hyperpolarizabilities at imaginary frequencies. We also make numerical estimates for the second- and third-order interaction energies due to charge-density fluctuations and compare those results with various other second- and third-order interaction energies. 4.1.1 Interaction Energy Consider two molecules A and B which are well-separated, so that the electronic overlap between the two molecules is essentially negligible. The energy of these two weakly interacting systems is equal to the sum of the energy of molecule A (E A ), the energy of molecule B (EB ), and the energy due to the interaction of A with B (EA+B ), as shown in equation (1). EAB=EA+EB+EA+B. (1) We obtain the operator for the interaction between A and B by considering the interaction between two classical charge distributions. If the two molecules are represented as collections of positive and negative point charges, the classical electrostatic interaction 98 energy is E A+B = qud)? where in is the charge of the ith particle in system A and i (DiB is the potential at the ith particle due to molecule B. If the potential due to B is expanded around an origin in A, the electrostatic interaction energy takes the form of equation (2), where QA , 11A , and @A are the overall charge, dipole, and quadrupole moment of system A, and FE and F33 are the field and field gradient generated by system B. Each Greek subscript refers to the x, y, or 2 component of the electric moment or field quantity. 1 ENE = QAoB 413 F0? 703;, F53 -... . (2) In equation (2), we follow the Einstein Convention of Summations over Greek indices, such that equation (2) equals equation (3). EA+B =QA “’8 'H? F)? ‘11? F? Til? F28 1 B 1 A B 1 A B 1 1 -399, F1, 70,, F1, 70,, Fx, 709,, F’yE 769, F}; (3) lABlABlAF-IBIAFB —§®yszz _ngx Féx ‘3'sz zy -§®zz zz —'" ° The dipole and field are tensors of rank one (or vectors) described by equations (4) and (5). u=ltXX+uyy+uzL (4) F=Fxx+Fyy+Fzz. (5) The quadrupole and field gradient are tensors of rank two and can be represented in matrix format as seen in equations (6) and (7). 99 ®xx ®xy 6on o: (9,, oyy 0y, . (6) 92x 92y 922 Fiat Pity 1‘12 F’= 1:}, FW By, . (7) Fix Féy F22 R is a vector, between the origin in A and the origin in B, which points from B to A. From the multipole expansion, equations (8), (9), and (10) give the potential, field, and field gradient due to B, respectively. B QB B 1 B <0 (R)=—R—- up, +§Tafl 0043+... . (8) a 1 1135811, ¢B(R)=‘Ta QB+Tap ug-Srw, 037+... . (9) FB. 32 B _ B B 1 9B 10 tits-"513312739 (R)-' aBQ +1111” 117 "5 days yo+~~ - ( ) Equations (11) and (12) are explicit definitions of the first and second rank T tensors. a 1 -R T ____ a 11 a 812,12 R3 ( ) 32 1 3RaRB 0,3112 lif a = B “‘3 akaaRBR R5 were “5 0ifa¢B ( ) Assuming that systems A and B have no net charge, the leading terms of the interaction energy depend on the dipole and quadrupole moments of both systems as shown in equation ( 13). 100 A B 1 A B EA+B =‘Pa Tali PB +3111: Tom 907 (13) 1 A B 1 A B —39013 Tam [.17 +§®al3T01375 975 +... . Using the dipole propagators or T tensors, we can determine the distance dependence of the interaction energy on a particular interaction. For example, - 115‘ Tab 11? is the energy of interaction between the dipoles on systems A and B. As the distance, R, between A . . . . 1 . and B is increased, the interactron energy decreases as —3— . For the second and thrrd R terms, the dipole-quadrupole and quadrupole-dipole interactions, the energy decreases as 1 ——4-. Therefore, the long-range interaction energy between the two systems depends R more on the leading dipole-dipole term than on the dipole—quadrupole or quadrupole- quadrupole terms. Next, we construct a Hamiltonian operator for the two interacting systems, H AB , for use in the time-independent Schrbdinger equation, HAB‘P = E‘I’. In equation (14), the unperturbed Hamiltonians for each of the two molecules, HA and H3 , are summed into the unperturbed Hamiltonian H0 , and the portion of the Hamiltonian from which the interaction energy originates (\A/AB) is treated as a perturbation. The form of the operator VAB is determined from the classical electrostatic interaction energy, given in equation (13). 101 fiABzfiA+fiB M—7—J H0 A B 1 A B “Pa 1118 118 +31% TaB'y 907 (14) + . 1 A B 1 A B "3311011100 117 +6909 Tums (975 +... Y A VAB In this work, we focus on the dipole-dipole interactions, which give the leading contribution to the interaction energy at each order. Corrections to the first- and second- order interaction energies due to higher multipolar effects have been given by Buckingham3, Stogryn“, Piecuch6‘7’8'9 etc. Thus we take HARM: rig—a: 11,, pg [9) =(r10+9,) |‘P)=EAB|‘P). (15) fi——J V1 4.1.2 Perturbation Theory Rayleigh-Schrbdinger perturbation theory is based on the premise that, for a particular system for which the eigenfunctions and eigenvalues of the time-independent Schr6dinger equation are unknown, there exists a second system, similar to the first, for which the eigenfunctions and eigenvalues are known. Using the eigenvalues and eigenfunctions of the second system we may approximate the eigenfunctions and eigenvalues of the first system. For example, we need to solve equation (15), but the eigenfunctions and eigenvalues are unknown; however, we do know the eigenvalues and eigenfunctions of equation (16), I“101‘1’01 = Eol‘l’o)~ (16) 102 where ‘110 = |0) = ‘1’8 ‘1’}; = |0AOB) ,which is the product of the unperturbed ground state wavefunctions of system A and system B, and where E0 = BOA + E8 is the sum of the unperturbed ground state energies of systems A and B. Electron exchange between A and B is neglected in the zeroth-order wavefunction. Introducing an ordering parameter is, which we will eventually set equal to one, we can expand the exact eigenfunctions and eigenvalues from equation (15) as series in A, yielding equations (17) and (18). EAB 43941331) +1.2 E32) +23 133” +... . (17) 1P=|irg°1>+x|rgll>+xz|w321>+x3|wg31>+... . (18) Substituting back into equation (15), we derive equation (19). (1‘10 +1.01) 011130)) + 1|r311>+ 1.411139%”): (19) (1339+ 1. E81) + 1.2 E82) +...) OPS») + AIMS”) + 1.2 I‘ll?) + ...) If we expand the expressions and equate terms with equal powers of X“, we obtain equations (20), (21), and (22): from) = Eg°)|0) , for n = 0. (20) frolir91>+vl|0)=Eg)|0)+Bg°)|~Pg)>,torn: 1. (21) 11481821) + 0411181) = 131,2) |0) + E91|wg)>+ 5304413)) , for n = 2. (22) Using the condition that the mth correction to the unperturbed wavefunction is a sum of the excited states of the unperturbed system, Tam) = Zefimhl’fio) where k is the kth k¢0 103 excited state (so k #0), and using the result that the excited states are orthogonal to the unperturbed ground-state wavefunction, (0| ‘11:?) = (0| m) = 0 , for m > 0, we can take the scalar product of equations (20), (21), and (22) with W60) 2 | 0). From these scalar product equations, we obtain equations (23), (24), (25) and (26). lag» = E0 . (23) Bf,” =(0|\‘71|0) . (24) 2 0 v k k v 0 k¢0 E0 “13k E83): 2 <018|k>,wm,=,1_Ep (,6, k,m¢0 (E30) -E§?’)(EE,°’ —E$2’) Equation (23) is an equality involving the unperturbed energy (in this case, the energies of the noninteracting systems A and B). Equation (24) gives the first-order energy correction, which yields the permanent dipole-dipole interaction, while equation (25) and equation (26) give the second- and third-order energy corrections, respectively. 4.2 Second-Order Energy Correction By defining an operator G known as the reduced resolvent, é =(1—P0Xfio-EOT10-PO): XML. (27) k¢O(E1< E0) where P0 = IOXOI , the second-order energy correction takes form in equation (28). B32) =_(o|9,<‘39,|o). (28) For a pair of molecules A and B, the G operator is equal to a sum of three operators. G = (GA +GB +GA$B) such that 104 GA = ZIJAOBXJAOBI. (29) j¢0 EA E0 éB_ _ Z IOAmBXOgmBI. (30) m¢0 EB m-EO GAoB = IJAmBXJAmBl . (31) ..Eoer—Esuei—Ea GA is the reduced resolvent for excitations of system A only, GB is the reduced resolvent for excitations of system B only, and GAEBB is the reduced resolvent for excitations in both system A and B. Substituting v, = 419 Tag it? into equation (28) results in equation (32): 502) = (OAOBI 1‘ 113 Tats 11113) (GA +GB "LG/ma) 1 15? T7811 “63) 1013013) (32) Expanding equation (32) results in equation (33). Em (0 0,. (4:: a, 1131G1A-11A7T ti) IOAOB) +<°A°Bl ('fiaT "11.511 “)9 B1— 5‘7 T76 51?) lOAOB> (33) +(0A03| (413 T “11‘; For simplicity, equation (33) is broken into portions of the second-order energy which depend on excitations only in A (ESE) ), excitations only in B (E?) ), and excitations in both A and B (1313298 ). The second-order energy correction now has the form in equation (34), where Bf) is given in equation (35), egg) is given in equation (36) and 1353291313 given in equation (37). 105 B32) = Bf) + BS) + 13ng . (34) Egg-(0410131 (“113‘ Tali 111331 9A (‘11? T76 8811014013} (35) El.” =-<0AOB| (...: To a?) 93 (4145401003). (36> E2298 ="<0A0B1 (”113 T913 £11133) GAeB 1" 1111A T75 11153) 10A0B>- (37) Equation (38) for E?) which simplifies to equation (39), where 113013 the static ground- state dipole moment of system B and 13$ is the energy of the mth-excited state of molecule A. E(2) _ _ (OAOB 1118 Tori 111133 ImAOBXmAOB 111$ Tye 918310.408) (38) A — 2 EA _EA ' m¢0 m 0 0 “A m m ”A 0 5(3):- a5 T75 113011830 2 ( AIPal [AX 211111 A). (39) m¢0 Em ‘50 If we expand equation (39) into a sum of two terms, it becomes equation (40). l 0 11" m m 11" 0 E13)”; apTysuiiouis’OZ ( Al al :11 2111A) m¢0 Em ’E0 (40) 1 B0 B0 (GA 1113 1mA> . Using these equalities and the definition of the frequency-dependent polarizability from equation (49), equation (48) becomes equation (50). h co E93098 = _ 013111757“ [00 any A(1w)aB mambo). (50) 108 Summing equations (39), (40), and (46) gives the second-order energy correction as a function of the static polarizabilities of A and B and the imaginary-frequency dependent polarizability of A and B, as seen in equation (51). 2 1 131)- )- __ 20113 T780400 “$0 (1:335 “([1530 “1530 (127+ 27: _J::amy (im)a35(ico)dto). (51) This result has been obtained previously by Buckingham3, Dalgarno'z, Longuet- Higgins'3‘14'15, Stogryn4‘5, Piecuchm‘g‘9 , etc. 4.3 Third-Order Correction to the Energy From equation (26), after substituting in the reduced resolvent, we see that the third-order correction to the energy takes the form of equation (52). B331 = 2(0|\‘q(oA +03 +GA$B)V (GA +03 +GA$B)v,|0). (52) k,m¢0 The V operator is defined by V = \71 — E81). If we substitute the perturbation into the V operator we have equation (53). ill-BE,” =41:as05+(0A0slainsngloios). (53) We can rearrange equation (53) into equation (54), where if = (if: — p.90. Vi -E( ) =-FuT (18 111133 413° 11061—11133 -F: Top 1111330- (54) If equation (54) is substituted into equation (52) and the result is expanded, a 27-term expression is generated. Fortunately, not all 27 terms are non-zero. For example, the left hand side of equation (55) equals zero, as shown below. (0h?l GA 11:,“ Tag 11,? GA mo) = 0. (55) Expanding equation (55), we obtain equation (56). 