' '—w—h q H I ‘ M «n MW HIVIxH IN PHOTOGRAPHlC DE AND ENTENSITY MEA THE COPPER HYDRI Wicsis fcr the Deg WCHIGAN STAT} R0136“ Lu 1 1940 .1 11mm . may JJJJ LLL -‘ -J' — LLLLL LLLLLL Fug; [5mg JJ J L TJJa LLJ UVKJJJ L" J L, JLLJLL LL LLL L L L L, LLLLLL LLL .LJ LL .1 LL LIBRARY , Michigan State University PLACE IN REFURN BOX to remove this chedcout from your record. TO AVOID FINE return on or before date due. MAY BE RECALLED with earlier due date if requested. "z’ PHOTO/emails DE fSIT-OLZETRY A231) Itz'rL‘QLeITI 2-..E1A12UBLILLFE-ETS HE C3?P}§E{ EIYDTLI DE SPEC"‘RUL{ H 52.: *3 BY RQLERT LEE ROWE A THESLS Submitted to the Graduate School or michigan State College of Agriculture and Applied Science in partial fulfilment of the requirements for the degree of EASTER CF SCIEfiCE Department of Physics 1940 TABLE OF CONTENTS Page Introduction 1 The measurement of Spectral Line Intensities by Photographic Means I 2 Intensity Distribution in the Rotational Structure of the 0-0 Band of Copper J Hydride 16 Temperature Measurements 28 Summary . ’ 34 Bibliographyl 55 2337129 IE‘LTRODEECTEQEE The need has been felt for several years in the Department of Physics at Eichigan State College for.a microdensitometer for spectrographie work. It was the purpose of this problem to study the basic photographic, optical, and mechanical principles involved in the const- ruction and operation of a microdensitometer. From the knowledge thus obtained, a working model of such.an 1n- strument was designed, constructed, and applied to a specific problem. The specific problem to which the completed apparatus was applied was a measurement of the intensity distribution in the rotational structure of the 0-0 band of Copper Hydride. Employment of this measured intensity distri- bution has yielded information as to the temperature at- tained in a copper are operated in an atmosphere of hy- drogen o TILE meanness-:21: OF smother. Lisa menarflss hir PI'E'IUGE‘uiPEilC more The problem of measuring Spectral line intensities is complicated by the fact that only small amounts of energy are available, measurements must be made over wide wave— length ranges, and that the Special dimensions of the spec- tral lines are relatively small. Because these difficul- ties are most easily overcome by the photographic method, that method has gained the widest acceptance for use in such measurements. The basis for the measurement of the intensities of spectral lines by the photographic process is the charac- teristic or calibration curve of a photographic emulsion. Such a curve for spectrographic purposes must be an inten- sity curve obtained from the measurement of the densities resulting from a standard series of intensities of the same wavelength as of the spectral line to be measured. Therefore, the method of construction of the calibration curve must take into account reciprocity law failure (which includes the intermittency effect) and the spectral re- sponse of the emulsion.l0 Hewever, it should be meted that while a calibration curve should be constructed for each wavelength used, it is found in practice that there are long wavelength ranges over which the calibration re- mains constant. After the calibration curve has been obtained, the intensities of the spectral lines may be measured by a comparison of their densities with the standard densities by means of a microdensitometer. Qne further difficulty of the photographic method is the problem of making background or fog intensity correc- tions. The method used in this problem is to subtract ' background intensities as found from the calibrationéurve.' A test of the background intensity equation I3: IT - in is illustrated in Fig. l and Plate I. I V Fig. 1. ‘Background Correction Test The total intensity (IT) results from the superposition of a continuous background intensity (18) upon part of the in- tensity calibration scale (1). IB and IT are found from the calibration curve and their differences compared with the calibration intensities. The results, as shown in the "Degree of Correction" graph, indicate that such a correction method is applicable to the present problem.u The design and construction of a rotating sector ‘ wheel for intensity calibrations and of a microdcnsitometer for spectrographic density measurements will now be con- 3 id Bred. Os OPACITV 8] DEGREE OF I connecrco an. MIT. CORRECTION T3 _ '01 l M 1 1 +01 REL. lN‘l’. '2 TEST OF .3 BACKGROUND INTENSITY ; """""""""" CORRECTION EQUA TION.’ E ‘ ; 1:= 17-15 r : T i T 01 L 5001: I 420:; i 301 1 m 149: 1c 1. Ir RELATIVE aurznsn‘rv PLATE I The revolving sector wheel was chosen as the means of calibration because an astigmatic grating spectrograph was used in this problem. While a sector wheel usually gives a time scale, the Justification for its use in the production or an intensity scale is that the speed of revolution of the wheel can be made high enough to give flashes above the minimum critical frequency of intermittency.fl) The flash frequency in this case was approximately 30 per second. The form of the sector wheel was that of an aluminum disk having 15 open arcs cut in a ratio of the square root of 2 from 1 to 128. See Figs. 2 and 3. For convenience of use the wheel was mounted horizontally under a slot in the top of a two compartment light tight box. One com- partment contained the sector wheel and its driving motor. The other contained the light source and transformers. Light from the source passes through a diffusing medium, filter holder, and adjustable diaphragm in the wall be- tween the two compartments. A mirror under the sector wheel reflects the light up through the Open arcs and mask- ing slot to the photographic plate which may be laid face down over the slot. The size of the slot and wheel is such that a calibration scale 0.3" by 3" results. See Figs. 1 and I4. In use for long eXposures a light tight cover comes down over the plate. The design of the instrument including the sector wheel Fig. 2. Sector Wheel Sensitometer Fig. 3. interior View is such that its use is not limited to Spectrographic intensity measurement but can also be applied to general photographic standardization and measurement. When the energy of a spectral line falls upon a photographic plate, the observable and measurable result is a blackening or an increase in the optical density of the plate. The density unit is defined as: D : loglo io/i where 10 is the intensity of a beam of light transmitted by a clear portion of the plate and i is the intensity of the same been transmitted by a blackened portion of the plate. The basis of this unit is the Lambert law of absorption.(2) The simple ratio 10/1 is called opacity. The measurement of density depends upon the measure- ment of i0 and i. That is, a densitometer is an instru- ment combining a beam of light of constant intensity and a photometer for measuring the intensity of the beam after transmission by the photographic plate. Such an instru- ment with a been small enough to pass through a single spectral line is referred to as a microdensitometer. The microdensitometer as constructed as part of this problem as the design as schematically diagramed in Plate 11 and photographed in Figs. 4 and 5. Referring to Plate ii: (8) is an adjustable slit illuminated by a ribbon filament lamp (F). An image of the slit is projected by the lens (L) and front surface totally reflecting mirror (£1) upon the emulsion side of the spectrographic plate (9). The light transmitted by mquEOFZZMGQmEZ S MF<4¢ Figs. 4 & 5. Yicrodensitometer (Working Model) .10.. the plate falls upon the photovoltaic cell (PC) whose electrical output is measured by a critically damped gal- venometer. In order to keep the plate in the focal point of the beam and to be able to move any required line into the beam, the plate rests upon a movable carriage (C). The carriage itself moves on steel rods (R). It is held in position on the rods and limited to one degree of freedom by five kinematic constraints in the form of double row radial ball bearings (B).(3) The five bearings are shown in Fig.6. Coarse adjustment for position is done by rack and pinion and fine adjustnent by a micrometer screw. Fig. 6. Kinematic Support.for the Plate Garrisge._ For plate orientation purposes a viewing system has been incorporated in the construction of the microdensi- tometer. in Plate 11 (O) is a flashed cpal bulb whose surface is projected in the same plane as the image of the slit. This is accomplished by the same lens (L) and a mirror (he) in the form of a sheet of clear glass. In addition there are two illuminating lights placed above the plate on each side of the photo cell. For the operation of the viewing