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The absorption and fluorescence of anthracene in the near ultra-violet Katagiri, Seiko 1964

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THE ABSORPTION AND FLUORESCENCE OF ANTHRACENE IN THE NEAR ULTRA-VIOLET  by  SEIKO KATAGLRI B. En., The U n i v e r s i t y o f N i i g a t a , Japan, 1962  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF M. S c . i n t h e Department of Chemistry  We a c c e p t t h i s t h e s i s as conforming t o t h e r e q u i r e d standard  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1964  In the  r e q u i r e m e n t s f o r an  British  mission  for reference  for extensive  p u r p o s e s may  be  cation  of  written  Department  of  degree at  the  study,,  copying of the  Library  for  Head o f my  agree for  that  not  per-  scholarly  Department  shall  of  make i t f r e e l y  or  t h a t : c o p y i n g or  f i n a n c i a l gain  Columbia,  fulfilment  University'of •  shall  this thesis  permission.  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  the  I further  I t i s understood  this thesis  w i t h o u t my  that  and  g r a n t e d by  representatives.  this thesis in partial  advanced  Columbia, I agree  available  his  presenting  be  by publi-  allowed  vii  ABSTRACT  The f l u o r e s c e n c e and a b s o r p t i o n s p e c t r a o f anthracene i n t h e near u l t r a - v i o l e t were i n v e s t i g a t e d i n n-heptane, f l u o r e n e , b i p h e n y l and n-hexane m a t r i c e s a t l o w temperature. The assignment o f t h e e x c i t e d e l e c t r o n i c s t a t e as Biu was l  confirmed.  I n t h e ground e l e c t r o n i c s t a t e e i g h t Q^and f i v e  |>^, and i n t h e five  'B| upper e l e c t r o n i c s t a t e seven  and  V  b j | fundamentals were a s s i g n e d .  I t was deduced  that  t h e p o t e n t i a l s u r f a c e s o f t h e ' A | and t h e '6, s t a t e s were u  s i m i l a r i n shape as t h e r e was an approximate agreement between t h e v a l u e s o f c o r r e s p o n d i n g fundamental v i b r a t i o n s i n t h e two e l e c t r o n i c s t a t e s .  The p o t e n t i a l s u r f a c e s were un-  u s u a l l y harmonic f o r a p o l y a t o m i c m o l e c u l e , a t l e a s t a l o n g the normal c o - o r d i n a t e s a v a i l a b l e t o t h i s s t u d y .  No evidence  f o r t h e presence of a n h a r m o n i c i t y was found i n even t h e h i g h e s t o v e r t o n e (the t h i r d ) measured, a l t h o u g h s e v e r a l p o s s i b l e examples o f F e r m i resonance between v i b r a t i o n a l modes were observed b o t h i n f l u o r e s c e n c e and i n a b s o r p t i o n . The F e r m i resonances were a s s i g n e d p r i m a r i l y on t h e b a s i s of i n t e n s i t y t r a n s f e r between l i n e s r a t h e r t h a n l i n e s h i f t s . . The presence o f a weaker l o n g - a x i s p o l a r i z e d ( 'B^u*- '/^ ) detected.  i  n  transition  anthracene p r e d i c t e d by t h e o r y was not  viii The l o w e s t energy e l e c t r o n i c t r a n s i t i o n i n f l u o r e n e was found t o be p o l a r i z e d a l o n g the l o n g a x i s o f t h i s molecule.  \  ACKNOWLEDGMENT  I am d e e p l y g r a t e f u l t o Dr. A l a n V. Bree f o r h i s guidance and encouragement i n every phase of t h i s work; h i s a s s i s t a n c e has developed my i n t e r e s t and u n d e r s t a n d i n g i n t h e work. I w i s h t o express my a p p r e c i a t i o n t o M i s s V.V.B. V i l k o s f o r h e r h e l p i n many ways, and a l s o t o t h e t e c h n i c i a n s i n t h i s department f o r t h e p r e p a r a t i o n o f some equipment.  iii  CONTENTS Page SURVEY OF PREVIOUS WORK  1  Theoretical Predictions  1  E l e c t r o n i c S t a t e s of Anthracene  1  V i b r a t i o n a l S t a t e s o f Anthracene  3  Mixed C r y s t a l Phenomena  5  P r e v i o u s "Experimental Work  6  EXPERIMENTAL ARRANGEMENT P r e p a r a t i o n of t h e Samples  8 . .  8  Measurement o f t h e S p e c t r a  10  Apparatus  10  Measurement o f t h e L i n e s  11  RESULTS  14  DISCUSSION  31  Fluorescence Spectra  31  Fundamental Modes .  . .  31  F e r m i Resonance  3#  Other F e a t u r e s  3§  Absorption Spectra  38  Fundamental Modes o f t h e ' B t u P P u  e r  State  38  Comparison o f t h e Fundamentals on t h e ' A | a n d on the  Electronic States  • 3§  iv Page Fermi Resonance  .  Other L i n e s . . . . . . . . .  41 43  S h i f t of t h e O r i g i n s o f tke 'B.^'A, T r a n s i t i o n i n t h e Different Matrices BIBLIOGRAPHY  .  49 50  V  TABLES Table 1  Page C h a r a c t e r T a b l e o f P*h and t h e A x i s C o n v e n t i o n of t h e Anthracene M o l e c u l e :  2  2  A Summary o f Some C a l c u l a t i o n s on t h e E l e c t r o n i c States, o f Anthracene i n t h e Near E l t r a - V i o l e t  3  0^ and  4  F l u o r e s c e n c e S p e c t r a o f Anthracene i n V a r i o u s Matrices  5  t>>^ Fundamentals Observed i n Anthracene  . 2 . 7  17  A b s o r p t i o n S p e c t r a o f Anthracene i n V a r i o u s Matrices .  24  6  A b s o r p t i o n Spectrum o f F l u o r e n e a t 4.2°K  31  7  P o s s i b l e Examples o f F e r m i Resonance i n t h e F l u o r e s c e n c e o f Anthracene  34  8  The Fundamentals of Anthracene i n t h e Ground and the  9  '  Upper S t a t e  P o s s i b l e Examples o f Fermi Resonance  40 i n the  A b s o r p t i o n o f Anthracene 10  41  S i m i l a r i t y o f t h e S t r u c t u r e around Some S t r o n g Absorption Lines  44  vi  FIGURES Figure  Page  1  Low Temperature Sample C e l l s  12  2  The F l u o r e s c e n c e Spectrum o f Anthracene i n nHeptane a t 4.20K  3  15  The F l u o r e s c e n c e Spectrum o f Anthracene i n F l u o r e n e a t 4.2°K  4  15  R e l a t i v e I n t e n s i t i e s of t h e L i n e s i n F l u o r e s cence (a) Anthracene i n n-Heptane a t 4.2°K (b) Anthracene i n F l u o r e n e a t 4.2°K  5  . . . .  A b s o r p t i o n Spectrum of Anthracene I n n-Heptane a t 4.20K  6  fZky  A b s o r p t i o n Spectrum of Anthracene i n F l u o r e n e a t 4.2°K  7  16  .vi ''.'2£.  R e l a t i v e I n t e n s i t i e s of the Lines i n Absorption (a)  Anthracene i n n-Heptane a t 4.2°K  (b)  Anthracene i n F l u o r e n e a t 4.2°K . . . .  SURVEY OP PREVIOUS WORK  Theoretical  Predictions  E l e c t r o n i c S t a t e s o f Anthracene Group t h e o r y may  be u s e f u l l y a p p l i e d t o the c a l c u l a -  t i o n of the m o l e c u l a r o r b i t a l s (MO's) of an anthracene m o l e c u l e u s i n g as a b a s i s s e t the atomic 2p* centred  on each carbon n u c l e u s .  m o l e c u l a r symmetry and a r e shown below. MO's  and  U  Anthracene possesses  i t s c h a r a c t e r t a b l e and  I t can be shown (1) t h a t the  are /\o, B I J , B a j  B i » B»u  functions  and  a x i s convention one-electron  symmetry, so s i n g l e t T T - e l e c t r o n  t r a n s i t i o n s a r i s i n g from the 8U  9  Ba*.  