109 (0|)?l GA a: Tag a}? GA v1|0) = .. "1 OBXmAOBl—A —B lnAOBXnAOBI ~ (voalvlzl A u T p Z VIIOAOB)- m¢0 (EQO'ESD) a QB Bil-to (EQO’Egob (56) Equation (56) then simplifies to equation (57). (6|v, GA a: Tag EEG/1‘ (7116): T 13 Z (OAOB lvllmAOBXmA IEQIDAXOB IHIIBBIOBXDAOB IVIIOAOB) (57) a I m.n¢0 (E:1 —E8 )(E: _E8) Now, because the (OB 1E1? [013) = 0as shown in equation (58), the term given on the left in equation (55) does not contribute to the third-order interaction energy in equation (52). (OB 11111331013) =(03 IfiglOB>-08 1113103) (B? $1003}3 ~13?) + (OB 1111331 kBXkB 11131 JBWB 1111331013) (Bi? 43803}3 -Er‘i) + (OB 1111153 I kBXkB 1111133 IJB>=ETGB T78 Tarp 118 118 1111) Bayer (82) The net contribution to the energy from this term is —%Ta5 T75 T8“, “[1330 pgo 113013373 . From equations (80) and (82), the 3-0 and 0-3 terms refer to a classical interaction between the two systems, where system A generates a static field, which polarizes system B through the B-hyperpolarizability of B, and vice versa. Figure 1 shows the 3—0 terms in a graphical manner. Figure 1: Representation of the 3-0 term. Images in this dissertation are presented in color. In the figure, the three solid black lines represent the field generated by A. The dotted green lines represent the polarization of system B through its B-hyperpolarizability. There has been previous study of this contribution to the third-order energy by Stogryn‘1‘5 and Piecuch6'7’8'9. 4.3.2 First-Order Terms in the Dipoles of Both A and B The next category of nonzero terms in the third-order energy correction are the l- 1 terms, two terms that are first-order in the ground-state dipoles of both A and B. Listed in equations (83) to (88) are those terms. 114 TH, = (0M GA a: Tag p133 GB v1|0). (83) THJ, = (0071 GB 11;,“ Tag it"? GA vl|0). (84) TH", =(0|\7l GA p30 Tag a}? GA6198 9.16). (85) T1_1,d=—(0|V1GA€BB uAO T g pg’ GA v1|0). (86) T1- 1, (=0|v1GBu§T,,g pg” GATE v1|0). (87) T1_ 1, =(0|v1GA$Bn:,ATag pg 0GB v1|0). (88) We begin with equation (83). If we expand the term on the left and simplify, we obtain equation (89). (0|)?l GA a: Tag 11,? GB v1|0)= GummuooukkpBo (89) T08 TyfiTgrpllerpBo Z (A171 AX AI (11 Ax BI 01 BX 3' I B). m,k¢0 (Em’EO )(Ek "Eo) If we expand equation (84) and simplify, we obtain equation (90). (0|vl GB a: Tag a}? GA v1|0) = 0 m m 0 0 k k 0 (90) TGBTYSTwllyAOPgo 2 (AIM? I AX Al"? I AX B11151 31113111131 13). m,k¢0 (Em -E0 )(Ek 1‘30) In equation (90), if we interchange y and e and Simultaneously interchange 5 and (p , then equation (90) becomes equation (91). (0|vl GB a: Tag fig’ GA v1|0) = T A0 B0 2 (OAIFQ ImAXmAh‘tA |0A)(OB|p3 IkBXkBIPBIOB) (91) Tali Tao 78118 118 m,k¢0 (Em-E0 )(Ek BO) 115 Then the Tm and T1“, terms both depend on the 8 component of the ground-state dipole of system A and the 8 component of the ground-state dipole of system B. Taking equation (85), after expanding and simplifying, we obtain equation (92). (0|?!1 GA “:0 Tat; LII? GA€913 Odo) = (OAlaé‘ImAxmAIu9I0A> T T TsfiAougo “‘3 8'" 7 °‘ “2:0 (E8—E8) In equation (92), interchanging e and a while simultaneously interchanging Band (p yields equation (93). (0M GA (130 T04; LIE GAEBB \‘Il|o) = T8 Tan T 5 {12° M21530 2 (0A lfiyAlmAXmA IHQIOAXOB IfiSIkBXkB lfiglon). (93) (p v m,k¢0 (E3, —E3)(E§; -53 +55 _Eg) Similarly, if we expand and simplify equation (87), we obtain equation (94). (0h?l GB n: T043 (130 GA613 Odo) = Ta TQBngAopgo Z (OA|fi9|mA> (97) BO A0 T TaT u u A” A *° °‘ 33 (E3—E8) To rearrange equation (97) so that it depends on the 8-component of the permanent dipole of system A and the 8-component of the permanent dipole of system B, we interchange (p with 8 and a with 8; we also assume that the dipole matrix elements are real. This gives equation (98). (oh?1 GA61913 “:0 TaB a}? GA \71|0) = (0A I99 l mA XmA luyAIOAXOB liq};3 I kBXkB lamog) (98) T T51" #:1530qu “B Y 8" 8 ago (E9.—E8> Expanding equation (88) and simplifying, we obtain equation (99). (o|\"/1GA‘BB a: Tap (150 GB \71|0) = B0 A0 (OA In? I mAXmA I“: IOAXOB Iii? I kexkn Ifig ‘03) (99) TysTapTwup ”5 X B B A A B B k,m¢0 (Bk -Eo )(Em -E0 +Ek —E0) O Rearranging Greek indices so that equation (99) depends on the s-component of the permanent dipole of system A and the 8-component of the permanent dipole of system B and assuming that the dipole matrix elements are real, we obtain equation (100). (0|\7l GA6913 ii: Tap “30 GB \71|0) = T a T a T .80 “A0 z (”A “‘9'me ITAIOAXOB lfifi lka> W» a 8 a Y ‘P k,m¢0 (BE —E8>(E:. 423 +13}: 4355 117 We combine equation (100) with equation (98), collect like terms, and obtain equation (101). (0|{11GA63B E8 Tag (130 GB \71|0)+(0|\71 GAEBB ”A“ Tag 11'}? GA (Mo) = B0 A0 (OA '1“: ImAXmA I”? IOAXOB 1111133 IkBXkB 1831013) (101) T15 Tali Tao P5 118 2 B B A A k.m¢0 (Ek "Eo )(Em -EO ) If we add equations (101), (96), (89), (91) we obtain equation (102). Tl—l,a +T1-1,b +T1—1,c +T1-1,d +T1—1,e +T1-1,f BO A0 = T78 TaB Tap P5 P8 ((0,, |fi¢lmA)(mA lflc'iIOAXOB 1811331 kBXRB 1831013) 1 (El? -BR)(E$ 438) + (GA 11191 mAXmA lfli‘lOAXOB 1831 kBka 18153108) X Z (EE-ERXEQ-Eé‘) k.m¢0 + (0A 1117A I mAXmA I“: M X013 1113 lkBXkB 113133 I013) (Elk3 -E(1i)(E$ 433‘) ' (102) + (0A lfiél mAXmA IHflOAXOB W? l kBXkB “131013) \ (BE-ngEQ—Eé) 2 The product of two polarizabilities, one on A and one on B, is shown in equation (103). .. . . ) (<0A InilmAxmA Infill/8X03 luEIkBXkB Ingloal (BE -E8)(E$ 438) + (0A lfifi‘lmAXmA IMO/axon lfigl kBXkB lfiEIOB) A Gap— 2 (BE-E8)(E$—EOA) Ya - A x x k.m¢0 + (0A I“? ImAXmA I“: lOAXOB IPEIRBXRB but}:3 1013) (BE -E8)(E3 -E6‘) + (0A 189 ImAXmA W IOAXOB 1% lkBXkB 1831013) ( (EE-EEXEQ-Eé‘) ) a . (103) Thus the sum of all of the 1-1 terms is given by equation (104). 118 Tl-l.a +T1-1,b +T1-1,c +T1-1,d +T1—1,e +T1-1.f B0 A0 A B = 78 TaB Tarp 115 148 “ya “Bo (104) We can further simplify equation (104). As shown in equation (105), the dipole on A produces a field that acts on B. A0 B A B0 A B A BO 148 Tao “Bo TaB aya T75 118 = F(p “Bo TaB aya T76 118 ° Ev—d FA ‘1’ That field then induces a dipole in B as seen from equation (106). A B A B0 B A BO F(p “Bo TaB “ya T78 P5 = 113 TaB “ya T78 1‘8 ° H—J B ”B The induced dipole in B then generates a field that acts on A. B A BO B A BO PB Tail “ya T75 148 = Fa “ya T76 145 - k—V—J F3? The field from the induced dipole in B induces a dipole in A. B Fa ayaTy8 H80 =uy Tyaltao - EH w?" The dipole induced in A then interacts with the permanent dipole of B. B0 A B0 11? T78 “6:135“ BF’ A PS This explanation of the 1-1 terms is represented in Figure 2. 119 (105) (106) (107) (108) (109) Figure 2: Representation of the 1-1 terms. Images in this dissertation are presented in color. The solid black line from A to B represents the field produced by the permanent dipole of A. That field induces a dipole in B, via the a-polarizability of B, as shown in dotted red lines. This induced dipole of B generates a field represented by the solid red line from B to A. This generated field influences A through the polarizability of A, as shown by dotted red lines. In turn, the induced dipole of A generates a reaction field which then acts back on B as shown by a solid red line from A to B. The same induction mechanism operates beginning with the field from the permanent dipole of B. The net contribution to the energy is ‘TaB Tyfi Tw “£0 011133,p 01¢}, (11,30. This contribution to the third-order energy has been analyzed by Stogryn“'5 and Piecuch6‘7‘8‘9. 4.3.3 First-Order Terms in the Static Dipole of System A or B, But Not Both The next category of nonzero terms includes the 1—0 and 0-1 terms. Listed in equations (110)-(112) are the 1-0 terms, which depend on the dipole of A to order 1 and the dipole of B to order 0. T1—0,a =<0|V1GB if: TaB if); GAeB VIIO). (110) Ti—o,b =(0|\71GAeB if? Tap if? GB Vllo). (111) 120 TH),C = (01v, GA61913 1190 TaB BE GAGBB 9,10). (112) If we expand and simplify equation (110), we obtain equation (113). " B —A —B A®B " AO Tl—O,a = = TaB T78 Tag) 147 x<°A|fi9|mAXmAlfi9|0A>03IHEIkBXkBmmoB) (113) <13}3 —E8> We know from equation (46) that we can rewrite equation (114) as equation (115), given that F is defined by equation (116). 2 F B B A A B B = m,j,k¢0(Ej -Eo)(Em"Eo +Ek ‘50) ( FX B1 B I (Ej ‘50) f 1 1 (115) h _ dw X + . 41: I: mgw ((EQ-Bg‘nhw) (EQ-BA—ith I 1 1 X B B - + B B - K \(Ek -E0 +1710) (Ek -E0 -lh(0) ) F = Tab T76 Tam “30 (DA I89 I mAXmA I11? IOA) (116) ><(03|1‘13|1'3X1'B I31? I kBXkB I11? I°B>~ 121 Expanding the integrand in equation (116) and then taking the first term T1,. 15 of the result we obtain equation (117). A0 T1,115 = (18 T75 Tarp P8 2 (0A |fi9lmAXmA IfiYAI0A> =TaB T75 Tap 14er x Z (OAIfiYAImAXmAIBQIOAXOBIfiglkBXkBIfigljBXjBlfig‘OB) (122) "‘J'kio (E? -E8> = T06 T78 T811) ”90 2 (0A IfivA I mA><1B IE1]; IkBXkB I113 I013) (127) j,k,m¢0 (E3. 438 +Ei? —E8) = T08 T75 Tao 118 2 (GA Ifi¢ImA> (129) 1.k.m¢0 (5;: -E6‘ +EE -Eg)(E$ _ng +13? _Eg) 124 Substituting equation (128) into (129) gives an integral with four frequency-dependent terms in the integrand. Rearranging the matrix elements in the numerator, we obtain the following equations for these four terms in the integrand. A0 T1,129 = Tali T78 ch) 143 x 2 (0A Iii? ImAXmA I113 IOAXOB 11183 IJ'BXJ'B 1831 kBXkB |0f33|03) (130) j.k.m¢0 (Ei’i‘. -‘EoA +ihm)(E}3 438 + ihmeE 438 +ih00) A0 T2,129 = 1013 T76 Tap Hg 2 (0A IfiélmAXmA IfiyAIOAXOB IfigljBXJB IfigIkBXkB I113 '08) (131) 13km" (EB "53‘ --ihco)(E}3 438 +ih00)(EE 428 + ihco) A0 13,129 = TaB Ty8 qu, “a Z (0AIfii‘lmAXmAlfiéloAXOBIfililiaxiaInglkgxkglaglog) (132) j.k,m¢0 (E8 436‘ +ihco)(13}3 +38 -ihm)(EE 438 —iha)) A0 T4,129 = TaB T76 Tarp 118 2 (CA In: I mAXmA IfiyA IOA XOB I111];3 11B )(13 IE]: I kB XkB I1183 IOB) (133) j,k,m¢0 (13$ 450 -i’i00)(13}3 —E3 —ihco)(Ef(3 —E8 -ih(0) If we use equations (118)-(121), (123)-(126), and (130)-(133), then for the sum of the 1-0 terms we obtain equation (134). By factoring equation (134), we obtain equation (135). Then from equations (136) and (137), we can see that equation (135) can be re-written as equation (138), which gives the contribution from the 1-0 term in terms of the imaginary frequency-dependent polarizability of A and B-hyperpolarizability of B. 125 A0 TaB T15 Tap 148 (IOA I11? I mAXmA I83 IOAIIOB Il‘lis3 I J'BXJ'B I11? I kBXRB I113 IOBI (13}3 438 +ihco)(E31 -E8‘ +ihm)(BE —Eg) (”A I83 I mAXmA Ifii‘ IOA X03 Ilia? IJB>(jB Iii? I kBXkB IBIS3 I013) (BB 458 +ihm)(B,A, 456A +ihco)(E? —E0A) (0A I83 I mAXmA I11? IOA X03 IBEIJ'BXJ'B Wis; I kB>(OB Ilfiii3 IJBIIJB I5? I kBXkB I113 I013) (13},3 438mg 453‘ —i1ico)(B}3 - BOA —ihc0) (0A Ifii‘ I mAXmA I113 IOAXOB Ifiis3 “Exits I53 I kBXI‘B I515 I013) (EA—153‘ “more? 438 +1120in3 -E8 + ihm) (0A Ifiél mA>J (Em ”Eo —Jh0)) (Em -Eo +ihco) (OB IBJ‘B IJBXJB I110 I kBXI‘B I116 I03) I (EB —E0 —lh(D)(Ek -E0 -lh0)) + (03 Illa IJBXJB I“? IkBXkB I? IOBI (EJB _EO —lh(1))(Ek “E0) xi 2 I” + (OBIJJSIIBJBXIJBB IEBZIkBIékB IFJJIOB) do, 4“ j,k,m¢0 °° (E,- —E0 )(E1. -Eo +ihm) + (OH Illa IJBXJB I144) IkBXkB I116 I013) (E? —E0 +lh(0)(Ek —E0 +1710) + (03 IFTIJBXJB I113: IkBXkB I115 I03) (13}3 E0 )(Ek E0 ”71(0) + (OB I”? IJBXJB I813 IkBXkB I113 I013) \ k (E? -E0 +lhO))(Ek -E(B)) ) } .(135) The dipole polarizability for A at the imaginary frequency ico is given by equation (136), A )_ X (OAlualmAXmAluyA |0A> MAI» ImAXmAlual 0A). 61,117 (1m _ (136) m¢o (Em -Eo -lh(t)) (Em _EO 4'th) and the B-hyperpolarizability with 0);: i0), (02- — 0, and (00: 1'00 is given by equation (137), according to Orr and Ward' '. 127 ((03 IFIJIJBXJB IfiglkBXkB IPiJIOB) I (13}3 453 -ih(t))(EE 438 -ih(0) + (“B IPIJ IJBXJB |fi§|k3Xk3 I11}? I03) (E? 458 —ihm)(EE— 4130) + (OB II'l‘PI-JBXJB I“? IkB)B(kB IHB I08) —E —EB + 'h 8386(-iw:iw,0)= Z (1:? 