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Multiplicity in the spectra of cadmium I, II, and III Argyle, Sidney Charles 1950

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L ^ 3 7 HULTIPLIGITY IS THE SPECTRA OF CADMIUM I, II and I I I by SIDNEY CHARLES ARGYLE A Thesis submitted i n P a r t i a l Fulfilment of the Requirements f o r the Degree of MASTER OF ARTS i n the Department of PHYSICS 6 o' THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1950 ABSTRACT A grating spectrograph has been constructed using a concave grating with a radius of curvature of 21.07 feet, and ruled at 600 lines/mm. on an aluminum surface. The plate holder, which i s loaded i n sections with 2 x 18 inch plates, i s 13 feet long, and adequately covers the wave-length range from 2000 A to 15,000 A. A water cooled Schuler tube, a helium p u r i f y i n g system and a vacuum arc have also been b u i l t and put into operation. The above equipment has been used to investigate the spectra of cadmium, and 51 l i n e s i n Cd I and Cd II have been confirmed. Several promising l i n e s , namely X 4415.62, X 3533.71 and X 3250.11, due respectively to the t r a n s i t i o n s 5p *T?i/> i n Cd I I have been c a r e f u l l y studied f o r isotope s h i f t . The 21 foot grating used i n t h i s study had not s u f f i c i e n t resolv-ing power to resolve any structure. A comprehensive table of wave-lengths has been compiled for Cadmium I, II and I I I . ACKHOWIEDG-EMBNTS The author wishes to express h i s gratitude to Dr. A. M. Crooker f o r h i s able assistance and guidance. In addition he would l i k e to acknow-ledge the work of Mr. A. J. Fraser and Mr. J. Lees i n connection with the construction of equipment required f o r t h i s research. TABLE OP CONTENTS Page I. INTRODUCTION 1 A. Object 1 B. Theory 1 C Experimental Technique 9 I I . APPARATUS 13 A. The Light Sources 13 B. The P u r i f y i n g System 16 C. The Spectrograph 19 III .EXPERIMENTAL 24 IV. RESULTS 26 V. APPENDIX 31 VI. BIBLIOGRAPHY 43 ILLUSTRATIONS Plate I. The Helium P u r i f y i n g System. Plate I I . The Grating Mount. Plate I I I . The Spectrograph Plate Holder. PLATE I. The Helium P u r i f y i n g System. PLATS I I I . The Spectrograph Plate Holder-MULTIPLICITY IN THE SPECTRA 03? CADMIUM I, II and III I. INTRODUCTION • A. OBJECT The object of t h i s research was to develop suitable sources and spectrographs to undertake the study of multiplet and hyperfine structures i n the spectra of Cadmium I, II and I I I . A beginning has been made i n establishing a wave-length l i s t of cadmium spectral l i n e s i n the o p t i c a l region, XX 2100 - 7400. B. THEORY 1. Pine Structure The theory of f i n e structure i s f u l l y treated i n many standard texts and w i l l be dealt with only b r i e f l y h e r e . 1 ' 2 ' 3 The energy of the atom and likewise the energy of the 1 S. Tolansky, Hyperfine structure i n Line Spectra and  Nuclear Spin, Methuen and Co. Ltd., London, 1948. 2 G-. Herzberg, Atomic Spectra and Atomic Structure, New York, Dover Publications, 1944. 3 E. "U." Condon and G. H. Shortley, The Theory of Atomic Spectra, Cambridge Press, 1935. 2. component electrons depends on the quantum numbers n^,!^, Ji» n 2 ' ^2* ^2* e - t c * ^ e r e n 1, 2, 3, 4 1 0, 1, 2, 3, 4 J 1 + s s ± 1/2 f o r i n d i v i d u a l electrons. The m u l t i p l i c i t y of the energy l e v e l i s 2 s + 1. The l e t t e r s s, p, d, f , g, h are used f o r values of 1 = 0, 1, 2, 3, 4, 5 respectively. An atomic state which i s v i r t u a l l y a descrip-t i o n of the energy and p o s i t i o n of the o p t i c a l electron i s -designated by the c a p i t a l l e t t e r s S, P, D, 3?, G. In the case of one-electron spectra these l e t t e r s coincide with the 1 values, but i n atoms with several valence electrons the 1 and s values of the i n d i v i d u a l electrons can combine i n di f f e r e n t ways to give a resultant J. E i t h e r the i n d i v i d u a l 1 1s and s's can combine to give j values which i n turn give a t o t a l value J or the i n d i v i d u a l l ' s and s's can combine to give resultant L and S values respectively which.in turn give a resultant J. The former i s known as JJ coupling, and the l a t t e r , LS coupling. I t i s also possible to have i n t e r -mediate forms of coupling. Whereas the s e l e c t i o n rules f o r one-electron atoms i s : J = ± 1 or 0 £ o—*0 excludedj I = ± 1 , 3 The s e l e c t i o n rules i n general become J s ± 1 or 0 '£(}'—*0 excluded^ L = ± 1. This m u l t i p l i c i t y of a term gives r i s e to a corresponding m u l t i p l i c i t y i n the l i n e pattern known as a f i n e structure mul t i p l e t . Standard spectroscopic notation w i l l be used, i n which the notation of LS coupling i s employed whenever t h i s can be done i n an unambiguous way. By the state of an atom i s meant an eigenvalue of the f i e l d free Hamiltonian, which can be s p e c i f i e d by the F value of the state. A hyperfine structure component r e s u l t s from a r a d i a t i v e t r a n s i t i o n between two states of an atom. A l i n e r e s u l t s from the t o t a l i t y of a l l allowed components between two l e v e l s spec-i f i e d by t h e i r respective J values. In LS coupling, a mult-i p l e t i s the t o t a l i t y of l i n e s between two terms, which are s p e c i f i e d by t h e i r term type, or L value, and m u l t i p l i c i t y . A group of terms of the same m u l t i p l i c i t y which aris e by adding to'a "core" term an s, p, d, e t c electron are c a l l e d respectively, monads, t r i a d s , pentads, e t c , i n general, polyads. A super multiplet i s the t o t a l i t y of multiplets connecting the terms of two polyads. A t r a n s i t i o n array i s the t o t a l i t y of permitted l i n e s connecting the l e v e l s of two configurations. 