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The raman effect in carbon disulfide MacDonald, John Campbell Forrester 1948

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THE  RAMAN EFFECT IN CARBON  DISULFIDE  by John Campbell F o r r e s t e r  A thesis the  MacDonald  submitted i n p a r t i a l  fulfilment of  requirements f o r t h e degree o f MASTER OF ARTS i n t h e Department of PHYSICS  The U n i v e r s i t y  of British  April,  19AS  Columbia  ACKNOWLEDGEMENTS  The  author  i s pleased  t o express  D r . A . M. C r o o k e r f o r h i s c o n t i n u a l a d v i c e ,  h i s gratitude to a s s i s t a n c e and  encouragement.  I n a d d i t i o n , he w i s h e s t o a c k n o w l e d g e t h e work o f Mr.  A. W . Pye i n c o n n e c t i o n  w i t h t h e many g l a s s b l o w i n g  prob-  lems i n v o l v e d i n t h e r e s e a r c h .  The  work was c a r r i e d o u t u n d e r a r e s e a r c h  f r o m the. N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a . the holder  o f a Studentship  from t h e C o u n c i l .  grant  The a u t h o r i s  INDEX  Page I.  INTRODUCTION A. B. C.  II.  The Raman s p e c t r o g r a p h . . . The l i g h t source . The Raman tubes  Tests I n v e s t i g a t i o n o f l i q u i d CS2 I n v e s t i g a t i o n o f , s o l i d CS2 • • Measurements and c a l c u l a t i o n s . . . . . .  29 30 31 31  A.  I n v e s t i g a t i o n of the l i q u i d  33  B.  I n v e s t i g a t i o n of the s o l i d  3A  RESULTS  V.  DISCUSSION  VI.  CONCLUSION  VII.  8 18 22  EXPERIMENTAL A. B. C. D.  IV..  1 1 3  APPARATUS A. B. •0;  III.  Objects History Theory  BIBLIOGRAPHY  . • •  35  37 :  39  ILLUSTRATIONS PLATES I.  Page The Raman spectrograph - side view. . .preceding  8  II.  «  »  "  - camera . . . .  «  8  III.  "  «  "  - collimator . .  "  8  IV.  "  "  - plate holder .  »  8  The Apparatus f o r the investigation of l i q u i d CS .  "  25  "  28  "  30  "  30  «  30  "  33  - eight hours «  33  V.  2  VI.  The Apparatus f o r the investigation of s o l i d CS2  VII. VIII. IX. X.  Iron arc spectrum Transmission of NaN0  2  Raman Spectrum of CCI4,. Raman Spectrum of l i q u i d CS - two hours 2  XI.  "  »  "  0  "  FIGURES 1.  Normal vibrations of CS molecule. . . . . 2  "  A  "  A  t  2.  P r i n c i p a l infrared and Raman t r a n s i t i o n s of CS 2  3.  Raman spectrograph  A.  C i r c u i t diagram - automatic tickler.. . . .  5.  "  "  11  pov/er supply  8 21 22  6.  Geometry of the Raman tube f o r the l i q u i d .  23  7.  Raman tube f o r the investigation of l i q u i d CS preceding 25 Raman tube f o r the investigation of s o l i d CS » 28 2  8.  2  9.  Geometry of the Raman tube f o r the s o l i d  .  27  THE RAMAN EFFECT IN CARBON DISULFIDE  I.  A.  INTRODUCTION  OBJECTS The objects of t h i s research were twofold: 1.  To develop apparatus and experimental techniques to  shorten the exposure times i n the study of the v i b r a t i o n a l Raman effect of l i q u i d s and l i q u i d s i n the s o l i d state. 2.  To use the above i n the i n v e s t i g a t i o n of the v i b r a -  t i o n a l Raman spectra of the l i q u i d and s o l i d states of Carbon Disulfide.  Concurrently, other workers were investigating  the infrared absorption spectrum of CS . 2  The two projects,  when integrated, should give a reasonably complete basis f o r the description of the CS2 molecule.  B.  HISTORY The study of the Raman spectrum of a substance i n  conjunction with that of the infrared absorption spectrum has been found to be of great importance i n the study of i t s molecular structure.  Since the prediction of the Raman E f f e c t i n  .1923 hy Smekal (32), and of i t s discovery i n 1928 by Raman (27),  2  some thousands of a r t i c l e s dealing with i t have appeared i n the l i t e r a t u r e .  In the intervening time the theory has been  b u i l t up to such an extent that, i n many cases, an' Interpretat i o n of v i b r a t i o n - r o t a t i o n a l Raman and infrared absorption spectra of a molecule now leads to an unambiguous description of i t .  Details of structure, inter-nuclear distances, normal  vibration and rotation frequencies, moments of i n e r t i a and force constants can be determined i n t h i s way. The p a r t i c u l a r molecule under investigation i n t h i s case i s that of C S 2 .  P r i n c i p a l l y because the CSg molecule i s  triatomic with a r e l a t i v e l y simple structure> i t s Raman and infrared absorption spectra have been rather thoroughly observed by previous investigators.  Very early iri the develop-  ment of Raman research, a number of workers (17), (28), (24), (30) found a strong vibration-rotation band at 656 cm" and a 1  weaker one i n the neighbourhood  of "SpO . cm"". Later Krishna1  murti (19) discovered a f a i n t companion to the' 656'^fcnr"" band 1  at approximately 647 cm" . 1  With improved technique and a  spectrograph of higher dispersion, Mesnage (21) resolved the 800 cm" band into two components. 1  Later Bhagavantam (12)  detected the presence of bands at 400, 1229, and 1577 cm . -1  Although the forme'r was subsequently confirmed at 395 cm" by 1  Ventkateswaran  (3$),  the bands at 1229 and 1577 have not been  found by other workers.  In 1934* Langseth, Sorensen and N i e l -  son (20) did a very complete study of the molecule i n the l i q u i d state with much improved  apparatus.  P a r a l l e l i n g these investigations, the infrared  3 absorption spectrum was being studied, by other workers i n order that a complete theory of structure could be developed. Dennison and Wright (15) and Bailey and Cassie (11) were the p r i n c i p a l investigators of t h i s aspect of the problem. The interpretation of the results l e d to the assumpt i o n of a l i n e a r symmetrical structure.  This assumption was  confirmed i n 1935 by the work of Sanderson (29) on the rotat i o n a l structure of the infrared hand at 2183 • 9 ' cm"". 1  Further,  Placzek (26) has shown that t h i s assumption checks t h e o r e t i cally.  C.  THEORY 1.  Theory of Apparatus The theory connected with the development of appara-  tus  i s so~closely linked with design that i t w i l l he discussed  under "Apparatus." 2.  Theory of CS? Molecule - General The mathematical theory of the l i n e a r symmetxic t r i a -  tomic molecule has been dealt with by Placzek (25) and i s f u l l y outlined by Herzberg (4). I t w i l l not be discussed here. Since the apparatus used i n t h i s research was.designed primarily f o r the observation of v i b r a t i o n a l Raman spectra, the discussion w i l l be r e s t r i c t e d to t h i s type only, to the exclusion of v i b r a t i o n - r o t a t i o n a l spectra. 3.  Normal Vibrations The possible normal vibrations of a l i n e a r and sym-  metric triatomic molecule are indicated i n Figure 1. A  0£  —  •%  Qg. 1 - normal VibraNona of fhe CS, Molecule. OZ'O  i  0*1  00*1 03'0 / I'O •W  OZ'O  I  nu  uejt  0*0  OI'O  X X flftiaw  Fig. 2 - Principal Infrared ond Raman Transitions of CS..  consideration  o f t h e "zero p o s i t i o n " o f the v i b r a t i o n s  c a t e s a n e t d i p o l e moment o f v e r y n e a r l y firmed it  by experiment.  zero.  This  With regard t o the normal  i s con-  vibrations,  may be n o t e d : ))  (a)  {  i s a symmetrical  w i t h n o change i n p o s i t i o n s  e x p a n s i o n and  contraction,  o f t h e p o s i t i v e and n e g a t i v e  c e n t r e s o f c h a r g e , i . e . no change i n d i p o l e moment the  throughout  cycle. l>i i s a d o u b l y d e g e n e r a t e v i b r a t i o n , i n t h a t a s  (b) the  d i r e c t i o n o f v i b r a t i o n i s a t r i g h t angles t o the i n f i n i t y -  fold  axis  o f symmetry, t h e r e  e x i s t two p e r p e n d i c u l a r  i n t o w h i c h t h e v i b r a t i o n c a n be r e s o l v e d . by  indi-  a periodic  change i n d i p o l e  ( c ) }J  3  i s also  I t i s accompanied  moment.  o f c h a n g i n g d i p o l e moment, b u t t h e  d i r e c t i o n o f c h a n g e i s a l o n g t h e symmetry 4.  