Sanyal, S B

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ON THE RAMAN SPECTRA AND FLUORESCENCE OF ORTHO AND PARACHLOROTOLUENE IN THESOLID STATE *S. B. SA N V A LOptics D i-pt., Im >ian Assf)ci\TU)N for thi- Ci ltivation of Sctknck, calcittta-3;>( K c c r iv r d  fo r  pu blication ,  In ly  i ,  1955)Plate X V IIIA B S T R A C T  T I k R a m a n  s p e c tr a  o f o rth o  a n d  p a r a c h lo r o io lt ie n c  in  th e  s o lid  s ta te  a t - iS n '^ C  h a v e  b e e n  p h o t o g r a p h e d  a n d  c o m p a r e d  w ith  th o s e  fo r  th e  l iq u id s  a t ro o m  t '- ' in p c r a tm c . F o u r  n e w  l in e s  in  t h s  lo w -fr e q u e n c y  r e g io n  h a v e  b e e n  o b se r v e d  in  ea c h  c a s e  t w o  o f  th e m  h a v in g  a lm o s t  th e  s a m e  fr e t ju e n c ic s  in  th e  tw o  c a s e s .  'H ie in t e n s i t ie s  of t h e s e  n e w  l i n e s  a r e  n ii ic h  s m a lle r  th a n  th o s e  o f  th e  i) r o m in c n t  l in e s  d u e  to  th e  li iju id s . I t  i s  fu r th e r  o b s f  iv e d  th a t in  th e  c a s e  (>f n -c h lo r o to lu e iic  s o m e  o f  th e  p io m in e n t  R a m a n  l in e s  o b s e r v e d  fo r  t h e  l iq u id  s t a l e  u n d e ig o  la ig c  c h a n g e s  in  in t e n s i ly  a n d  p o s it io n  a n d  th e  l in e  2QJ>S c m * ’ s p l i t s  u p  in to  t h i e e  l in e s  w h e n  th e  l i( |u id  is  s o lid il le d  a n d  c o o le d  lo  — i8 o ”C. I t  i s  s i i e g e s t e d  th a t  t l ie  l in e  163 c m  ‘ o f l iq u id  o -c h lo r o to lu e n e  w h ich  sh ift  s lo  185 cm  ’ in  th e  c a s e  o f  t h e  s o l id  m ig h t  b e  d u e  to  a d im e r . It is  « )h served  th a t these* s n b s ta n c i s e x h ib i t  b r o a d  in l c i i s c  l lu o r e s r e n c c  l)a n d s  in  t in  v is i l) lc  r e g io n  in  th e  s o lid  s ta le  a t — ^So®C, a n d  in  th e  lif ju id  s t a t e  th e r e  is  n o  flu«>rescLm e in th e  c a - e  o f  /> -c lilo io to liie iu * , h u t o -ch l')r o to lu e n e  s h o \^ s  a c o n t in u o u s  f lu o r e s c e n c e  in  th e  wholi* v is d d e  ic g iu n .1 N T R O 1) r  C' T I O NT n e  R a n u i n  s p e c t r a  o f  m a n y  s i i l i s t i t i i l e d  b e n / c n c  c o i n p o i i n d s  in  t l i e  s o l i d  s t a t e  a t  l o w  t e m p e r a t u r e s  w e r e  s t u d i e d  p r e v i o u s l y  b y  v S ir k a r  a n d  B i s h u i  ( 1 9 4 6 )  a n d  R a y  ( 1 9 5 0 ,  1 9 5 1 ,  1 9 5 2 ) .  I t  w a s  o b s e r v e d  b y  t h e  l a t t e r  a u t h o r  t h a t  i n  a l m o s t  a l l  t h e  s u b s t i t u t e d  b e n z e n e  c o m p o u n d s  s e v e r a l  n e w  l i n e s  a p x r e a r  i n  t h e  l o w  f r e q u e n c y  r e g i o n  w h e n  t h e  s u b s t a n c e s  a r c  s o l i d i f i e d ,  a n d  w h e n  t h e y  a r e  f u r t h e r  c o o l e d  d o w n ,  s o m e  o f  t h e  l i n e s  s h i f t  a w a y  f r o m  t h e  R a y l e i g h  l i n e .  T h e  p o s i t i o n s  o f  t h e  l i n e s  o b s e r v e d  in  t h e  d i f f e r e n t  s u b s t i t u ­t i o n  c o m p o u n d s ,  h o w e v e r ,  d o  n o t  d e p e n d  e s s e n t i a l l y  o n  t h e  m o m e n t s  o f  i n e r t i a  o f  t h e  m o l e c u l e s ,  a n d  f r o m  t h i s  f a c t  it w a s  c o n c l u d e d  b y  R a y  ( 1 9 5 O  t h a t  t h e  l i n e s  a r e  n o t  p r o d u c e d  b y  r o t a t i o n a l  o s c i l l a t i o n s  o f  t h e  m o l e c u l e s  p i v o t e d  i n  t h e  l a t t i c e  a s  p o s t u l a t e d  b y  s o m e  p r e v i o u s  w o r k e r s  ( K a s t l e r  a n d  R o u s s e t ,  1 9 4 1 ) .  