r e t a i n the symmetry g i v e n above.  fc excited  A,  &30 y i e l d i n g the c o n f i g u r a t i o n s  A c c o r d i n g t o Weissman (2) a n t i s y m m e t r i c s p i n t i o n s have  PaW  Thus the only  func-  configurations allowed  ground s t a t e a r e t o & i  s t a t e s p o l a r i z e d a l o n g the l o n g and  short  0  and  axis  of the m o l e c u l e , r e s p e c t i v e l y . Many c a l c u l a t i o n s ( 3 ) - ( l 3 ) have been c a r r i e d out t h e e n e r g i e s of the e l e c t r o n i c t r a n s i t i o n s of anthracene the c o r r e s p o n d i n g o s c i l l a t o r s t r e n g t h s  on and  (f) i n different  a p p r o x i m a t i o n s (e.g. a l l o w i n g f o r the i n t e r a c t i o n between many c o n f i g u r a t i o n s , the i n c l u s i o n o f many-centred i n t e g r a l s  2 Table 1 C h a r a c t e r Table o f D2h and t h e A x i s Convention of t h e Anthracene M o l e c u l e *  D2h E C2 Ag Au Big Blu B2g B2u B3g B3u  V  *  C2  C2  yt  1 1 1 1 1 1 1 1 1-1-1 1 1 -1 -1 1 1-1 1-1 1-1 1-1 1 1 - 1 - 1 1 1 - 1 - 1  i 1 1 1 1 1 1 1 1  rj  1 -1 -1 1 -1 • 1 1 -1  xx  xy  tf"  f  1 -1 -1 1 1 -1 -1 1  T  1 -1 1 -1 -1 1 -1 1  i n the secular equation, e t c . ) .  R  Tz Ty Tx  z(M>  Rz Ry Rx  A l l calculations  put o n l y  Diu and ' B w l e v e l s i n the r e g i o n o f t h e 3800 A system. Only one c a l c u l a t i o n 'feto*  T t l e  (9) found t h e ' B I l e v e l l o w e r than U  Vljf  o s c i l l a t o r s t r e n g t h of the  was much h i g h e r than t h a t o f t h e ' ^ i y - ' / , } -  a p p r o x i m a t i o n , and f o r t h e l a t t e r P a r i s e r calculated  transition  i n every (8) and Mataga (10)  zero. Table 2  A Summary o f Some C a l c u l a t i o n s on t h e E l e c t r o n i c  States of  Anthracene i n t h e Near U l t r a - V i o l e t  ref. V.B. M.O.  3 4 5 Modified 6,7 MO Methods 8  • Blu (HI) 0.836 Jr 3-72 < 3.6  v  f  0.11 0.10 0.4  'BlutflO 3.07 1.261 Jr  0.005  X =resonance i n t e g r a l  3 Table 2 continued  ref.  '&1 («M)  „ ev 3.6 3.48 3.15 3.44 3.44 3.23 3.15 .31-3.47 13 3  Modified 9 MO Methods 10 11 12  f  * B i (BL)  0.39  3.2 3.91  0.283 0.265 0.395 0.290  3.51 3.61 3.51 3.63  f  ev 0.00 0.116 0.063 0.162 0.087  TBX IRX TBM IRM  Approximation Approximation Approximation Approximation  V i b r a t i o n a l S t a t e s o f Anthracene The anthracene molecule has 66 fundamental modes c l a s s i f i e d as | 2 ft|, S Qu , and  6 bju .  , II bm  vibrational  , bb*j , II bau , II  Among them o n l y Q) and bt^ modes a r e expected t o  be b u i l t on t h e a l l o w e d &w and B»u o r i g i n s by v i b r a t i o n a l p e r t u r b a t i o n of t h e e l e c t r o n i c No c a l c u l a t i o n s vibrations  transitions.  o f t h e e n e r g i e s o f t h e fundamental  have been r e p o r t e d .  However,  and  ^funda-  mentals a r e a c t i v e i n Raman s p e c t r a and so any a v a i l a b l e d a t a may be c o n s u l t e d t o a i d i n t h e assignment t i o n a l structure  o f the v i b r a -  i n fluorescence.  The energy d e v i a t i o n o f c o m b i n a t i o n bands from t h e i r harmonic v a l u e can occur due t o a n h a r m o n i c i t y o f t h e p o t e n t i a l f i e l d i n the molecule.  F o r a c c i d e n t a l l y degenerate o r v e r y  close l y i n g v i b r a t i o n a l l e v e l s the anharmonicity gives r i s e t o a F e r m i resonance  (14) which causes a s p l i t t i n g o f t h e two  degenerate l e v e l s , o r a f u r t h e r s e p a r a t i o n o f two l e v e l s o f the same symmetry.  These two e f f e c t s  ( a n h a r m o n i c i t y and  4  Fermi resonance) a r e mentioned here because t h e y might he expected t o appear i n the observed s p e c t r a . The m a t r i x element of the d i p o l e moment o p e r a t o r M i s d e f i n e d as  where m =  JVef  wave f u n c t i o n s  (15)  M ^tl  S"<*<wc|  •  T i l e  i n i t i a l and f i n a l v i b r a t i o n a l  and f ^ o t l a r e s t a t i o n a r y s t a t e f u n c t i o n s  o f a many-dimensional , ' a s c i l l a t o r .  The Franck-Condon  principle  s t a t e s t h a t m does not depend on the c o o r d i n a t e s of the nuclei.  At a s u f f i c i e n t l y low temperature the m o l e c u l e  n o r m a l l y e x i s t s i n i t s v i b r a t i o n l e s s ground s t a t e , and s i n c e o n l y t h o s e t r a n s i t i o n s a r e p o s s i b l e f o r which the o v e r l a p i n t e g r a l ^ (Tnucl € n u c l o i l n u c l does not v a n i s h , t o t a l l y symmetric v i b r a t i o n s a r e a c t i v e i n the upper s t a t e .  For  anthracene t h e s e a r e Q| fundamentals o r any odd o v e r t o n e . 2  A l t h o u g h the i n t e n s i t y of a l i n e i s g i v e n by M , i t cannot be p r e d i c t e d because the o v e r l a p i n t e g r a l depends on the change i n geometry o f the m o l e c u l e between t h e ground and t h e e x c i t e d s t a t e s which i s not known.  C o n v e r s e l y from  the.observed i n t e n s i t i e s o f members o f a v i b r a t i o n a l p r o g r e s s i o n , changes i n m o l e c u l a r dimensions may be d i s cussed, ( 1 6 ) , ( 1 7 ) .  5  Mixed C r y s t a l Phenomena I f the s o l u t e m o l e c u l e does not i n t e r a c t w i t h the s u r r o u n d i n g s o l v e n t m o l e c u l e s t h a t make up the h o s t c r y s t a l l a t t i c e , t h e n t h e s o l u t e m o l e c u l e s may be regarded as an " o r i e n t e d gas".  The s o l v e n t m o l e c u l e s would t h e n o n l y  s e r v e t o h o l d the guest m o l e c u l e s i n a f i x e d  orientation  i n space and the observed spectrum would be i d e n t i c a l w i t h the  f r e e m o l e c u l e spectrum observed i n the vapour phase.  However, v a r i o u s m o d i f i c a t i o n s on the f r e e m o l e c u l e spectrum are  found i n t h e mixed c r y s t a l spectrum and t h e s e a r i s e from  the  p e r t u r b a t i o n s caused by t h e s u r r o u n d i n g s o l v e n t molecules  (18) ( 1 9 ) . the  These a r e ( i ) a s h i f t o f the e n t i r e spectrum t o  red o r t o the b l u e and  ( i i ) a change i n t h e i n t e n s i t i e s  of t h e i n d i v i d u a l l i n e s i n the spectrum due t o i n t e n s i t y s t e a l i n g from o t h e r nearby systems.  Effect ( i ) i s d i f f i c u l t  to p r e d i c t and o n l y one c a l c u l a t i o n has been made  (20);  c a l c u l a t i o n s of e f f e c t ( i i ) have been made u s i n g secondo r d e r p e r t u r b a t i o n t h e o r y f o r some systems S h p o l ' s k i i (22)  (23)  (21).  has shown t h a t w e l l - r e s o l v e d  s p e c t r a o f o r g a n i c m o l e c u l e s may be o b t a i n e d i n normal p a r a f f i n s o l i d s o l u t i o n a t 77°K.  T h i s method p r o v i d e s an  abundance o f p r e c i s e d a t a c o n c e r n i n g the v i b r a t i o n a l structure of electronic states.  A t h e o r e t i c a l treatment  of the S h p o l ' s k i i e f f e c t has been p r e s e n t e d by Rebane and Khizhnyakov (24)  (25).  