directions  axis.  Selection Rules i n the Infrared Although t h e exact d e r i v a t i o n  o f the selection  for  t h e fundamental frequencies  i n t h e i n f r a r e d would  the  methods o f quantum m e c h a n i c s , i t happens t h a t  require  this i s a  case where t h e Correspondence P r i n c i p l e i s a p p l i c a b l e , purely  classical  treatment w i l l  those v i b r a t i o n s which give can  influence,  magnetic f i e l d s  rise  o r he i n f l u e n c e d  lead  to correct  hy, t h e a l t e r n a t i n g  In the case o f a t r i a t o m i c  and a  results.  t o a changing d i p o l e  o f r a d i a t i o n , a n d so he a c t i v e  in  rules  Only  moment  electroabsorption.  molecule w i t h a centre o f  symmetry, t h o s e v i b r a t i o n s w h i c h a r e s y m m e t r i c w i t h r e s p e c t t o that  c e n t r e w i l l n o t he o b s e r v e d  i n the infrared.  Thus  will  5  not  appear i n t h e i n f r a r e d a b s o r p t i o n  s p e c t r u m , w h i l e U. a n d  l£ - w i l l . The  above i s t h e o n l y  general  appearance o f v i b r a t i o n a l f r e q u e n c i e s All  other  S e l e c t i o n Rules It  Raman l i n e levels while  be  i n V i b r a t i o n a l Raman  absorption.  the t h i r d  (hypothetical) level  r u l e s i s then  Spectra  between t h r e e  two o f w h i c h a r e known  The s t r i c t  theory  i s some  energy  completely  unobseryable  f o rthe d e r i v a t i o n o f these-  of necessity very  complicated.  Placzek  h a s shown, however, t h a t a s e m i - c l a s s i c a l t r e a t m e n t employed w h e r e b y t h e s e  t h e unknown t h i r d  state.  e n e r g y s t a t e s , a n d on t h e s e  reference  H i s method i s t o i n v e s t i g a t e t h e  dependence o f t h e p o l a r i z a b i l i t y  o f t h e molecule on i t s n u c l e a r  alone.  For this  t o be p o s s i b l e ,  t h e r e must be no a p p r e c i a b l e p e r t u r b a t i o n o f t h e n u c l e a r by  electronic  or incident radiation frequencies.  have seen t h a t t h e appearance o f a f r e q u e n c y tion  i s determined  associated with frequency  it,  may  r u l e s a r e deduced s o l e l y from t h e  symmetry p r o p e r t i e s o f t h e " t w o known s t a t e s , w i t h o u t to  here."  t o consider that t h e occurence o f a  i n v o l v e s a double t r a n s i t i o n  upper s t a t e .  (25)  i n infrared  a n d w i l l n o t be d i s c u s s e d  i s convenient  o f the molecule,  lection  governing t h e  r u l e s d e p e n d on t h e s y m m e t r i c p r o p e r t i e s o f i n d i v i -  dual classes o f molecules, 5.  rule  states  J u s t a s we  i n infrared  absorp-  c l a s s i c a l l y b y t h e change i n d i p o l e moment so now we d e t e r m i n e t h e a p p e a r a n c e o f a  i n t h e Raman s p e c t r u m f r o m t h e c h a n g e i n t h e i n d u c e d  moment a s s o c i a t e d w i t h t h e v i b r a t i o n . C o n s i d e r i n g t h e CS2 m o l e c u l e w i t h t h i s  i n mind, i t  6 is  s e e n t h a t )/j  will  he " a l l o w e d " i n t h e Raman s p e c t r u m ,  the  polarizability will  the  vibrations.  zability  a t t h e extreme phases o f  I n t h e c a s e s J£ a n d  (not being a d i r e c t e d  , however, t h e p o l a r i -  q u a n t i t y ) w i l l n o t change  1  periodically, the  he d i f f e r e n t  since  a n d so f r e q u e n c i e s j/  and  w i l l n o t appear i n  Raman s p e c t r u m . . It  i s important t o note that,  f o ra molecule w i t h a  c e n t r e o f symmetry, c e r t a i n o f i t s v i b r a t i o n s i n both i n f r a r e d  a b s o r p t i o n a n d Raman s c a t t e r i n g .  s i z e s t h e c o m p l e m e n t a r y n a t u r e o f t h e two 6.  Combination In  cannot  be a c t i v e  T h i s empha-  studies.  Frequencies  the f i r s t  approximation used  it  i s customary  be  simply l i n e a r l y harmonic.  i n molecular theory,  t o c o n s i d e r t h e vibratdcns o f t h e molecule t o Then t h e t o t a l  energy o f t h e  m o l e c u l e w o u l d be g i v e n b y :  where fUj^ i s t h e v i b r a t i o n a l rules  quantum number.  f o r i n f r a r e d a b s o r p t i o n w o u l d be o f t h e f o r m :  where Z U j  r e p r e s e n t s t h e change i n quantum number Since every molecule  exhibits  and  c o m b i n a t i o n bands g i v e n b y :  the  a n a l y s i s must be a m p l i f i e d  monicity. form:  The s e l e c t i o n  The t o t a l  £  ^ ^  overtones given by: .  t o i n c l u d e a degree  o f anhar-  e n e r g y may t h e n b e g i v e n i n t h e g e n e r a l ^  fe J +t  +^  £  fe  Jfe^J  +±  7 •where the second term introduces the anharmonicity. The changes i n quantum numbers ^  w i l l not now be  so r e s t r i c t e d , and the frequency of the most general band may be given by:  V = XT**  ^ f  S  i  ^  Although t h i s anharmonicity and i n t e r a c t i o n of the vibrations apparently allows a l l possible Aflf  k  symmetry considerations  w i l l l i m i t very greatly the number of allowed overtones and combination bands. From considering a Raman frequency as the result of two;transitions, one of which must be an absorption, we see that c e r t a i n combination frequencies w i l l appear i n the Raman e f f e c t as a result of the extensions and r e s t r i c t i o n s mentioned above.  These combination hands are i n most cases less  intense than the fundamentals. 7.  Fermi Resonance When two energy levels of the same symmetry l i e  close together, the r e s u l t i n g large perturbation causes the appearance of a Raman hand which i s normally forbidden. In t h i s way Fermi (16) explained the appearance of the two nearly equally intense hands i n the Raman spectrum of CG^.  Since the  CSg molecule i s assumed to be of the same point group (J^j, ) as CO2, the weaker hand at 796 cm , indicated i n Figure 2 , i s -1  considered to be due to the accidental coincidence of j / and 2^.  c  fe  a  Plate I I The Raman S p e c t r o g r a p h - Camera w i t h L i d Removed. (a) Camera l e n s  tube.  (b) P r i s r a . (c) C o l l i m a t o r  lens.  Plate I I I The Raman S p e c t r o g r a p h - C o l l i m a t o r w i t h L i d Removed. (a) S l i t s u p p o r t i n g b l o c k . (b) B a f f l e . (c) C o l l i m a t o r l e n s .  Plate  17  The Raman S p e c t r o g r a p h ' - The P l a t e H o l d e r . In the o p e r a t i n g p o s i t i o n , the p i n s i n the curved h a c k i n g (a) f i t i n t o the h o l e s i n the f o c a l plane b l o c k s (b), and the l i g h t p r o o f door (c) i s c l o s e d .  II.  A.  APPARATUS  THE RAMAN SPECTROGRAPH 1.  General The requirements of a good Raman spectrograph are  great light-gathering power and high speed, i n combination with a reasonable dispersion and resolving power over the required range.  The problem of f i l l i n g such a spectrograph  with l i g h t has been dealt with by Neilson (23), and h i s r e sults have been extended hy Newton (22) to slits, of f i n i t e dimensions. The construction of the spectrograph here described was begun i n 194-5 hy Mr. T. E. Whittemore. and r e b u i l t hy the author i n  I t was  redesigned  194-7.  Plates I, I I , III and IV show the general construct i o n , and Figure 3 i s a side elevation and plan.  A l l refer-  ences i n the following discussion are to Figure 3. 2.  Optical Elements (a)  •  Prism The prism at hand was one made at Research  Enterprises according to the s p e c i f i c a t i o n s of Dr. A. M. Crooker.  I t was designed e s p e c i a l l y for incorporation into  just such a Raman spectrograph.  I t i s a 6 0 ° prism of face  9 15.5 of  cm by 11 cm high, made of very transparent f l i n t glass  type EDF 649338.  The great size of t h i s prism (c) makes  possible a correspondingly large o p t i c a l system, with great light-gathering power as a r e s u l t . (b)  Collimator Since the speed of the spectrograph i s inde-  pendent of the f/number of the collimator, we are.not rest r i c t e d i n our choice of a collimator lens by t h i s consideration.  