0)(Ek" o z (0) 308111511003 11(06ka 16103) (13}3 438 +ih03)(Ek -E8 +ih(0) + (Osln8|13)<13 lib: IkBXkB Ins IOB) (E? —E0 )(Ek —E0 "17103) + (OB I“? IJBXJB III-(J3 I kBXkB I113 I013) ( (Bi-53 ”rimming-E03) ). (137) The net contribution to the energy from the 1-0 terms is 3 A0 h °° A . B . ,. EE _-)0 — — a3 TY5 Tm, 118 ‘47; Lm0m(zm)Bfia¢(—zm,zm,0)dm , (138) to third order in the interaction. This same type of manipulation can be done in the case of the 0-1 terms to generate a term that depends on the imaginary-frequency polarizability of B and the [3- hyperpolarizability of A. Listed as equations (139) - (141) are the 0-1 terms. T04,a = (0|\"/1 GA B: Tag 51133 GA$13 (7)6). (139) T0_l,b=(0|V1GA®B'1I§TaB it}? GA v1|0). (140) T04“, = (0|\‘I1 GAG9B 6;} Tag 113° GA€913 v1|0). (141) If we expand equation (139), we obtain equation (142). 128 TO-l,a = (13 T76 Tap 111830 0 aA —A AAO 0 AB ' ' ABo (142) Z < A I“? ImAXmA Iva lnA> 4" °° j,m,n¢0 (Bf? -E6‘)(E$ —133‘+ihm)(1=.}3 =58 +ih00) X 129 B TO-Laz = 1913 T75 T89 “9 xi L“ d0, 2 (OAIIAEImAXmAII"aInA>0 do) 2 (OAIH‘: ImAXmAI-I’ia InA>(150) 41: j,m,n¢0 (EA- E8)(EnA -E8 +ihw)(Ej —E0 —ihm) B TO-l,b3 = 1013 Ty8 T88 liq, Xifodco 2 (GAIN: ImAXJJlAIJJf,A InAXnAIBQ IOAXOBIFJ: |JB)(JB|“BIOB) (151) 41!: 0° j,m.n¢0 (En ’Eo )(Em—E8 -1h(0)(Ej -E8 +1710» B T0-1,b4 = TaB Ty8 Tetp 11¢ X1 If d0) 2 (OAIfia ImAXmAIp‘Y InAXnAIPeA IOA) 4n °° ' X j,m,n¢o (139-133 -ihm)(E§; — £3 -ihm)(E}3 438 —ih(o) Summing the terms in equations (145)-(148), (149)-( 152), and (155)-(158), we obtain the net T04 term given in equation (159). 132 TO—l = Tali T78 Tap F50 ‘1 (“A le ImAXmA lFa JFAXM lFe IOAXOB |F6 lJB JJ[ 2“ (r 1 J J (E3, 438 +1111»)(E}3 —E8 +1111») 1 + fmdw fwdm' L (EJ’J’:I 433* +1111»)(E}3 -E8 -1h1»)J { 1 J J + (E: -E(} -1-ih(1)’)(Elk3—E(1)3 +ihm’) 1 \ ( (E9 —E8‘ +1111»’)(E,£3 438 -1h1»’)) \ By use of equation (165), we obtain equation (166). h 2 TO—O = T1113 Tyfi Tao (‘2?) x 1:: do» [:0 dd 2 j,k,m,n¢0 (f K 1 \ (E9, -E8 +1711»)(E}3 —E8 +1711») + 1 3 —E3 +1111»)(E}3 —E8 —1h1»)J ( 1 \ (E3 —E3 +1r11»’)(E{(3 —E8 +1111») 1 + ( (13:,A —E6A +1h1»’)(EE —E8 -ihm’) ) X<°A va ImAXmA lFa l“AJ("A IFe IOAJ NOB |F6 IJBXJB IFBB “‘8st IF» IOBJ J (165) (166) Equation (166) can be rewritten as equation (167), where the b tensor elements are given by equation (168). T0_ 0=(O|V1GA$BE11§‘TGB 115 BGA61313 V1|O)= Tap T75 Tap tzt‘: «01:66 136 X[b59¢( (10); —im— in)’ ,iw')+b53¢(— 1(1) 1(1) iw', in) ')] 9,861»;- -’11»—11» ,’,11»)+b‘JAa£(11»--11»+11»’,—11»’)] (167) 0 ftAm m EAn n fiAO b1?y[3(‘(0)1+(02J3w21w1J= 2 (Al 0| AX Al ‘1' AX Al 5' A) .(168) A A 111,11160 (E31 ‘EQ ‘FFDI +032JJ(E11 ‘50 4‘01) The result in equation (167) is new. It gives the third-order pure dispersion energy as a double integral over imaginary frequencies, since E6330 = —T0_0. Figure 4 shows a graphical representation of the 0-0 term. Both A and B are mutually polarized by each other through specific terms in the frequency-dependent hyperpolarizability. This interaction energy is a nonlinear analog of the second-order van der Waals dispersion energy. A fluctuation in the charge density of molecule A polarizes B nonlinearly, via [3, inducing a fluctuating charge in B. The field from the fluctuating charge in B acts on A, shifting the energy of A in a way that depends on the B- hyperpolarizability of A, because it depends on the correlation of the original fluctuation in the charge density of A and the nonlinear response to the field from B. There is a corresponding contribution to the energy with the roles of A and B reversed. Equation (167) provides an efficient means of computing the third-order dispersion energy for various A-B pairs. Figure 4: Representation of the Third-Order Pure Dispersion Energy. Images in this dissertation are presented in color. 137 The effects of hi gher—multipole interactions can be derived by replacing the dipole operators with polarization density operators, replacing the dipole propagators Tap with point-to-point dipole propagators Tag (r, r') , and then Taylor-expanding about the vectors RA and R3 as origins of the spatial variables. 4.4 Numerical Estimates Although the derivation of the third—order interaction energy provides insight into the types of interactions that occur at third order, estimates of the magnitude of these interactions will aid in their interpretation. To determine rough, approximate values of the third-order terms, we have assumed that all excitation energies are approximately equal to the ionization potential. This approximation allows us to simplify the perturbation expressions and find numerical values for the frequency-dependent polarizability and hyperpolarizability. The definition of the static polarizability is shown in equation (169). O k k 0 0 k k 0 . aa=2< 1161 >< WI >+< 11111 x 1161 1. 111» 1,10 (511 '50) (511 '50) Since the eigenstates are real, (OlpaIkalyfilO) = (OlyfllkalpaIO) . We are assuming all excitation energies are approximately equal to the ionization potential, (Ek - E0) = Ionization Potential (IP). Then, we solve for the sum of the matrix elements as shown in equation (170). a Z=%IP- (170) 11:60 Equation (171) gives the frequency-dependent polarizability. Now that we have solved for the sum of the matrix elements in the static polarizability, we can use those results to approximate the numerical value of the imaginary-frequency dependent polarizability. 138 . _ 1 1 aaB(JwJ-[JP+W+JP_JaJl§)(0lflalkJ2 +032 The same method can be used to find a numerical value for the frequency- dependent hyperpolarizability. Starting with the static hyperpolarizability in equation (173), we can again solve for the sum of the matrix elements. ’(0lflalJXJIIIAkaIfion)J(Oluylixilfifllkxklfian) ‘ (Ej-EoXEk ‘50) (Ej-EoXEk ‘50) J(OIFBIJ'XJIfialkJFIFyIOJJ(OIFJIJ'XJlfialkaIFBIOJ .117.» (Ej—EOXEk -Eo) (EJ—EOXEk —Eo) + (OI/Jal J'J=——,—— (193) R TX), = Tyx = 0. (194) sz(R.¢)=sz(R.¢>= 3°°S‘:)§“““”’. (195) l Tyy(R)=—E—3. (196) Tyz = sz = 0. (197) 2 _ Tzz (R, (P) = 3COSR(3¢) l - (198) 4.4.1.1 Second-Order Two-Body Terms Recall from the previous section that the second-order interaction energy for two bodies is approximated by equation (199). ( \ B 113011900135 2 1 BO BO A E8)=-E GBTY5 +1.”; [.15 (lay . (199) h A B 2 2 °° l +_“GY“B51PAIPBL.‘ 2 2” 2 2d“) ( 21: (IPAm XIPBm) ) The second-order two-body interaction energy is a sum of a classical induction effect given by equation (200) and a dispersion effect approximated by equation (201). The notation E (m’n) is used for the mth-order interaction energy for 11 bodies. (2.2) _ 1 (FAO A0 B B0 B0 A ) Eclassical "' —§TGB T75 a “y 0136 +143 “6 any (200) (2.2) __ h A B 2 2 ”L .1. . EdisPe'Sio“ — “‘3 T75 21? any “Ba IPA IPBJ:°"(IP,112, + 012 1ng +012)“. (201) 147 We have used Mathematica 4.0 to evaluate the expressions in equations (200) and (201). The second-order two-body interaction energy for the collinear configuration is given in equation (202), and the result for the stacked configuration is given in equation (203). 2,2 _ -90.7O AE£olli)near - R6 ' (202) 2,2 _ -91.58 AEEmcr)... - R6 - (203) 4.4.1.2 Third-Order Two-Body Terms The third-order interaction energy for two bodies is approximated by equation (188). The third-order two-body energy is a sum of classical induction, induction- dispersion, and pure dispersion interactions. Equation (204) shows the classical induction interactions, equation (205) describes the induction-dispersion energy, and equation (206) describes the pure dispersion interactions. 3.2 BO A0 A B Egnd ) = ‘116 lie TaB T78 Tarp “ya “[310 BO BO BO A l T05 T78 Tarp “B ”8 Prp Bays (204) 6 +.../2° 119° 1.901.. n. T... as... (3 2) A0 “:1 [3113380 Eind-disp = ‘TaB T115 T80 “8 _3 x_r._ °°d 3mg.rpg..2 1p}, oo 2 2 41: (IPg+0)2Y IPA'H” BO “[1335 [3de " TaB T75 T80 “<11 “—3 _ (205) xi fa dw 31Pfi+n>§m2 [pg 00 2 2' 411 (11%“to IPBH” 148 A 2 (3,2) _ BayeIPA Edisp " “TaB T75 T89[ 6 ][ [383811111313 6 1 1 (206) 27: K \ [ h )2 oo oo , [(IPA +iw)(IPA —ia)’) +(IPA +ia))(IPA +1203] x Lwdmiwdm . l l \X[(IPB +ia))(IPB -—ia)’) +(IP13 -iw)(IPB -i(0’):l} Again, using Mathematica 4.0 to evaluate the expressions, we have obtained the third-order two-body interaction energy for the collinear configuration as shown in equation (207) and the energy for the stacked configuration as shown in equation (208). The experimental values for the dipole, a-polarizability, B-hyperpolarizability, and ionization potential are listed in Table l. Table 1. Values for Use in Approximations Value in Value in Property atomic units electron volts References 112 0.4643 Maroulisrr on 17.96 Maroulis" a,“ = 01,, 16.17 Maroulis17 B... -lO.6 Maroulis" Bl“ = Bl” = 3"“ = 2.2 Maroulis” Byzy = Bxxz = Byyz [P 0.46852 12.749 CRC‘8 (3,2) _ 492.35 collinear _- R9 ‘ (3.2) _68.90 stacked _ R9 ' (207) (208) There is a much larger difference at the third order for the HCl dimers. Within the approximation used here, there is a stronger interaction for the collinear dimer than for the stacked dimer. 149 4.4.2 HCl Trimer Using the HCl trimer as an example, we have estimated the third-order three-body interaction energy and the third-order two-body interaction energy, and we have compared their values for three geometrical configurations. The first configuration is shown in Figure 8, where the centers of mass of three HCl molecules lie on the laboratory Z—axis and the internuclear axis for each molecule runs parallel to the Z-axis. 00¢ Figure 8: First Trimer Configuration. Images in this dissertation are presented in color. X The second configuration has the three centers of mass on the Z-axis, but each of the HCl molecules is rotated 90 degrees, so that the internuclear axis runs parallel to the laboratory X-axis as shown in Figure 9. Figure 9: Second Trimer Configuration. Images in this dissertation are presented in color. The final arrangement has the HCl molecules arranged such that the centers of mass generate an equilateral triangle with the internuclear axis for each molecule still parallel 150 to the laboratory Z-axis. This configuration, known as the triangle formation, is shown in Figure 10. Y Figure 10: Third Trimer Configuration (the triangle formation). Images in this dissertation are presented in color. For three-body interactions, we need three dipole propagators. The first dipole propagator connects systems A with B. These tensors are described by equations (209)— (213). - 2 35m -1 T33 = ((30.11)) _ (209) Rab TQB=TQB=0 (210) 3cos s‘n TQB =TZI§B = ((0:12 1 (¢ab)_ (211) ab 1 TAB = _ _ (212) W 3 Rab 2 _ T33 =——3°°s (fab) 1. (213) Rab 151 A second dipole propagator connects system A with system C. These propagators are described in equations (214)-(218). 38in2 —l TS‘A 2 (fear) . (214) RC8 T3“ =T§A =0. (215) 3cos sin TSZA = TzCiA = ((aca; (wca). (216) RC3 1 TCA = ——. (217) W 3 RC8 2 Boos —1 T5». = (gca) _ (218) RC3 The third and final dipole propagator is needed to connect system B with system C. These propagators are described by equations (219)-(223). 3s'n2 —1 T2? = 1 ((é’bc) . (219) Rbc 133C = T5,? = 0. (220) 3 'n TXBZC =TZBXC = COS(%RC;SI (wa) . (221) be BC _ l Ty), —-—R—3—. (222) be 3 2 -1 TszC = cos ((3%) . (223) Rbc 152 4.4.2.1 Third-Order Three-Body Terms The third-order three-body terms were derived in terms of nonlocal susceptibilities by Li and Hunt”. Li and Hunt separated the third-order three-body energy into three categories: energy due to induction, energy due to a mix of induction and dispersion forces, and energy due solely to dispersion interactions. (3.3)_ (3,3) (3,3) (3.3) E —Eind +15i+d +Edisp. (224) The induction energy consists of classical forces, which fall into one of three sub- categories. (3.3)_ (3,3) (3,3) (3,3) Eind .13srf +Ehyp +13tbf . (225) The first component is the static reaction field energy, which is a sum of three components represented in equations (226) and (227). ES?” =E§3€1+E§3€r§+5§3€é- (226) 133,3; = - Idr---drVP6°‘ (r)-T(r, r’)-aB(r', r')-T(r', r')-aC(r",r‘")-T(ri",r").135‘ (rV) . (227) The second is the third-body field terms described by equations (228) and (229). (3.3) _ (3.3) (3.3) (3.3) (3.3) (3.3) (3.3) Etbf - Etbf,ABC + Etbf,ACB + Etbf,BAC + Etbf,BCA + Etbf,CAB + Etbf,CBA .