6 P r e v i o u s E x p e r i m e n t a l Work A l l p r e v i o u s workers have i n t e r p r e t e d the 3800 A  0  a b s o r p t i o n system of anthracene as a r i s i n g s o l e l y from a 'Al t r a n s i t i o n . has not been observed.  'A% t r a n s i t i o n  The p r e d i c t e d  The system has been a n a l y s e d i n the  vapour ( 2 6 ) , s o l u t i o n ( 2 7 ) , s o l i d s o l u t i o n (28) and (29) a t v a r i o u s temperatures as low as 4*2°K.  crystal  A t 20°K  s e v e r a l ftj fundamentals were r e s o l v e d i n the mixed  crystals  of naphthal||ne and phenanthrene b o t h i n a b s o r p t i o n and i n fluorescence spectra (30).  I n a r i g i d s o l u t i o n o f n-heptane  a t 77°K B©lj©tnikova a l s o r e s o l v e d many f r e q u e n c i e s ( 2 8 ) . Some Raman (31) and IR (32) (33) d a t a are a v a i l a b l e f o r anthracene.  I n t a b l e 3 the a v a i l a b l e d a t a c o n c e r n i n g (k% and  k*§ fundamentals i n the  and  'Bio  e l e c t r o n i c s t a t e s are  summarized. The aim of the p r e s e n t e x p e r i m e n t a l i n v e s t i g a t i o n i s t o a n a l y s e t h e v i b r a t i o n a l and e l e c t r o n i c s t a t e s of the o  molecule i n t h e 3800 A r e g i o n and t o s e a r c h f o r the o r i g i n o f '&zo *— ' A ^ t r a n s i t i o n w i t h i t s a s s o c i a t e d v i b r a t i o n a l structure.  7  Table 3 <Xj and  bjj Fundamentals Observed i n Anthracene  d a t a from anthra- anthracene cene i n pure naphc r y s t a l thalene 4.20K  20OK  (29)  350 1170 1400  415  I A  c  (30)  m  399  c  1164 1401 403  m  Data from Raman spectra (31) anthra- anthracene cene pure solucrystal tion  absorption spectra anthra- anthra- anthracene i n cene i n cene i n phenan- MeoH-F*oH nt h r e n e 90°K heptane 20°K (27) 77°K (30) (28) 393  c  739 1031 1159 1389  m  400  c  m  1450 -1  390  397  475 522 606 655  757  752  1163  1165  1165  1264 1407  1264 1416  1265 1407  1567  1567 1645  *  400  C  k  474  522  652  749 ( ? ) 745 (?)"1012 1009  -  1559  C  H  1165 1180 1261 (?) 1262(?) 1403 1413 1439  1481 1555  1632  -  b„  *%  bn bH  1397  1444  bis  1551 1631  ft*  1481  EXPERIMENTAL ARRANGEMENT  P r e p a r a t i o n o f t h e Samples 3  S c i n t i l l a t i o n grade anthracene o b t a i n e d from R e i l l y  Tar and Chemical C o r p o r a t i o n was s u b j e c t e d t o f o u r t e e n passes i n a F i s h e r zone r e f i n e r .  Solutions of the purified  anthracene  w i t h c o n c e n t r a t i o n s r a n g i n g from 0.73 x 10 ^M t o 5.0 x 10 ^"M were prepared i n s p e c t r o q u a l i t y n-heptane and n-hexane s u p p l i e d by Matheson Coleman & B e l l .  A l l s o l u t i o n s were  s t o r e d i n darkness t o a v o i d p h o t o - o x i d a t i o n o f a n t h r a c e n e . Mixed c r y s t a l s o f anthracene i n f l u o r e n e and i n b i p h e n y l were grown i n an evacuated pyrex tube u s i n g a Bridgeman f u r n a c e ( 3 4 ) .  Eastman r e d l a b e l b i p h e n y l was used  without f u r t h e r p u r i f i c a t i o n .  The anthracene i m p u r i t y con-  t a i n e d i n a s o l u t i o n o f Eastman r e d l a b e l f l u o r e n e d i s s o l v e d i n petroleum e t h e r was e x t r a c t e d i n t o c o n c e n t r a t e d s u l f u r i c acid.  The e x t r a c t i o n  procedure was r e p e a t e d u n t i l t h e  s u l f u r i c a c i d l a y e r remained c o l o u r l e s s (about t w e l v e t i m e s ) . The p u r i f i e d f l u o r e n e was r e c o v e r e d and was passed times t h r o u g h a zone r e f i n e r .  forty-six  I n g o t s about 10 cm l o n g and  0.8 cm d i a m e t e r were grown over a p e r i o d o f about 24 hours i n a Bridgeman  furnace.  Monocrystalline portions of the  i n g o t s were i s o l a t e d u s i n g a p o l a r i z i n g microscope.  Selec-  t i o n o f a s i n g l e c r y s t a l sample was made a f t e r c h e c k i n g f o r  9 complete e x t i n c t i o n i n o r t h o s c o p i c p r o j e c t i o n under a L e i t z WetzLar p o l a r i z i n g m i c r o s c o p e .  The d e s i r e d c r y s t a l f a c e was  found a f t e r l o c a t i n g t h e c r y s t a l axes under examination.  conoscopic  The chosen samples were chopped up a l o n g c l e a v -  age p l a n e s u s i n g t h i n r a z o r b l a d e s , and p o l i s h e d by hand t o the,,required t h i c k n e s s . f i r s t on f i n e emery-paper and then on Kleenex t i s s u e s o r l e n s t i s s u e s soaked i n e t h a n o l water mixture  (1:1).  The c r y s t a l t h i c k n e s s and the c o n c e n t r a t i o n  o f anthracene were a d j u s t e d so t h a t t h e o p t i c a l , d e n s i t y o f the 389 cm~"^"  fundamental mode i n k p o l a r i z a t i o n was about  0.5 - 1.5 a t room temperature.  T h i s range o f t h e o p t i c a l  d e n s i t y was chosen t o d e t e c t t h e v a r i o u s l i n e s o f d i f f e r e n t intensity.  The c o n c e n t r a t i o n s o f t h e mixed c r y s t a l s were  0.993 - 8.00 x 10~ M/M and the f u l l t h i c k n e s s range a v a i l 4  a b l e (about 0.2 mm t o 2 mm) *was3 used. were prepared  The t h i n n e r c r y s t a l s  by mounting a l a r g e r s i n g l e c r y s t a l w i t h c o r r e c t  a x i s alignment i n a b r a s s r i n g packed w i t h p l a s t e r o f P a r i s . The samples were c a r e f u l l y ground and p o l i s h e d a f t e r t h e p l a s t e r o f P a r i s had s e t .  Before the f i n a l p o l i s h the packing  around t h e t h i n c r y s t a l p r o t e c t e d i t from breakage.  This  method produced c r y s t a l s of about t h e same t h i c k n e s s as t h e ring.  Large s i n g l e c r y s t a l s o f f l u o r e n e were e a s i e r t o grow  than biphenyl c r y s t a l s .  10  Measurement o f t h e S p e c t r a Apparatus I t was important  t o work a t a s u f f i c i e n t l y  low  temperature t o r e s o l v e t h e v i b r a t i o n a l s t r u c t u r e . helium as  Liquid  (4.2°K) and l i q u i d n i t r o g e n (63°K and 77°K) were used  refrigerants. The b i g g e s t problem i n t a k i n g s p e c t r a a t l o w  temperature i s t o ensure good t h e r m a l c o n t a c t between sample and  refrigerant.  (35)  Some l i q u i d cements o r n a i l p o l i s h  have been recommended  f o r t h i s purpose.  Silicone  grease,  r u b b e r cement ( 3 6 ) , n a i l p o l i s h and OE 7031 cement were used i n t h e work a t 4.2°K.  GE 7031 cement gave t h e b e s t  s i n c e t h e l i n e s were s h a r p e s t l i n e i n n-heptane).  results  (IQLdth 4 cm""'" f o r an average  F o r t h e work a t 4.2°K t h e c r y s t a l was  a t t a c h e d t o a copper d i s c w i t h GE cement and the d i s c was secured  f i r m l y t o t h e i n n e r h e l i u m can.  The b r a s s s o l u t i o n  c e l l ( F i g u r e 1) f o r n-heptane and n-hexane were a t t a c h e d with, b o l t s and GE 7031 cement t o ensure a good t h e r m a l  con-  t a c t between t h e c e l l h o l d e r and copper h e l i u m can. The n-heptane and n-hexane s o l u t i o n s were a l s o s t u d i e d a t l i q u i d n i t r o g e n temperatures u s i n g t h e c e l l s shown i n F i g u r e 1.  