We,  therefore, choose a lens of angular aperture  smaller than that of the camera lens, though of large enough aperture to completely u t i l i z e the area of the prism presented, to  i t . . We dp t h i s since a lens of smaller angular aperture  i s usually less expensive, and even more important, i s l i k e l y to have less spherical aberration and coma than one of larger angular aperture.  Further, since the dimensions of the spec-  t r a l l i n e image are to those of the s l i t as the r a t i o of the f o c a l lengths of the camera and collimator lenses, a larger s l i t may be used to obtain the same size l i n e image. The collimatD r lens (d) incorporated into the spectrograph under discussion i s a flint-crown achromat of f o c a l length 167 of  Jena.  cm and aperture 11.5  cm made by Carl Zeiss  The method of mounting. and adjustment w i l l be d i s -  cussed l a t e r . (c)  Camera The speed of a spectrograph i s inversely pro-  portional to the square of the f/number of the camera, and i s independent of the f/number of the collimator.  Accordingly,  '10  s i n c e we  wish  . a high-speed  lens of l a r g e aperture imagery i n as trograph  flat  compared t o  a focal  camera l e n s  spectrograph,  we  its focal  should  be  This  ideal  Spherical aberration  minimized, but  the  so  An  important.  will  toward the  of a  I t i s obvious that a  coma s h o u l d  good  spectrographic at a l l costs  a c h r o m a t i c l e n s , c o r r e c t e d f o r two  colors.  camera, w i l l  prism.  T  he  be not  colors,  or  i n the  in  same  the  does not  give  gives  curve  image an  convex surface  increase  a corresponding  in in-  image i s w i d e r  ratio. camera l e n s  telestigmat  (b) u s e d i n t h i s  lens of f o c a l  Lomb f o r t h e K-16  s a t i s f a c t o r y f o r the f o c a l plane  o f the  r e s o l v i n g power s i n c e e a c h l i n e  The a 1/1  curvature  a focal  of such a lens  s p e c t r a l d i s p e r s i o n , but  crease  Such a l e n s , i f used i n a  u s u a l l y give  tilt  which r e s u l t s from the use  and  and  e l i m i n a t i o n of chromatic a b e r r a t i o n i s  f o r other  spectrographic  is  spec-  however, and  suitable in a  and  good  show " s e c o n d a r y c h r o m a t i c a b e r r a t i o n , " o r v a r i a t i o n o f  focal length  the  ideal  curvature  to r e a l i z e ,  adopted.  p h o t o g r a p h i c l e n s w o u l d a l s o be camera.  The  corrected f o r chromatic  i s impossible  w o r k i n g compromise must be  camera  length, with  plane.as p o s s i b l e .  s p h e r i c a l a b e r r a t i o n , coma, a s t i g m a t i s m and field.  choose a  aerial  l e n g t h 100  camera.  This  purpose, although the  curvature  place of plates, with  spectrograph  cm  lens  made by  Bausch  i s eminently  above-mentioned  n e c e s s i t a t e d the  adoption  the  i n c o n v e n i e n c e i n camera  accompanying  of f i l m  in  loading. (d)  Slit The  D-  slit .  ( f ) i s a standard  Hilger  unilateral  11  with b u i l t - i n shutter, mounted on a tube of length 4«5 It  i s so designed as to give widths of 0 to 1 . 0 mm  d i v i s i o n s of 0 . 0 2 mm.  cm.  i n scale  The undiaphramed s l i t length i s 7  mm.  Ways are provided before the s l i t to permit the use of d i a phragms.  This s l i t i s unsatisfactory f o r the purpose, f o r  reasons to be discussed l a t e r . 3.  Construction (a)  In order to find'the angle between the camera  and collimator mounts of the spectrograph, we must calculate the angle of minimum deviation f o r a number of wavelengths over the desired range. N^= where:  From the well-known r e l a t i o n : sin sin  S±±sL 2  ©x = angle of minimum deviation f o r ~X. o(. = apex angle of prism N = index f o r A. A  we get: \ -  whence:  Line F g h (b)  2 jarcsin ( N s i n x  X.  4861.3 4358.6 4046.8  *  £ 52°29' 53*40' 54°42'  The r i g i d mount., (h) of the spectrograph con-  s i s t s of two pieces of 5 " by 5 " (18.9 l b s / f t ) H-section s t e e l of  lengths 218 cm and 128 cm, welded together at an angle of  127 degrees.  The upper surface i s finished f l a t to 1  mm.  Bolted securely to the beam are the 1^" mahogany base of the camera and prism tube and the 5-ply base of the collimator  12  s i d e s o f the tubes are o f f  tube.  The  braced  wherever p o s s i b l e .  is  i n two  5-ply,  and  The t o p i s o f t h e same m a t e r i a l and  s e c t i o n s , one c o v e r i n g t h e c o l l i m a t o r and t h e  c o v e r i n g t h e camera  and p r i s m .  The  The m o u n t i n g s  f o r the l e n s e s , stops, s l i t  sure r i g i d i t y o f the whole (c)  The S l i t  lathe into  end t o t h e t u b e a s w e l l a s a  t h e shape o f a cone i n o r d e r  permitting a s l i t  table  3 - l i " mahogany  The i n s i d e o f t h e s e b l o c k s was  solid  t u r n e d out on a  t o e n s u r e no  reflec-  F i r m l y b o l t e d to the outside block  b r a s s tube w h i c h accomodates  axis.  and p l a t e h o l d e r e n -  end o f t h e c o l l i m a t o r t u b e i s a  frame t o w h i c h i s a t t a c h e d  t i o n o f f the w a l l s .  necessary.  Mount  blocks which provide a r i g i d mount.  light-  assembly.'  At the s l i t strengthening  other  s e c t i o n s make a s n u g ,  p r o o f f i t w h i c h a l l o w s , h o w e v e r , f o r r e m o v a l when  slit  strongly  is a  the tube o f the H i l g e r s l i t ( f ) ,  t r a v e l o f approximately  3.5  cm a l o n g  the  B o l t e d t o t h e beam b e y o n d t h e end b l o c k s i s a wooden (g) on which l i g h t , s o u r c e s (d)  supported.  The C o l l i m a t o r L e n s Mount The l e n s  into a hole  c a n be  ( d ) i s mounted b y f i x i n g  i t s tube  i n a b r a s s p l a t e w h i c h c a n be b o l t e d t o a mahogany-  b l o c k mounted i n t h e c o l l i m a t o r t u b e p e r p e n d i c u l a r t o t h e  axis.  The b l o c k i s c u t o u t i n t h e c e n t r e t o a l l o w t h e p a s s a g e o f light.  The p o s i t i o n o f t h e p l a t e c a n be a d j u s t e d t o a l i g n  lens i n the o p t i c a l (e)  the  system.  T h e , P r i s m Mount The p r i s m  ( c ) i s mounted on a t r i a n g u l a r  table,  "  so p l a c e d t h a t p a r a l l e l  light  from t h e c o l l i m a t o r l e n s  a maximum a r e a o f t h e a d j a c e n t deviation.  fills  f a c e o f t h e p r i s m a t minimum  Once s e t f o r minimum d e v i a t i o n , t h e p r i s m  clamped i n p l a c e b y p r e s s u r e o n t h e t o p .  c a n be  I t s edges a r e a c c u -  r a t e l y perpendicular to the axis of the spectrograph. provision  13  i s made f o r t h e r o t a t i o n o f t h e p r i s m ,  No  since the  wave-length range i s predetermined. • ( f ) The Camera Mount S i n c e t h e camera l e n s was o r i g i n a l l y an a e r i a l purpose,  camera a n d was mounted i n a r i g i d i t was d e c i d e d  into the spectrograph.  tube  used i n  (b) f o r t h e  t o i n c o r p o r a t e t h e whole tube  assembly  Two p i e c e s o f f " 5 - p l y a r e i n s e r t e d i n  t h e camera b o x w i t h h o l e s i n them l a r g e e n o u g h t o a c c o m o d a t e the tube, the tube  i n s u c h a way t h a t b y t h e t i g h t e n i n g o f a f i n a l i s ' f i x e d as r e g a r d s  position.  l o n g i t u d i n a l as w e l l a s t r a n s v e r s e  T h e h o l e s a r e so l o c a t e d a s t o p e r m i t  l e n s t o r e c e i v e a maximum o f l i g h t axis i s p a r a l l e l  screw  from  t h e camera  the prism.  The l e n s  t o the direction o f the r e f r a c t e d l i g h t  from  t h e m e r c u r y 4 3 5 8 AU l i n e . (g)  The w h o l e o f t h e . i n s i d e o f t h e s p e c t r o g r a p h  (excluding the o p t i c a l  elements) i s p a i n t e d w i t h a matt  p a i n t made o f a s u i t a b l e m i x t u r e methyl a c e t a t e .  A baffle  o f lampblack,  black  s h e l l a c and  (e) i s l o c a t e d i n the c o l l i m a t o r  tube. 4.  