4 2. Hyperfine Structure Two d i s t i n c t types of hyperfine structure, h f s . , occur i n l i n e spectra. The f i r s t type r e s u l t s from the f a c t that d i f f e r e n t elements or isotopes have d i f f e r e n t nuclear s p i n s . 1 The theory of thi s type of h f s . i s very si m i l a r to that f o r the gross multiplet structure of an LS term. For the h f s . the int e r a c t i o n i s between the i n t r i n s i c nuclear spin moment, represented i n the vector model by I, and the t o t a l angular momentum of the external electrons, represented by J, to form the resultant t o t a l angular momentum, Fj of the whole atom. The m u l t i p l i c i t y of the l e v e l i s given by 21. + 1 or 2J + 1, which ever i s smaller. It can be seen that a l l spectral terms with J = 0 show no hyperfine structure, regardless of nuclear spin. Likewise, a l l atoms with 1 = 0 have no struc-ture of thi s type. This magnetic dipole i n t e r a c t i o n between the nucleus and the f i e l d at the nucleus due to the motion of the external electrons may always be written i n the form A T = A (I • 1) (cm"1) where A i s the h f s . i n t e r v a l factor of the given J state and i n general depends on the configuration and coupling s i t u a -t i o n pertaining to the given J l e v e l . This formula expresses W. P a u l i , Haturwiss, 12, 741, 1924. 5 the f a c t that the h f s . i n t e r v a l s obey the i n t e r v a l r u l e , namely, that the i n t e r v a l between two states i s proportional to the higher F bounding the i n t e r v a l . This i n t e r v a l rule and the f a c t that each F state i s (23? + l ) - f o l d degenerate form the basis of the experimental methods f o r determining I from atomic spectra. Fermi has. shoxra1 that f o r a, single s electron t h i s i n t e r v a l factor can be written as where /j, i s the nuclear magnetic moment, JU.Q that of an electron and {jj (0) the wave function of the s electron at the nucleus. This equation and i t s l a t e r refinements 2 form the basis of determining the magnetic moment of the nucleus from observa-tions of the h f s . i n atomic spectra. This subject and the effect of a nuclear e l e c t r i c quadrupole moment i s well treated i n Casimir 1s monograph.3 Since the magnetic moment of the proton i s much smaller than that of the electron, i t i s to be expected that the h f s . energy differences are much smaller than the energy d i f f e r -1 E. Fermi, Zs. f . Phys., 60, 320, 1930. 2 E. Fermi and E• Segre, Zs. f . Phys., 82, 729, 1933. 3 H. B• G. Casimir, On the Interaction between atomic ' " nuclei and electrons, Archives du Musee Teyler , 8,2 02, 1936. 31 • 6 ences encountered i n gross structure. In pra c t i c e i t i s found that the former are of the order of 1000 times smaller than the l a t t e r . The second type of hfs• arises from the f a c t that-many elements consist of a number of isotopes. Since the isotopes vary only i n the number of neutrons i n the nucleus, t h i s e f f e c t i s small. Four main factors contribute. They are as follows: 1) E f f e c t of the "reduced mass," wobbling motion of the nucleus 2) S p e c i f i c mass effect 3) E f f e c t of nuclear size 4) E f f e c t of nuclear p o l a r i z a t i o n . The f i r s t of these effects i s the t o t a l mass eff e c t f o r the c l a s s i c a l two body problem. The existence of the s p e c i f i c mass eff e c t i n non-hydrogen l i k e spectra was emphasized by Eckart and Hughes. 1 The eff e c t of the f i n i t e s i z e of the nucleus i n decreasing the binding energy of the electrons was apparently f i r s t understood by B r e i t . This l a t t e r author has also recently showed3 that the eff e c t of nuclear p o l a r i z -ation i s not n e g l i g i b l e . The odd mass isotopes of even-Z elements show greater p o l a r i z a t i o n and therefore the centre of 1 D. S. Hughes and C. Eckart, Phys. Rev. , 56, 694, 1930. 2 G-. B r e i t , Phys. Rev., 42, 348, 1932. 3 G. B r e i t , Phys. Rev., 77, 569®, 1949. gravity of the hfs- spectral l i n e i s s h i f t e d towards the li g h t e r even isotope as i n H g 1 9 9 , H g 2 0 1 , P t 1 1 7 , Sm 1 4 3, Sm14^, B a 1 3 5 , B a 1 3 7 . The simple mass ef f e c t i s predicted by Bohr's theory. In general the series terms of a spectrum can be f i t t e d to a Hick's formula which i s of the form R Z 2 E = — 5— (n + a + b_) n 2 a and b are numerical constants n i s the e f f e c t i v e quantum number Z i s the e f f e c t i v e nuclear charge R i s Rydberg's constant. Since Rydberg's constant i s not s t r i c t l y constant but involves the reduced mass of the electron, we have f o r the frequency \) of a l i n e V - R x A where A i s of the form ,2 A"" £ h (n x+ a + _b_ ) 2 (n 2+ a + b ); n 2 n 2 Now f o r the isotope constituent of a l i n e , A i s constant since i t does not involve the mass of the nucleus. It follows that f o r two isotopes the difference i n wave number A V i s 8 given by 4\> = (R-L - R 2 ) (A) . Making use of the f a c t that R i s proportional -to ' me^n ^ where me i s the mass of the electron and M^ i s the mass of the nucleus, i t i s e a s i l y shown that /IV = V me Mi - Mp, . Mi M 2 Of the eight stable isotopes of cadmium t h i s energy difference would be greatest f o r the isotopes 106 and 108. A simple c a l -culation shows that f o r these two isotopes&V = 2.1 x 10 cm7x This e f f e c t i s so small as to be masked by l i n e width i n even the f i n e s t l i n e sources. An effect that comes under the (3) heading i s Isotope Displacement. This e f f e c t i s much too large to be the re s u l t of simple mass s h i f t and must be attributed to other causes. In a mixture of even isotopes, when t h i s effect i s