The s o l u t i o n was s y r i n g e d i n t o t h e c e l l  t h r o u g h a s m a l l h o l e t h a t was l a t e r s e a l e d w i t h a s m a l l l e a d b a l l h e l d under p r e s s u r e a g a i n s t t h e opening by a s p r i n g s t r i p . The two q u a r t z windows were s e a l e d w i t h indium 0 - r i n g s .  11  Temperatures lower t h a n 77°K were obtained by pumping on the l i q u i d n i t r o g e n , the temperature b d i n g estimated by measuri n g the n i t r o g e n vapour p r e s s u r e . reduced i n t h i s way  The  temperature  was  t o about 63°K, the t r i p l e p o i n t of  n i t r o g e n , and t h i s temperature was maintained minutes b e f o r e the n i t r o g e n was  f o r about 50  c o m p l e t e l y pumped o f f .  Some s p e c t r a a t 77°K were o b t a i n e d u s i n g the apparatus shown i n F i g u r e 1.  The  sample was  p l a c e d i n the spade-shaped  i n n e r s i l i c a c e l l and f r o z e n by immersion i n l i q u i d n i t r o g e n . R e s i s t a n c e w i r e was wound i n a coarse s p i r a l around a s i l i c a dewar t o a v o i d f r o s t i n g .  I n t h i s arrangement the  l i g h t had t o t r a v e r s e b o t h the p o l y c r y s t a l l i n e the l i q u i d n i t r o g e n around the  sample and  cell.  Measurement of the L i n e s A l l low temperature s p e c t r a i n t h i s t h e s i s were o b t a i n e d u s i n g a H i l g e r and Watts E 201 graph.  The source f o r a b s o r p t i o n and  h i g h p r e s s u r e Xenon lamp C&sram XBO 103-F  large Littrow spectro-  e m i s s i o n s p e c t r a was  162).  Kodak 103  a  a-0,  and I I I - F s p e c t r o s c o p i c p l a t e s were s u b j e c t e d t o a  wide range of exporsures  t o b r i n g out a l l the l i n e s i n optimum  c o n t r a s t and were processed  i n the manner recommended by  the  manufacturers. The p l a t e s were enlarged by a f a c t o r of about t e n on to high contrast photographic  paper ( I l f o r d Bromide - B 3 26  and Kodabromide A5) and the s p e c t r a l l i n e s were measured from  K  FIG I  LOW TEMPERATURE SAMPLE CELLS  13 the p r i n t s by i n t e r p o l a t i o n  o r e x t r a p o l a t i o n u s i n g nearby  i r o n s t a n d a r d l i n e s ( 3 7 ) . D i s t a n c e s between l i n e s were measured t o an a c c u r a c y o f about 0.1 mm by means o f a engraved r u l e r o r a t r a v e l l i n g microscope.  precisely  An e r r o r o f about  1 cm~l was i n t r o d u c e d by t h e s e measuring methods f o r even the sharpest l i n e s .  Kayser's t a b l e  (38) was used t o c o n v e r t t h e  wavelengths i n a i r t o t h e wave numbers i n vacuum.  RESULTS  I n F i g u r e s 2 t o 7, o r i g i n a l p r i n t s used f o r l i n e measurement and sketches r o u g h l y i n d i c a t i n g  the r e l a t i v e  l i n e i n t e n s i t y a r e shown b o t h i n n-heptane (4.2°K) and i n fluorene matrices.  More p r e c i s e energy v a l u e s a r e t a b u l a t e d  i n Tables 4 and 5 f o r t h e f l u o r e s c e n c e and a b s o r p t i o n s p e c t r a , respectively.  The numbering i n t h e f i g u r e s  those i n t h e t a b l e s , absorption data. spectral  correlate  with  s e p a r a t e l y f o r t h e f l u o r e s c e n c e and  Some d o t t e d l i n e s i n F i g u r e 4  indicate  l i n e s which were found o n l y i n s p e c i a l samples and  whose i n t e n s i t i e s r e l a t i v e t o o t h e r l i n e s a r e n o t known. Not a l l t h e i m p u r i t y l i n e s f o r t h e f l u o r e n e m a t r i x a r e shown; these e x t r a l i n e s p r o b a b l y a r i s e from f l u o r e n e i t s e l f and/or some i m p u r i t y such as c a r b a z o l e o r phenanthrene.  Table 6  shows a b s o r p t i o n l i n e s a r i s i n g from t h e f l u o r e n e m a t r i x a t 4.20K.  (a) fluorene lb)  tlb(M)  n-heptane  (c) fluorene  llc(L)  FIGS 2 AND3 THE FLUORESCENCE SPECTRA OF ANTHRACENE IN n-HEPTANE AND FLUORENE AT 4 . 2 °K H  II i —J—LLJ  L  n.  h l.n  i i  1.. J . Ii. 1 1 .,,1,1 .. 1 i 1 IIfl 1 II . 1 . i u 1i —LIU 1—i_i—1—I 11—| I 9 1  1  1  1 11 • l. 1 1• 1. i . i  . .  (a) Anthracene in n-heptane at 4.2°K  |b or fla i  llll. 36  n — i — r  » «  «  I  55  62 m  • • l . i ' T782 87 rn—TT-  93 98  KB  «»  (b) Anthracene m fluorene at 42°K  FIG 4 RELATIVE INTENSITIES OF THE LINES IN FLUORESCENCE  -I 1 1 1 , , l_ 120 E3 |27  17 Table 4 F l u o r e s c e n c e S p e c t r a o f Anthracene i n Various Matrices ?^ /^f h  1 , a , 4  11M (b) 1 1 1  1 2 3 4 5 6 7 8 9 10 11 12 26056 13 14 15 136 16 184 17 18 406 19 20 466 532 21 22  ? ? 2  K  (c)  n  ~ fluorene, 4.20K n-heptane remarks hexane 11M (b,a) 1 1 L ( c ) 6 3 , 7 7 0 £ 4 . 2 0 K 770K  -2744 -2446 -2154 -1814 -1600 - 809 - 282 - 226  26056  26498  25975  -2744 -2446 -2154 -1814 -1600 - 809 - 282 - 226 - 164 - 131 - 46 25975 16 51  136 184  148 196  406  398  466 532  396 429 471 527  620 675  620 675  621 670  754  754  795  795  880  880  962 1025  905 962 1025  - 166 26247  31 32  33 34 35 36 37 38  794  26211 0-0, o r i g .-„c in 179  398  214 368 394-25 3 9 4 3 9 4 , ag  625 670  627  510 510, a g ? 553 i m p u r i t y 575 589 629 629, ag  755  755  763  794 828 870 894  792  792  23  24 25 26 27 28 29 30  b.  950 1019 1130  734 759 759, ag 778 787 2x394-1 874  917 1022 1052  911 911, b3g 1021 1044  1020 1 0 2 0 , ag 1045 1 0 4 5 , b 3 g ? 1141 3 9 4 + 7 5 9 - 1 2 . FR 1163 1 1 6 3 , ag  d  39  1173  1173  1177  1175  1175  1169  18 Table 4 continued  biphenyl,a.4.20K nF l u o r e n e . 4.2°K n-heptane remarks b. 11M (b) 11L (c) hexane 11M (b,a) I L L ( c ) 63,77°K 4.2°K ~ 77°K - ~ 40 41  1186  1194  1268  1268  1267  1305 1356  1305 1356  1411 1442  1411 1442  1484 1501  1484  1193  42 43 1244 44 45 46 47 48 1414 49 1454  1244  1272  1269  1414 1454  1415  50  51 52 1516 53 54 55 1559 56 1620 57 58 59 60 61  1516 1559 1620  1567 1699  1562 1598 1640  62 1810 63  1810  65 1877  1877  1806 1826 1848 1877  1962  1963  1906 1922 1957  2039  2037  2030 2061  64  66 67 68  69 1962  70 71 2039 72 73 •  76  1809  1562 1597 1640 1675 1706  1568 1643  ?  e  1516 1538 1652 1568  2x759-2 1568-25-5 394+1163+5 1568, ag  1639 1660 1715 1736 1781  1639, b3g 1660, b3g 2x394+911-16  1808  1803  1957  1963  2030 2061  2037  1888 1910 1924 1960 1996 .2033 2049 2072  1806  2100 2160  1413  1180 •1180, b3g 2x616 (b2u) 1233 + 1? 1257 2x629-1,FR . 1267 1267, ag 1283 1305 394+911 1340 1383 1409-25-1 1409 1409, ag 1431 629+2x394 +14,FR  2124 2163  629+1163-10; 759+1020+2; 394+1409-25 +3 394+1409  629+1267-8 394+2x759-2 759+H63-2 394+1568-2  ?  394+1639 394+1660-5 510+1568-6,? 759+1409-5  19  Table 4 continued  b i p h e n y l , a . 4 . 2 0 K nF l u o r e n e . 