Alignment (a)  through  Setting of the collimator  the prism.  The f i r s t  requirement  for parallel was t o e n s u r e  light that  14, the  plane of the  axis of the c o l l a r was  collimator.  perpendicular T h i s was  made w h i c h f i t t e d  lens tube. in  l e n s was  Two  s u c h a way  as t o  cross  done as  snugly  narrow brass  t o and  centred  follows.  over the  on  A  the  plywood  slit  end  of  s t r i p s were f i x e d on  the  collar  i n f r o n t of the  a thread  whose o t h e r  slit  and  pulled taut.  T h u s when l i g h t  was  passed through  the  slit  by means o f a r i g h t - a n g l e d p r i s m ,  the  focal point  of  the  be  made  t o l i e on hind.  o f f the the  back  thread  by  was  this  fnn  p o i n t was  passed through the  top  of  the  of the  shimming t h e  mounting p l a t e from  the  slit  fastened  through the  lens  affixed  (prism) face  When t h e m o u n t i n g p l a t e was  procedure, l i g h t  centre  lens  c o l l a r was  end  To  of the  when t h e  reflection  i n place.  centre  the  after  could  the  lens l e f t  be-  foregoing  the  lens  parallel. (b) for  the  and  The  prism  was  next  s e t f o r minimum d e v i a t i o n  4358 fl. l i n e i n t h e m e r c u r y s p e c t r u m by t h e u s u a l method  secured. (c)  In the mounting o f the  camera l e n s , t h e  s u p p o r t s were so p l a c e d  of l i g h t ' from the however, l e f t the f i x i n g  prism  t h r o u g h the  so t h a t i t c o u l d  tion of this f o c a l  s u r f a c e was  step.  .The  original  small  H i l g e r spectrograph,  of the  i r o n a r c was  spectrograph  the  plate-holder and  and  camera l e n s .  focal last  the  as t o e n s u r e a maximum  be moved a l o n g  of the p o s i t i o n of the  An  t u b e '(b) c o n t a i n i n g  ( a ) was  one  took standard  most  The  was,  during determina-  difficult  adapted from 3 i x 41"  accurately placed  a condensing l e n s  tube  i t s axis  surface. and  The  on  so p l a c e d  a  plates. the as  axis to  image  15  the arc on the collimator lens through the s l i t , i n such a as to get a maximum of l i g h t on the lens.  The s l i t was  way  then  set at the optimum calculated width (Baly ( l ) , Vol. I, p.  285),  i.e.: s = 2fX A 2 x 167.5 » 0.02 Using a two  = f o c a l length of lens . A « e f f . aperture » " A= wavelength f  x 4360 x 7  ,«-7 10"'  mm  step Hartmann diaphragm and blocking o f f f i r s t  one  side of the o p t i c a l system and then the other, a series of focus plates corresponding to d i f f e r e n t positions and degrees of t i l t of the plate-holder were taken (See Sawyer (8), p. From the i n t e r p r e t a t i o n of the data obtained, i t was  100),  determined  that the f o c a l surface.was convex toward the camera lens with a radius of 150 mm, the camera lens.  and the red end was Since i t was  t i l t e d 8 degrees toward  impossible  to bend a plate to  conform to such a radius, f i l m 'had to be adopted.  The p l a t e -  holder had to be r e b u i l t to take 35 mm movie f i l m and to hold i t accurately on the f o c a l surface.  The method of so doing i s  obvious from an inspection of Plate IV.  Once the f i l m was  so  positioned, minor adjustments of the s l i t p o s i t i o n were enough to bring the whole of the  v i s i b l e range into perfect focus.  Plate VII shows a sample Iron arc spectrogram of double l i n e a r enlargement, exposure one-half second. 5.  Constants of the Spectrograph (a)  Dispersion From the spectrogram i n Plate VII, a large  16 number o f l i n e s o v e r t h e v i s i b l e range were measured, and from t h i s data t h e d i s p e r s i o n f o r d i f f e r e n t p a r t s o f t h e range was calculated.  I t was found t o v a r y from 59 A/mm a t 5590 A t o  1 2 . 6 A/mm a t 3850 A , w i t h v a l u e s o f 26 and 22.5 a t 4500 A and A358 A r e s p e c t i v e l y . The t h e o r e t i c a l l i n e a r d i s p e r s i o n may be o b t a i n e d from the r e l a t i o n : dX » dA dN do ds dN d.9 ds  where:  dX i s o b t a i n e d f r o m d i f f e r e n t i a t i n g t h e Hartmann i n t e r p o l a t i o n dN formula: N = N - C Q  i.e.:  dX = ( X - A ) 2 Q  dN  C  where f o r t h i s p r i s m : A  - 2 0 4 7 . 9 A and C - 1 4 6 . 5 7 A.  0  dQ depends on t h e f o c a l l e n g t h o f t h e . c a m e r a l e n s and t h e ds a n g l e of t i l t o f t h e p l a t e pi where l i g h t o f t h e w a v e - l e n g t h considered s t r i k e s i t .  That i s :  d9 - cos <t> We l e t zjJ = 0 ° a t 4358 A . ds F dN d9  i s o b t a i n e d by a c o n s i d e r a t i o n o f S n e l l ' s Law a p p l i e d t o t h e p r i s m a t minimum d e v i a t i o n , 'and f o r a 6 0 ° p r i s m g i v e s : dN = / 1 - N V 4  d9 Hence:  y  .  d ^ = (A - A )  ds.  Q  2 X  . /l-N^/4  '  x cos &5  F  = 3 6 4 5 0 x 0.548 x ' l 1000  o  = 20 A/mm a t 4358 A . w h i c h i s i"n~ r e a s o n a b l e agreement w i t h t h e e x p e r i m e n t a l l y  17  determined v a l u e . (b)  R e s o l v i n g Power According to Rayleigh, the t h e o r e t i c a l R . P . of  a prism i s given by: R . P . • t dN dX  where t - e f f e c t i v e t h i c k n e s s o f p r i s m = 1 5 . 5 cm h e r e , s i n c e a l l o f prism i s used.  Then, t h e o r e t i c a l l y ,  a t 4358 A :  R . P . = 15.5 x 1 0  8  x 1 36^450 .  w 43,000 The p r a c t i c a l R . P . u s u a l l y d i f f e r s q u i t e w i d e l y from t h i s t h e o r e t i c a l v a l u e due t o t h e e f f e c t o f s u c h f a c t o r s a s t h e relative intensities  o f t h e two a d j a c e n t l i n e s , t h e w i d t h and  method o f i l l u m i n a t i o n o f t h e s l i t , and t h e g r a i n i n e s s o r c o n t r a s t of the photographic emulsion. The p r a c t i c a l R . P . o f f a s t s p e c t r o g r a p h s as t h i s one i s l i m i t e d hy d i s p e r s i o n and t h e of the photographic emulsion.  such  characteristics  Considering the l i n e a r R . P . of  t h e f i l m u s e d as 50 l i n e s / m m , t h a t i s , 0 . 0 2 mm, and w i t h a v a l u e o f t h e d i s p e r s i o n o f 2 2 ; 5 A/mm a t 4358 A , we see t h a t '.a dA d i f f e r e n c e a t 4358 A .  o f (22.5 x 0 . 0 2 ) o r 0.45 A s h o u l d be r e s o l v e d  This  gives: R . P . = _X = A358 - 9700 dA 9.45  (c)  I n t e r p o l a t i o n Formula From t h e measurements  c o n s t a n t s \ , C and d  Q  referred to i n (a), the  o f t h e Hartmann i n t e r p o l a t i o n f o r m u l a : d  Q  - d  18  are calculated f o r i n t e r p o l a t i o n i n the range A000 to 5000 A i  ,  i  by the method outlined on page 230 of Sawyer (8).  \  =4936.691  3  d  58.887  3  - 4531.155  *2 — 46.371  Xi  - 4134*684  dl  *i  = 396.471  Ai  802.007  <*2-  dl  d -  dl  3  d - d 3  d -dx  = a - .04^32  2  A  2  = 28.798  - 17.573 - 30.089 = 12.516 d  2"Al  3~ l d  =  b  = .03751  Ay-X£ a - b = .00681  d  3" 2 = C a-h d  - 1837.89  d  ^o=\  Q  ~ £  = .2296.79 0  (A-X>) = a  d= a  (2234-37) = 99.027  2  0  C - C x d d  Q  - 182,000  0  d  Q  = d  0  •+ d  - 127.825  x  Then: A = /\  0  +  C - 2296.79 + d - d 0  182000 127.825 - d  which i s the interpolation formula f o r the range indicated.  B.. THE LIGHT SOURCE 1.  Considerations In the Rayleigh scattering of l i g h t , the i n t e n s i t y  19  of  the scattered  the  frequency.  light  i s p r o p o r t i o n a l t o t h e f o u r t h power o f  T h i s h o l d s I n g e n e r a l f o r Raman  scattering.  A c c o r d i n g l y , t h e b e s t s o u r c e f o r Raman e x c i t a t i o n w o u l d monochromatic s o u r c e o f v e r y s h o r t wavelength sity.  Since the size o f the optics  precluded the use o f quartz,  and h i g h i n t e n -  i n the spectrograph used  t h e a v a i l a b l e wavelengths  lower l i m i t , namely t h e lower t r a n s m i s s i o n l i m i t Thus t h e i d e a l  s o u r c e would  chromatic r a d i a t i o n absence this  b e one w h i c h  the test  by u l t r a - v i o l e t  I t was t h o u g h t a t f i r s t  o The 4046 A l i n e o  adequate lines  i s n o t appreradiation.  ( r e d ) s i d e o f 4358  f o r t h e purpose without t h e n e c e s s i t y o f f i l t e r i n g " •  Description In  liquid,  ang-  to eliminate .  f o r the exciting  s p a c e " on t h e S t o k e s  o f l o n g e r wavelength. 2.  source  i s reduced i n  b u t t h e 4358 A l i n e  c i a b l y weakened, a n d s o c a n be u s e d "clear  s h o r t e r t h a n 3660  the use o f a f i l t e r  radiation.  i n t e n s i t y b y such- a f i l t e r ,  1  this  However, CS2 i s decomposed  r a d i a t i o n o f wavelength  stroms, and t h i s n e c e s s i t a t e s  46OO cm""  that  a n d , i n d e e d , i t was so u s e d i n o b -  C C l ^ spectrograms.  traces of this  spectrum, i n  a r c g i v e s a spectrum o f reasonably f e w  c o u l d be u s e d u n f i l t e r e d ,  out  In the  filter.  well-separated l i n e s .  is  o f 4 0 0 0 AU.  i n the neighbourhood  The m e r c u r y  The  of glass.  o f s u c h a s o u r c e , a t t e m p t s a r e u s u a l l y made t o a p p r o a c h  conjunction with a  all  had a  e m i t s a s t r o n g mono-  i d e a l with a suitable a r c emitting-a l i n e  taining  be a  o r d e r t o g e t t h e maximum l i g h t  i t was d e c i d e d t o b u i l d  onto the  t h e a r c i n the form o f a h e l i x .  20  The  form  of the arc f i n a l l y  as f o l l o w s . tubing  adopted  A 100 cm l e n g t h o f 10 mm.  i s bent  i n t o t h e form  The  anode and cathode  cathode  cathode  i n s i d e diameter  Pyrex  o f a h e l i x o f I.D. 5.5 cm a n d o f  A j t u r n s o v e r a l e n g t h o f 11 cm. affixed  for the investigation i s  To the. ends o f t h e h e l i x a r e  bulbs with appropriate  orientation.  b u l b c o n t a i n s a p o o l o f mercury which forms t h e  e l e c t r o d e , w h i l e t h e anode i s a s p i r a l o f h e a v y  sten wire. greatest  The m e r c u r y i n t h e cathode  care; sprayed  water, and f i n a l l y  distilled  i s purified, with the  10% HNO3,  through  twice.  tung-  t  n  e  Before  through  n  distilled  introducing the  mercury, t h e whole assembly i s c l e a n e d i n s i d e w i t h h o t chromic cleaning tilled  solution, d i s t i l l e d  water and f i n a l l y  w a t e r , h o t c o n c e n t r a t e d HNO3,  d r i e d o n a vacuum pump.  dis-  After the  m e r c u r y i s i n t r o d u c e d , a Hyvac pump i s a t t a c h e d t o t h e anode bulb through  a connecting  tube.  The whole assembly, w i t h t h e  e x c e p t i o n o f t h e pump, I s mounted o n a s u i t a b l e be f a s t e n e d t o t h e s l i t then  (See P l a t e V)  The s y s t e m i s  e v a c u a t e d - b y means o f t h e Hyvac pump a n d the]  glass degassed 3.  by h e a t i n g when t h e pump i s o p e r a t i n g .  method o f s t a r t i n g  i t t o a 220 VDC s o u r c e  w i r e r h e o s t a t and an i r o n ductance. the c o i l  mercury and  Operation The  nect  table.  stand which can  the a r c i s as f o l l o w s .  t h r o u g h a 22 ohm, A.A,amp  cored c o i l  Conslide  o f t h e o r d e r o f 50 mh i n -  (The r h e o s t a t s e r v e s t o c o n t r o l . t h e c u r r e n t , w h i l e opposes any tendency  operating.)  Start  a bunsen burner,  f o r t h e a r c t o s t o p once i t i s  t h e pump, and h e a t  being  the helix strongly with  c a r e f u l n o t t o a l l o w any p a r t t o g e t  21  red hot.  Switch the burner  same t i m e , starting a r c can  a p p l y the f u l l  electrode.  to the  cathode  voltage of a Tesla c o i l  at  to  the  the  W i t h a c e r t a i n amount o f e x p e r i e n c e ,  be made t o f i r e  immediately.  The  amps.  T h i s optimum o p e r a t i n g v a l u e v a r i e s  c r o s s e c t i o n a l area of the T h i s type  o f a r c has  -  directly with  b e e n made t o o p e r a t e  5.0 the  i . e . when  without  evacuated  S u c h an a r c i s , h o w e v e r , e x t r e m e l y  both i n starting-and operation. was  be  tube.  t h e r a t h e r cumbersome pump a r r a n g e m e n t ; sealed o f f .  the  rheostat should  t o a d j u s t t h e c u r r e n t t o an o p e r a t i n g v a l u e o f 4*5  used  and  p o o l and,  unreliable  A c c o r d i n g l y , the above  type  adopted. .4.  As  an a d d i t i o n a l  ping' w h i l e 'unattended  safeguard to prevent  during long  the arc  ,  stop.  MAC.  Cotu  exposures,  a relay i s attached to  50 mh  i n t h e 220  coil  and w i r e d circuit way  i n t o t h e 110  DC  volt  of the T e s l a c o i l  coil will  supply  out,  a the  Figure  5.  light  figure  4-  source  d e s c r i b e d above i s e m i n e n t l y  i n v e s t i g a t i o n of the l i q u i d .  c o u l d p r o b a b l y be cal reflector,  4«.  1  See  able f o r the  D.C. CmcoiT  instantaneously " t i c k l e ' i t , causing i t to  again. The  AC  circuit  i n such  t h a t , s h o u l d t h e a r c go  Tesla fire  volt  the  hut  i n c r e a s e d by cooling  surrounding  efficiency  i t with a  cylindri-  p r o b l e m s w o u l d he much i n c r e a s e d .  T h i s type o f arc i s u s e l e s s f o r experiments o f d e p o l a r i z a t i o n o f Raman  Its  suit-  lines.  involving  degree  22  6.  The  spectrum of  a r c f o r use solid  CS  i n the  i n v e s t i g a t i o n of the  is essentially  2  the  same a s  c r i b e d above, except t h a t i t i s designed vertical  position.  See  P l a t e VI.  t o - e l e c t r o d e l e n g t h , and across  i t when  7.  Power  the  able.  An  plying  the  provided  (see  VAC  cm.  voltage  VDC  5) are  VDC  to  VDC  THE  RAMAN  1.  i s neces-  required value.  This  is  sup-  alone  \  A  is  r 1  i r o n arc used i n  + +  The  |  L  'w  system i s d i s t r i b u t e d  Figure  i n c o r p o r a t i n g an  5.  ammeter.  TUBES  General The  methods o f c o n t a i n i n g t h e  v e s t i g a t i o n are  a l m o s t a s numerous as  design  most f r e q u e n t l y u s e d , and  simple  Pyrex tube w i t h  end.  avail-  avail-  through a s u i t a b l e switchboard C.  DC  that  comparison s p e c t r a .  of the  volts  VDC  motor g e n e r a t o r  the  a d d i t i o n a l connection  b u i l d i n g 110  120  GMCMBR  output  in a  electrode-  a p o t e n t i a l d r o p o f 170  t o 120  Figure  t o 275  f o r the  obtaining  des-  operated  I t i s o f 130  a r c s r e q u i r e more t h a n t h e  s a r y to i n c r e a s e the  v o l t a g e s up  one  Supply  a b l e , a 3 p h a s e 220  connected  the  operating.  Since  so  has  t o be  Raman  The  other  when b l a c k e n e d  end on  the  investigators.  a p l a n e - p a r a l l e l window c l o s i n g  outside,  The  which i s here adopted, i s a  i s drawn o f f i n t o a  the  substance under i n -  serves  one  "Rayleigh horn" which,  to prevent  light  being  23 reflected  from that  d e s i g n was f i r s t of  end o f t h e tube i n t o  U s e d b y Wood (36),  a s a d o p t e d f r o m t h e work  i s important t h a t no l i g h t  s i d e s o f t h e tube e n t e r t h e s l i t , light  tained  therein.  The dimensions  fore the s l i t  con-  o f the tube, then, w i l l  depend  the quantity of the  of the spectrograph. o f d e s i g n and c o n s t r u c t i o n  very w i d e l y f o r the tubes used CS2, t h e y w i l l  differ  i n t h e study o f t h e l i q u i d and  be d i s c u s s e d  separately.  Raman Tube f o r I n v e s t i g a t i n g L i q u i d CS? (a)  Design In  light  only  and t h e method o f m o u n t i n g t h e t u b e b e -  S i n c e t h e problems  2.  o f f the  s i n c e we w i s h t o s t u d y  o f the collimator lens,  substance a v a i l a b l e ,  solid  reflected  scattered o f f the molecules o f the substance  on t h e f o c a l r a t i o  the  This  Rayleigh. It  the  the s l i t .  o r d e r t o e n s u r e t h a t a maximum o f s c a t t e r e d  enters the s l i t ,  the tube  i s mounted w i t h t h e p l a n e  dow i m m e d i a t e l y i n f r o n t o f t h e s l i t . calculated  Then t h e r a t i o  to  length i s easily  It  i s seen from a c o n s i d e r a t i o n o f F i g u r e 6  win-  of radius  from t h e geometry o f t h e system.  