(228) 13:32ch = - J’dr---dr"P(l)3(r)-T(r,r’)-01C(r',r')-T(r",r").1113(r"',ri")-T(ri",rv 136‘ (H). (229) The third contribution to the classical induction energy comes from the three-body hyperpolarization effects, described by equations (230) and (231). (3,3) _ (3,3) (3,3) (3,3) Ehyp _ Em}, + Ehyp’B + Eth. (230) 153 130,3) =-i J.dr--~dr"BA(r,r’,r')[T(r,r")-P(§3(r')] "”‘A 2 xmririb-P§(r‘V)11T(r'.rV)P€(rV)1 1 ---dr"BA(r.r’.r')[T(r.r')-PoC(r')] 2 x [T(r', ri" ) . p53 (r‘V )] [T(r', r" m? (rV )1. (231) The induction-dispersion interaction energy is described by equations (232) and (233). 3,3 Ei(+d) = E(A---B)—)C + E(C---A)-—)B + E(B---C)—)A . (232) {BBAW (r', r', r : i010),OI‘Y5 (r', r')\ (3,3 __ h B p ’ . ' E(A--)-B—)C) ——--2; [)mdcoj'drmdrv x05£(r ,r'v,10)(0Tsp(r‘v,r’) Kx'r,,,q,(r,rv)POSPu") ( B \ (233) B3,,“ (rt, r" r : i0)00,OTY5 (1,, r') __ 17“” Japan xag,(r~,riv,immrefl(ritr3 \XT‘I‘P (r,rV)1>(§3p (rV) The dispersion energy is described by equation (234). T rV,riV -aC riv,r";' wT ”,r' 13535) = l fdm jar-um" Tr ( ) ( “D (r ) (234) P 7‘ B I I, - I A V, . xa (r ,r ,100)-T(r ,r)-a (r,r ,rw) Combining equations (224)-(234), we calculated the third-order three-body interaction energy at each of the three geometrical configurations. From the integrals over imaginary frequencies, we used the approximations to the frequency-dependent values of 01 and B described above. The results are listed in equations (235)-(237). AE(3’3) _ _ 1369.34 collinear - R9 (235) (3,3) _ 223.68 AEstacked - ——R9 - (236) 154 AE(3.’3) = ___-_, (237) 4.4.2.2 Third-Order Two-Body Terms Finally, we compared the third-order three-body energies from equations (235)- (237) with the third-order two-body energies to generate the full third-order two-body results, we added three third-order two-body equations. as shown in equation (238). (3,2) _ (3,2) (3,2) (3,2) E —EAB +133C +EAC . (238) Listed in equations (239)-(241) are the results for the calculation of the third-order two- body terms. £313.... =-981:'965- (239) AEiifr’... = ”1:593 (240) 1359.53,... - 6313331 (241) 155 4.5 References 1. F. London, Z. Phys. 63, 245 (1930); Z. Phys. Chem. Abt. B 11, 222 (1930). 2. AD. Buckingham, Propriétés Optiques et Acoustiques des Fluids Comprimés et 5A.;:tions Intermoléculaires (Centre National de la Recherche Scientifique, Paris, 1959), p. 3 . A. D. Buckingham, Adv. Chem. Phys. 12, 107 (1967). 4 . D. E. Stogryn, Phys. Rev. Lett. 24, 971 (1970); J. Chem. Phys. 52, 3671 (1970). 5. D. E. Stogryn, MOLPhys. 22, 81 (1971). 6. P. Piecuch, Chem. Phys. Lett. 110, 496 (1984). 7. P. Piecuch, Mol. Phys. 59, 1067 (1986). 8. P. Piecuch, Mol. Phys. 59, 1085 (1986). 9. P. Piecuch, Moi. Phys. 59, 1097 (1986). 10. Lafuente, R. Dissertation requirement for PhD. 11. B. J. Orr, J. F. Ward, Mol Phys, 20, 513 (1971). 12. A. Dalgamo, Adv. Chem. Phys. 12, 143 (1967). 13. H. C. Longuet-Higgins, Proc. R. Soc. London Ser. A 235, 537 (1956) 14. H. C. Longuet-Higgins and L. Salem, Proc. R. Soc. London Ser. A 259, 433 (1961). 15. H. C. Longuet-Higgins, Discuss. Faraday Soc. 40, 7 (1965). 16. Craig, D. P.; Thirunamachandran, T. Chem. Phys. Lett., 80, 14 (1981). 17. G. Maroulis, J Chem Phys. 108, 5432 (1998). 18. David R. Lide, ed., CRC Handbook of Chemistry and Physics, Internet Version 2006, , Taylor and Francis, Boca Raton, FL, 2006. 19. X. Li, K. L. C. Hunt, J. Chem. Phys.105, 4076 (1996). 156 Chapter 5 Molecular Frame Distortions in CH4+X Pairs, with X=He, N2, or H2 157 5.1 Introduction Compressed gas mixtures containing CH4-H2, CH4-N2, and CH4-He, although pertinent to astrophysics mainly due to the gaseous composition of the atmosphere of Titanl'2’3’4, Satum‘u, and Neptune“, are of interest in chemical theory because of their collision-induced absorption in the infrared and far-infrared region. Induced dipoles produced during collisions within the compressed gas cause nearly all compressed gases to absorb infrared radiation. This behavior is true even if the individual constituents of the gas are infrared inactive6’7’8. The same is also true of CH4-N2, CH4-H2, and CH4-He gas mixtures. Although the symmetric vibrational modes of CH4 and the bond stretch of the homonuclear diatomics are infrared inactive, part of the collision-induced absorption in the infrared region is due to interacting CH4-N2, CH4-Hz, and CH4-He pairsg'm'l 1. Absorption in the far-infrared is due to translational and rotational modulation of the collision-induced dipoles. These collision-induced dipoles originate from four sources: multipolar induction, dispersion forces, intermolecular exchange forces, and frame distortions“ "2. Although theorists have been able to predict the collision-induced infrared (IR) spectra and IR absorption intensities of other simple gas mixtures, they have been unable to predict absorption intensities correctly in the range8 150 cm"1 — 450 cm'1 of the IR spectra of CH4-N2, CH4-H2, and CH4-He mixtures“ "'3. The discrepancy between experiment and theory is due to an incomplete treatment of the forces between molecules in these gas mixtures. Previous theoretical examinations of other gas mixtures have taken into consideration the more commonly studied causes of collision-induced absorption: multipolar induction, dispersion forces, and intermolecular exchange forces, but the 158 influence of frame distortion has been investigated in only one case thus far: Weiss12 studied frame distortion effects in He collisions with CO2. He concluded that in CO2-He gas mixtures frame distortions due to collisions between the He atom and CO2 molecule generated induced dipoles of comparable size to exchange force-induced dipoles. Collision-induced frame distortion in CH4 mixtures has the potential to produce dipoles similar to those found in CO2-He gas mixtures”. In the CH4 molecule, the bending constants are smaller than those in CO2. Frame distortion in CH4 will generate a dipole, due in large part to the bond dipoles in CH4. In the equilibrium geometry, the bond dipoles cancel due to symmetry, but the movement of any hydrogen from its equilibrium position will generate a dipole". Not only will the frame distortion generate a dipole in the CH4 molecule, but the CH4 dipole generated by distortion may in turn influence the collision partner, adding to the electron cloud distortion in the collision partner. It is expected that in CH4-He gas mixtures the frame-distortion dipole will be on the order of 0.003-0.03 Debyes. In this chapter, we study frame distortion in CH4-N2, CH4-H2, and CH4-He pairs due to interactions within the mixed pairs. 5.1.1 Approaches To examine the frame distortion of CH4, we need to see the effects of approaching molecules on the methane molecular frame. Figure 1 shows that methane has two vertical planes of symmetry, A and B, such that plane A bisects the H1, H2, and C atoms, and plane B bisects H3, H4, and C atoms. Using this diagram, one can describe the collision paths used in this study. 159 Figure 1: Reflection Planes in CH. In our work on collisions of helium and methane, we have positioned the helium atom on the C2 axis, which bisects both HCH bond angles in methane. This axis is the line labeled L, where the two planes intersect, in Figure 1. In the work on collisions of a diatomic molecule with methane, we considered two approaches termed linear and perpendicular. In the linear approach, the nuclei (they are both terminal) of the homonuclear diatomic lie in both planes A and B along line L. This configuration is shown in Figure 2 and Figure 3. 160 Figure 2: Diagram of Linear Approach, Viewed Looking Down on Plane A Rotating the geometry in Figure 2 90 degrees about the axis bisecting the HCH bond angles, we reach the view in Figure 3. Figure 3: Diagram of Linear Approach, Viewed Looking Down on Plane B In the perpendicular approach, plane B contains the nuclei of the diatomic, and plane A bisects the homonuclear diatomic bond. This configuration is shown in Figure 4 and Figure 5. 161 Figure 4: Diagram of Perpendicular Approach, Viewed Looking Down on Plane A Rotating the geometry in Figure 4 90 degrees about the axis bisecting the HCH bond angles, we get Figure 5. Figure 5: Diagram of Perpendicular Approach, Viewed Looking Down on Plane B Using both paths of approach, the center of mass of the diatomic molecule, or the helium atom, was moved closer to the carbon atom along the line L. 162 5.1.2 Methods At specific separations, single-point calculations were made at a range of Hl-C- H2 bond angles. By fitting the energy values versus the H1-C-H2 bond angle to a third- order polynomial, the bond angle at the minimum of the potential well was determined; this is the optimized bond angle at that particular separation of helium, or the diatomic, from methane. Using this optimized bond angle, we calculated the dipole due to the collision-induced frame distortion, as well as the energy change on the potential surface due to the frame distortion. The dipole was calculated using equation (1), where 131,13, F3, and {'4 are unit vectors along the bonds in the CH4 molecule, and the potential change was calculated from a potential energy surface generated by Marquardt”. Bind =Bbond(fr+?2+f3+f4)- (1) The bond dipole was determined as described in a paper by Hollenstein” et al. 5.1.3 Computational Details Single point CCSD(T) calculations were performed with the Gaussian9816 software package using the Dunning aug-cc-pvtz basis sets for carbon'7"8, hydrogen”, ”"8, and helium"). Mathematica 4.020 was used to fit the raw data to the third- nitrogen order polynomial and to determine the optimized bond angle, as well as to determine the potential and interaction energies. 5.2 CI-I4-N2 For this study, the experimental geometries for methane and nitrogen were used, as provided by the 86th edition of the CRC Handbook of Chemistry and Physics“. The methane bond lengths are RCH = 1.087 A, and all the HCH bond angles are equal to 109.47120 except for the Hl-C-H2 bond angle, which is varied as described below. For 163 nitrogen, the bond length is RNN = 1.9077 A. Using these parameters, we collected two sets of single-point energy calculations: single-point energy values from the linear approach and single point energy values from the perpendicular approach. The linear approach is discussed first. 5.2.1 Linear Approach The separation between the N2 center of mass and the methane center of mass was set to distances of 5.0 A, 4.0 A, 3.5 A, 3.25 A, and 3.0 A. At each distance, the H1-C-H2 bond angle was varied from 1040 to 1140 in increments of 1°, also including the angle 109.47120. The minimum of the curve in each slice is the optimized Hl-C-H2 bond angle for the respective nitrogen-methane separation. Using the aforementioned data points, the minimum of the potential curve was determined. Plots of the total energy of the system as a function of the H1-C-H2 bond angle can be seen in Figures 6-10. 164 CH4-N2 Linear Approach 104105106107108109110111112113114 -149.8212 1 ‘r 1 1* P P 1 i 1 -149.8213 1 -149.8214 7 -149.8215 ~ K -149.8216 - __1 449.8217 — *5 an 449.8218 — -149.8219 . 