4.2°K n-heptane remarks b. 11M (b) 11L ( c ) hexane 11M (b,a) 11L (c_) 63,77°K 4.2°K 77°K 77 2202 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97  2202  2193  2237  2198  2286 2322  2340  2340  2352  2354  2435  2435  2427  2427  2587  2577  2523  2523  2587 2681  2681  2671  2828  2819 2828  2906  2906  98 2978 99  100 3047 101 102  103 3122 104 105 3205 106 3273 107  2204  2978  2821  2580  2580 2594  2737  2729  2815  2815  2897  2897  2195  2x394+1409-2  2270 2290 2329  629x1639+2 1020+1267+3 759+1568; 2x1163+3 2x394+1568+2 759+1639+1 1020+1409-3  2358  2435 2572 2677 2819  2399 2426 2502 2523  2571 2591 2637 2669 2730 2753 2818 2831 2894 • 2905 2923  2966  2965  2973  2969  3047  2999 3050  2999 3050  3041  3043 3064  3122  3084 3131  3084 3131 3199  3220  2967  . 3211  3136 3212  3273 3359  109' 3425  3425  3208 3271 3301  3303  108 3359  3090 3129  3434  3440  3365  3363  3450  3438  2x1267-11 1163+1409-1 1180+1409+2 1020+1639-22 1267+1409-7 1163+1568-1 1180+1568+5 2x1409 1267+1568-4 1267+1639-12 1267+1660-4; 2x759+1409-4 394+2x1267-5 1409+1568-8; 394+1163+ 1409+3 1409+1639-5 394+1267+ 1409-3 3090, ag? 2x1568-7 1568+1639 394+2x1409-4 2x1639-7 629+1267+ 1409-4 394+1409+ 1568-8; 2x394+1163+ 1409+3 629+2x1409-9 394+1409+ .. 1639+4  20 Table 4 continued  biphenyl,a.4.2°K nF l u o r e n e 4.20K n-heptane remarks b. 11M (b) 11L ( c ) hexane 11M (b,a) 11L ( c ) 63,77°K 4.20K 77°K ~ " 110 3492 111 3579  3492 3579  3521 3598  3526 3596  3598  113 3778  3756  3758  3754  114 3841  3838  3838  3833  2x394+2x1408 -11; 629+1409+ 1568-11; 2x394+1163+ 1409+4 759+1409+ 1568-4; 911+2x1409+3 394+759+1163 +1409+9 2x394+1409+ 1568-13 1020+2x1409-  115 3935 116 3992  3912 3984  3978  1163+2x1409  3732  112  5  -3» ?»  117 4087  4080  118 119 4164 120 4246 121 122 4398  1  4138 4222 4301 4372  123  4228 4379 4450  124  4524  4524  125  4600  126  4692  4681  127  4765  4757  128  4832  1020+1409+ 1568-19 4075 1267+2x1409 -6 4125 394+1409+ 2x1163-4 4154 4224 3x1409-3 4297 4372 1568+2x1409 -14 4449 1639+2x1409 -8 4524 1409+2x1568 -21 4605 394+3x1409 -16 4696 394+1267+ 1409+1639+7 4767 394+1568+ 2x1409-13; 2x1568+1639 -8 2x394+1163+ 2x1409-2  21 Table 4 continued a.  C r y s t a l axes a r e shown i n b r a c k e t s w h i l e M and L  show m o l e c u l a r s h o r t and l o n g axes, b.  respectively.  Assignments a r e made u s i n g t h e d a t a from t h e  n-heptane spectrum. c.  The o r i g i n s i n t h e d i f f e r e n t m a t r i c e s a r e g i v e n  i n cm""'", and a l l t h e o t h e r e n t r i e s i n t h e t a b l e show from t h e o r i g i n . d.  (FE.) Fermi  resonance.  e.  D o u b t f u l i n i t s appearance.  differences  fa) fluorene || b IM) (b) n-heptane (c) fluorene It c (L)  F I G S 5 A N D 6 T H E A B S O R P T I O N S P E C T R A O F A N T H R A C E N E IN n - H E P T A N E A N D F L U O R E N E A T 4.2 ° K  ill.••il..i.lLl.,iill .JL,IJ,II11IIIII,J. JH.11.II1.IL 30  «3  SO  58  60  ••••  | l  '  ,1 INI l l l i l - . U I I..i. 173  71  i. - l . - i . IN  IW  N)  IM  20  (a) Anthraoene in n-heptane at 4.2°K  lb or lis _Lu 30  u  43  SO  56  I .M.I_lLi 65  71  89  03  KM  IO  123  133  Jiiiil  138  148  135  Il I  166  II 171 I.I  HO  186  -rr-rr  (b) Anthracene in fluorene at 4.2°K  FIG 7 RELATIVE  INTENSITIES OF THE  LINES IN ABSORPTION  1193 _ JlUL 199  205  Table 5 A b s o r p t i o n S p e c t r a o f Anthracene i n V a r i o u s  Matrices  b i p h e n y l nfluorene, n-heptane a. 4 . 2 0 K hexane 4.20K 11M 11L 77°K 11M 11L 77°K 63°K 4.2°K (b) (o) (b,a) ( c ) 1 2 3  -136  4  5  6 7 8 9 26056 10 11 12 13 14 15 16 17 18 19  -73  c  26498  105  118 133 146 178 187  219  21 22 25 26 27 28 29 30 31 32 33  25975 29  Q  20  23 24  -154 -144 -127 -112 - 92 -:-80 - 73 ~ - 43 26247 26239 26221 0-0, o r i g i n ' ' 24 24 25 25, l a t t i c e 47 2x25-3?; 47? 70 5  211  253 273 317 391 385  389  392 385 422  387  389  590  589  34 35 36 37  38  523  39  40 41 42  43  583  581  585  229 236 254 262 279 299 316 340 351 389 410 420 436 457 464 474 484 521 531 539 553 566 590  389, ag 389+25-4 , 2x211-2 FR ? 389+2x25-3?  590, ag  25 T a b l e 5 continued b i p h e n y l nfluorene, n-heptane a. 4.2°K hexane 4.2°K remarks 11M 11L 77°K 11M 11L 77°K 63°K 4.2°K (b) ( c ) (b,a)(c) 610  44 45  652  46  47 48 49  50 51 52  735 778  729 773  658  733 780 812  740 777  740 780  890  892  53  54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86  836 859 882  891 927  ( 1024  977 1023  1028 1055  1024 1027 1055 1062  1096 1158  1152  1169 1199  1166  1155  1143 1160  1199  1239  1311  1285 1327  616 628 663 687 703 709 744 779 798 809 823 840 857 871 894 918 926 941 955 979 1005 1030 1057 1084 1102 1126 1135  1157 1166 1190 1199 1213 1247 1266 1283 1297 1304 1318 1338 1354  1391  1386.  1396 1422  1396  1397  1374 1399 1418  590+25+1 663, ag?  744. ag 2x389+1 2x389+25-5 389+2x211-2 FR?  894,b3g  389+590 2x211-7 FR? 1030, ag 389+663+5, FR?  389+744+2 1157, ag 1166, b3g 11L:1166+24+9 1247, ag? 389+894 2x663-8? 590+744+4, FR? 590+2x389+6, FR 1399, ag 389+1030-1, FR  26 Table 5 continued biphenyl a -  fluorene,  a. 4 . 2 0 K hexane 4.2oK 11M 111 77°K 11M 11L 7 7 ° E  (b)  87 88 89 90  (b,a) ( c )  1467  9 1 1496 92  93 94 95 96 97 98 99 100 101 102 103 104 105  (c)  1541  1491  1498 1532  1554-  1555  1779  1431 1447 1464 1480 1503 1533  1547 1551  1547 1559 1578 1604 1619 1641 1658 1700 1720 1727 1749 1785 1788 1809  1560  1786  1783  1699  1789  1814  109 110 1890 111 112 1935 113 1 1 4 1979 115  116 2048  1932  1860 1892 1917 1941  2035  1978 2006 2056  1880  1853 1853 1860 1887 1893 1959 1971 1986 1990 2052 2051 2094  117  118  1 1 9 2128 120 2178 121 122 123 2243  124  2322  2171  2276 2321  4.20K  1427 1443 1462 1458 1463 1482 1495 1498 1504  1591  107 108  127  63°K  1601  106  125 126  n-heptane  2145 2141 1177 2181  2176 2202  2286 2336  2220 2225 2248 2256 2287 2287 2336 2331  1822 1834 1855 1885 1917 1936 1963 1993 2008 2051 2071 2112 2141 2178 2220 2254 2285 2296 2319 2329  remarks b.  1399+25+7, FR 111:1464, b3g 590+894-4, FR 1503, ag 744+2x389+11, FR; 1503+25+5 389+1157+1 389+1166+4 389+1157+25+7 590+1030-1 389+1247+5? 663+1030+7? 389+2x663+5? 590+1157+2 2x894-3 389+1399 2x389+1030+1; 389+1399+25-4 663+H57+2, FR? 663+3x389+4? 389+1464+2 389+1503-7 2x389+1157+1 590+1399+4 2x1030-9 663+1399+9? 2x389+2x663+8? 744+1399-2 2x389+1399+1 389+663+1157+6 744+1503+7 2x389+1503+4 894+1399+3 2x1157+5 1157+1166+6  27 Table 5 continued  b i p h e n y l hfluorene, n-heptane a. 4.2°K hexane 4.2°K 11M 11L 77°K 11M 111 77°K 63°K 4.2°K (b) ( c ) (b,a) ( c ) 128  2348  129  130 2416 131 132 133 2481 134 135 136 2560 2548 137 138 139 140 141 2710 142 143 144 145 146  2422 2555  2425 2426 2482  2449  2428 2458  2561  2561 2560  2562  2637  2623 2607 2637  2617  2650  2665  2715  2701 2751  2668 2655  2665  2729 2728 2796  2783 2816  2730 2800  2428 2457  2490  2508 2533 2559 2620 2638 2648 2660  2886 2947  2890 2945  2855 2861 2897 2945 2947  2978  151 2964 152 3007 153 154 3039  3053  3022 3057  2863 2901 2955 3010 3052  389+1157+1166+8  2734 2798 2818  590+744+1399+2, FR 2x1399 389+1030+1399; 2x1399+25-5 663+2x389+1399+8?; 2x389+894+1157+4? 