present, the l i n e s due to the d i f f e r e n t isotopes do not f a l l together as would be expected from spin considerations, but are slight-l y displaced from each other. When odd isotopes are present the centre of gravity of the h f s . pattern i s often displaced from the expected p o s i t i o n . Large isotope s h i f t s , due to the factors (3) and (4) above , are expected f o r l i n e s Involving t r a n s i t i o n s between configurations with d i f f e r e n t numbers of s electrons. In the l i n e s e s p e c i a l l y checked f o r isotope s h i f t i n t h i s investiga-t i o n t h i s condition i s f u l f i l l e d , since they involve the electron p Q o ? double A transition:; Sp^P 0 5d y 53^ T). C EXPERIMENTAL TECHNIQUE 1. Light Source In order to excite the required spectra i t i s necessary to consider the following points: (a) excitation,, (b) l i n e width, (c) i n t e n s i t y . Several types of source i n use to-day w i l l be discussed. The Schuler tube, which i s very widely used at the present time, i s a development of the o r i g i n a l hollov/ cathode source used by Paschen. 1 This source emits very f i n e l i n e s e s p e c i a l l y when cooled with l i q u i d a i r . The i n t e n s i t y i s high, and.the window remains clear even afte r several hours of operation. These l a s t two considerations are of great importance when long exposures are necessary to bring up f a i n t components. The exc i t a t i o n , however, i s r e s t r i c t e d by the i o n i z a t i o n p o t e n t i a l of the c a r r i e r gas used. The emit-ted spectrum i s therefore, according to theory, confined to the arc and f i r s t spark; but according to Shenstone, 2 Cd III l i n e s are emitted with great i n t e n s i t y , and even more completely than those of Cd I I . This high e x c i t a t i o n i s probably due to the high vapour pressure of the metal and 1 A. G. Shenstone, R. P. P., 1938, page 210. 2 A. G. Shenstone, J . 0. S. A., 39, 210, 1949. - 10 consequent electron e x c i t a t i o n . The electrodeless discharge tube used with a condensed spark i s very valuable i n exc i t i n g the higher spark s p e c t r a . 1 This source i s not as suitable f o r the emission of f i n e l i n e s as the cooled hollow cathode because of Doppler broadening. This i s p a r t i c u l a r l y true when the spectrum of low vapour pressure metals i s to be observed. The degree of i o n i z a t i o n can be roughly controlled by the size of the external spark gap, the capacity and inductance i n the c i r c u i t , and the p o t e n t i a l applied. For extreme ex c i t a t i o n , capacities up to .25 jM charged to a p o t e n t i a l of 100,000 v o l t s have been used. Sorting out of l i n e s of a p a r t i c u l a r i o n i z a t i o n i s s i m p l i f i e d by the f a c t that i n any p a r t i c u l a r vacuum spark only two degrees of i o n i z a t i o n occur with great i n t e n s i t y . If extremely f i n e l i n e s are required f o r the separation of very -close components then an atomic beam can be used. The beam-can be so well collimated by the use.of appropriate s l i t s that a Doppler width equivalent to a few degrees absolute can be obtained i n absorption spectra. ;Meissner greatly extended the use of this'type of source by bombarding the atomic beam with a strong beam of electrons to give an emission spectrum with a l i n e breadth equal to 5° K. An arc or spark i n nitrogen i s useful f o r the ex c i t a t i o n 1' C. R. Msenwanger, J. R. Holmes and G. L. Weissler, J. 0. S. A., 36, 581 - 7,. (1946). 2 H. A. Robinson,. Z. Phys., 100, 636 (1936). 11 of arc or f i r s t spark spectra. There are two reasons f o r the, usefulness of t h i s type of source: (a) Pure nitrogen i s trans-parent down to at least 1000 A) (b) Low spark or arc l i n e s are almost absent from the usual vacuum spark or arc. 2. Spectrographs When high resolution i s not necessary f o r the separation of close structure, or when the instrument i s to be used only" f o r the i d e n t i f i c a t i o n of l i n e s , a glass or quartz prism spectrograph i s indispensable. However, i f close doublets i n the gross structure or i f hyperfine structure patterns are to be resolved, i t - i s necessary to use some type of i n t e r -ferometer . Interferometers can be divided into four general groupsJ (a) the ruled grating, (b) the Lummer plate-interferometer, (c) the echelon-grating, (d) the Fabry-Perot interferometer. -In terms of the resolving l i m i t , which i s defined as the h a l f width of the instrumental d i f f r a c t i o n pattern, we have i n p r a c t i c e f o r the above c l a s s i f i c a t i o n s resolving l i m i t s of 0.06 cm."1, 0.025 cm."1, 0.01 cm."1 and 0.0025 cm. - 1 respect-i v e l y f o r the region of 5000 A. For the ruled grating t h i s l i m i t i s attained i n the fourth order. 1 1 S. Tolansky, High Resolution Spectroscopy, Methuen and Co. Ltd., London, 1947. - • 12 As well as the resolving l i m i t , three other factors must be considered i n the selection of a suitable instrument. They are as follows: • (a) the e f f e c t i v e range of usefulness, (b) the ease of int e r p r e t a t i o n of observations, (c) the r e l i a b i l i t y of the instrument. The l i n e grating and the r e f l e c t i n g echelon can be used over the whole spectral range from the i n f r a - r e d to the f a r u l t r a -v i o l e t but the resolving l i m i t of these instruments i s pro-p o r t i o n a l to the wave number. The Fabry-Perot interferometer and the Lummer plate can work within the range of transmission of quartz. In theory the resolving l i m i t of these two i n -struments i s almost uniform over the range, but i n p r a c t i c e , because of mechanical considerations, the resolving l i m i t f a l l s towards the u l t r a - v i o l e t . From the point of view-of ease of interpretation-the l i n e grating i s f a r superior to the other instruments under consideration. The Fabry-Perot interferometer, because of i t s complete freedom from ghosts, i s i n general more r e l i a b l e than the other three instruments mentioned. This subject i s well treated by Tolansky. 