I n  o r d e r  t o  f i n d  o u t  w h e t h e r  in  a  d i - s i i b s t i t u t e d  b e n z e n e  compound t h e  r e l a t i v e  p o s i t i o n s  o f  t h e  t w o  s u b s t i t u t i o n  g r o u p s  h a v e  a n  i n f l u e n c e  o n  t h e  n u m b e r  a n d  p o s i t i o n s  o f  t h e  n e w  l i n e s  i n  t h e  l o w  f r e q u e n c y  region w h i c h  m a y  a p p e a r  i n  t h e  R a m a n  s p e c t r a  o f  t h e s e  s u b s t a n c e s  i n  t h e  s o l i d  s t a t e ,  t h e  R a m a n  s p e c t r a  o f  o r t h o - a n d  p a r a c h l o r o t o l u e n e  i n  t h e  s o l i d  State h a v e  been s t u d i e d  in  t h e  p r e s e n t  i n v e s t i g a t i o n ,  a n d  t h e  r e s u l t s  h a v e  been d i s c u s s e d  i n  t h e  l i g h t  o f  t h e  v a r i o u s  t h e o r i e s  p u t  f o r w a r d  r e g a r d i n g  t h e  origin of the new l i n e s  i n  t h e  low f r e q u e n c y  r e g i o n .•  Communicated by Prof. S. C. Sirkar3— 18 32?—955448 S . B . SanyalB X P E R I M E N T A I ,Ortho and parachlorotoluene supplied by May and Baker of U. S. A. were distilled in vacuum, as usual. A  preliminary investigation showed that the Raman spectrum of the second liquid does not exhibit any appreciable fluorescence although the first one shows a continuous fluorescence spectrum. The number of lines in each case, however, agreed with those published by previous workers. This proved the purity of the substances. The method used for studying the Raman spectra of these substances in the solid state at the temperature of liquid oxygen was the same as that used by previous workers in this laboratory (Bishiii, 1948). Ilford Special Rapid plates were used to photograph the spectra for the solid state and a Fuess spectrograph with a dispersion of about 10.8 A per mm. in the 4046 A region was employed. The Raman spectra for the liquids at room tempeiature were also photographed with the same spectrograph in order to compare these with the Raman spectra for the solid state. The experimental tubes contain­ing the solid was at — i8o “C. No attempt was made to record very weak lines which might be present in the Raman spectra of the two substances in the liquid state.R E  S  IT L  T  S  A N D  D I S  C U S S I O N(a) Raman spectra. The spectrograms for the two substances in the liquid state and in the solid state at — iSo®C are reproduced in Plate X V I I I .  The frequency-shifts are given in Tables I  and I I .  The frequencies of the Raman lines of the two substances reported by previous workers and given by Magat (1936) are also included in the tables for compaiison.A  comparison of the data given in Tables I  and I I  shows that both the substances yield four new Raman lines in the low frequency region in the solid state at — i8o “C and two of these lines have the same frequencies in both the cases. The other two lines are at 78 and 102 cm~’ in the case of o-chlorotoluene and at 85 and 129 cm~* in the case of />-chloroto]uene. These lines are, however, much feebler than similar lines observed in other disubstituted benzene compounds, such as f^-dichlorobenzene or f>-dibromo- benzene. It was pointed out by R ay (1951) that all the monosubstituted benzenes studied by him yield in the solid state at — i8o®C five new Raman lines