1399+1464+1 1399+1503-2 111:1464+1503-11; 11M:389+1399+1157+7 2x744+1503, FR 2x1503-2 389+1157+1464+10 11M:389+1157+1503+1 111:389+1166+1503-1 3x1030-9; 2x389+2x1157-11 2x389+1157+1166-1 C-H s t r e t c h , b3g? 590+1157+1399+6 11M:389+2x1399+6 111:389+590+744+1464 +6 2x389+1030+1399+5  2864 2900 2954 2954 3004 3020 3048  155  3081  156 157 158 159 3174  3100 3119 3152 3193  160  3126 3178  3176  3191 3187  3189  389+590+1399 1157+1247?; 894+1503+7? 11M:1030+1399-1? 389+663+1399+6? 1030+1464-4 389+663+1464-8? 1030+1503 11M:1157+1399+3; 111:1166+1399 1157+1464-1 11M:389+744+1503+2; 111:3x389+1464-7? 1247+1399+2? 11M:1503+1157 111:1503+1167+1  2720  2832  147 148 149 2893 150 2941  2347 2378 2404  remarks  3212  28 Table 5 continued  biphenyl a. 4 . 2 0 K 11M I L L & £> (  161 162 163 3283 164 3333 165 166 167 168 169 170 3565 171 172 173 174 175 176 177 178  n  fluorene, hexane 4.2°K 77°K IIM HL (£,a) ( c )  n-heptane  _  3277 3339  3433 3569  3280 3340 3365 3416 3443 3476 3564 3602 3668  3666 3718 3813  3718 3750 3804 3838  179 180 181  77°K 63°K 4 . 2 0 K  3227 3248 3254 3258 3264 3288 3292 3293 3342 3345 3348 3389 3384 3394 3414 3446 3439 3442 3460 3573 3580 3574 3588 3609 3634 3654 3648 3678 3688 3678 3714 3723 3737 3731 3823 3823 3826 3858 3857 3853 3886 3903 3922  182 183 3955 184 185 186 187 188 189 190 1 9 1 4177 192 193 194 195 4280 196 4328 197 198  3944  3968 3955 3985  3948  4017 4030 4055 4100 4118 4160 4197 4199 4195 4214 4013  4042 4108 4180  4278 4339  4066 4097 4117 4149 4172 4198  4280 4327  4035 4058 4073 4112 4118 4134  4227 4261 4265 4225 4262 4294 4301 4297 4349 4352 4351 4368 4380 4388  remarks  389+590+744+1503+1 389+1399+1464+12 389+1399+1503+2 2x389+1164+1399+7? 590+2x1399-4 389+2x1503-1 744+1157+1503+7 2x389+1157+1503+4 1399+2x1030+1 2x389+2x1399-3 1030+1157+1399+2 590+2x1503+13 e 744+1399+1503+2 2x398+1399+1503 1399+2x1157+1 3x389+1157+1399+8 1030+2x1399-2; 1503+2x1157+9? 389+663+2x1399+3? 1030+1399+1464-7? 1157+1247+1503-4? 894+2x1503+3? 1030+1399+1503-10; 389+744+2x1399-9? 1157+2x1399 389+1030+1166+1399+1; 389+1030+1157+1399+10 1157+1399+1464-3 1030+2x1503-6 1157+1399+1503-4 389+1399+2x1157-2 1157+1464+1503-6 1157+2x1503-1 3x1399-2 389+1030+2x1399-3; 389+2x1157+1503+8 663+2x389+2x1399-12? 1464+2x1399+3 1503+2x1399-4 389+1157+2x1399-7 392+1166+2x1396+18 1399+1464+1503+14  29 Table 5 continued  b i p h e n y l nfluorene, a. 4 . 2 0 K hexane 4.20K 11M 111 77°K 11M 111 (b) ( c ) (b,a) ( c ) 199 200 201 202 203 204 205 206 207  4433  4572 4668 4723  n-heptane 77°K 63°K 4 . 2 0 K  4438  4447 4446  4515 4552 4582 4630 4667 4700  4513 4509 4545 4589 4584 4656 4655 4691 4683 4741 4739  4829  4585 4630 4699 4684 4739  4832 4890  208 209  4973 5047  210 211  5076 5126  212  5227  213  5366  214 215 216 217 218  5417 5437 5458 5522 5567  219 220  5596 5672  221 222  5684 5741  223  5825  224 225 226 227  5846 5910 5983 6053  remarks  389+1157+1399+1503+2; 389+1166+1399+1503-7? 3x1503 389+1157+2x1503-7 389+3x1399-2 389+1464+2x1399+4 389+1503+2x1399-7 2x389+1157+2x1399+6; 2x389+1166+2x1399-3 2x389+1157+1399+1503-5 389+3x1503-8; 590+1503+2x1399-1 2x389+3x1399-2 2x389+1464+2x1399+7; 744+1503+2x1399+2 2x389+1503+2x1399-3 2x1157+2x1399+14?; 1157+1166+2x1399+5 1030+3x1399; 1030+1503+2x1399-4; 1399+1503+2x1157+11? 1157+1166+1399+1503+2^ 1157+3x1399+12; 1166+3x1399+3 1157+1464+2x1399-2; 1247+3x1399+7? 1157+1503+2x1399 1157+1399+1464+1503-1 1464+3x1399+6; 1157+1399+2x1503+5? 4x1399 1157+3x1503+6; 1464+3x1399+11 1503+3x1399-16 389+1157+3x1399-2; 389+1166+3x1399-11? 389+1166+1464+2x1399+8 389+1157+1464+2x1399+ 17 389+1157+1503+2x1399-1 1399+3x1503+2 389+4x1399-3 389+3x1399+1464+3  30  Table 5 continued  b i p h e n y l nfluorene, n-heptane ( a 4 . 2 °K hexane 4.2 OK im 111 77°K 11M 11L 77°K 63°K 4.20K (bf (c) (b,a) ( c ) 228 229  6084 6135  a.  389+1503+3x1399-5 2x389+1157+3x1399+3; 2x389+1166+3x1399-6  C r y s t a l axes a r e shown i n b r a c k e t s w h i l e M and L  show m o l e c u l a r s h o r t and l o n g axes, b.  remarks  respectively.  Assignments a r e made u s i n g t h e d a t a from t h e n-  heptane spectrum. c.  The o r i g i n s i n t h e d i f f e r e n t m a t r i c e s a r e g i v e n  i n cm " ", and a l l t h e o t h e r e n t r i e s i n t h e t a b l e show d i f f e r e n c e s -  1  from t h e o r i g i n . d.  (FR) Fermi  resonance.  e.  This l i n e i s doubtful.  31 Table 6 A b s o r p t i o n Spectrum o f Fluorene a t 4.2°K  11M ( b ) * b  31062  1 2  31080 31130 31141  3  4 5  6  7 8  9  10 11 12  13  14  15 16 117 18 19 20 21 22  123 24  31290  31318 31363 31377 31409  27  28  31524 31550  30 31 32 33  31619  34 103 104  31350  31499 31512  31524 31548 31584 31651 31623  31636 31656 32766  a. b.  39  43 44 45 46 47 48 49  31473 31478  32787  38  31190  31379 31410 31417  31439  35 36 37 40 41  31211 31230 31255 31264 31290 31299 31319  31256  31517 31520  29  31157  31182  25  26  11L ( c )  42  50 51 52 53 54 55  56 57 58 59  60 61 62 63 64  65  66 67 68 105  106  11M (b)  111 ( c )  31665 31666 31695 31716  31668 31696  31742 31795 31809  31857 3186 3 31919 31959 31984 32005  32066 32086  32109 32130 32148 32154 32206  31738 31750 31813 31835  31844 31857 31860 31892 31902  31928 31956  31961 31967 31992  11M (b) 111 69  70 71 72 73 74  75 76 77 78  79 80 81 82  32110  32161 32203  32805 32815  32246 32254 32274 32298 32319  32367 32381 32394  83 84 ' 32420 85 32433 86 32455 87 32481 88 32494 89 32502 90 32526  91  .32001 32017 32049  32082  32219  92 93 94 95  96  97 98 99 100 101 102  107 108  The frequency o f each l i n e i s  s h o r t and l o n g axes, r e s p e c t i v e l y .  32230 32262  32323 32359  32385 32398 32455  32480  32543  32569 32590 32603 32619  32644 32672 32687 32706 32731 32752 32761 32829  32858  -1  g i v e n i n cm C r y s t a l axes a r e shown i n b r a c k e t s w h i l e M and L  show m o l e c u l a r  {'o)  32755  DISCUSSION  Fluorescence Spectra Fundamental Modes S p e c t r a l l i n e s i n f l u o r e s c e n c e may a r i s e from a n t h r a cene m o l e c u l e s , m o l e c u l e s o f t h e m a t r i x o r some o t h e r imp u r i t y molecule.  Unknown i m p u r i t i e s present a r e a l  problem  i n fluorescence spectroscopy since a very small trace of i m p u r i t y (as low as 10  M) can make a l a r g e c o n t r i b u t i o n t o  t h e o v e r a l l emission... L i n e s due t o fundamental modes o f anthracene may be d i s t i n g u i s h e d from o t h e r e m i s s i o n l i n e s s i n c e o n l y these form combinations b u i l t on t h e o r i g i n and t h e o r i g i n can be a s s i g n ed from t h e a b s o r p t i o n spectrum.  On t h e b a s i s o f t h e i r  i n t e n s i t i e s , p o l a r i z a t i o n and a b i l i t y t o form combinations e i g h t 0^ fundamental modes o f t h e  e l e c t r o n i c s t a t e were  a s s i g n e d : 394, 629, 759, 1020, 1163, 1267, 1409 and 1568 cm" . 1  T h e o r e t i c a l l y twelve  fundamentals a r e p r e d i c t e d f o r  anthracene and among them t h r e e due t o C-H s t r e t c h e s i n t h e r e g i o n o f 2900 - 3100 c m nine  (i^ modes s h o u l d be found.  - 1  (39).  