1 1 S. Tolansky, High Resolution Spectroscopy, Methuen and Go. Ltd.-, London, 1947. 13 I I . APPARATUS A. THE LIGHT SOURCE In order to excite the cadmium spectra three types of sources were used. These were as follows: (a) An electrodeless discharge tube, (b) A vacuum arc, (c) A Schiller tube. The electrodeless discharge tube used by the author Was very simple i n form and consisted of a quartz tube 1 1/4 inches i n diameter and 16 inches long with an evacuation tube at one end. The operation of t h i s source i s as follows. Several small pieces of cadmium are placed i n the tube, which i s then connected to a mechanical vacuum pump and evacuated. The' tube i s then heated by means of bunsen lamps to vaporize the. cadmium and swamp out impurities. The evacuation and heating process i s continued throughout the exposure. E x c i t a t i o n can be obtained either by placing the source inside the o s c i l l a t -or inductance or by tapping off from each end of t h i s inductance and exciting the spectra by means of external electrodes i n the form of bands placed around each end of the tube. This source was used with both R.E. and condensed- <~ spark e x c i t a t i o n . The former was more convenient to operate than the l a t t e r , hut can he expected to give a more gentle e x c i t a t i o n . In both cases, hut e s p e c i a l l y i n the former, great d i f f i c u l t y was experienced i n obtaining a clean spec-trum. This r e s u l t s from the f a c t that t h i s type of source favours the e x c i t a t i o n of minute impurities. Tolansky recommends the use of a c a r r i e r gas, with the element to be analysed being introduced as an "impurity". I f the c a r r i e r gas i s introduced through a p u r i f y i n g system, l i t t l e d i f f i -culty should be experienced from the presence of molecular bands. This method was not used, since t h i s modification would severely l i m i t the e x c i t a t i o n . Another d i f f i c u l t y arose from the f a c t that the windows soon became coated with cadmium. In order to remove t h i s f i l m during an exposure i t was necessary to heat the windows to a d u l l red heat, and th i s was not e n t i r e l y s a t i s f a c t o r y because the windows soon gathered a brown coat on the inner side which could not be removed even by the use of acids. The outcome was that very long exposures were required. This i n turn introduced a further d i f f i c u l t y i n that a l l the cadmium condensed i n the evacuation tube before the exposure was completed." This d i f f i c u l t y could be eliminated by sealing off the tube once a pure spectrum was obtained; the whole tube could then be heated. In t h i s case, however, i f a quartzr tube were used i t Would have to be heated e l e c t r i c a l l y , as the seepage of hydrogen from bunsen lamps through the wall of the tube would soon cause a pressure increase. 15 Two Schiller tubes, both of the same general form but d i f f e r i n g i n size and cooling methods, were b u i l t and put into operation. The large tube, which had a hollow cathode 1 cm. i n diameter and 3 cms. deep,was b u i l t f i r s t and put into use. This tube operated most s a t i s f a c t o r i l y at a helium pressure of about 1 mm. of mercury. Because of the large metal surfaces involved i n t h i s model, the p u r i f y i n g system was unable to handle the large volume of impurities present, and a r e a l l y clean spectrum was never obtained. For this reason the tube was discarded and a smaller one of improved design was b u i l t . This model, which i s i l l u s t r a t e d below, gave ,a spectrum which was free from molecular bands within a few minutes after c i r c u l a t i o n was commenced. c A Scale - Actual s i z e . The materials used are as follows: A. mild s t e e l C. pyrex B. brass D- quartz. 16 This tube operates best at the rather high helium pressr. ure of 5 ram. At lower pressures the discharge refuses to remain i n the cathode hole. Operating currents vary from 50 to 250 ma. at 400 to 800 v o l t s . A 2 0 0 0 b a l l a s t r e s i s t o r i s used to provide stable operation. It i s possible that a larger value of t h i s resistance or the use of a constant current device, which i s of great value f o r insuring s t a b i l i t y over a wide range of operating conditions, would improve the c h a r a c t e r i s t i c s of t h i s source. Such a device f o r use with hollow cathode sources i s described by Shenstone. 1 A vacuum arc with externally adjusted electrodes and quartz windows f o r operation with or without a magnetic f i e l d was b u i l t as an aid! i n i d e n t i f y i n g e x c i t a t i o n l e v e l s . This source i s shown on page 17• B. THE PURIFYING SYSTEM The p u r i f y i n g system , which i s well described by Tol-2 ansky, i s i l l u s t r a t e d on Plate I. In the operation of t h i s system, some care must be taken i f the system i s to function properly. The f i r s t step i s to 1 A. G. Shenstone,-R. P. P., 1938, page 210. 2 S. Tolansky, High Resolution Spectroscopy, Methuen and Co. Ltd., London, 1947. 