LENS  Figure  6  that:  2A  a 4- h F hence:  r = h +  =  I  (a 4- h ) / F  Since the  the  where t h e  considered,  w i l l no  longer  h)  (r -  length w i l l  than i n the  vertical.  be  less  the  a v a i l a b l e i s small  (b)  window  point The  (w)  f l a m e and  result  central 21  chemical a filter  tube i s b u i l t  i s fuzed any  end  of the  tube  (a) w i t h  i s a window w h i c h i s p l a n e  and  strain-free  i n s i d e diameter i s 2 . 2  decomposition of the i s necessary.  CS2  This  slit.  cm.  (n) a r e p r o v i d e d  annealing. in  Overall  In order  i s a concentrated Hibben  (5)  and  to  the length  prevent  e f f e c t e d as  for f i l l i n g .  Bhagavantam  The  is fitted  waxed o n .  solution  transmission  i s shown i n P l a t e V I I I .  i s o f i n s i d e d i a m e t e r 3 . 9 - c m and  c o o l i n g being  a  by u l t r a - v i o l e t r a d i a t i o n ,  s u g g e s t e d by  l a y e r o f NaN02  7.  indicated i n Figure  removed by  (d)  shape.  i s by  are  and  circulated,  tube  strains  t u b e b y means o f r u b b e r s t o p p e r s  tubes  as  A H i l g e r medium-quartz s p e c t r o g r a m o f the  o f a 7 mm jacket  to the  resulting  o f N a N 0 2 . i n water, as (2).  the  slit.  zone i m m e d i a t e l y i n f r o n t o f t h e  cm  this  Construction The  The  in  that  readily available cylindrical  l e n g t h o f the  the  It i s only  s i n c e a l l o w i n g f o r i t means t h a t  have t h e  that  in  a l t e r n a t i v e method o f o v e r c o m i n g t h i s d i f f i c u l t y  reducing  is  F  rectangular, i t i s obvious  amount o f l i q u i d  n e e d be  /=  a 4- h  radius required f o r a given  cases  An  or  •  slit.is  horizontal direction  h  r -  filter  to the  Raman  The  filter  i s not  described  below.  Side  A l l parts of the  assembly  Plate V The A p p a r a t u s f o r the I n v e s t i g a t i o n of the L i q u i d The l e t t e r s r e f e r t o the t e x t . I n a d d i t i o n : (t) i s the a r c h e l i x . (u) i s the cathode b u l b . (v) i s the vacuum c o n n e c t i o n t o the anode, (w) i s the c o n n e c t i o n t o the a i r s u p p l y , (x) i s the a r c mounting  table.  CS  25  i n d i c a t e d by h e a v y l i n e s l e n g t h o f 11  cm.  (c)  are blackened.  f o r r e c e i v i n g the  start  the  Once s t a r t e d ,  i t can through  t i o n w i t h t h e ' w i n d o w (w) i s indicated  through parts  across the of  the  mount  exact  exact (s).  To  to  before  hole  whose e f f e c t i v e  then  split  of  (g£)  info and  i s fixed  is drilled two  unequal  horizontally a b r a s s bar  Q)  o f the  reduced  to  i s i n position,  be a  (a) i s i n s e r t e d i n -  t o 3 mm.  end  slit,  Thumbscrews  i n t o the b l o c k s . the horn  (h)  slit  so p l a c e d a s  i s e x a c t l y o p p o s i t e the  ( f ) supports  the  method o f  A mahogany, b l o c k  e a c h s i d e clamp t h e t u b e r i g i d l y  Plate  The  Thus when t h e t u b e  l e n g t h i s now  r e s t i n g on. a b l o c k  and  sup-  slit.  when t h e b l o c k  t h e b l o c k s , t h e window (w)  the  the  c e n t r e o f t h e bar,, and  is drilled.  posi-  posi-  the f r o n t  slit  damaging  position  s i z e t o f i t t h e Hartmann s l o t In the  necessary  centre of the h e l i x to a  centre of the h o l e  exactly opposite the 3 mm.  the  i n F i g u r e 7.  (g£).  the flame  be moved i n t o  to. r e c e i v e t h e t u b e and  (gj.) and  is  removed f r o m i t s o p e r a t i n g  started to prevent  Raman t u b e i n s e r t e d  port  radiation.  from a Bunsen flame  a r c , i t must be  t i o n while being slit.  incident  clear  Mounting S i n c e heat  to  This leaves a  on  A collar  o f t h e tube-.  1  (e) See  V. (d)  Alignment To  m a t o r , an  a l i g n the  incandescent  camera, a n d  t u b e along- t h e  lamp i s shone i n t o  the  a p o i n t e r i s p l a c e d at the exact  l i m a t o r l e n s on  the  slit  side.  On  a x i s of the exit  slot  colliof  centre of the  looking through  a  the col-  pinhole  26  at  (p) i n the d i r e c t i o n o f t h e s l i t , t h e . c o l l i m a t o r l e n s  can  -be seen w i t h t h e p o i n t e r i n t h e c e n t r e o f i t i f the tube  is  properly aligned. (e)  Cooling The p r o x i m i t y o f t h e a r c t o t h e tube  causes t h e C S dly.  2  assembly  t o r e a c h i t s b o i l i n g p o i n t o f 4-6.5°C v e r y r a p i -  T h i s i s p r e v e n t e d hy a system o f a i r c o o l i n g .  o f J i n c h copper t u b i n g (m), c l o s e d a t one end and t o a compressed a i r s u p p l y a t t h e o t h e r ,  A piece connected  i s bent i n t o a  o f a p p r o p r i a t e s i z e and f i x e d t o the b l o c k ( g ) . 2  circle  Holes,  0.5  cm. i n d i a m e t e r , a r e e q u a l l y spaced around t h e c i r c l e so as d i r e c t a stream o f c o o l a i r a l o n g the f i l t e r j a c k e t , i s p r e c o o l e d and f r e e d o f o i l - by a s u i t a b l e 3.  to  '^he a i r  filter.  Raman Tube f o r I n v e s t i g a t i n g S o l i d CS? (a)  Design Since the f r e e z i n g p o i n t of C S  2  i s -111°C,  Raman tube must he surrounded by some' s u c h s u b s t a n c e as a i r throughout t h e exposure . t i m e . shown i n F i g u r e 8 was a d o p t e d .  d i s c u s s e d by K o h l r a u s c h ( 6 ) .  liquid  A c c o r d i n g l y , a d e s i g n as  T h i s i s an a d a p t a t i o n o f  used by S u t h e r l a n d , Lee and Wu (34)  the  and S u t h e r l a n d (33)  that as  S i n c e i n t h i s case the window  (wx)  cannot be p l a c e d i m m e d i a t e l y b e f o r e the s l i t , a condensing system must be d e s i g n e d . The problem i s  (See F i g u r e 9 ) ,  p l a c i n g a lens of c a l c u l a t e d f o c a l l e n g t h f ,  by s u i t a b l y  t o image a p l a n e  P a t p l a n e Y w i t h m a g n i f i c a t i o n s / d , and to-image p l a n e Q a t plane £ w i t h m a g n i f i c a t i o n A / d .  27  y  Figure 9. The equations of condition are: (I  f  = ) _ 1 _  L f u  (d =. )  + 1=1 + v  u-  1 F + v  (L + u)s = uA v F + v  Solving, and substituting the fixed values: F = 167 cm  A • 11 cm  S = 0.3 cm  L m 15 cm  f = 6.9 cm  d = A.45 cm  u = 7.2 cm  v = II.64. cm  we get:  By this method (referring to Figure 8), a single lens ( l ) focusses the front window (w^) of the Raman tube (a) on the collimator lens, and at the same time focusses the back end of the tube on the s l i t , (b). Construction In the sectional diagram of Figure 8, (d) i s a NaN0 f i l t e r which i s f i l l e d at ( f ) , (c) i s a s p e c i a l l y con2  structed Dewar f l a s k to contain the l i q u i d a i r at (b), and (a)  P l a t e VI The Apparatus f o r the I n v e s t i g a t i o n of the S o l i d C 3 The l e t t e r s r e f e r to the t e x t . I n a d d i t i o n : (t) i s the a r c h e l i x . (u) i s the anode b u l b . (v) i s the vacuum connection t o the a r c . (w) i s the connection to the a i r supply, (x) i s the mounting t a b l e .  2  I  <j t  b  u  I  !  Flg.8  b e d  28  is  t h e Raman t u b e p r o p e r .  the.filter is  24  The  cm  The  w i t h the e x c e p t i o n o f  (including  The  assembly  by a c i r c u l a r  that  from  from  (s).  An a i r b l a s t  as p r e v i o u s l y d e s c r i b e d t o c o o l t h e a s s e m b l y frost away.  f r o m c o a t i n g t h e t o p where t h e l i q u i d The  heavy distance  d e g r e e p r i s m ' ( p ) and t h e l e n s ( l ) .  account the index o f the prism.  ( l ) to the s l i t  vertical helical  (w]_) t o ( l ) ,  The  distance v i s  (m)  i s provided  and t o p r e v e n t a i r i s boiling  arc (previously described) i s  mounted so a s t o s l i d e downward o v e r t h e t u b e a s s e m b l y operating. table.  A r c and a s s e m b l y  See P l a t e (c)  mounting  are fixed  to a  when  rigid  VI.  