appear  So below 2000 cm"  1  From t h e i r i n t e n s i t y and  p o l a r i z a t i o n b e h a v i o u r e i t h e r 510, 874 o r 1340 cm-1 may be s e l e c t e d as t h i s n i n t h fl| fundamental. 510 and 1340 c m  - 1  Among these  modes appeared one and f o u r times r e s p e c t i v e l y  i n combination w i t h known A 3 modes w h i l e 874 cm appear a t a l l .  From t h i s p o i n t of view, the n i n t h  i s most p r o b a b l y t h e l i n e a t 1340 c m 510 cm""'" p r e f e r r e d n e x t .  -1  -1  as ag i n anthracene  fundamental  w i t h the l i n e at  However, 1340 cm"  i n b i p h e n y l w h i l e t h e o t h e r two d i d . shows 522 c m  d i d not  1  d i d not appear  F u r t h e r , Raman d a t a (31)  c r y s t a l and i n s o l u t i o n  which i s p r o b a b l y c l o s e enough t o our 510 cm" . 1  No l i n e s  c o r r e s p o n d i n g t o t h e o t h e r two v i b r a t i o n s were found i n t h e Raman.  Thus a l t h o u g h no d e f i n i t e assignment c o u l d be made  f o r the n i n t h £)g fundamental,  t h e l i n e a t 510 cm"  1  seems t o  be the most p r o b a b l e contender i f emphasis i s p l a c e d on i t s appearance i n the Raman s p e c t r a .  The o t h e r two must be  i n t e r p r e t e d as i m p u r i t y l i n e s , o r b j | b e l o n g i n g t o t h e e l e c t r o n i c s t a t e i f f o r some reason f l u o r e s c e n c e appears from a  origin.  1  fundamental  3090 cm"  1  may be a s s i g n e d as an  due t o C-H s t r e t c h i n g s i n c e i t does not a n a l y s e  as a c o m b i n a t i o n l i n e , i t agrees w i t h p r e v i o u s e m p i r i c a l d a t a (39) and i t has t h e expected p o l a r i z a t i o n . 3526 c m  -1  stretching  However,  i s p r o b a b l y t o o h i g h t o be a s s i g n e d as an a<j C-H frequency.  Five  b ^ fundamentals  were found f o r the  electronic  ground s t a t e a t 911, 1045, 1180, 1639 and 1660 c m .  They  -1  were u s u a l l y weaker i n i n t e n s i t y than the d e t e c t i o n o f combinations was d i f f i c u l t .  modes and so However, combina-  t i o n s i n v o l v i n g a l l modes except 1045 cm"! were found. bj|assignment r e s t s p r i m a r i l y on p o l a r i z a t i o n d a t a  The  (i.e.,  a l l these l i n e s appeared more s t r o n g l y i n the c d i r e c t i o n of  34" the  fluorene matrix).  The modes a t 1180 and 1639 c m  c l o s e l y w i t h Raman d a t a ( 3 1 ) . A l t h o u g h the 1045 c m  agreed  -1  -1  mode d i d  not combine w i t h o t h e r fundamentals, i t i s t e n t a t i v e l y a s s i g n e d as a 1012 cm"  fundamental s i n c e i t i s c l o s e t o the fundamental observed i n the Raman spectrum ( 3 1 ) .  -1  F e r m i Resonance Three p o s s i b l e examples of F e r m i resonance were observed i n f l u o r e s c e n c e (Table 7 ) .  A l l of t h e s e occured  near s t r o n g Q| fundamentals as e x p e c t e d .  I n s e t (a) energy  s h i f t s o f t h o s e two l i n e s were found, i n s e t (b) i n t e n s i t y t r a n s f e r was more s i g n i f i c a n t , w h i l e i n s e t (c) b o t h i n t e n s i t y and energy were a f f e c t e d s t r o n g l y . Table 7 P o s s i b l e Examples o f Fermi Resonance i n the F l u o r e s c e n c e o f Anthracene  set (a)  (b)  (c)  i n n-heptane  i n fluorene  38  1141=394+759-12  1130=396+755-21  39  1163 ag  1175  42  1257=2x629-1  43  1267 ag  48  1409 ag  49  1431=2x391+629+14 1442=2x396+621+29 1454=2x406+620+22  line  No.  i n biphenyl  ag  1411 ag  1414 ag  35 Other F e a t u r e s I f e r r o r s o f measurement due t o l i n e broadening (see l i n e s 59, 86 and 95) a r e t a k e n i n t o account, t h e combinations suggest t h e u s u a l d i a t o m i c type o f p o t e n t i a l anharmonic i n h i g h quantum r e g i o n .  c u r v e , which i s  Combinations o f f o u r  fundamentals r e p r e s e n t e d t h e most complex l i n e s observed i n our s p e c t r a and these were perhaps beginning, t o show anh a r m o n i c i t y o f t h e 'A^ p o t e n t i a l potential  surface.  s u r f a c e was s u r p r i s i n g l y  However, the  harmonic f o r such a l a r g e  polyatomic molecule. The o r i g i n and t h e 25 cm" l a t t i c e mode b u i l t on t h e 1  o r i g i n d i d n o t appear i n f l u o r e s c e n c e and t h i s can be e x p l a i n e d i n terms o f r e a b s o r p t i o n o f t h e e m i s s i o n .  Both o f these l i n e s  appeared s t r o n g l y i n a b s o r p t i o n . Theoretically,  fundamental modes o f any symmetry  s p e c i e s may combine p r o v i d e d t h a t t h e c o m b i n a t i o n has t h e symmetry  or  .  type do n o t appear. interpreted  In practice,  combinations o f t h i s g e n e r a l  However, l i n e 41 a t 1233 cm" might be 1  as t h e overtone o f t h e b  observed i n the i n f r a - r e d  iu  mode a t 616 c m  - 1  ( 3 2 ) ; no c o m b i n a t i o n o f t h e observed  Gl^ and b ^ c a n account f o r t h i s l i n e , a l t h o u g h t h e p o s s i b i l i t y of a r i s i n g from i m p u r i t y must be c o n s i d e r e d . Some l i n e s appeared, which c o u l d n o t be a s s i g n e d i n terms o f t h e observed fl^ and baj. fundamentals.  These may be  s e p a r a t e d i n t o two k i n d s : ( i ) l i n e s which appeared i n o n l y one o f t h e f o u r m a t r i c e s , and ( i i ) l i n e s which appeared i n  36 more than one  matrix.  The l i n e s b e l o n g i n g t o ( i ) may  a r i s e from i m p u r i t i e s  i n the m a t r i x or from the host m o l e c u l e . a "solvent'  1  F u r t h e r i f we assume  'A| o r i g i n d i f f e r e n t from t h a t  s h i f t of the  'Aj o r i g i n , t h e n the u n e x p l a i n e d  of the  l i n e s could  i n t e r p r e t e d as ground s t a t e v i b r a t i o n a l modes from a upper e l e c t r o n i c s t a t e .  l  because they a r e isomorphic w i t h those i m p u r i t i e s .  anthracene.  Bao  Phenanthrene, c a r b a z o l e and a c r i d i n e  are p o s s i b l e i m p u r i t i e s i n the m a t r i c e s , f l u o r e n e and  (41) (42) and c a r b a z o l e  be  biphenyl  Phenanthrene  (43) f l u o r e s c e near the o r i g i n of  S i n c e a c r i d i n e does not f l u o r e s c e i n i t s c r y s t a l  s t a t e or i n o r g a n i c s o l v e n t (44) a t l e a s t a t room temperature and s i n c e i t s f l u o r e s c e n c e spectrum i s t o the r e d of the anthracene spectrum ( 4 4 ) , the presence of a c r i d i n e i s not important  i n the a n a l y s i s of f l u o r e s c e n c e .  In general i f a  l i n e appears o n l y i n a s p e c i a l " m a t r i x and i f the  intensity  r e l a t i v e t o t h e o t h e r common l i n e s d i f f e r s over a number of samples, i t may  be t a k e n as an i m p u r i t y l i n e .  o n l y l i n e 22 a t 533 cm""  1  I n t h i s sense  a p p a r e n t l y arose from some i m p u r i t y .  