17 The Vacuum Arc• hake out the charcoal trap under vacuum at a temperature of 500° C for several hours i f a i r has leaked into the system. This can he done by means of an e l e c t r i c furnace which was b u i l t f o r the purpose. The required temperature i s obtained by applying 75 v o l t s to the terminals by means of a va r i a c . This voltage should also be applied to the furnace on the copper oxide trap during the baking process to prevent the condensation of mercury and other impurities i n t h i s trap. Having baked out the trap, the system i s now ready f o r operation. The following procedure should be followed i f satisfactory r e s u l t s are to be obtained. The two cold traps on the system should be cooled w i t h either l i q u i d a i r or a mixture of alcohol and dry ice f o r a period of 15 minutes 18 before the c i r c u l a t i o n pump i s put into operation. This prevents mercury vapour from reaching the l i g h t source and being absorbed by the cadmium and brass. A few mm. of helium should then be introduced into the system i n small quantities. If a large quantity i s introduced at once, or i f the copper oxide i s heated f i r s t , the cooling l i q u i d on the charcoal trap i s sure to b o i l over. The copper oxide should now be heated by applying 90 v o l t s to the terminals of the furnace. Voltage should not be applied to the source u n t i l the gas has c i r c u l a t e d f o r some 5 or 10 minutes, since, i f there i s any oxygen present, the cadmium w i l l oxidize r a p i d l y and the tube may have to be dismantled and cleaned with n i t r i c acid. This operation necessitates re-oxidizing the cathode. Under no circumstances should the source be operated i f i t i s known that a i r has leaked into the system. The mercury pump should be operated at about 1 cm. pressure. On a long exposure i t may be necessary to introduce an addi t i o n a l small quantity of helium into the system to re-place the helium absorbed by the charcoal. I f these pre-cautions are taken, no d i f f i c u l t y should be experienced i n obtaining a clean, b r i l l i a n t spectrum. 19 C . T H E S P E C T R O G R A P H 1 . T h e G r a t i n g M o u n t T h e 2 1 f t . c o n c a v e g r a t i n g • w h i c h i s r u l e d a t 6 0 0 l i n e s p e r m m . f o r 5 1 / 2 i n c h e s o f t h e s u r f a c e i s m o u n t e d s o a s t o h a v e r o t a t i o n , t r a n s l a t i o n a n d v e r t i c a l i t y a d j u s t m e n t s . T h e g r a t i n g b a s e i s m a r k e d i n d e g r e e s , w h e r e a s t h e v e r n i e r d i a l i s d i v i d e d i n t o 4 5 s e c t i o n s , e a c h d i v i s i o n b e i n g e q u i v a l e n t t o . i - ° , t h u s g i v i n g a g r a t i n g r o t a t i o n o f 4 . 5 ° f o r o n e r o t a t i o n o f t h e v e r n i e r . T h e g r a t i n g t r a n s l a t i o n i s e q u i p p e d w i t h a d i r e c t r e a d i n g s c a l e c a l i b r a t e d i n c m s . a n d a v e r n i e r s c a l e c a l i b r a t e d i n i n c h e s , s u c h t h a t o n e d i v i s i o n = 0 . 0 0 5 i n c h e s . T h e c m . s c a l e w a s u s e d t e m p o r a r i l y , s i n c e a s u i t a b l e s c a l e c a l i b r a t e d i n i n c h e s w a s n o t a v a i l a b l e . T h e g r a t i n g c o n s t a n t s a r e : R = 6 4 2 . 2 1 4 c m s . G r a t i n g s p a c e = 1 6 , 6 6 6 . 6 A . D i s p e r s i o n r 2 . 5 9 5 1 8 8 c o s ft A / m m . n T h e o r e t i c a l r e s o l v i n g p o w e r = n x 8 2 , 5 0 0 w h e r e n i s t h e o r d . e r i n w h i c h t h e g r a t i n g i s u s e d . 20 2- The P l a t e Holder The p l a t e h o l d e r , which i s load e d w i t h e i g h t e i g h t e e n -i n c h p l a t e s , i s designed f o r ease of l o a d i n g . The p l a t e s are h e l d snugly i n p o s i t i o n hy means of c l i p s t h a t f i t i n t o s l o t s i n the p l a t e h o l d e r . The whole p l a t e h o l d e r beam can be r o t a t e d through any angle r e q u i r e d . T h i s r o t a t i o n i s c a l -i b r a t e d i n inches w i t h a c o n v e r s i o n f a c t o r of 1 i n c h =.97276°. The use of such a long p l a t e h o l d e r e l i m i n a t e s the n e c e s s i t y of f r e q u e n t r e - s e t t i n g i n order t o cover the spectrum. L e t t i n g i = 19° i n the fundamental g r a t i n g f ormula nX = d ( s i n i + s i n 0) g i v e s 0 a 2° 9* and 35° 51 1 f o r the two ends of the p l a t e h o l d e r . T h e r e f o r e , the l i m i t s on nX are 6051 and 1587 A r e s p e c t i v e l y . n i s the order i n which the spectrum i s observed. X i s the wave-length i n A. d i s the g r a t i n g space i n A. i i s the angle of i n c i d e n c e . 0. i s the angle to the spectrum l i n e b e i n g observed. On a l l o w i n g some t o l e r a n c e at the ends of the p l a t e h o l d e r , the u s e f u l wave-lengh range i s ; 1 s t order 6100 15150 2 nd order 3050 7575 3 r d order 2050 5050 21 4th order 2000 3780 5th order 2000 3000 7575 15150 occurs only i n the 1st order. 5050 7575 occurs only i n the 2nd order. 3050 5050 occurs only i n the 2nd and 3rd order. 2050 • 3050 occurs only i n the 3rd and 4th order. 2000 2050 occurs only i n the 3rd, 4th and 5th order. 3. The Measurement of Wave Lengths f o r Multiplet; Analysis Since, f o r the purpose of multiplet analysis, the meas-urement of Wave-lengths should be correct to .01 cm - 1 i n order to reduce the p r o b a b i l i t y of chance coincidences i n the a n a l y s i s , 1 i t i s quite es s e n t i a l to make corrections to the wave-lengths, calculated by the method of coincidences, f o r changes i n atmospheric pressure and temperature. An o r i g i n a l analysis of the problem i s presented below. In the grating equation nX = b ( s i n i + s i n /$) X i s the wave-length measured i n a i r . I f i t i s wished to reduce the wave-length to vacuum i t i s necessary to write nX = Hb(sin i + s i n 0) where N i s the index of the a i r . Then, f o r a d e f i n i t e spectral l i n e , 1 H. H. Russell and I. S. Bowen, Mount Wilson Contribution No. 375, 1929, Astr. J n l . , 69, 196, 1929. 