449.8220 . -149.8221 —— -- ~- Energy (H) HCH Bond Angle Figure 6: Energy as a Function of Bond Angle at 5.0 A Separation for Methane- Nitrogen: Linear Approach A first glance at Figures 6-8 may give the impression that the H1-C-H2 bond angle is unaffected by the approach of the nitrogen molecule, but a closer examination reveals the bond angle has changed from its equilibrium value. At a 5 A separation, the optimized bond angle is 109.340 compared to the equilibrium bond angle of 109.47120. 165 CH4-N2 Linear Approach 104105106107108109110111112113114 449.8212 ‘ 4 i i 4 4 + i i 1 -149.8213 -149.8214 — -149.8215 — -149.8216 4 -149.8217 - -149.8218 2 -149.8219 4 -149.8220 ~ ~---——— ~4— Energy (H) HCH Bond Angle Figure 7: Energy as a Function of Bond Angle at 4.0 A Separation for Methane- Nitrogen: Linear Approach At a 4 A separation, the optimized bond angle is 109.190. This data suggests that the bond angle is becoming more acute as the nitrogen approaches. 166 CH4-N2 Linear Approach 104105106107108109110111112113114 -149.8172 L i i i 4 i i i i 1 -149.8173 -149.8174 — -149.8175 ~ -149.8176 ~ -149.8177 -1 -149.8178 - -149.8179 ~ -149.8180 — -149.8181 - -149.8182 4 @521 Energy (H) HCH Bond Angle Figure 8: Energy as a Function of Bond Angle at 3.5 A Separation for Methane- Nitrogen: Linear Approach When the separation is decreased to 3.5 A, the bond angle Opens to an angle of 109.870. 167 CH4-N2 Linear Approach 104105106107108109110111112113114 4498096111: 41111: -149.8098 -149.8100 ~ -149.8102 ~ -149.8104 . -149.8106 2 -149.8108 — -149.8110 — -149.8112 - -149.8114 ~ -———— ______ HCH Bond Angle [+ 3.25 angj Energy (H) Figure 9: Energy as a Function of Bond Angle at 3.25 A Separation for Methane- Nitrogen: Linear Approach At 3.25 A the bond angle opens to 111.340, and at 3 A the bond angle opens to 114.830, as shown in Figure 10. (In this case, we expanded the set of the H1-C-H2.bond angles to include angles that range from 104 to 119 degrees in one degree increments.) The range shown in Figure 1018 1090 to 119°. 168 CH4-N2 Linear Approach 109110111112113114115116117118119 449.7941 1 I ' . I ' I ' -149.7943 A -149.7945 — 33, 5 449.7947 ~ 2 449.7949 — LIJ -149.7951 2 449.7953 1 -149.7955 A——----— —- _- HCH Bond Angle Figure 10: Energy as a Function of Bond Angle at 3.0 A Separation for Methane- Nitrogen: Linear Approach It is evident that as the nitrogen molecule approaches methane, in the configurations shown in Figures 2 and 3, the H1-C-H2 angle decreases at first, and then increases as N2 approaches more closely. Table 1 lists the optimized bond angle at each N2-CH4 separation. Table 1. CH4-N2 Linear Approach Distance (A) Distorted bond angle 5.00 109.34 4.00 109.19 3.50 109.87 3.25 l l 1.34 3.00 l 14.83 We have calculated the potential energy difference between the equilibrium CH4 structure and the distorted CH4 structure twice, once with a potential surface generated by Marquardt and Quackl4 and again using Gaussian98. Also calculated twice was the 169 dipole moment, once using Gaussian98 and a second time using equation (1). These results are listed in Table 2 where 11 is the dipole moment and V(YXY) is the potential energy difference between the unperturbed and distorted methane molecule. Table 2. Dipole and Potential from Molecular Distortion in the CH4-N2 Linear Approach Gaussian 98 Quack et a1” Gaussian 98 Quack et a1” distance (A) u (a.u.) u (a.u.) V(YXY) (H) V(YXY) (H) 5.00 2.9356E-04 2.E-04 5.E-07 4.07070E-07 4.00 6.2890E-04 4.7E-04 2.0E-06 1.86641E-06 3.50 -8.9378E—04 -6.7E-04 4.0E-06 3.96732E-06 3.25 -4.2071E-03 -3.lE-03 8.79E-05 9.78689E-05 3.00 -1.2189E-02 —9.01E—03 7.014E-04 7.03584E-04 Table 2 shows that the potential energy differences due to the distortion of the methane molecule are of the same magnitude. For the Marquardt potential energy surface and Gaussian98, the difference between the values is less than 20 percent. These results seem reasonable considering that the Marquardt potential is based on a MRD-CI potential energy surface calculated using CC-PVDZ basis sets for carbon and hydrogen and that the Gaussian98 values are only converged to 1x10‘7 Hartrees. The difference between the dipole moment values is more noticeable; however, the simple bond-dipole model provides a good approximation to the actual dipole. 5.2.2 Perpendicular Approach Using the same procedure as used for the linear approach, we performed the same collection of calculations for the perpendicular approach of the N2 molecule to the CH4 molecule. 170 11.11 t CH4-N2 Perpendicular Approach 104105106107108109110111112113114 449.8210 1 111%4411 449.8211 3 449.8212 ~ 449.8213 ~ 449.8214 — K 449.8215 ~ 449.8216 ~ 449.8217 ~ 449.8218 4 449.8219 1 449.8220 J- —— —-—- 4 HCH Bond Angle Energy (H) Figure 11: Energy as a Function of Bond Angle at 5.01 Separation for Methane- Nitrogen: Perpendicular Approach At 5A separation, N2 has very little effect on the geometry of the CH4 molecule. The optimized angle is 109.480, which is only a hundredth of a degree different from the magnitude of the equilibrium bond angle. In contrast, the magnitude of the equilibrium bond angle of CH. changed by 0.130 for the linear approach of N2 at 5A. 171 CH4-N2 Perpendicular Approach 104105106107108109110111 112113114 449.8215'111111111 449.8216 449.8217 ~ 449.8218 — 449.8219 — 449.8220 ~ 449.8221 4 449.8222 ~ 449.8223 ~ 449.8224 4 - - —— - - __,_ HCH Bond Angle Figure 12: Energy as a Function of Bond Angle at 4.0 A Separation for Methane- Nitrogen: Perpendicular Approach Energy (H) In fact, when the distance is decreased to 4.0 A, the magnitude of the minimized bond angle is almost equivalent to the magnitude of the tetrahedral angle, at 109.470, which suggests that the bond angle is essentially unaffected by the N2 molecule at this distance. 172 CH4-N2 Perpendicular Approach 104105106107108109110111112113114 449.8214'111111111 449.82151 449.8216— 449.8217~ 449.8218~ 44982191 449.8220~ 449.8221 1 44932221 -149.8223~——~~-—<~-—— [-O- 3.5 agg] Energy (H) HCH Bond Angle Figure 13: Energy as a Function of Bond Angle at 3.5 A Separation for Methane- Nitrogen: Perpendicular Approach It is not until the distance is decreased to 3.5 A that the H-C-H angle expands to 109.680. 173 CH4-N2 Perpendicular Approach 104105106107108109110111112113114 -149.8203 ' l + [L l % 1L % w‘ 1‘ -149.8204 -149.8205 4 -149.8206 ~ -149.8207 ~ -149.8208 4 -149.8209 * -149.821 - -149.8211 - -149.8212 - -149.8213 1 -149.8214 ~ ——* * m~ —— + 3.25 angj Energy (H) HCH Bond Angle Figure 14: Energy as a Function of Bond Angle at 3.25 A Separation for Methane- Nitrogen: Perpendicular Approach At 3.25 A the H-C—H angle is disturbed to 109.960, which becomes noticeable as shown in Figure 14. 174 CH4-N2 Perpendicular Approach 104105106107108109110111 112113114 -149.8172L + l ‘fil l i l ll -149.8174 ~ -149.8176 a -149.8178 ~ -149.818 ~ Energy (H) -149.8182 - 449.8184 - -149.8186 ~ ——~~~ — -~-—- - —- HCH Bond Angle Figure 15: Energy as a Function of Bond Angle at 3.0 A Separation for Methane- Nitrogen: Perpendicular Approach Finally, at 3.0 A, the distortion angle is 110.810. In contrast to the distortion on the linear approach, the bond angle distortion for the perpendicular approach is less extreme. Also, squeezing of the bond angle as the N2 first approaches is seen in the linear approach but not in the perpendicular approach. Listed in Table 3 are the Nz-CH4 distances and the distortion angles at these distances. Table 3. CH4-N; Perpendicular Approach distance (A) distorted bond angle 5.00 109.48" 4.00 109.47° 3.50 109.630 3.25 109.960 3.00 110.810 Listed in Table 4 are the dipoles and potential differences calculated using Gaussian98 and the Marquardt potential surface. 175 Table 4. Dipole and Potential from Molecular Distortion in the CH4-Nz Perpendicular Approach Gaussian 98 Quack et a1" Gaussian 98 Quack et a1" distance (A) p (a.u.) p (a.u.) V(YXY) (H) V(YXY) (H) 5.00 0.E+00 -l.9699E-05 0.0000000 3.07966E-09 4.00 0.E+00 2.6861E—06 0.0000000 1.28879E-09 3.50 -3.E-04 -3.5564E-04 7 .E-07 5.95173E-07 3.25 -8.3E-04 -l.0958E-03 5.9E-06 5.84582E-06 3.00 -2.2E-03 -3.0091E-03 4.42E-05 4.43188E-05 Table 5 shows that the potential values agree more closely between methods than the dipole moments. It is also noticeable that for the 5.0 A and 4.0 A values that the magnitudes of the dipole and potential difference for Gaussian98 are so small that they are reported as zero. 5.3 CH4-Hz For this portion of the study, again, the experimental geometry of methane was used, RCH = 1.087 A with all the HCH bond angles equal to 109.47120 except for the H1- C-H2 bond angle, which is described below. For molecular hydrogen, the geometry used was RH“ = 0.7414 A. These geometries are provided by the CRC Handbook of Chemistry and Physics” . Using these parameters, two sets of single-point energy calculations were again performed: single-point energy values from the linear approach and single-point energy values from the perpendicular approach. The linear approach is discussed first. 5.3.1 Linear Approach The separation between the H2 center of mass and the CH4 center of mass was set to distances of 4.0 A, 3.5 A, 3.25 A, and 3.0 A, 2.75 A, 2.50 A, and 2.25 A. At each distance, the Hl-C-HZ bond angle was varied from 1040 to 1140 in increments of 1°, also including the angle 109.4712". The minimum of the curve in each slice is the optimized 176 Hl-C-HZ bond angle for the respective hydrogen-methane separations. Our results are listed in Table 5. Table 5. CH4-H2 Linear Approach distance (A) distorted bond angle 4.00 109.53“ 3.50 109.620 3.25 109.770 3.00 110.120 2.75 110.880 2.50 112.480 2.25 115.530 Table 5 shows that as the H2 molecule approaches the CH4 molecule, the bond angle under investigation widens. Table 6 lists the potential differences and dipoles of the distorted CHa molecule. Table 6. Dipole and Potential from Molecular Distortion in CH4-H2 Linear Approach Gaussian98 Quack et a1I4 Gaussian98 Quack et a]14 distance (A) p. (a.u.) p (a.u.) V(YXY) (H) V(YXY) (H) 4.00 -8.E—05 -l.3164E-04 1.E-07 8.27122E—08 3.50 -2.E-04 -3.3323E-04 6.E-07 5.22746E-07 3.25 -5.lE-04 -6.6946E-04 2.2E-06 2.10298E-06 3.00 -1.lE-03 -l.4552E—03 1.04E-05 1.03475E-05 2.75 -2.4E-03 -3. 167 1E-03 4.90E-05 4.90498E-05 2.50 -5.04E-03 -6.7967E-03 2.224E-04 2.23087E-04 2.25 -1.02E-02 -l.3809E-02 8.952E—04 8.97715E-04 Agreement of the distortion potential energy differences is very good. The bond-dipole model is useful as a first approximation, but it is not very accurate. 177 5.3.2 Perpendicular Approach Using the same procedure as for the linear approach, similar sets of data were calculated and collected for the perpendicular approach of the H2 molecule toward the CH4 molecule. Table 7 lists the bond angle at each of the H2-CH4 separations. Table 7. C114 -H2 Perpendicular Approach distance distorted bond angle (A) (degrees) 4.00 109.40 3.50 109.360 3.25 109.380 3.00 109.510 2.75 109.920 2.50 111° 2.25 113.390 Again, we see a shrinking of the bond angle as the diatomic first approaches CI-Ia, but at 3.00 A, the angle begins to expand. Table 8. Dipole and Potential from Molecular Distortion in the CH4-H2 Perpendicular Approach Gaussian98 Quack et a1” Gaussian98 Quack et a1" distance (A) p (a.u.) u (a.u.) V(YXY) (H) V(YXY) (H) 4.00 l.E-04 1.5934lE-04 2.E-07 1.21E-07 3.50 l.E-04 2.48828E-04 2.E-07 2.24E-05 3.25 2.E-04 2.04088E-04 2.E-07 1.97E-07 3.00 -8.E-05 -8.68616E—05 l.E-07 3.67E-08 2.75 -7.5E-04 -l.00600E-03 5.0E-06 4.96E-06 2.50 -2.6E-03 -3.438l6E-03 5.76E-05 5.78E-05 2.25 -6.57E-03 -8.8763lE-03 3.764E-04 3.78E-04 In Table 8, there is a stray value at 3.50 A separation which might be due to some mathematical error in the potential energy surface. Otherwise, the potentials are close in value and the dipoles are of the same magnitude. 