Alignment The method o f a l i g n m e n t i s s i m i l a r t o  described  cm.  b l o c k (g) c o n t a i n i n g ' a b r a s s  d i s t a n c e u as c a l c u l a t e d a b o v e i s t h a t into  length  is 6  the f i l t e r )  i s supported at the c a l c u l a t e d  ( h ) s u p p o r t i n g t h e 45  taking  Overall  i s b l a c k e n e d w i t h Duco where i n d i c a t e d by  before the s l i t tube  assembly,  i s a s i n g l e u n i t o f Pyrex.  and o u t s i d e d i a m e t e r  glass  lines.  jacket,  The  f o r the tube o f F i g u r e  7.  that  29  III.  A.  EXPERIMENTAL  TESTS During the course of the construction and alignment  of the Raman tubes, numerous test plates were taken, using Carbon Tetrachloride as the scattering substance.  CCl^ was  used i n preference to CS2 f o r the following reasons: 1.  I t i s inexpensive, easy to handle and r e a d i l y a v a i l -  able i n a reasonably pure form. 2..  I t has a B o i l i n g Point.of 76.8°C. as compared with  that of A6.3°C. for CS2, and hence i s better f o r t r i a l s i n volving methods of cooling. 3.  The vapor i n small concentrations is. non-poisonous,  while that of CS2 i s quite poisonous. A. bands.  Most important, C C I 4 has a number of very strong Raman Hence suitable test plates may be obtained-w-ith rea-  sonably short exposures. Plate IX shows the Raman bands of CCI4 which appeared with an exposure of 30 minutes. The test plates showed up a.number of errors i n the design which were subsequently corrected. T  n e o  n  e  flaw which  could not be completely eliminated was a ring which appeared  P l a t e V I I : I r o n A r c Spectrum. Exposure of One-Half Second.  P l a t e V I I I : H i l g e r Medium q u a r t z Spectrograms: Bottom: I r o n A r c Spectrum. Top: T r a n s m i s s i o n Through a 7 mm L a y e r of NaN0 . 2  P l a t e IX: Raman Spectrum of Carbon T e t r a c h l o r i d e  Excited  by the 4358 A L i n e of Mercury, Exposure 30 M i n u t e s .  30  on the plate around each strong exciting l i n e on long exposure. This ring was due to r e f l e c t i o n from the i n t e r n a l components of  the s l i t tube.  Attempts made to eliminate i t included modi-  f i c a t i o n s to s l i t components, b a f f l i n g , and f i n a l l y r e s t r i c t i o n of  the s l i t length.  the  The result was a d e f i n i t e reduction i n  i n t e n s i t y of the r i n g , but not a complete elimination.  On  Plate XI at (a) part of the ring around the 4-358 l i n e appears, while at (b) the corresponding part around the 54-61 l i n e appears.  In order to eliminate t h i s ring altogether, a complete  redesign of the s l i t would be necessary.  This has not beeh  attempted.  B.  INVESTIGATION OF THE LIQUID CS? The samples used were of 'commercially available Baker  CP.  Carbon D i s u l f i d e , Lot Number 12134-6.  Since t h i s brand i s  •highly p u r i f i e d i n manufacture, no attempts were made to p u r i f y i t further. of  Every precaution was.taken to ensure cleanliness  the Raman tube before f i l l i n g . The Sodium N i t r i t e f i l t e r  solution was freed of a l l  suspended matter before i n s e r t i o n into the f i l t e r All  jacket.  exposures were taken with the CS2 sample held at  a temperature of 37.0 £ 0.5°C. Ansco 35 mm panchromatic U l t r a Speed f i l m was used for  all  exposures.  Development was f o r 5 minutes i n a tray  using Kodak D-19 developer. Useful exposures were obtained as follov/s: 1.  Exposure 2 hrs. S l i t ¥idth .02 mm (See Plate X)  2.  Exposure  3 hrs. S l i t  .04  Width  mm  (See P l a t e  One-half second I r o n a r c comparison applied-to  each p l a t e w i t h s l i t  for  t h e Raman e x p o s u r e .  C.  INVESTIGATION OF THE CS2  The  SOLID  XI)  s p e c t r a were  w i d t h t h e same a s t h a t  used  CS?  sample u s e d was  f r o m t h e same l o t . number  as  1  was  used i n the i n v e s t i g a t i o n o f the l i q u i d .  was  u s e d as t h e c o o l a n t .  Unfortunately,  Liquid  before a useful  c o u l d he o b t a i n e d , t h e Dewar f l a s k  assembly  t i m e was  It is felt  bly  available  d e s i g n was  to rebuild  not at fault,  it.  but r a t h e r  that  temperature  D.  caused the  MEASUREMENTS AND 1.  that  The  no  the assem-  small undetected variation  shattering.  CALCULATIONS  A l l measurements were made w i t h a H i l g e r m o v i n g  comparator;  plate  s h a t t e r e d , and  s t r a i n s were p r e s e n t i n t h e g l a s s a n d t h e e x t r e m e in  nitrogen  average o f f i v e  i n d i v i d u a l measurements  table was  t a k e n f o r each* l i n e . O b s e r v a b l e Raman bands were m e a s u r e d p r i n c i p a l l y the  S t o k e s s i d e o f t h e 4358 A m e r c u r y  number o f l i n e s  o f known w a v e l e n g t h  s p e c t r u m were m e a s u r e d and tion  In a d d i t i o n ,  i n the i r o n  the i r o n  of all'involved  l i n e ' s were  l i n e s o f known w a v e l e n g t h ,  the  a  comparison  t h e a p p r o p r i a t e Hartmann  formula c a l c u l a t e d for. the range i n v o l v e d .  mula t h e w a v e l e n g t h s For  line.  on  interpola-  Using t h e f o r calculated.  quantity  32  was determined and plotted against wavelength. curve the appropriate  From this  corrections were determined and applied  to the unknown l i n e s .  F i n a l l y , the wavelengths of - the unknown  l i n e s were converted to t h e i r wave-number equivalents, and hence the wave-number differences f o r the Raman l i n e s were determined. 2.  >  Sample Calculation f o r Plate XI (a)  Hartmann formula f o r range 413A.68A - 4531.155 A ^  = X -t__C_ = Xo(d -d) - C do-d (d -d) 0  n  =  Q  = (b) Line  d  2359.482 (141.523 - d) - 170602 A (HI.523 -d)  Method of Tabulation d -d 0  ^ calc  AX  ^correct  y  AJ/  413A.68A 45.420- 96.103 4134.692 + .002 4 1 3 4 . 6 8 4  Fe  4V=648(?) 61.254 8 0 . 2 6 9 4484.860 + .073 4484.933 22296.9 6 4 7 . 6  Raman  P l a t e X: Raman S p e c t r u m o f L i q u i d C a r b o n D i s u l f i d e . E x p o s u r e Two H o u r s . I r o n A r c C o m p a r i s o n  Spectrum,  P l a t e X I : Raman S p e c t r u m o f L i q u i d C a r b o n D i s u l f i d e . Exposure E i g h t Hours. I r o n A r c Comparison  Spectrum.  33  IV.  RESULTS  A.. INVESTIGATION OF THE LIQUID The observed Raman l i n e s are tabulated and compared with those reported by Langseth, Sorensen and Nielsen (20). The i n t e n s i t i e s as reported by these workers are also l i s t e d . Ay observed  Intensity  LS&N 383 395 403 640 648.3 656.5 787.7 796.0  0.05 —  -  •  4.2 18.9 0.01 1.5 0.5 0.1  8O4.9  812.2  648.2 —  656.8 •—  798.2 808.1 —  No evidence of the other l i n e s reported by the above-mentioned workers was found.  The 656 cm"  1  l i n e was measured as an a n t i  r  Stokes displacement from 4358 A and checked within experiment a l error.  In addition, two previously unreported l i n e s were  measured on an eight hour plate.  One of these l i n e s was i n  the halation from the 4358 l i n e at 140.8 cm" , while, the other 1  formed a d e f i n i t e boundary to the halation at 222.7 cm" . 1  The 656 and 798 l i n e s are estimated to be accurate to within ± 1.0 cm" . 1  The accuracy of measurement of the  1  weaker l i n e s i s somewhat l e s s , because of t h e i r proximity to  the  s t r o n g l i n e s and t h e i r  B.  INVESTIGATION  OF THE  No r e s u l t s  smaller  relative  intensity.  SOLID  are available  f o r the s o l i d .  35  V.  DISCUSvSION  The f r e q u e n c i e s o b t a i n e d f o r the observed l i n e s agree, w i t h i n the combined experimental e r r o r , w i t h those found by the p r e v i o u s  investigators.  The 656.8 l i n e has been i n t e r p r e t e d page 277, asithe Raman fundamental t i o n between the s t a t e s  ( 0 0 0 ) and a  observed l i n e s are a t t r i b u t e d  a r i s i n g from the t r a n s i - ' (10°0).  The  remaining  t o t r a n s i t i o n s as  648  cm" :  ( O l ^ ) to  798  cm -1  (00°0) t o (02°0)  808  cm"  (Ol^-O) t o (03 0)  1  by Herzberg (4),'  follows:  (ll ©)  3  1  1  1  A l l these t r a n s i t i o n s are i n d i c a t e d  i n F i g u r e 2.  