in the low frequency region and that the positions of these lines cannot be correlated with the moments of inertia of the molecules about their three axes. The lines are also quite sharp and intense in all these cases. In the present case the two chlorotoluenes do not yield any such intense Raman lines and the lines are rather broad. Had these lines been due to rotational oscillations of the molocules pivoted in the lattice, as postulated by Kastler and Rousset (1941) they would be as intense as in the case of other similarRam an Spectra and Fluorescence of 0 -&  p-Chlorotoluene 449T a b l e  IOrthochlorololueneA V inLiqnid, M agat (1936) Liquid at 25*C  Present author163 i8) ^ 6 3 (5) e, k247 (5) 24 > (4) e. k361 (3) 36i (i) e447 (4) 443 (3) e, k552 ••7) 550 (3) e, k675 (6) 673 (5) c, k745 (I)803 (4) 800 (4) e, k852 (00)989 (i)1016 (0)1043 (8) 1040 (8) c, k113 2 (a)1156 (2) 1155 (2) e, k1204 (5) 1205 (5) c, k1279 (0)1378 (a) 1376 U) e, k1426 (O)(3^1574 (3) 1572 c, k(3) 1593 (3) e, k28.59 (0)(5)2926 (5) 2928 e, k3<^ 23 (0)(7)3062 (7) 3062 e, kSolid at — i8o*C36 (o) c, k 50 (1) e, k 7 8  ( o )  e, k 103 (2) e, k 186 (5) e, k 243 (ob) e, k 363 (o) e 448 (i) e. k 550 (3) k673 (5) c, k 803 (3) e, k1^ 34 (5) e. k1156 (i) e, k 1210 (2) e, k1378 (i) e, k1572 (1) c, k 1596 (1) c ,k  2905 (2) k 2930 (2) k 2956 (lb) k 3066 (5) c, kT a b l e  IIParachlorotoluene, A  v in cm *'Liquid, M agat (1936)307 (8)376 (12)634 (5)692 (i) 796 (12)  822  (2) 1090 (12)12 7 7  (*> 1208 (7) 1303 (o)1379 (4) 1454 (o) 15 ^  (8)2924 (8 I) 8031 (4)  ^3064 (10 I)Liquid at 2 5 'C , Present author306 (3) e, k374 (5) c. ^636 (3) c, k796 (8) e, k818 ( i ) c , k  1092 (10) e, kJ 2IO (5) e , k1383 f 2) e,  k 1598 (8) e, k2930 (5) 5» t3040 (30)3062 (10) c, kSolide at -i8o*C38 {2) e. k 50 (lb) c, k 85 (lb) e, k 1S9 (a) e, k390 (lb) e, k 37a (3) e, k 630 (1) c, k79a (5) e, k1090 (5) e, k '*laio (3) e, k1590 (a) e, k 39ao (a) e, k306a (5) e, k450 5. 6. Sanyalmolecules. Hence these lines may be due to intermolecular oscillations in groups of associated molecules as pointed out by Sirkar (1937) and also recently by Ray (1950, 1951).Some of the other Raman lines undergo changes in intensity and posi­tion with the solidification of these two substances. For intance, in the case of orthochlorotoluene the line 163 cm“  ^ shifts to 1S6 cni“  ^ the line 246 cm“  ^ becomes much weaker and broader and the line 2928 cm"’  ^ splits up into three lines at 2905, 2930 and 2956 cm^^ when the liquid is solidified and cooled down to ~ i8o®C . In the case of paraclilorotoluene the line 306 cm”  ^ shifts to 320 cni“  ^ and becomes broader while the lines 1598 and 2930 cm“  ^ shift to T5QO and 2020 respectively with the solidification,P^urther, the lines 1572 and 1503 cm***^  of o-clilorotoluene and the line 1598 cm“”  ^ of />-chlorololuenc ])ec'(>me much weaker when the liquids are solidified. Since these Hues are due to C =  C oscillation, this diminution of intensity may indicate a diminulioii in the number of such double bonds in the molecule with the solidification. All these facts clearly indicate a strong influence of intermolecular field on the frequencies of oscillation of certain modes and this influence may be due to association of the molecules in the solid state which may be rcsi)onsible also for the ongin of the new lines in the low-frequency region.(6) F l u o i c s c v n c e  s t> cctra .  