178 5.4 CH4-He For this portion of the study, again, the experimental geometry of methane was used, RCH = 1.087 A with all the H-C-H bond angles equal to 109.47120 except for the Hl-C-HZ bond angle, which is varied as described below. This geometry is provided by the CRC Handbook of Chemistry and Physics” . Using these parameters we calculated the energies for separations between the He atom and the methane center of mass of 4.0 A, 3.5 A, 3.25 A, and 3.0 A, 2.75 A, 2.50 A, and 2.25 A. At each distance, the mom bond angle was varied from 1040 to 1140 in increments of 10 also including the angle 10947120. The minimum of the curve in each slice is the optimized Hl-C-H2 bond angle for the respective helium-methane separation. The results are listed in Table 9. Table 9. CH4-He Approach distance distorted bond angle (A) (degrees) 4.00 109.46" 3.50 109.460 3.25 109.470 3.00 109.550 2.75 109.810 2.50 110.550 2.25 112.350 The potential differences and dipole moments are shown in Table 10. 179 Table 10. Dipole and Potential from Molecular Distortion in CH4-He Apm'oach Gaussian98 Quack et a1” Gaussian98 Quack ct a1]4 distance (A) u (a.u.) p. (a.u.) V(YXY) (H) V(YXY) (H) 4.00 0.E+00 2.50696E-05 0.E+00 4.21E—09 3.50 0.E+00 2.50696E—05 0.E+00 4.21E-09 3.25 0.E+00 2.6861 lE-06 0.E+00 1.29E-09 3.00 -l.E-04 -l.76431E-04 2.E-07 1.48E-07 2.75 -5.5E-04 -7.59173E-04 3.E-06 2.70E-06 2.50 -1.8E-03 -2.42282E-03 3.E-05 2.87E—05 2.25 -4.80E-03 -6.50056E-03 2.E-04 2.04E-04 Again, Gaussian98 is not sensitive enough to measure the smaller potential differences and dipoles. The values are of the same magnitude and the potential energies agree more closely than the dipole values. 5.5 Discussion We have proven that frame distortion occurs as N 2, H2, or He approaches a CH4 molecule. The change in the equilibrium bond angle produces a dipole moment on methane, thus proving an additional mechanism for absorption in the far-IR or IR by compressed gas mixtures containing methane. This is the principal conclusion from our work. In addition, we have found that the methane Hl-C-H2 bond angle first narrows and then widens as N2 approaches in the “linear” configuration shown in Figure 2 and Figure 3. At the separations of 4 A and 5 A, the bond angle decreases in magnitude from the tetrahedral angle. This behavior may be due to the interaction of the negative quadrupole of nitrogen and the slightly positive charge of the hydrogen atoms in the methane molecule. In the presence of N2 at 3.5 A, 3.25 A, and 3.0 A, the methane bond angle widens, probably due to steric effects associated with electron repulsion. On the 180 perpendicular approach of N2, we have found that the bond angle simply increases as the intermolecular distance decreases. However, this behavior does not mirror the methane-hydrogen approaches. The reverse is seen. On the perpendicular approach, we find first a slight closing and then the reopening of the bond angle, while the linear approach shows only a widening of the bond angle. This behavior would follow since in the linear conformation the positive portion of the hydrogen quadrupole is facing the C114 molecule; while in the perpendicular conformation, the negative portion of the H2 quadrupole moment can interact with the partially positively charged H nuclei in CH4. At shorter range, steric effects predominate. 181 5.6 References l. J. L.Hunt, J. D. Poll, D. Goorvitch, and R. H. Tipping, Icarus , 55, 63 (1983) 2. C. P. McKay, J. B. Pollack, and R. Courtin, Icarus 80, 23 (1989). 3. A. Borysow and C. Tang, Icarus 105, 175 (1993). 4. L. M. Trafton, Planetary Atomospheres: The Role of Collision-Induced Absorption (World Scientific, Singapore, 1998), pp. 177—194, chap. 6. 5. A. Borysow, L. Frommhold, Astrophysical Journal, 304, 849, (1986). 6. H. L. Welsh, in MTP Int. Reveiew of Science-Physical Chemistry, Spectroscopy, Vol. 3, edited by A. D. Buckingham and D. A. Ramsey (Butterworths, London, 1972), Series, 1, Chap. 3, pp. 33—71. 7. L. Frommhold, Collision-induced Abosrbtion in Gases (Cambridge University Press, Cambridge, NY, 1993). 8. M. Buser, L. J. Frommhold, J Chem. Phys. 122, 24301 (2005). 9. Phenomena Induced by Intermolecular Interactions, edited by G. Birnbaum (Plenum, New York, 1985). 10. Collision- and Interaction-Induced Spectroscopy, NATO ASI series C, Vol. 452, edited by G. C. Tabisz and M. N. Neuman (Kluwer, Dordrecht, 1995). 11. M. Buser, L. Frommhold, M. Gustafsson, M. Moraldi, M. H. Champagne, and K. L. C. Hunt, J. Chem. Phys. 121, 2617 (2004). 12. S. J. Weiss, Phys. Chem. 86, 429 (1982). 13. X. Li, M. H. Champagne, and K. L. C. Hunt, J. Chem. Phys. 109, 8416 (1998). 14. Marquardt, M. and Quack, M. J Chem Phys, 109,10628 (1998). 15. H. Hollenstein, R. R. Marquardt, M. Quack, and M. A. Suhm, J Chem Phys 101, 3588, (1994). 16. Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. B.; Robb,M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann, R. B.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; 182 Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J .; Ortiz, J. V.; Stefanov, B. B.; Lin, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.6; Gaussian, Inc., Pittsburgh, PA, 1998. 17. TH. Dunning, Jr. J. Chem. Phys. 90, 1007 (1989). 18. R.A. Kendall, T.H. Dunning, Jr. and RJ. Harrison, J. Chem. Phys. 96, 6769 (1992). 19. DE. Woon and TH. Dunning, Jr. J. Chem. Phys. 100, 2975 (1994). 20. Mathematica 4.0, Wolfram Research Inc., Champaign IL, 1999. 21. David R. 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SCF Quadrupoles of HCCH Property Calculations Field Gradient calculations Basis sets Property 6) Field Grad ('9 0.0001 -0.0001 0 cc-pVDZ 5.21 121 5.21 120 46.82520 46.82625 46.82572 cc-pV'I‘Z 5.41863 5.41865 46.84884 46.84993 46.84938 cc-pVQZ 5.43455 5.43455 46.85385 46.85494 46.85439 cc-pVSZ 5.44436 5.44435 46.85497 46.85606 46.85551 cc-pV6Z 5.44423 5.44420 46.8551 1 46.85620 46.85565 aug-cc-pVDZ 5.46892 5.46890 46.82790 46.82899 46.82844 aug-cc-pV’I‘Z 5.45771 5.45770 46.84961 46.85070 46.85016 aug-cc-pVQZ 5.44559 5.44555 46.85402 46.8551 1 46.85456 aug-cc-pVSZ 5.44453 5.44450 46.85499 46.85608 46.85553 aug-cc-pV6Z 5.44352 5.44350 46.8551 1 46.85620 46.85566 d-aug-cc-pVDZ 5.45567 5.45565 46.82825 46.82934 46.82879 d-aug-cc-pVTZ 5.44564 5.44565 46.84971 46.85080 46.85025 Table 2. CCSD(T) Quadrupoles of HCCH Field Gradient Calculations Basis sets Field Grad 9 0.0001 -0.0001 0 cc-pVDZ 4.50785 47.10868 47.10958 47.10913 cc-pVTZ 4.80095 47.18708 47.18804 47.18756 cc-pVQZ 4.84280 47.20880 47.20977 47.20929 cc-pVSZ 4.86080 47.21527 47.21624 47.21576 cc-pV6Z 4.86520 47.21747 47.21844 47.21795 aug-cc-pVDZ 4.77215 47.1 1908 47.12004 47.1 1956 aug-cc-pV’I‘Z 4.84505 47.19161 47.19258 47.19161 aug-cc-pVQZ 4.85700 47.21048 47.21 145 47.21096 aug-cc-pVSZ 4.86345 47.21597 47.21695 47.21646 aug-cc-pV6Z 4.86615 47.21791 47.21888 47.21839 d-aug-cc-pVDZ 4.75840 47.12003 47. 12098 47. 12050 d-aug-cc-pVTZ 4.83335 47.19201 47.19297 47.19249 Table 3. DFT(B3LYP) Quadrupoles of HCCH Property calculations Field Gradient Calculations. Basis sets Property ('9 Field Grad 9 0.0001 -0.0001 0 cc-pVDZ 4.61713 4.61715 47.281 17 47.28209 47.28163 cc-pVTZ 4.90139 4.90140 47.31166 47.31264 47.31215 cc-pVQZ 4.89813 4.89810 47.31741 47.31839 47.31790 cc-pVSZ 4.90903 4.90915 47.31933 47.32031 47.31982 cc-pV6Z 4.90791 4.91 155 47.31968 47.32066 47.32017 aug-cc-pVDZ 4.87387 4.87390 47.28640 47.28737 47.28688 aug-cc-pV’I‘Z 4.91726 4.91715 47.31266 47.31365 47.31315 aug-cc-pVQZ 4.87216 4.87225 47.31767 47.31864 47.31815 aug-cc-pVSZ 4.90775 4.90680 47.31939 47.32037 47.31988 aug-cc-pV6Z 4.89025 4.89015 47.31988 47.32086 47.32037 d-aug-cc-pVDZ 4.86497 4.86435 47.28709 47.28806 47.28757 d-aug-cc-pVTZ 4.89342 4.89400 47.31290 47.31388 47.31339 d-aiggc-pVQZ 4.89071 4.88965 47.31768 47.31865 47.31816 210 Table 4. Quadrupoles of FCCF SCF Quadrpoles of FCCF Property calculations Field Gradient Calculations. Basis sets Property (9 Field Grad 6) 0.0001 -0.0001 0 cc-pVDZ -0.97258 -0.97255 -274.47696 -274.47676 -274.47686 cc-pVTZ -0.84572 -0.84570 -274.56734 -274.56717 -274.56726 cc-pVQZ -0.89863 -0.89860 -274.58903 -274.58885 -274.58894 cc-pVSZ -0.92249 -0.92250 -274.5947l -274.59453 -274.59462 aug-cc-pVDZ - 1 .03349 -1 .03 345 -274.49362 -274.49341 -274.4935 1 aug-cc-pVTZ -0.94298 -0.94295 -274.57137 -274.571 19 -274.57128 aug-cc-pVQZ -0.91302 -0.91305 -274.59007 -274.58989 -274.58998 aug-cc-pVSZ -0.91678 -0.91680 -274.59489 -274.59471 -274.59480 d-aug-cc-pVDZ -0.85468 -0.85465 -274.49569 -274.49552 -274.49560 d-aug-cc-pVTZ -0.9067 1 -0.90670 -274.57214 -274.57 196 —274.57205 d-aug-cc-pVQZ -0.91185 -0.91185 -274.59034 -274.59016 -274.59025 d-aug-cc-pVSZ -0.91572 -0.91570 —274.59491 -274.59473 -274.59491 Basis sets CCSD(T) Quadrupoles of FCCF cc-pVDZ -0.40895 ~275. 12056 -275. 12048 -275. 12052 cc-pVTZ -0.45690 -275.39150 -275.3914l -275.39l45 cc-pVQZ -0.5 8250 -275.47592 -275.47580 -275.47585 cc-pVSZ -0.63430 -275.50423 -275.50410 -275.50416 aug-cc-pVDZ -0.78600 -275. 17600 -275. 17585 -275. 17592 aug-cc-pVTZ -0.64850 -275.41 182 -275.41 169 -275.41 176 aug-cc-pVQZ 063565 -275.48398 -275.48386 -275.48392 aug-cc-pVSZ -0.64005 -275.50746 -275.50733 -275.50739 d-aug-cc-pVDZ -0.63670 -275. 18089 ~275.18076 -275.18082 d-aug—cc-pVTZ -0.61565 -275.4l468 -275.4l455 -275.41461 d-aug-cc-pVQZ -0.63315 -275.48517 -275.48504 -275.48510 d-am-pVSZ -0.63885 -275.50798 ~275.50785 -275.50791 Basis sets DFT(B3LYP) Quadrupoles of FCCF cc-pVDZ -0.05337 -0.05335 ~275.64631 -275.64630 -275.646298 cc-pVTZ -0.27828 -0.27830 -275.74266 -275.74261 —275.742634 cc-pVQZ -0.44190 -0.44190 -275.76648 -275.76639 -275.766429 cc-pVSZ -0.5 1039 05 1080 -275.77397 -275.77386 -275.773912 aug-cc-pVDZ -0.60025 -0.60045 -275.66684 -275.66672 -275.666775 aug-cc-pVTZ -0.54044 -0.53910 -275.74753 -275.74742 -275.747474 aug—cc-pVQZ -0.5 1631 -0.5 1800 -275.76799 -275.76789 -275.767939 aug-cc-pVSZ -O.52176 —0.52450 -275.77428 -275.774 1 7 -275.774224 211 Table 5. Quad rupoles of ClCCCl SCF Quadrupoles of CICCCI Property calculations Field Gradient Calculations. Basis sets Property (E) Field Grad 6) 0.0001 -0.0001 0 cc-pVDZ 3.93167 3.93165 -994.64186 —994.64265 -994.64225 cc-pV'I‘Z 3.93428 3.93425 -994.69678 -994.69756 -994.69716 cc-pVQZ 3.92530 3.92525 -994.71019 -994.71097 -994.71057 cc-pVSZ 3.93531 3.93520 -994.71417 -994.7 1496 99471455 aug-cc-pVDZ 4.05863 4.05860 -994.64677 -994.64758 -994.64716 aug-cc-pVTZ 3.85683 3.85675 -994.69794 -994.69871 -994.69832 aug-cc-pVQZ 3.87828 3.87815 -994.71048 -994.71 126 -994.71086 aug-cc-pVSZ 3.89883 3.89875 -994.71425 -994.71503 ~994.71463 d-aug-cc-pVDZ 3.93806 3.93790 -994.64829 -994.64908 -994.64868 d-aug-cc-pVTZ 3.82185 3.82175 -994.69831 -994.69907 -994.69868 d-aug—cc-pVQZ 3.86852 3.86840 -994.71062 -994.71 139 -994.71099 d-aug-cc-pVSZ 3.90064 3.90050 -994.71427 -994.71505 -994.71465 Basis sets CCSD(T) Quadrupoles of CICCCI cc-pVDZ 3.73365 -995.20710 -995 .20785 -995.20747 cc-pVTZ 3.85235 -995.43348 -995.43425 -995.43386 cc-pVQZ 3.78920 -995.50274 -995.50350 -995.5031 1 cc-pVSZ 3.80535 -995.52592 -995.52668 ~995.52629 aug-cc-pVDZ 3.77545 -995.24246 -995.24322 —995.24283 aug-cc-pVTZ 3.79695 -995.44800 -995.44876 —995.44837 aug~cc-pVQZ 3.75945 -995.50830 -995.50905 -995.50867 aug-cc-pVSZ 3.76720 -995.52878 -995.52954 —995.52915 d-aug-cc-pVDZ 3.66855 -995.24726 -995.24799 —99S.24762 d-aug-cc-pVTZ 3.74915 -995.45044 -995 .45 1 l9 -995.45080 d-aug-cc—pVQZ 3.74780 -995 .50935 -995.51010 -995 .50972 d-aug-ccopVSZ 3.76825 -995.52949 -995.53025 -995.52986 Basis sets DFT(B3LYP) Quadrupoles of CICCCI cc-pVDZ 4.10418 4.10370 -996.37300 -996.37382 -996.37341 cc-pVTZ 3.99562 3.99600 -996.43262 -996.43341 -996.43301 cc-pVQZ 3.91567 3.91670 -996.44733 -996.4481 1 -996.44771 cc-pVSZ 3.89775 3.89495 -996.45723 -996.45801 -996.45761 aug-cc-pVDZ 3.82461 3.82360 -996.38013 —996.38089 -996.38050 aug-cc—pVTZ 3.76884 3.76740 -996.43419 -996.43494 -996.43455 aug-cc-pVQZ 3.77873 3.77875 -996.44784 -996.44859 996.4482] aug-cc-pVSZ 3.79085 3.79055 -996.45746 -996.45822 -996.45783 212 Table 6. Quadrupoles of Linear QC; SCF Quadrupoles of Linear Li2C2 Property calculations Field Gradient Calculations. Basis sets Property ('9 Field Grad (9 0.0001 -0.0001 0 cc-pVDZ 35.921 13 35.92090 -90.55783 -90.56501 -90.56142 cc-pV'I‘Z 36.1 1907 36.1 1890 -90.58353 -90.59075 -90.58714 cc-pVQZ 36.36871 36.36855 -90.5 8902 -90.59630 —90.59266 cc-(SZ-QZ) 36.42224 36.42210 -90.58997 -90.59725 -90.59361 cc-(6Z-QZ) 36.48779 36.48765 -90.59016 -90.59745 -90.59380 aug-cc-pVDZ 36.65677 36.65660 -90.56656 -90.57389 -90.57022 aug-cc-pVTZ 36.51928 36.51915 -90.58514 -90.59245 -90.58879 aug—cc-pVQZ 36.50940 36.50925 -90.58933 -90.59663 -90.59297 aug(SZ—QZ) 36.50828 36.50820 -90.59010 -90.59740 -90.59375 M6Z-QZ) 36.50784 36.50770 -90.59021 -90.59751 90.59385 Basis sets CCSD(T) Quadrupoles of Linear Li2C2 cc-pVDZ 34.77075 -90.84527 -90.85222 -90.84874 cc-pVTZ 35. 