22 dN + db + cos 0 6.0 - Q 3sT b s i n i + sin0 And i f f o r N the G-lads-tone-Daie-app-roximat-ion (N - l ) T/p - a constant (where T i s the temperature and p the pressure) i s used with the condition f o r sharp l i n e s , i . e . , 6.0 = 0, the follow-ing r e l a t i o n i s obtained: dH N db = - oC d T where c< i s the l i n e a r c o e f f i c i e n t of expansion of the grating. On using the r e l a t i o n d¥ (* - .1) dp _ dT P T for dU i n the above equation i t becomes (* - i ) p \7S-1 T J - 0 It i s proposed to s a t i s f y these equations approximately with a barothermograph. In many instances i t i s s u f f i c i e n t to hold T constant; then (N - 1) dp_ + cos 0 6.0 m U p s i n i + s i n 0 and 6.0 - - {TS - l) dp_ ( s i n i + -sin 0) _ (TS - 1), dp_ nX TS p cos 0 "S p Nb , c o s 0 and the s h i f t i n p o s i t i o n of the spectral l i n e ds i s given by ds = R d $ = (3ST - 1 ) dp_ A S p D where D i s the plate f a c t o r , or r e c i p r o c a l dispersion dX/ds a (Mb cos 0)/nR. Therefore the apparent s h i f t of wave-length dX s Dds i s . dX = - (N - 1 ) dp_ A IT p Or to achieve a p r a c t i c a l resolving power of R 1 s x/dX i t i s necessary to keep dA < X/Ri i . e . (* ; 1 ) SB. A < J L . IT p R x D * < RJ& - 1 ) which f o r R-^  = 2 0 0 , 0 0 0 requires dp < 1 2 . 6 mm. at 7 6 0 mm. In a sim i l a r manner i t can he shown that f o r a given coincidence at nX, ds = nX (R/b (cos ^ T 1 ) ( l ^ . - 3STr) dp/p gives the displacement of the coincidence on a pressure change. 24 I I I . EXPERIMENTAL D u r i n g t h e p r o c e s s o f d e s i g n a n d c o n s t r u c t i o n o f t h e l i g h t s o u r c e s , numerous t e s t p l a t e s w e r e t a k e n f o r t h e p u r p o s e o f i n v e s t i g a t i n g i n t e n s i t y , e x c i t a t i o n a n d p u r i t y o f s p e c t r u m . T h i s e x p e r i m e n t a l e v i d e n c e showed t h a t a h o l l o w c a t h o d e s o u r c e was most s u i t a b l e f o r t h e p u r p o s e a t h a n d . S p e c t r o g r a m s o f t h i s s o u r c e showed t h e p r e s e n c e o f f a i n t c o p p e r l i n e s w h i c h w e r e a t f i r s t b e l i e v e d t o come f r o m t h e b r a s s a n o d e . A s p e c t r u m a n a l y s i s , h o w e v e r , showed t h e p r e s -e n c e o f c o p p e r i n t h e cadmium s u p p l y . As t h e i n t e n s i t y o f t h e s e l i n e s was l o w , no a t t e m p t was made a t p u r i f i c a t i o n . A n o t h e r m i n o r i n c o n v e n i e n c e r e s u l t e d f r o m t h e p r e s e n c e o f i r o n l i n e s w h i c h , i n s p i t e o f t h o r o u g h o x i d i z a t i o n o f t h e i r o n c a t h o d e , c o u l d n o t b e e l i m i n a t e d c o m p l e t e l y . The l i n e s t h a t r e m a i n e d , h o w e v e r , w e r e l o w i n i n t e n s i t y a n d c a u s e d l i t t l e d i f f i c u l t y . To f a c i l i t a t e t h e f o c u s i n g o f t h e c o n c a v e g r a t i n g , a l o w p o w e r e d m i c r o s c o p e was m o d i f i e d so a s t o h a v e k n i f e e d g e s a t t h e f o c a l p l a n e o f t h e o b j e c t i v e l e n s . The m i c r o s c o p e c o u l d t h e n b e p l a c e d i n t h e p l a t e h o l d e r a n d t h e d i s c r e p a n c y i n t h e g r a t i n g f o c u s r e a d o f f on t h e m i c r o s c o p e s c a l e . T h i s i n s t r u m e n t p r o v e d t o b e w e l l w o r t h t h e t i m e s p e n t on i t s c o n s t r u c t i o n . 25 When the equipment Was working s a t i s f a c t o r i l y , spectro-grams were taken on a Hilger E . l spectrograph and on the 21 foot grating. Total exposure time for the Hilger spectrogram was 52 minutes. It was necessary to change the operating conditions of the Schiiler tube at i n t e r v a l s during the expos-ure to maintain the required e x c i t a t i o n . Data f o r the expos-ure i s given below. Helium Pressure Current Voltage Time 3 mm. 100 ma. 450 v o l t s 15 min 3 mm. 125 » 500 II 5 » 3 u 150 » 600 II 3 " 4 tt 150 «' 630 II 14 " 4 II 175 " 660 II 10 " 4 ti 200 » 700 II 5 » 52 minutes. The exc i t a t i o n was determined by viewing the source with a d i r e c t v i s i o n spectroscope from time to time during the exposure. Two exposures were taken on the grating with exposure times of 30 minutes and 7 minutes. Data i s given below. Helium Pressure 5 mm. 7 mm. Current 170 ma. 200 ma-Voltage 600 v o l t s 750 v o l t s • Time 30 min. 7 min. 26 RESULTS A 21 foot concave grating, three l i g h t sources and a p u r i f y i n g system f o r helium were b u i l t and put into operation. Spectrograms were taken, and 51 l i n e s i n Cd I and Cd II were confirmed. Several promising l i n e s , namely X 4415.62, X 3535".71 and X 3250.11 due respectively to the t r a n s i t i o n s 5P 2 ? i l / 2 4 d 9 5 s 2 2 D 2 y 2 , 5p 4d 9 5 s 2 2 ] ^ , and 5p 2P°. 4d 9 5s 2 2I>^j, i n Cd II have been c a r e f u l l y y 2 J-72 studied f o r isotope s h i f t . The 21 foot grating used i n t h i s study had not s u f f i c i e n t resolving power to resolve any structure. Since the doublet laws and Mosley diagrams applied to on i s o e l e c t r i c sequences provide the experimental foundation f o r the discovery and assignment of spectral terms, the doublet laws were applied to representative doublets i n the i s o e l e c -t r o n i c sequences involving Cd I, Cd II and Cd III i n order to check the assignments of configurations i n the spectra. For the rapid c a l c u l a t i o n of the regular doublet law A \ ) : Rc(2 (z - s ) 4 n 3 1(1 + l) a table of the quantity log n 3 l i t + l) was made. R o(2 27 This table and applications of the doublet laws are tabulated below. The value of Rc<2 used 1 i s 5.844 cm."1 Table of log n 3 I { Rot :i + l ) 2 P d f g h i 2 .4374 3 .9657 1.4428 4 1.3405 1.8176 2.1187 5 1.6312 2.1084 2.4094 2.6312 6 1.8688 2.3460 2.6469 2.8688 3.0449 7 2.0696 2.5468 2.8477 3.0696 3.2456 3.3919 8 2.2436 2.7207 3.0218 3.2436 3.4917 3.5658 9 2.3971 2.8142 3.1752 3.3971 3.5732 3.7193 10 2.5343 3.0115 3.3125 3.5343 3.7104 3.8565 1. Application of the Regular or Spin Doublet Law to the iso e l e c t r o n i c sequence Cd I, In I I , Sn I I I , Sb IV, ;. involving the t r a n s i t i o n (5s 5p ^FQ — — 3 P P ) . Element Z (Z - s) s A s Cd I 48 1,613 16.21 31.79 • 2.53 In II 49 3,552 19.74 29.26 1.46 Sn III 50 5,681 22.20 27.80 1.22 Sb IV 51 8,125 24.42 26.58 R. T. Birge, Rev.Mod.Phys., 15, 233, 1941. 