It can be seen from Plate X V II  that the both the substances in the solid state at~i8o^’C exhibit fluorescence bands in the visible region. The j>osilions of centres and width of the intense bands are are given in Table TILT a b l e  IIIr'luoresccncc bandso -C h lo r o to lu e n c /> -C l 1 lo r o to l 11 e n cP o s it io n  o f  b a n d 1I n t e n s i t yrW id th  ini1 P o s it io n  o f b a n d I n t e n s i t y W id th  inin  A . IT. A . U . { ill A . U A . U .4400 S 10011 4500 5 50; 4 5 0 0 2 50i 4 64 0 J O 1004760 2 50 11iThe spectrogram for o-clilorotoluene in the liquid state also shows a stronger continuous background extending from 4100 A upto about 5100 A. Even after distilling the liquid in vacuum repeatedly it was not possible to get rid of this fluorescence. The spectrogram for the substance in the solid state, however, shows weak continuous fluorescence over the region from about 4250 A upto about 4400 A and two bands, one strong and wide band at 4400 A and a feebler band at 4760 A. The frequency-difference is about 1565 cm” ' .  This frequency corresponds to the C =  C valence oscillation.sanyal PLATE XVIII<CO r fo CObc hrX XFig. IFig. 2Fig. HFig. 4Raman s]>(*iiiaFip;. 1. «-Chl()iololu(‘iu\ liciuul at iMi'C FijE^ . 2. ,, ,, solid at -  J SO'ClIdg. 3. //-Cliloroiolurnf", li(]iiid ai 21) C  Fig. 4. ,, solid at - Iso C'.tiaman Spectra and Fluorescence oj o- &  p-chlorotoluene 451It is also an interesting fact that although i>-chlorotoluene does not yield any Raman line with frequency-shift below 306 cm” ,^ o-chlorotoluene gives an intense line at 163 cm” ’ . This fact may indicate a fundamental difference between the nature of the molecules in the liciuid state in two cases. Probably in the case of c-chlorololuen® the molecules exist as dimers w'hich give rise to this line at 163 cm” ’ and also the continuous fluorescence mentioned above may be due to these dimers. lii the case of /’-chloio- toluene in the liquid state probably the molecules do not foim such dimers and, therefore, the line 163 cm” ’ is absent in this case and no fluorcscncc is exhibited by this liquid. When the liquid is solidified, probably groups of strongly associated molecules arc formed - in this ca.se also and they give rise to the fluorescence bands given in Tabe III as well as the new Raman lines given in Table II. The frequency-difference between the first and the second and the first and the third bands are approximately i and 1650 cm” ’ respectively. It is significant that these frequencies correspond to those of the lines due to C —C and C =  C oscillilions of the molecule. Of course, the b.inds are very broad but this coincidence indicates that Ihcse valence oscillations are coupled to the electronic energy level of the ground state of the associated molecule during emission of the fluorescence ridialion.A C  K  N  O W  L  H I> ('> M R  N  TThe author is indebted to Prof. S. C. Sirkar for his kind interest and guidance throughout the progress of the work.R  R  1- R  R  R  N  C  ]•: vSBishiii, Ik M., 1948, Jnd. k P h y s  , 22, 167.Kfustler, A. and Ronsset, A,, 1941. Compics Kendu’;, 212, 645.Magat, M,, 1936, Annual Table of Constants, Paits, p. 26-77.Ray, A. K., 1950, Ind. J. Phys., 24, in .Ray, A. K , 1951. /• 29. i 3i-Sirkar, S. C., i937> /• 343-Siikar, S. C. and Bishui, B, M., J. Phys., 20, iir.

On The Raman Spectra and Fluorescence of Ortho and Parachlorotoluene in the Solid State

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On The Raman Spectra and Fluorescence of Ortho and Parachlorotoluene in the Solid State

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