19595 -90.92645 -90.93349 -90.92997 cc-pVQZ 35.49270 -90.94952 -90.95662 -90.95306 cc-(SZ-QZ) 35.57165 -90.95594 -90.96305 -90.95949 cc-(6Z-QZ) 35.64430 -90.95843 -90.96555 -90.96199 aug-cc-pVDZ 35.74955 -90.86463 -90.87178 -90.86820 aug-cc-pV'I‘Z 35.65855 -90.93329 -90.94042 -90.93685 aug-cc-pVQZ 35.66620 -90.95 196 -90.95910 -90.95552 aug(SZ-QZ) 35.67495 -90.95730 -90.96443 -90.96086 jung-QZ) 35.67865 -90.95927 -90.96641 -90.96283 Basis sets DFT(B3LYP) Quadrupoles of Linear Li2C2 cc—pVDZ 34.23046 34.22950 -91. 1 1920 -91. 12604 -91. 12261 cc-pVTZ 34.54174 34.54115 -91.14847 -9l.15537 -91.15191 cc-pVQZ 34.79379 34.79340 -91. 15494 -91. 16190 -91. 15841 cc-(SZ-QZ) 34.84033 34.83875 -91 . 15668 -91 . 16365 -91. 16016 cc-(6Z-QZ) 34.89727 34.89780 —9 1 . 15708 -91. 16406 -91. 16057 aug-cc-pVDZ 35.08634 35.08545 -91. 12795 -91. 13497 -91. 13146 aug-cc-pVTZ 34.92038 34.91845 -91 . 15007 -91. 15705 -91. 15356 aug-cc-pVQZ 34.92334 34.92280 -9 1 . 15532 -91. 16230 -91. 15880 aug(SZ-QZ) 34.92483 34.92415 -91 . 15690 -91 . 16388 -9 1. 16039 aug(6Z-QZ) 34.63372 34.91735 -91. 15727 -91. 16425 -9 l . 16075 213 Table 7. 9.2.2. Component of Planar Li2C2 Quadrupole SCF SCF 9,, Component of Planar Li2C2 Quadrupole Property calculations Field Gradient Calculations. Basis sets Property (9 Field Grad (9 0.0001 -0.0001 0 cc-pVDZ 26.42364 26.42345 -90.57130 -90.57658 -90.57394 cc-pVTZ 26.26211 26.26195 -90.59421 -90.59946 -90.59683 cc-pVQZ 26.28749 26.28735 -90.59907 -90.60433 -90.60169 cc-(SZ-QZ) 26.30007 26.29995 -90.59991 -90.60517 -90.60254 cc-(6Z-QZ) 26.30757 26.30740 -90.60005 -90.60531 -90.60267 aug-cc-pVDZ 26.42695 26.42670 -90.57578 -90.58107 -90.57842 aug-cc-pVTZ 26.31244 26.31235 -90.59501 -90.60028 -90.59764 aug-cc-pVQZ 26.31155 26.31140 90.59920 -90.60446 -90.60183 aug(SZ-QZ) 26.30941 26.30925 -90.59997 -90.60524 -90.60260 flwZ-QZ) 26.30894 26.30880 -90.60009 -90.60535 -90.60272 Basis sets CCSD(T) 6,, Component of Planar Li2C2 Quadrupole cc-pVDZ 25.83225 -90.861 1 1 -90.86628 -90.86369 cc-pVTZ 25.83985 -90.94040 -90.94557 -90.94298 cc-pVQZ 25.90455 -90.96264 -90.96782 -90.96522 cc-(SZ-QZ) 25.93655 90.96884 -90.97403 -90.97143 cc-(6Z-QZ) 25.95380 -90.97124 -90.97643 -90.97383 aug-cc-pVDZ 26.04780 -90.87582 -90.88103 -90.87842 aug-cc-pVTZ 25.95015 -90.94588 -90.95107 -90.94847 aug-cc-pVQZ 25.95380 -90.96459 -90.96978 -90.96718 aug(SZ-QZ) 25.95645 -90.96993 -90.97512 -90.97252 me-QZ) 25.95780 -90.97194 -90.97713 -90.97453 Basis sets DFT(B3LYP) 92.1 Component of Planar L12C2 Quadrupole cc-pVDZ 25.37237 25.37200 -9l.13161 -91.13668 -91.13414 cc-pV'I‘Z 25.20428 25.20235 -9l.15839 -91.16343 -91.16091 cc-pVQZ 25.26415 25.26320 -9l.16484 -91.16989 -91.16736 cc-(SZ-QZ) 25.28720 25.28715 —91.16660 -91.17 166 -91. 16913 cc-(6Z-QZ) 25.30170 25.29990 -91.16696 -91.17202 -91.16948 aug-cc-pVDZ 25.41788 25.41980 -91. 13640 -91. 14148 -91.13893 aug-cc-pVTZ 25.29770 25.29675 91.15965 -91.l6471 -91.16217 aug-cc-pVQZ 25.30683 25.30675 -91.16516 -91. 17022 -9l.16768 aug(SZ-QZ) 25.30699 25.30540 -91.16674 -91.17180 -91.16926 Lung-QZ) 25.30645 25.30510 -91.16710 -91.17216 -91.16963 214 Table 8. 9,1 Component of Planar Li2C2 Quadrupole SCF SCF 9,, Commnent of Planar Li2C2 Quadrupole Property calculations Field Gradient Calculations. Basis sets Property 9 Field Grad (9 0.0001 -0.0001 0 cc-pVDZ - 16.06928 - 16.06925 -90.57555 -90.5723 -90.57394 cc-pVTZ —16.18292 -16. 18290 -90.59845 -90.59522 -90.59683 cc-pVQZ -16.23168 -16.23165 -90.60332 -90.60007 -90.60169 cc-(SZ-QZ) -16.26629 -16.26630 -90.60417 -90.60092 -90.60254 cc-(6Z-QZ) - 16.28308 -16.28310 -90.60431 -90.60105 -90.60267 aug-cc-pVDZ -16. 19942 -16. 19945 -90.5 8004 -90.57680 -90.57842 aug—cc-pV'I‘Z - 16.28427 - 16.28430 -90.59927 -90.59602 -90.59764 aug-cc-pVQZ - 16.27610 - 16.27615 -90.60346 -90.60020 -90.60183 aug(SZ-QZ) - 16.27387 - 16.27395 -90.60423 -90.60098 -90.60260 fl(6Z-QZ) - 16.27356 - 16.27365 -90.60435 -90.60109 -90.60272 Basis sets CCSD(T) 9,, Component of Planar Li2C2 Quadrupole cc-pVDZ - 15.87020 -90.86528 -90.8621 1 -90.86369 cc-pVTZ - 16. 16610 -90.94460 -90.94137 -90.94298 cc-pVQZ - 16.26935 -90.96686 -90.96360 -90.96522 cc-(SZ-QZ) - 16.33000 -90.97307 -90.96980 -90.97 143 cc-(6Z-QZ) -16.36865 -90.97547 -90.97220 -90.97383 aug-cc-pVDZ -16.33085 —90.88006 -90.87680 -90.87842 aug-cc-pVTZ - 16.37980 -90.9501 1 -90.94683 -90.94847 aug-cc-pVQZ - 16.37065 -90.96882 -90.96555 -90.96718 aug(SZ-QZ) - 16.36970 -90.97417 -90.97089 -90.97252 flwZ-QZ) -16.36990 -90.97617 -90.97290 -90.97453 Basis sets DFT(B3LYP) (9,, Component of Planar Li2C2 Quadrupole cc-pVDZ - 15.40464 - 15.40470 -9 l . 13569 ~91 . 13260 -91. 13414 cc-pVTZ -15.69964 -15.69950 -91.16248 -91.15934 -9l.16091 cc-pVQZ -15.81193 -15.81105 -91.16895 -91.16578 -9l.16736 cc-(SZ-QZ) -15.86851 - 15.86735 -91 . 17072 -91. 16754 -91.16913 cc-(6Z-QZ) - 15.90546 - 15.90465 -91 . 17108 —9 1 . 16790 -91 . 16948 aug-cc-pVDZ -15.83735 -15.83840 -91.14052 -91.13735 -91.13893 aug-cc-pVTZ -15.91843 -15.91650 -91.16377 -91.l6059 -91.16217 aug-cc-pVQZ -15.91138 -15.90880 -91.16928 -91.16610 —91.16768 aug(SZ-QZ) - 15.90995 - 15.91070 -91. 17086 -91 . 16767 -91 . 16926 _a_ug(62-QZ) 45.90946 -15.91120 -91.17122 -91.l6804 -91.16963 215 Table 9. Quadrupoles of Linear Na2C2 SCF Quadrupole of Linear Na2C2 Property calculations Field Gradient Calculations. Basis sets Property (9 Field Grad (9 0.0001 0.0001 0 cc-pVDZ 47.51559 47.51435 -399.34140 -399.35091 -399.34615 cc-pVTZ 48.47527 48.47410 -399.37163 -399.38133 -399.37647 cc-pVQZ 48.69636 48.69525 -399.37900 -399.38874 -399.38386 cc-(SZ-QZ) 48.69327 48.69215 -399.37999 -399.38973 -399.38485 cc-(6Z-QZ) 48.70123 48.70010 -399.38019 -399.38993 -399.38505 aug-cc-pVDZ 49.04743 49.04625 -399.34785 -399.35766 ~399.35275 aug-cc-pVTZ 48.85053 48.84945 -399.37366 -399.38343 ~399.37853 aug-cc-pVQZ 48.70649 48.70540 -399.37953 -399.38927 -399.38439 Basis sets CCSD(T) Quadru le of Linear NazCz cc-pVDZ 44.471 10 -399.63410 -399.64299 -399.63852 cc-pVTZ 46.00460 -399.71897 -399.72817 -399.72356 cc-pVQZ 46.44525 ~399.74362 -399.75291 -399.74825 cc-(SZ-QZ) 46.5 1530 69945024 -399.75954 -399.75487 cc-(6Z-QZ) 46.55900 ~399.75278 -399.76209 -399.75742 aug-cc-pVDZ 46.45305 -399.65245 -399.66174 -399.65708 aug-cc-pVTZ 46.59030 -399.72672 -399.73603 -399.73136 aug-cc-pVQZ 46.56340 -399.74660 -399.75591 -399.75 124 aug(SZ-QZ) 46.56630 -399.75197 -399.76128 -399.75661 flng-QZ) 46.54900 -399.75407 -399.76338 -399.75871 Basis sets DFT(B3LYP) Quadrupole of Linear Na2C2 cc-pVDZ 42.43210 42.42575 40059468 40060316 40059890 cc—pVTZ 43.29595 43.28935 400.62965 400.6383 1 400.6396 cc-pVQZ 43.5 1357 43.50595 40064037 40064907 400.64470 cc-(SZ-QZ) 43.52969 43.52410 40064239 40065109 40064672 cc-(6Z-QZ) 43.53921 43.52600 40064320 40065191 40064753 aug-cc-pVDZ 43.89563 43.88895 400.60179 400.6105? 400.60615 aug-cc-pVTZ 43.67435 43.66385 40063181 40064054 40063615 fl-cc-pVQZ 43.55906 43.55635 40064153 40065025 400.64586 216 Table 10. 92.21 Component of Planar Na2C2 Quadrupole SCF SCF 92 Component of Planar Na2C2 Quadrupole Property calculations Field Gradient Calculations. Basis sets Property 6) Field Grad (9 0.0001 -0.0001 0 cc-pVDZ 36.36619 36.36545 -399.36385 —399.371 12 -399.36748 cc-pVTZ 36.42261 36.42180 -399.39214 -399.39942 -399.39577 cc-pVQZ 36.40388 36.40320 -399.39861 -399.40589 -399.40224 cc-(SZ-QZ) 36.39636 36.39570 -399.39946 -399.40674 -399.40309 cc-(6Z-QZ) 36.37383 36.37315 -399.39971 -399.40699 -399.40335 aug-cc-pVDZ 36.70472 36.70400 -399.36737 -399.37471 -399.37103 aug-cc-pVTZ 36.47252 36.47185 -399.393 19 -399.40048 -399.39683 aug-cc-pVQZ 36.33939 36.37450 -399.39891 ~399.40619 -399.40255 aug(SZ-QZ) 36.36187 36.36120 -399.39971 -399.40698 -399.40334 fl6Z-QZ) 36.34475 36.34410 -399.39994 -399.40721 -399.40357 Basis sets CCSD(T) (9z_z Component of Planar Na 2C2 Quadrupole cc-pVDZ 35.33375 -399.65565 -399.66272 -399.65917 cc-pVTZ 35.76320 -399.73951 -399.74666 -399.74308 cc-pVQZ 35.855 85 -399.76308 -399.77026 -399.76666 cc-(SZ-QZ) 35.88545 -399.76948 -399.77666 -399.77306 cc-(6Z-QZ) 35.88460 -399.77202 -399.77919 -399.77560 aug-cc-pVDZ 36.03205 -399.67052 -399.67772 -399.6741 1 aug-cc-pVTZ 35.93175 -399.74568 -399.75287 -399.74927 aug-cc-pVQZ 35.87685 -399.76548 -399.77265 -399.76906 aug(SZ-QZ) 35.87775 —399.77085 -399.77803 -399.77443 flwZ-QZ) 35.86695 -399.77293 ~399.7801 1 39947651 Basis sets DFT(B3LYP) 6);; Component of Planar Na 2C2 Quadrupole cc-pVDZ 33.46820 33.46450 400.61235 400.61904 400.61568 cc-pVTZ 33.50279 33.49895 400.64601 400.65271 400.64935 cc-pVQZ 33.5 1679 33.51595 400.65617 400.66287 400.65950 cc-(5Z-QZ) 33.52760 33.52655 400.65843 400.66513 400.66176 cc-(6Z-QZ) 33.53103 33.52985 400.65922 400.66593 400.66256 aug-cc-pVDZ 33.89736 33.89145 400.61673 400.62351 400.6201 1 aug-cc-pVTZ 32.97706 33.61345 400.64765 400.65437 400.65099 aug-cc-pVQZ 33.45609 33.45060 400.66397 400.67066 400.66730 aug(SZ-QZ) 33.52892 33.53235 400.65924 400.66594 400.66257 __aung-QZ) 33.52248 33.52465 400.65974 400.66645 400.66308 217 Table 11. But Component of Planar Na 2C; Quadrupole SCF (9,. Component of Planar Na 2C2 Quadrupole Property calculations Field Gradient Calculations. Basis sets Property (9 Field Grad (9 0.0001 -0.0001 0 cc-pVDZ -21.35167 41.35155 -399.36962 -399.36535 -399.36748 cc-pVTZ -21.52509 -21.52495 -399.39793 -399.39362 -399.39577 cc-pVQZ -21.58987 -2 1 .5 8980 -399.40440 -399.40009 -399.40224 cc-(SZ-QZ) -21.60388 -21.60385 -399.40526 -399.40094 -399.40309 cc-(6Z-QZ) -21.59570 -21.59570 -399.40551 -399.401 19 -399.40335 aug-cc-pVDZ -21.68500 41.68505 -399.37320 -399.36887 -399.37103 aug-cc-pVTZ ~21.65632 —21.65635 ~399.39900 -399.39467 ~399.39683 aug-cc-pVQZ -2 1.57 139 -2 1 .5 8985 -399.4047 1 -399.40039 -399.40255 aug(SZ-QZ) -2 1 .5 8440 -21.58440 -399.40550 -399.401 19 -399.40334 fing-QZ) -21.57575 -2 1 .575 80 -399.40573 -399.40142 -399.40357 Basis sets CCSD(T) 91.2 Component of Planar Na 2C2 Quadrupole cc-pVDZ -20.86890 -399.66126 -399.65709 —399.65917 cc-pVTZ -21.41470 —399.74522 -399.74094 -399.74308 cc-pVQZ -21.60855 -399.76883 -399.76451 -399.76666 cc-(SZ-QZ) -21.65005 -399.77523 -399.77090 -399.77306 cc-(6Z-QZ) -21.66595 ~399.77777 -399.77344 -399.77560 aug-cc-pVDZ 41.70495 -399.67629 -399.67 195 -399.6741 1 aug-cc-pV’I‘Z -21.71720 -399.75145 -399.74710 -399.74927 aug-cc-pVQZ -21.67125 -399.77 123 -399.76690 -399.76906 aug(SZ-QZ) -21.67290 -399.77661 -399.77227 -399.77443 au (6Z-QZ) -21.66680 -399.77869 -399.77435 -399.77651 Basis sets DFT(B3LYP) (9,_z Comment of Planar Na 2C2 Quadrupole cc-pVDZ -19.66378 -19.66335 400.61765 400.61372 400.61568 cc-pVTZ 40.01005 40.00925 400.65136 400.64736 400.64935 cc-pVQZ -20. 