system, the photo cell is carried in and out of the transmitted beam by the movable arm (A). The movement of the arm operates a switch which controls the viewing lights. The operating cycle is such that the viewing lights are off when the photo cell is in the measuring position and on where it is moved out of position. Direct observation is accomplished either by a simple magnifier which is moved into the viewing position by the photo cell arm or by a fixed viewing microscOpe above the photo cell. The sensitivity and reliability of the microdensito- meter depends upon the intensity and constancy of the light source, the sensitivity and constancy of the photo cell and galvanometer, the efficiency of the projecting lens and viewing system, and the accuracy of the plate carriage move- ment. In order to get high intensity and constancy of the light source, a 6 volt 18 ampere ribbon filament lamp operated through a voltage stabilizer was used. The -l2‘- necessity for voltage stabilization and the results ob- tained by stabilization are graphically illustrated by gal- vahometer movement and recording voltometer record in Figs. 7, 8, and 9. In the selection or a photo cell for use in this microdensitometer, several cells of different manufacture were tested and the one which had the highest sensitivity combined with the lowest drift or fatigue effects was chosen. This cell was the G-E Visitron F—B. For meas- uring the electrical output of the photo cell a galvano- meter having a short period, high sensitivity, and capable of being critically damped by the internal resistance of the photo cell is the ideal. A short focus, high aperture anastigmatic lens was used to focus the measuring beam on the photographic plate. In order to gain high intensity combined with narrowness of beam and freedom from diffraction patterns, the lens pos- ition was such that a reduced image of a relatively wide slit was used. The procedure for the measurement of the relative intensities of spectral lines is as follows. The plate is taken from the spectrograph and exposed through the revolv— ing sector wheel to radiation of the appropriate wavelength. The plate, after processing, is placed on the carriage of the microdensitometer with its emulsion side in the focal plane of the photometer beam. The galvanometer deflections F's. 7. BEFORE Fla. 8. VOLTAGE VARIATION Fue.?. AFTER STABILIZATION '14.. are recorded for clear plate, for each step of the cali- bration sector scale, for each spectral line whose inten- sity is to be measured, and for background next to each such line. (In case the background is small and relative- ly constant an average background deflection may be used). From the recorded data, a calibration curve of density against the common logarithm of the standard intensity ratios (or of Opacity against the standard intensities) is drawn. See Plate ill. The total line intensities and background intensities are read from the calibration curve and substituted into the background intensity correction formula. The final result of this method of measurement is the relative intensity of each spectral line in arbitrary inten- sity units. These units may be calibrated in absolute intensity units if the absolute intensity or energy of the standard is known. H: u._.<.._n_ + M _ ..<.7 whim . f I N. o. o r _ _ om O. ..u.ou:.& 0 m k a b b - E23... 3:32. no u:- no .. m._ or 334 1 2 222,533 $3252. it .m.m ALIOVdO rm, .m. mg; m -<.. 35.. a e ..V. 31nd N‘ I a... . i. a. F. Wu -Ib‘ IhTEWSITY DISTELEUTICN 15 THE ROTATICNAL STRUCTURE OF THE O-O BAND OF COPBER HYDRLDE A very efficient source for the production of the spectra of the metallic hydrides may be arranged by oper- ating an electric arc with metallic electrodes in an atmos- phere of hydrogen. Such a procedure was adapted here. An enclosed 220 volt d. c. are with water cooled copper electrodes was constructed such that the are could be op- erated in any desired gaseous atmOSphere. See Figs. 10 and 11. numerous tests were made as to best operating condit- ions an. it was found that the CuH spectrum was obtained with reasonable efficiency when the arc was operated in. hydrogen at 10.15 cm Hg pressure with an arc current of 20 amperes. ordinary tank hydrogen was employed without purification. With this are current and hydrogen pres- sure the arc does not maintain itself