28 2. A p p l i c a t i o n t o the sequence Ag I, Cd I I , In I I I , Sn IV i n v o l v i n g the t r a n s i t i o n (Sp P y g Element Z ( Z - s ) s A a Ag I 47 920.6 14.09 32.91 2.96 Cd I I 48 2483 18.05 29.95 1.71 In I I I 49 4342 20.76 28.24 1.22 Sn IV 50 6518 22.98 27.02 3. A p p l i c a t i o n to the sequence Ag I I , Cd I I I , In IV, Sn V i n v o l v i n g the t r a n s i t i o n ( 4 d 9 5s 3 D 3 — - 3 D 1 ) . Element Z (Z-s) s Ag II 47 4574.8 23.42 23.58 .38 Cd I I I 48 5766.1 24.80 23.20 .06 In IV 49 7108 25.74 23.26 + .31 Sn V 50 8620 27.43 23.57 A p p l i c a t i o n o f t h e I r r e g u l a r - D o u b l e t L a w t o t h e i s o e l e c t r o n i c s e q u e n c e s ( C d I , I n I I , S n I I I , S h I V ) , ( A g I , C d I I , I n I I I , S n I V ) , ( P d I , A g I I , C d I I I , I n I V ) i n v o l v i n g t h e t r a n s i -t i o n s ( 5 s 2 5 s 5p 3 p £ ) , ( 5 s 2 S - ^ . 5p 2 P y g ) , ( 4 d 9 5 s 3 D 1 4 d 9 5p 3 P - ^ ° ) • . E l e m e n t 5 s 2 1 S Q 5s 5p 3 P ° C d I 3 0 , 6 5 6 1 2 , 6 9 3 I n I I 4 3 , 3 4 9 1 1 , 8 4 2 S n I I I 5 5 , 1 9 1 1 1 , 5 0 9 S b I V 6 6 , 7 0 0 E l e m e n t A v A g I 2 9 , 5 5 2 1 4 , 5 8 3 C d I I 4 4 , 1 3 5 1 3 , 0 5 0 I n I I I 5 7 , 1 8 5 1 2 , 4 7 4 Sb I V 1 ' 6 9 , 5 5 9 E l e m e n t 4 d 9 5 s 3 D 1 4 d 9 5 p 3 P 1 ° A V P d I 2 6 , 0 8 6 1 3 , 7 9 6 A g I I 3 9 , 8 8 2 1 2 , 6 5 4 C d I I I 5 2 , 5 3 6 1 2 , 2 3 3 I n I V 6 4 , 7 6 9 30 A c o m p r e h e n s i v e l i s t o f w a v e - l e n g t h s o f C d I , C d I I a n d C d I I I w a s c o m p i l e d , s h o w i n g i n t e n s i t y , w a v e - l e n g t h a n d c l a s s i f i c a t i o n . T h i s t a b l e i s d i s p l a y e d i n t h e A p p e n d i x . T h e w a v e - l e n g t h s c o n f i r m e d b y t h e a u t h o r a r e m a r k e d w i t h a n a s t e r i s k . T h e v a l u e s f o r t h e i n t e n s i t i e s o f t h e l i n e s w e r e c o l l e c t -e d f r o m f o u r s o u r c e s . F o r c o l u m n s 1 , 2 a n d 3 r e f e r t o ( 1 7 ) , ( l l ) a n d ( 1 2 ) i n t h e b i b l i o g r a p h y . C o l . 4 g i v e s t h e v a l u e s a s o b t a i n e d b y t h e a u t h o r . APPENDIX Table of 'Wave-Lengths of Cadmium I, II and III showing Intensity, Wave-Length and C l a s s i f i c a t i o n 39,086 16,482 16,433 16,401 15,713 15,258 15,154 14,853 14,474 14,354 • 14,327 13,979 11,630 11,268 10,395 8,200.07 8,066.99 II - 70 7,399.2 l u 7,396.67 800 7,385.3 1000 7,383.9 1000 7,346.2 100 7,284.38 II 10 7,275.75 II 50 7,237.01 II 30 7,132.27 5h 6,935.46 II 20 6,818.39 II 30 6,778.10 100 10 6,759.189+ II 500 100 6725.780+ II 10 6684.161 II 5 6574.098 II 25 6567.648 II 6468.6 400 30 6464.936+ II 15 6449.456 II 2000 1000 6438.4 69 6 + I 500 50 6359.982+ II 400 50 6354.724+ II 30 6329.97 10 6325.19 + 15 6198.26 6165 . 15 6128.66 15 6116.19 100 6111.52 300 6099.18 30 6031.38 5 5895.8 + 50 5880.220 II 10 5868.502 II 40 3 5843.305+ II 10 5802.801 II 5 5783.93 5762. 5761. 5736. 5716. 10 5708.77 II 5673. 10 5637.26 5 5606.85 10 5604.683 15 5598.769 2 5568.36 II 2 5471.25 II 1 5449.41 II 200 20 5381.887 II 1000 100 5378.134"*" II I X c 1 2 3 4 5339.50 1000 75 5337.484+ II 5297.65 100 5 5271.600+ II 5268.007 II 5194.66 II 5182. 6r 20 5154.68 + 10 5142.90 II 1000 1000 5085.824"1* I 10 5025.50 + 20 • 4918.85 ^ II 50 10 4881.725+ II 10 4834.64 II 5 4828.52 II 30 Ow 1500 4799.918+ I 30 4744.693 II 20 4741.776 II 20 Ow 1000 4678.156 I 8r 50 4662.352* I 2 4615.75 I 3 4615.39 I 4 4614.17 I 2 4605.71 II 1 4588.45 II 3 4535.16 II 5 4511.34 I 2 4451.00 II 5 4441.76 II 30 4440.45 II 20 4437.91 II 1000 1500 4415.63 + II 3 4413.042 I 100 50 .4412.41 II 5 4384.52 II 8 10 4306.82 + I 100 5 4285.078+ II 5h 4245.760 II 5h 4243.428 II 4216.9 50 200 5h 5b. 1 100 20 15 15 1 5 3 20 10 1 lOr 15r 4141.49 3"* 4140.5-4134.7 68"* 4127. 4112.367 4110.169 4094.8 4044.830a 4029.124 4006.867 3981.77 3957.244 3905.1 3852.L 3827.41 3826.71 3779.63 3767.336 3729.06 3723.2. + II I II II II II II II I II I II II II I 20 20 60 800 1000 100 40 500 800 3666.756 3649.597 3614.450 3612.88 ] 3610.510H + II I I I I 100 100 150 25 100 50 20 30 3595.5 , 3535.69 + 3524.11 + 3500.00 3495.436+ I II 100 50 8 5 20 50 800 1000 800 500 600 20 10 5 20 500 3481.71 3467.66 + 3466.2D.rJ" 3464.426* 3442.416 3422.998 3422.228 3420.194* 3417.491* 3403.653* I I II II II II II II I I G 1 2 3 4 30 5 3388.884+ II 50 6 3385.486+ II 10 . 1 3376.866* II 10 1 3355.362* II 50 10 3343.209+ II 15 3298.97 I 3 2 3283.565 II 300 1500 3261.057+ I 300 100 3252.525+ I 150 25 150 3250.328+ II 100 3250.17 II 10 5 3238.742 II 5 2 3232.26 II 2 2 3222.614 II 3215.95 1 3194.42 II .10 2 3179.96 II 1 3164.34 II 50 10 3146.76 II 200 3133.17 I 10 3129.21 10 3124.40 10 3121.80 3 2 3118.92 2 3112.96 3 2 3112.206 4 3104.59 20 3093.769 II 100 10 15 3092.337 II 3 3089.856 10 40h 3084.866 30 3082.68 I 25 3081.484 II 150 3080.83 I 12 3077.2 2 3071.65 2h 3068.79 15h 3064.955 2 2 3063.725 4 5 3060.28 I X C 1 2 3 4 2 3059.22 2 3057.51 1 2 3056.41 10 3053.1 2h 3048.82 4 3039.572 10 3035.72 III 50 3030.605 II 12 3017.32 3014.3 10 3011.3 25 4 3005.41 I 10 3001.51 10 2996.5 . 