15 104 -20. 14980 400.66153 400.65750 400.65950 cc-(SZ-QZ) -20. 17747 -20. 17605 400.66379 400.65975 400.66176 cc-(6Z-QZ) -20. 19390 -20. 19765 400.66459 400.66055 400.66256 aug-cc-pVDZ «20.31 136 -20.30910 400.62215 400.61808 400.6201 1 aug-cc-pVTZ 49.92045 -20.27225 400.65303 400.64898 400.65099 aug-cc-pVQZ -20. 17 168 -20.21010 400.66286 400.65882 400.66083 aug(SZ-QZ) -20.20684 40.20820 400.66460 400.66056 400.66257 au (6Z-QZ) -20.20483 -20.20495 400.66511 400.66107 400.66308 218 APPENDIX C CHAPTER 5 RAW DATA 219 Table 1. CPL-N2 Perpendicular Approach using aug-cc-pvtz basis set for 5.0 and 4.0A Separations 5.0 A separation 4.01 separation Angle Energy Angle Energy Hartrees Hartrees 104 -149.821128 104 -149.821584 105 -149.8213782 105 -149.821834 106 -149.8215775 106 -l49.822033 107 -149.8217278 107 -149.822183 108 -149.8218247 108 -149.82228 109 -149.8218733 109 -149.822328 109.4712 -149.821879 109.4712 -149.822334 109.48 -149.821879 109.47 -149.822334 110 -149.8218723 109.5 -149.822334 111 -149.821822 110 -149.822327 112 -149.8217228 111 -l49.822276 113 -149.8215751 112 -149.822177 114 -149.8213791 113 -149.822029 114 —149.821833 Table 2. CH4-N2 Perpendicular Approach using aug-cc-pvtz basis set for 3.5 and 3.25 Angstrom Separations 3.5 A separation 3.25 A separation . Angle Energy Angle Energy Hartrees Hartrees 104 -149.8214405 104 -149.820398 105 -149.821699 105 -149.8206748 106 -149.8219064 106 -149.8209002 107 -149.8220646 107 -149.821076 108 -149.8221694 108 -149.8211983 109 -149.8222256 109 —149.8212715 109.4712 -149.8222348 109.4712 -149.8212886 109.6 -149.8222354 109.96 —149.8212946 109.63 -149.8222354 l 10 -149.8212946 110 -149.822232 111 -149.8212679 111 -149.822189 112 -149.8211917 112 -149.8220969 113 -149.8210665 113 -149.8219561 114 -149.8208925 114 -149.8217668 220 Table 3. CPL-N2 Perpendicular Approach using aug-cc-pvtz basis set for 3.0 A Separations 3.0 A separation Angle Energy Hartrees 104 -149.817287 105 -149.817612 106 ~149.817884 107 ~149.818105 108 ~149.818273 109 -149.81839 109.4712 -149.818428 110 -149.818457 110.8 -149.818473 110.81 -149.818473 111 -149.818472 112 -149.818437 113 -l49.818352 114 -149.818218 Table 4. CPL-N2 Linear Approach using aug-cc-pvtz basis set for 5.0 and 4.0 A Separations 5.0 A separation 4.0 A separation Angle Energy Angle Energy Hartrees Hartrees 104 -149.8213045 104 -149.8212801 105 -149.8215469 105 -149.8215138 106 -149.8217386 106 -149.8216971 107 -149.8218813 107 -149.8218317 108 -149.821971 108 -149.82l9l41 109 -149.8220125 109 -149.8219483 109.34 -149.8220153 109.19 -149.8219493 109.4712 -149.8220148 109.2 -149.8219493 110 -149.8220045 109.4712 -149.8219474 111 -149.8219474 110 -149.8219335 112 -149.8218415 111 -149.8218698 113 -149.8216872 112 -149.8217576 114 -149.8214848 113 -149.8215973 114 4498213892 221 Table 5. CPL-N2 Linear Approach usinfig aug-cc-pvtz basis set for 3.5 and 3.25 A Separations 3.5 A separation 3.25 A separation Angle Energy Angle Energy Hartrees Hartrees 104 -149.8172923 104 -149.8097708 105 -149.8175600 105 -149.8101183 106 -149.8177772 106 -149.8104143 107 -149.8179450 107 -149.8106596 108 -149.8180613 108 -149.8108530 109 -149.8181288 109 -149.8109963 109.4712 -149.8181435 109.4712 -149.8110463 109.87 -149.8181473 110 -149.8110891 109.9 -149.8181473 111 -149.8111318 110 -149.8181469 111.34 -149.8111350 111 -149.8181159 111.4 -149.8111350 112 -149.8180362 112 -149.8111248 113 -149.8179080 113 ~149.8110682 114 -149.8177316 114 -149.8109623 115 -149.8108076 116 -149.8106042 117 -149.8103525 118 -l49.8100529 1 19 -149.8097056 222 Table 6. CPL-N2 Linear Approach using aug-cc-pvtz basis set for 3.0 A Separations 3.0 A separation Angle Energy Hartrees 99 -149.7885192 100 -149.7893414 101 -149.7901081 102 -149.7908196 103 -149.7914759 104 - 149.7920775 105 - 149.7926245 106 -149.7931173 107 -149.7935562 108 -l49.7939410 109 -149.7942725 109.4712 -149.7944103 1 10 -149.7945508 1 1 1 -149.7947763 1 12 -149.7949491 1 13 -149.7950697 114 -149.7951382 114.8 -149.7951558 114.83 -149.7951558 115 -149.7951551 116 -149.7951206 1 17 -149.7950350 1 18 -149.7948988 119 -149.7947122 Table 7. CPL-H2 Perpendicular Approach using aug-cc-pvtz basis set for 4.0 and 3.5 A Separations 4.0 A separation 3.5 A separation Angle Energy Angle Energy Hartrees Hartrees 104 41.6130504 104 41.6130603 105 41.6132963 105 41.613304 106 41.6134914 106 41.613497 107 41.6136375 107 41.613641 108 41.6137305 108 41.6137321 109 41.6137751 109 41.6137749 109.4 41.613779 109.36 41.6137781 109.4712 41.6137789 109.4 41.6137781 110 41.6137701 109.4712 41.6137779 111 41.613716 110 41.6137682 112 41.613613 111 41.6137123 113 41.6134615 112 41.6136077 114 41.6132618 113 41.6134546 114 41.6132534 223 Table 8. CH4-1-12 Perpendicular Approach using aug-cc-pvtz basis set for 3.25 and 3.0 A Separations 3.25 A separation 3.0 A separation Angle Energy Angle Energy Hartrees Hartrees 104 41.6127939 104 41.6119134 105 41.6130384 105 41.6121644 106 41.6132322 106 41.6123647 107 41.613377 107 41.6125158 108 41.6134691 108 41.6126143 109 41.6135127 109 41.6126642 109.38 41.6135163 109.4712 41.6126705 109.4 41.6135163 109.5 41.6126706 109.4712 41.6135162 109.51 41.6126706 110 41.613507 110 41.6126646 111 41.6134521 111 41.6126159 112 41.6133484 112 41.6125184 113 41.6131964 113 41.6123723 114 41.6129962 114 41.612178 Table 9. CH4-H2 Perpendicular Approach using aug-cc-pvtz basis set for 2.75 and 2.5 A Separations 2.75 A separation 2.5 A separation Angle Energy Agle Energy Hartrees Hartrees 104 41.6095553 104 41.6038628 105 41.6098284 105 41.6041942 106 41.6100504 106 41.6044737 107 41.6102228 107 41.6047025 108 41 .6103426 108 41 .6048783 109 41.6104132 109 41.6050039 109.4712 41.6104289 109.4712 41.6050445 109.9 41.6104342 110 41.6050789 109.92 41 .6104342 1 1 1 41.6051035 110 41.6104341 112 41.6050781 111 41.6104054 113 41.605003 112 41.6103277 114 41.6048785 113 41.610202 114 41.610027 224 Table 10. CPL-H2 Perpendicular Approach usingaug-cc-pvtz basis set for 2.25 A Separations 2.25 A separation Angle Energy Hartrees 104 41.5910364 105 41 .59 15061 106 41 .591921 8 107 41 .5922841 108 41.5925918 109 41 .5928469 109.4712 41 .5929459 1 10 41 .5930493 111 41.5931991 1 12 41.5932968 1 13 41 .5933428 1 13.39 41.5933468 113.4 41.5933468 1 14 41 .5933373 1 15 41 .5932808 Table 11. C1-14-H2 Linear Approach using aug-cc~pvtz basis set for 4.0 and 3.5 A Separations 4.0 A separation 3.5 A separation Angle Energy Lngle Energy Hartrees Hartrees 104 41.613106 104 41.6131301 105 41.6133592 105 41.6133881 106 41.6135615 106 41.6135952 107 41.613714? 107 41.613753 108 41.6138145 108 41.6138573 109 41.6138659 109 41.6139131 109.4712 41.6138728 109.4712 41.613922 109.5 41.6138729 109.6 41.6139227 109.53 41.6138729 109.62 41.6139227 110 41.6138676 110 41.6139191 111 41.6138199 111 41.613875? 112 41.6137236 112 41.6137832 113 41.613578 113 41.6136419 114 41.6133844 114 41.6134523 225 Table 12. CPL—H; Linear Approach using aug-cc-pvtz basis set for 3.25 and 3.0 A Separations 3.25 A separation 3.0 A separation Angle Energy Angle Energy: Hartrees Hartrees 104 41.6128024 104 41.6117048 105 41.613068? 105 41.6119908 106 41.6132838 106 41.6122251 107 41.6134495 107 41.6124095 108 41.6135615 108 41.6125398 109 41.613624? 109 41.6126209 109.4712 41.613637 109.4712 41.6126411 109.7? 41.6136394 110 41.6126516 109.8 41.6136393 110.1 41.6126519 110 41.613638 110.11 41.6126519 111 41.613601? 110.12 41.6126519 112 41.6135161 111 41.6126322 113 41.6133816 112 41.6125632 114 41.6131985 113 41.612444? 114 41.6122773 Table 13. CH4-H2 Linear Approach using aug-cc-pvtz basis set for 2.75 and 2.5 A Separations 2.75 A separation 2.5 A separation AngLe Energy Angle Energy Hartrees Hartrees 104 41.6087869 104 41.6018304 105 41.6091178 105 41.6022598 106 41 .6093959 106 41.6026339 107 41.6096231 107 41.6029548 108 41 .6097951 108 41.603218 109 41.6099169 109 41.6034289 109.4712 41.6099554 109.4712 41.6035074 1 10 41.6099872 1 10 41.6035862 110.88 41.6100069 111 41.6036904 110.89 41.6100069 112 41.6037419 110.9 41 .6100069 112.48 41.603748 111 41.6100066 112.49 41.603748 112 41.6099753 112.5 41.603748 113 41.609893? 113 41.6037411 1 14 41 .6097622 1 14 41 .6036886 226 Table 14. CPL-H2 Linear Approach using aug-cc-pvtz basis set for 2.25 A Separations 2.25 A separation Angle Enggy Hartrees 104 41.586458? 105 41.5870911 106 41.5876632 107 41.5881776 108 41.5886288 109 41.5890235 109.4712 41.589185 110 41.5893603 1 1 1 41 .5896398 112 41.5898626 113 41.5900292 114 41.5901403 115 41 .5901964 115.5 41.590204 1 15.53 41.5902041 116 41.5901981 117 41.590146 Table 15. CH4-He Approach using aug-cc- pvtz basis set for 4.0 and 3.5 A Separations 4.0 A separation 3.5 A separation Agle Energy Angle Energy Hartrees Hartrees 104 43.3408519 104 43.340872? 105 43.3411011 105 43.341121? 106 43.3412995 106 43.3413198 107 43.3414488 107 43.3414688 108 43.3415449 108 43.3415646 109 43.3415925 109 43.3416121 109.46 43.3415978 109.46 43.3416172 109.4712 43.3415978 109.4712 43.3416172 109.5 43.341597? 109.5 43.3416171 110 43.3415906 110 43.3416099 111 43.3415394 111 43.3415584 112 43.3414392 112 43.3414581 113 43.3412905 113 43.3413092 114 43.3410935 114 43.341112 227 Table 16. CH4-He Approach using aug-cc-pvtz basis set for 3.25 and 3.0 A Separations 3.25 A separation 3.0 A separation ALgle Energy flgle EnergL Hartrees Hartrees 104 43.340??? 104 43.3403936 105 43.341026? 105 43.3406476 106 43.3412256 106 43.340850? 10? 43.3413754 107 43.3410045 108 43.3414721 108 43.3411051 109 43.3415203 109 43.3411574 109.47 43.3415258 109.4712 43.341164? 109.4712 43.3415258 109.5 43.3411648 109.5 43.3415258 109.55 43.3411648 110 43.3415189 110 43.3411599 111 43.3414682 111 43.3411132 112 43.3413686 112 43.3410169 1 13 43.3412204 1 13 43.3408722 l 14 433410239 114 43.3406792 Table 17. CPL—He Approach using aug-i-pvtz basis set for 2.75 and 2.5 A Separations 2.75 A separation 2.5 A separation Angle Energy Angle Energy Hartrees Hartrees 104 43.3392281 104 43.3360642 105 43.3394966 105 43.3363742 106 43.3397138 106 43.3366321 107 43.3398813 107 43.3368391 108 43.3399956 108 43.3369924 109 43.3400609 109 43.3370956 109.4712 43.340074] 109.4712 43.337125? 109.8 43.3400772 110 43.3371478 109.81 43.3400772 110.5 433371549 1 10 43.3400762 1 10.54 43.337155 111 43.3400419 110.55 43.337155 112 43.3399582 111 43.3371495 113 43.3398255 112 43.3371009 114 43.3396441 113 43.3370025 1 14 43.3368546 228 Table 18. CPL-He Approach using aug-cc-pvtz basis set for 2.25 A Separations 2.25 A separation Angle Energy Hartrees 104 43.3280358 105 43.3284556 106 43.3288205 107 43.3291319 108 43.3293874 109 43.32959 109.4712 43.3296649 1 10 43.3297394 1 1 1 43.329835? 1 12 43.329879 1 12.3 43.3298825 1 12.34 43.3298825 l 12.35 43.3298825 113 43.3298712 1 14 43.32981 1 229 u111111111111111111"