and continual strik- ing is necessary. The are was so constructed that it could be started and re-ignited without disturbing the atmosphere in which it was operating. The spectrograms were taken with a concave grating spectrograph in an Eagle mounting. The grating itself was of 1 meter focal length ruled with 30000 lines per inch over a 4 inch surface. Fig. 10. Grating Spectrograph Fig. 11. Enclosed Arc and CuH Source ”'6‘ The ruling of the grating and the construction of the mounting is such that considerable background intensity is present. This relatively high background intensity in connection with a background which is probably the many line spectrum of hydrogen is the reason for the great at- tention paid to the method of its correction in this prob- lem. Because the band whose intensity distribution was studied extended from 4280 to 4420 A0 with an average at 4350 X , the 4358 line of mercury was used for intensity calibration. Eastman Process film used in conjunction with a Wratten filter No. 85 gave perfect isolation of this line. For this reason the spectrograme were taken on Eastman Process film and developed in D-19. mamas, wt m w: 5W wavelength - D Continuous Continuous with Wratten E;.85 I | I 8 ‘ l I Hg with Wratten No.85 Fig. 12. Isolation of ‘A4358 The 0-0 Band of Sufi The specific problem to which the completed micro- densitometer was applied was a measurement of the intensi- ty distribution in the rotational structure of the 0-0 band of Copper Hydride. The analysis of this hand has been given the most completely by Heimer and fielmer (4). A given line in the band system arises when a transi- tion occurs from an excited state of the molecule with given electronic, vibrational, and rotational energies to a lower state possessing different energies. For a con- stant electronic and vibrational change, the structure which results is a band due entirely to rotational energy changes in the transition. This energy change expressed in wave numbers (V=%-) is represented by: \fzfe‘rI/Zv +101 for the total energy as a sum of the electronic, vibration- al, and rotational energies. For a given band vgv~Vt— is a constant and fa varies for each line in the band. The complete energy expression is given by: (5) V:- v; m, + (B'm'hn +(I3'-B")”"1 for a band, such as the 0-0 band of CuH, having a P and an R branch. For this particular band VZ-iV; : 23,311.1 om'1,. B' 3 6.75, a" ; 7.81 (4;). The factor m is a running number having integral values and is related to the rotational quantum numbers of the loser state. The rotational quantum numbers for the upper or excited state are J' = 0,1,2...... and for the lawer are J" : 0,1,2’00900 For the P branch of the band, m 3 -J" and for the R branch m : J” + 1. The designation P and R branch comes from the selection rules for possible transitions. The selection rule for this case limits the changes in J be- tween the upper and lower states to + and - 1. The spectral lines which result from AJ : r 1, as shown in Fig. 13 forms the P branch of the band. The R branch results from a £>J : - 1. Each line of the band is given its appropriate J” value as an index. Thus the lines of the : ’ 2’ 3’ 4’... and those of the R branch, R I f o P branch are Pl P P P O, R R 33,..... ”‘1 1’ 2’ i\’ i t \r 1 As a result of the se— lection rule and the termin- ology for the branches, the m's in the energy expression are: I l m z “’1’ -2, “3,0000. for the R0 RI 5“” J- Ve‘i‘er P branCh and m : 0’1’2’3,h'000 Fig. l} for the R branch. Energy level diagram n for the 0-0 band of CuH NHO \ooo-sloxmbu 10 11 12 13 14 15 16 17 18 19. 20 TABLE I. P Branch 23.295.54 23,277.81 23,257.94 23,235.94 23,211.92 23,185.81 23.157.72 23,127.53 23.095.36 23,061.24 23,025.19 22,987.16 22,947.26 22,905.46 22,861.88 22,816.42 22,769.26 22,720.25 22,669.52 22,617.13 0 A 4,291.5 4,294.7 4,298.4 4.302.5 4,305.9 4,311.8 4,317.0 4,322.6 4,328.7 4.335.1 4,341.9 4,349.0 4,356.6 4,364.5 4.372.9 4,381.6 4,390.6 4,400.1 4,410.0 4,420.2 THE 0-0 BAD-ID OF OUR R Branch cm"l 23,324.66 23,336.05 23,345.23 23,352.22 23,357.05 23,359.67 23,360.20 23.358.52 23,354.62 23.348.5e 23,340.38 23.329.87 23,317.27 23,302.48 23,285.50 23,266.43 23,245.13 23,221.71 23,196.13 23,168.52 23,138.74 A0 4,286.1 4,284.0 4,282.3 4,281.0 4,230.2 4,279.7 4,279.6 4,279.8 4,280.6 4,281.7 4,283.2 4,285.2 4,287.5 4,290.2 4,293.3 