25 2996.03 10 2992.3 25 2987.2 50 10 2981.89 I 200 40 2981.34 I 1000 2980.63 I 10 2971.2 10 2964.3 20 15 2961.47 I 5 2960.83 5 2953.2 25 2951.82 35 2948.16 15 2943.831 II 2 2934.15 5d 2931.14 200 50 2929.271 II 50 8 2927.867 II 3 2926.93 3 2919.13 200 45 2914.672 II 5 2 2912.491 II 20 15 2911.627 II 30 2910.8 51 2908.74 I 5h 2903.13 I 10 3 2893.740 I I 2 2893.28 10 3 2886.607, I I 50R 30 2881.23 I 200R 2880.77 I 100 2868.26 I 15 2862.31 I 25 8 2856.458 I I • 5 2841.60 200 2836.91 I 20 100 2834.08 I I 2833.06 30 20 2823.19 I I 10 3 2819.865 I I 5 10 2813.389 I I 0 3 2810.894 I I 3 2809.01 30 30 2805.59 I I I 1 2799.57 I I 20 3 2799.000 I I 3 2798:.14 25 2780.28 3 2776.08 50 2775.05 I 20 5 2771.923 I I 5 2768.47 2 2 2767.320 I I 12 2767.15 2766.96 I I I 501a 2764.11 1001a 2763.89 I 5 2757.83 501a 2756.79 I 2 2753.80 5 2751.88 1000 200 2748.55 I I 50 2733.86 I 15 2726.93 20 2723.363 I I 2 2720.2 5 2716.00 75 2712.57 I 3 2707.93 50 30 2707.003 5 2702.7 1 2691.386 II 0 2688.195 II 3. 2687.69 3 2685.08 10 2679.968 II 100 2677.64 I 2d 2675.36 4 2674.69 II 50 10 2672.624 II 15 2670.202 IT 25 10 2668.20 II 5011 2660.40 I 40 2659.226 • II 10 2659.021 10 2657.00 2 2654.27 8 3 2650.293 II 5 2649.52 2 2646.84 5 2645.86 5 2640.69 75 2639.50 I 3 3 2638.326 2 2636.29 3 2633.63 2 2633.20 40 2632.24 I 5 2630.558 III 0 2 2630.371 II 50 2629.05 I 3 2626.11 0 2622.937 II 15 2618.807 III 2 2617.87 2 2617.13 I X G 1 2 3 4 2 2614.96 2 2613.12 3 2612.19 2 2611.81 25h 2602.18 I 2 2601.48 2 2600.79 2 2600.32 3 2596.13 30 2592.14 I 4 2588.51 5 2586.43 3 2585.07 I 50 2580.30 I 500 150 2572". 930 II 3 10 2565.88 I 2 2564.02 3 2559=.3 3 2558.0 3 2554.51 I 25 2553.56 1 10 2552.91 15 10 2552.827 II 50 5h 100 2551=.976 II 50 2544.71 I 2 2541.64 I . 1 2533.91 2 2 2526.05 II 25h 2525.389 l u 2525.45 1 2524.68 2521.6 0 2520'.954 II 15h 2518.79 I 3 2517.25 30 25 2516.22 II 2512.37 2 2510.15 50 30 2509il07 II 10 2508.91 I 2502.99 2 2500.86 25 15 2499.81 III 4 2496.53 40 30 2495.584 II 40 15 2487.92 II 2 2476.18 II 2 2475.23 50 2470.61 50 500 2469.733 II 2 2468.25 2 2457.87 3 2445.6 2 2434.3 10 8 2433.42 II 5 3 2427.075 II 10 5 2426.355 III 25 2419.49 50 20 2418.70 II 7 5 . 2418.243 III 2 2387.326 II 15 2377.63 40 5 2376.83 II 2 2367.93 5 10 2367.13 II 3 2366.19 5 10 2365.36 II 2h 2360.64 10 2350.30 2 2349.86 2 2347.65 2 2346.625 10b. 2345.51 2 2332.98 2 2330.11 50 2329.282 I 1 5 2322.50 III 200 lOOh 2321.074 II 20 2321.94 3 2317.46 41 1000 2 20 20 1500 20 1000 5 80 2 2316.51 30 2313.. 49 2312.77 II 2312.42 II 3 2307.78 2306.61 I 3 2304.46 3 2301.18 2296.76 II 2 2295.83 3 2295.32 2 2294.28 4 2292.02 4 2290.86 2290.11 II 20 2288.74 2288.02 I 2 2284.67 2 2271.63 3 2269.82 2267.47 30 2265.81 300 2265.02 II 2263.65 II 2 2256.11 2 2255.77 2251.54 II 2d 2246.80 2 2242.43 2 2240.99 3 2240.45 2239.86 3 2238.57 5 2236.32 2 2233.96 2230.37 3 2224.39 2 2223.57 3 2222.67 2 2222.08 42 I X 0 1 2 3 4 10 2221.229 II 5 2219.12 2 2213.70 2 2211.15 10 2210.37 20 3h 2209.65 II 2 2204.18 1000 10 Oh 2194.56 II 5 2 2188.81 III 50 2188.55 100 5 2187.80 II 5 2186.95 15 2186.30 II 3 2182.64 5 2181.88 II 2 2181.39 3 2176.88 1 2168.77 2 2162-94 ' 5 2156.64 II 30 2155.70 50 2155.06 II 3 2151.06 2 2148.96 2 2147.76 20 2145.04 1000R 2144.408 II 10 2129.12 20 2128.488 II 5 2116.80 II 50 2111.60 III 5 2100.47 III For Intensity, Col 1. Shenstone (17); Col. 2. Kayser &i); Col. 3. M. I. T. wave-length tables (12); Col. 4. Author. 43 BIBLIOGRAPHY 1. Baly, E. C. C., Spectroscopy, Longman's, Green and Co., London, 1929, Vol. I. 2. Birge, R. T., A new table of values of the general phys-i c a l constants, Review of Modern Physics, 13, 233, 1941. 3. B r e i t , G., Isotope displacement i n hyperfine structure, Physical Review, 42, 348, 1932. 4. B r e i t , G., Arfken, G. B. and Clendenin, W. W., Spectro-scopic isotope s h i f t and nuclear p o l a r i z a t i o n , P h ysical Review, 77, 569 (L), 1949. 5. Casimir, H. B. G., On the i n t e r a c t i o n between atomic nuclei and electrons, Archives du Musee ;TeyIer, 8, 202, 1936. 6. Condon, E. U., and Shortley, G. H., The theory of atomic spectra, Cambridge Press, 1935. II 7. Eermi, E. -P., Uber die Magnet i s chen Moment e der Atomkerne, Z e i t s c h r i f t f u r Physik, 60, 320, 1930. 8. Herzberg, G., Atomic spectra and atomic structure, Dover Publications, New York, 1944. 9. Hughes, D. S. and Eckart, C , Effect" of motion of the nucleus on the spectra of L i I and L i I I , Physical Review, 36, 694, 1930. 10. Kayser, H., Tabelie der Hauptlinlen der Linienspektren A3-ler Elemente, J. Springer, B e r l i n , 1939. 11. Kayser, H., Handbuch der Spectroscopic, S. H i r z e l , L e i p z i g . 12. Massachusetts Inst i t u t e of Technology wave-length tables, J. V/iley and Sons Inc.,,-New York, 19.39. 13. Mazumder, K. C , Spectrum of doubly-ionized cadmium, Indian Journal of Physics, 17, 229, 1943. 44 14. Nisenwanger, C. R., Holmes," J. R., and Weis'sler, G. L«, Electrodeless discharge at high frequencies  and low pressures, Journal of the Optical Society of America, 36, 581, 1946. 15. Robinson, | (H. A., Bemerkungen uber die Spektxali nt e ns i t -aten i n Pernen U l t r a v i o l e t und Schatzung von  Temperaturen und Drucken im Vakuumfunken, Z e i t s c h r i f t f u r Physik, 100, 636, 1936. 16. Russell,. H. N., and I. S. Bowen, Mount Wilson Contrib-ution No. 375, 1929, Astrophysical Journal, 69, 196, 1929. 17. Shenstone, A. G. and Pittenger, J. T., Cadmium Spectra, Journal of the Optical Society of America, 39, 210, 1949. 18. Shenstone, A. G., Atomic spectra, Reports on progress i n Physics, Page 210, 1938. 19. Tolansky, S., High resolution spectroscopy, Methuen and Co., Ltd., London, 1947. 20. Tolansky, S., Hyperfine Structure and nuclear spin, Methuen and Go. Ltd., London, 1948. 21. White, H. E., Introduction to atomic spectra, Mc-Graw -H i l l Book Co. Inc., New York and London, 1948. 

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