2V2 (=793.4) l i e s c l o s e enough to V-± (-656) f o r there t o e x i s t a Fermi resonance hence 796 cm"*  1  648 harmonics  e f f e c t between them, and  appears, a l t h o u g h weakly compared t o 656 cm"" . 1  and 808 cm"  are' due to t r a n s i t i o n s between  1  and combination l e v e l s as i n d i c a t e d ,  very small i n t e n s i t y . The V2 investigators,  and hence have  •  (396.7 cm" ) s  1  frequency, observed by p r e v i o u s  i s . f o r b i d d e n i n the r i g o r o u s t h e o r y o f the  i s o l a t e d CS2 molecule.  Herzberg  (loc c i t ) attributed i t s  36  appearance to a perturbation due to the close association of the molecules i n the l i q u i d state.  I t should not appear i n  the Raman spectrum of the gas. The-non-appearance o f t h i s l i n e i n the present i n vestigation may be explained i n one of two ways: 1.  I n s u f f i c i e n t l y long exposures.  This appears u n l i k e l y  because of the speed and great light-gathering power of the spectrograph.  Further work i s to be done i n this' regard,  however. 2.  I f Herzberg's assumption i s correct, then, since the  degree of association of the molecules i s less at temperatures close to the temperature of vaporization, t h i s l i n e should be weaker at these temperatures.  Langseth, Sorens.en and Nielsen  (20) give no information as to t emperature of t h e i r during exposure.  samples  I f the temperature of their sample was con-  siderably lower than the 37°C. of the present i n v e s t i g a t i o n , then the absence of the 396.7 l i n e possibly may be explained i n t h i s way. The l i n e s at 14-0.8 and 222.7 cm  -1  have not been r e -  ported by other investigators and there appears to he no t h e o r e t i c a l explanation f o r t h e i r presence.  They must, there-  fore, be put down to halation effects u n t i l such time as further work i s done on them.  37  VI.  CONCLUSION  A s p e c t r o g r a p h has been b u i l t  f o rthe investigation  o f t h e Raman e f f e c t , a n d u s i n g i t t h e Raman s p e c t r u m CS2 h a s b e e n i n v e s t i g a t e d .  The r e s u l t s  of liquid  check c l o s e l y  those  o f previous  investigators.  solid  as o u t l i n e d  i s t o he done i n t h e i m m e d i a t e f u t u r e .  To  The i n v e s t i g a t i o n  with  f u t u r e investigators,, the author  ofthe  suggests the  f o l l o w i n g m o d i f i c a t i o n s and improvements: 1.  The s l i t  o f the spectrograph  s h o u l d be  completely  r e d e s i g n e d o r r e p l a c e d . i n o r d e r t o e l i m i n a t e t h e appearance of t h e r i n g p r e v i o u s l y mentioned. 2. tained that  Because o f the extremely  large optical  i n the c e n t r a l part o f the spectrograph,  some f o r m  o f temperature  elements  con-  i ti s felt  control f o rthis part  s h o u l d he  built. 3.  Some b e t t e r method f o r t e m p e r a t u r e  control of the  sample d u r i n g e x p o s u r e s h o u l d b e d e v e l o p e d .  The a i r b l a s t  method d e s c r i b e d h e r e i n i s t o o a p p r o x i m a t e , disadvantage  o f c o a t i n g t h e tube  during  exposures.  4.  long  Apparatus  and t e c h n i q u e s  and has t h e f u r t h e r  w i t h o i l from  the a i r supply  f o r measuring t h e i n t e n s i t y  and  degree o f d e p o l a r i z a t i o n  loped.  A Wollaston  depolarization  o f a Raman l i n e  should  he  deve-  p r i s m mount h a s a l r e a d y b e e n b u i l t f o r  measurements.  39.  Til,  A. (1)  BIBLIOGRAPHY  BOOKS B a l y , E . C.  C  " S p e c t r o s c o p y " (3 v o l s ) 3rd E d i t i o n (1929), - Longmans, London. :  (2)  Bhagavantam, S.  " S c a t t e r i n g o f L i g h t and t h e Raman E f f e c t " (1940), Andhra U n i v e r s i t y , W a l t a i r , India.  (3)  H e r z b e r g , G.  "Molecular S p e c t r a and M o l e c u l a r S t r u c t u r e (Diatomic Molec u l e s ) " (1939), - P r e n t i c e H a l l , New Y o r k .  (4)  H e r z b e r g , G.  "Infrared New  (5)  H i b b e n , J . H.  and" Raman S p e c t r a " - Van N o s t r a n d , York.  (1943),  "The Raman E f f e c t a n d i t s Chemic a l A p p l i c a t i o n s " (1939), R e i n h o l d , New Y o r k .  (193D,  (6)  Kohlrausch,  K. W. P.  "Der S m e k a l - R a m a n - E f f e k t " - J u l i u s Springer, B e r l i n .  (7)  Kohlrausch,  K. W. 2P.  "Der S m e k a l - R a m a n - l f f e k t " ( E r g a n z u n g s b a n d 1931-1937)" (1938), - J u l i u s S p r i n g e r , Berlin.  (8)  Sawyer, R. A .  (9)  Sutherland,  (10)  Wood, R. W.  G. B. B. M.  "Experimental Spectroscopy" (1941), - P r e n t i c e - H a l l , New Y o r k . "Infrared  (1935),  a n d Raman S p e c t r a " - Metheun, L o n d o n .  " P h y s i c a l O p t i c s " (1934), M a c M i l l a n , New Y o r k .  -  4-0.  . 11)  PAPERS B a i l e y , C. R. and Cassie, A . B. D. Bhagavantam,  S.  Proceedings of the Royal Society, A 132, 236 (1931). N a t u r e , 126, 995 (1930).  Dennison, D . M .  P h y s i c a l R e v i e w , 4 1 , 304 (1932).  Dennison, D. M.  Reviews o f Modern P h y s i c s , 3» 280 (1931).  D e n n i s o n , D . M . and Wright, N .  P h y s i c a l Review,  38,  2077  (193D.  Fermi, E . Ganesan, A . S. and Ventekateswaran, S .  Z e i t s c h r i f t f u r P h y s i k , . 7 0 , 84 (1931). N a t u r e , 124, 5 7 (1929).  G l o c k l e r , G.  Reviews o f Modern P h y s i c s , 13", 112 ( 1 9 4 3 ) .  Krishnamurti, D.  I n d i a n J o u r n a l o f P h y s i c s , 3, 103 (1930).  Langseth, A . Sorensen, J . U . and N i e l s e n , J . R .  J o u r n a l of Chemical P h y s i c s , 402 (1934).  2,  Mesnage  J o u r n a l de P h y s i q u e e t l e Radium, 2 , 403 (1931).  Newton, T . E ,  T h e s i s f o r t h e Degree o f M a s t e r of A r t s ; U n i v e r s i t y o f B . C . (1941).  Nielsen, J . R.  Journal of the O p t i c a l Society o f A m e r i c a , 20, 701 (1930).  F e t r i a k a l n , A . and Hoohberg, J .  Z e i t s c h r i f t f u r Physikaldsche Chemie, B 3 , 217, 405 (1929).  P l a c z e k , G.  Z e i t s c h r i f t f u r P h y s i k , 70, 84 (1931).  P l a c z e k , G.  Handbuch d e r R a d i o l o g i e , Band 6, T i e l 2 , 205 (1934).  41 (27)  Raman, G. V.  Indian Journal o f Physics,-2,  (28)  Raman, C. V. a n d K r i s h n a n , K. S.  N a t u r e , 1 2 2 , 882 ( 1 9 2 8 ) .  S a n d e r s o n , J". A.  P h y s i c a l Review, 5 0 , 209 (1935).  (29) (30)  S c h a e f e r , M a t o z z i and ..Alderhold S. 0.  387 (1928).  P h y s i k a l i s c h e Z e i t s c h r i f t , 30,  581 (1929).  Indian Journal of Physics,  10,  (3D  Sirkar,  (32)  Smekal, A.  Die Naturwissenschaften,  (33)  S u t h e r l a n d , G. B. B . M.  Proceedings of the Royal S o c i e t y , 141, 535 (1933).  (34)  S u t h e r l a n d , L e e a n d Wu  Proceedings Society,  (35)  V e n t e k a t e s w a r a n , S.  Philosophical  (36)  Wood, R.  Physical  W.  189 (1936).  873 (1923).  o f the Royal 1 7 6 , 484, (1940). Magazine, 15,  263 (1933).  Review, 36,  (1930).  11,  1421  ABSTRACT  A high-speed great l i g h t  spectrograph o f  g a t h e r i n g power h a s b e e n b u i l t  duce t h e exposure gations.  single prism glass  times necessary  Two l o w - p r e s s u r e  i n order to r e -  i n Raman E f f e c t  h e l i c a l mercury a r c s o f over  one m e t e r e l e c t r o d e - t o - e l e c t r o d e l e n g t h h a v e a l s o for  use a s h i g h i n t e n s i t y  sources o f e x c i t i n g  hours.  CS2 h a s b e e n o b t a i n e d w i t h a n e x p o s u r e T h e 6 4 8 , 656,  796 and 804 cm"  1  been  spectrum of eight  l i n e s as r e p o r t e d  by p r e v i o u s i n v e s t i g a t o r s have b e e n c o n f i r m e d w i t h i n mental found.  error.  built  radiation.  By means o f t h e s e t h e v i b r a t i o n a l Raman of l i q u i d  investi-  No e v i d e n c e o f t h e 3 9 7 cm"* l i n e 1  experi-  has been  

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