4,296.8 4,300.8 4.305.1 4.309.8 4.315.0 4,320.5 PZZ" It should be observed that for the P branch of this band, both the linear and quadratic terms in m are negative. The result is that the wavelengths of the different lines of the P branch continually increase. But for the R branch the linear term is positive and the quadratic term is negative. This difference in sign causes the wavelengthd of the lines of the R branch to decrease at first and then begin to increase as the quadratic term becomes more effective than the linear term. This reversal of direction causes the lines of the R branch to double back upon themselves and form a so called band head. For the appearance of this band see Fig. 15 and Plate IV. Data as to J" value and wave number for the individual lines of this band as given by Heimer and Heimer (4-) as well as the correspond- ing wavelengths as converted from wave number are given in Table II . These data are the basis for the wavelength scale in Plate IV. The intensity Distribution of the Rotational Structure of the 0-0 Band of Cepper Hydride It may be seen from Fig. 15 that there is a non- uniform distribution of intensity among the individual lines of the band. The intensity of the individual lines of the band depends not only upon the frequency of the energy causing the spectral line, (Energy of the quantum : Jar ), ___; on???“ .8993 mo comm 010 039 m. .mHm i mfio mo Ufidm ..:_ mosmsmcmm so 2 z. ____ __ _ ___ __ _ see no seam 0-0 _ _2 iamnexv concespnaeo acumemceH henna finances. _.._ a aemymmme _ 1: E :5: OIO mflu. .HO GBHMOHPOEQW +_ eMHnH _ _ -24.... but also upon the probability of occurrence of the transi- tions which result in the spectral energy, and upon the number of molecules in the initial state. The distribution of intensity, from emission in the rotational structure of a diatomic molecule, as given by Herzberg, is: 67 . .. ~[B'J'U'+n)h%n I'=(:(J'*J'+0 e The C in the expression for intensity distribution is proportional to the fourth power of the frequencies in the band. For any particular band 0 is approximately con- stant, and therefore may be regarded as a proportional- ity constant. The factor (J’ + J” 4 1) is an expression of the fact that the intensity distribution depends upon the statisti- cal weight of both upper and lower state. The dependence of the intensity distribution upon the number of molecules in the initial state which.in tunn is dependent upon the temperature of the emitting source is expressed by the Boltzmann factor. Since the P branch arises from successive transitions in union :1 J g + 1 and the R branch 6. J 3 - 1, the ex- pression (J' - J") representing the transition which results in a single line becomes: .1"-J" - 1 for the P branch, and J" = J' + 1 / J‘ - J" - + 1 for the R branch, and J” : J' - 1 _25- Therefore the expression (J'+J"+l) in the intensity distribution becomes: (J'+J"+l) : 2J'+2 for the P branch (J'+J”+l) : 2J for the R branch The intensity distribution function may now be written for the P branch for example as: I = C( 13‘». z) e’LB'J'U'HMC/“J The intensity distribution for both P and R branches or the band as measured by the method outlined in this problem are shown in Plate IV. Shown also are the total inten— sity and background intensity for the P branch. It is to be noted that the background intensity is from one to three times the intensity of the lines themselves. This fact illustrates the necessity for a reliable method of back- ground correction. The data for this intensity measure- ment is to be found in Plate III (for Plate A) and Table ll. TABLE II IHTERSITY DISTRIBUTIOE IN THE 0-0 BARB OF CuH a. KOCDQQU'ik'UTOF-‘O: n) i4 P' v4 :4 r4 id #4 1“ s: +4 O K) (D ‘4 Ci U1 $P \fl '0 I“ 0 Total 11.60 13.16 15.69 16.60 18.04 18.42 18.h2 18.42 19.67 20.23 18.42 16.76 17.57 15.24 14.81 13.55 12.36 11.49 11.34 D 1 Branch Fog 9.55 9.55 9.91 9.80 9.55 10.38 9.91 9.67 11.73 12.38 17.72 11.85 11.72 10.25 10.37 10.63 9.19 9.51 9.06 9.06 Line 2.05 3.61 5-78 6.80 8.49 8.04 8.51 8.75 7.94 7.85 6.57 5.04 7.32 4.87 4.18 4.36 3.05 2.43 2.28 R Branch Total 11.68 13.98 16.41 17.99 20.65 18.65 18.82 17.03 15.97 15.37 14.94 14.53 13.96 13.45 12.92 Fog 9.66 9.31 9.90 9.45 9.&5 9.45 9.45 9.43 9.43 9.43 9.20 9.31 9.31 Line 2.02 4.67 6.71 8.54 11.20 vr~ 521. 33 3M1V138 “Jail!“ 9' 21 El 51' Call ./\ a. fine . A >g mFh.w2uhz. J