S i n c e the s p e c t r a of phenanthrene and under the same e x p e r i m e n t a l  c a r b a z o l e measured  c o n d i t i o n s as here a r e not  avail-  a b l e , the p r e c i s e assignment of i m p u r i t i e s i s not p o s s i b l e a t present.  F l u o r e n e f l u o r e s c e s t o the b l u e of the o r i g i n of  anthracene (43) and the l i n e s 1 and  2 probably form p a r t o f  t h e f l u o r e n e f l u o r e s c e n c e spectrum because they agree c l o s e l y w i t h the d a t a t a k e n a t 77°K i n n-heptane (43).  B i p h e n y l does  3'7 not f l u o r e s c e i n t h i s r e g i o n (27) and n e i t h e r do n-heptane nor n-hexane.  The r e m a i n i n g p o s s i b l e i n t e r p r e t a t i o n o f t h e  l i n e s ( i ) i n v o l v e d a t r a n s i t i o n from a ' B  a y  upper s t a t e .  If  t h i s i s t r u e , a somewhat s i m i l a r i n t e n s i t y and energy s e p a r a t i o n t o v i b r a t i o n a l modes from t h e served.  1  system s h o u l d be ob-  However, t h i s was not so and t h i s l a s t  possibility  may be e x c l u d e d . For the l i n e s belonging t o ( i i ) three possible i n t e r p r e t a t i o n s may e x i s t : i m p u r i t i e s i n a n t h r a c e n e , l i n e s from the l i g h t s o u r c e , and v i b r a t i o n a l modes due t o f l u o r e s cence from t h e  s t a t e assuming no " s o l v e n t " s h i f t .  'feay  As  i m p u r i t i e s i n a n t h r a c e n a n t h r a q u i n o n e must be c o n s i d e r e d i n a d d i t i o n t o c a r b a z o l e and phenanthrene, f o r t h e o x i d a t i o n o f a n t h r a c e n c o u l d o c c u r e s p e c i a l l y i n t h e presence o f l i g h t and oxygen.  Anthraquinone vapour (45) f l u o r e s c e s i n t h e r e g i o n  20,000 - 23,000 cm" . 1  Thus t h e l i n e s 115 and 121 c o u l d be  due t o a n t h r a q u i n o n e , and t h e l i n e s n e a r t h e o r i g i n (9, 15, 16, 20 and 35) might a r i s e from e i t h e r c a r b a z o l e o r phenanthrene, but a g a i n p r e c i s e assignment i s i m p o s s i b l e f o r the l a c k o f data.  I f e m i s s i o n from t h e source appeared, t h e  l i n e must show t h e same energy independent o f t h e m a t r i x . From t h i s p o i n t o f view no l i n e s a r o s e from t h e common source xenon.  Thus t o account f o r t h e presence o f t h e unassigned  l i n e s i n t h e f l u o r e s c e n c e s p e c t r a , t h e e x i s t e n c e o f some i m p u r i t i e s must be c l a i m e d .  3?" Absorption Spectra Fundamental Modes of the ' & p Upper S t a t e t  From a p r e l i m i n a r y e x a m i n a t i o n o f t h e i r p o l a r i z a t i o n , i n t e n s i t y and appearance i n c o m b i n a t i o n s , f i f t e e n  intervals  may be chosen as fundamentals w i t h energy l e s s t h a n 2000 e.g. e l e v e n &% fundamentals: 389, 590, 744, 1030, 1157, 1503, 663, 1057., 1247 and 1338 cm" , 1  894, 1166, 1464 and 926 cm" . 1  and f o u r  cm ; -1  1399,  fundamentals  S i n c e t h e r e can be o n l y t w e l v e  Q$ fundamentals i n a l l and t h r e e a r e expected i n the r e g i o n of  C-H  s t r e t c h i n g f r e q u e n c i e s near 3000 cm"  o n l y n i n e fl^ fundamentals below 2000 cm" .  The f i r s t  1  fundamentals and t h e f i r s t t h r e e assigned with c e r t a i n t y .  t h e r e must be  1  seven  fundamentals a r e  Thus two more ft| fundamentals must  be s e l e c t e d from the l a s t f o u r l i s t e d . i n n-heptane might be added as a The l i n e a t 663 cm"  1  The i n t e r v a l 3119  cm"  1  kjjc-H s t r e t c h i n g f r e q u e n c y .  may be a s s i g n e d as an fl^ funda-  mental w i t h some c e r t a i n t y a l t h o u g h i t d i d not appear i n nhexane or i n b i p h e n y l .  No a l t e r n a t i v e e x p l a n a t i o n f o r i t was  p o s s i b l e , and many l i n e s c o u l d be b e s t i n t e r p r e t e d as t i o n s i n v o l v i n g 663 1057 cm"  1  cm"  1  as an ft^ fundamental.  was s l i g h t l y s t r o n g e r than 663  n-heptane a t 77°K w h i l e 663 so u s e f u l as 663  cm"  1  cm~l d i d n o t .  cm"  1  combina-  The l i n e a t and appeared i n  However, i t was not  i n i n t e r p r e t i n g combinations and 1057  c o u l d i t s e l f be i n t e r p r e t e d as the c o m b i n a t i o n (590+663)  cm  cm-1  e s p e c i a l l y when the p o s s i b i l i t y of F e r m i resonance between  39  fundamental 1030 c m  t h i s c o m b i n a t i o n and the s t r o n g considered.  Thus 1057 cm"  t h a n an ft^ fundamental.  was  -1  was t a k e n as a c o m b i n a t i o n r a t h e r  1  B o t h 1247 and 1338 cm"  1  c o u l d be  t a k e n as fundamentals o r as the combinations 1247 = 590+663-6 and 1338 + 590+744+4; a l t h o u g h the l i n e s appeared t o be too i n t e n s e t o be s i m p l e c o m b i n a t i o n s .  The l i n e a t 1338 cm"  was  1  s u f f i c i e n t l y c l o s e t o the s t r o n g e s t l i n e i n the spectrum a t 1399 cm" for.  1  f o r i t s i n t e n s i t y as a c o m b i n a t i o n t o be accounted  However, the l i n e a t 1247 cm"  was more i s o l a t e d from  1  o t h e r s t r o n g l i n e s so t h a t , i n t h i s c a s e , a F e r m i resonance c o u l d not r e a d i l y be assumed.  A g a i n the l i n e 1247 cm"  i n t h e f l u o r e n e m a t r i x w h i l e the o t h e r d i d n o t . grounds, 663 and 1247 cm"  1  1  appeared  Thus, on t h e s e  a r e t e n t a t i v e l y a s s i g n e d as  ftj  fundamentals and added t o the p r e v i o u s l i s t o f seven. As a  bj|  fundamental 926 cm"  1  i s q u i t e d o u b t f u l , how-  ever the a l t e r n a t i v e e x p l a n a t i o n (894+25+7) i s a l s o d o u b t f u l , and t h e l i n e a t 2428 em"  1  c o u l d be accounted f o r as a combina-  t i o n of 926 and 1503 cm" ( l o n g a x i s p o l a r i z e d ) . The combina1 1 t i o n o f 926 cm w i t h the stronger fundamental a t 1399 cm 1  c o u l d not be found s i n c e i t was h i d d e n beneath the c o m b i n a t i o n 2329 = 1157+1166+6. Comparison of t h e Fundamentals  on t h e 'Aft and on the  'Biu  E l e c t r o n i c States A l l p o s s i b l e fundamentals of anthracene i n the ground and i n the e x c i t e d s t a t e  't^mare summarized i n Table 8,.  40  For the fundamentals which have been a s s i g n e d w i t h c e r t a i n t y , a correspondence between each fundamental a t t h e two e l e c t r o n i c s t a t e s have been observed b o t h i n energy v a l u e and i n t e n s i t y .  T h i s i n d i c a t e s t h a t the p o t e n t i a l  energy  s u r f a c e s of t h e ground and the e x c i t e d e l e c t r o n i c s t a t e a r e s i m i l a r i n t h e s e normal c o o r d i n a t e s a t l e a s t .  This leads to  the e x p e c t a t i o n t h a t t h e r e w i l l be a correspondence f o r a l l the i n t e r v a l s , and the two (X^ fundamentals t e n t a t i v e l y a s s i g n e d (663 and 1247 c m )  might be added t o the s i x c e r t a i n ones t o  -1  account f o r t h e n i n e  fundamentals as p r e d i c t e d .  F u r t h e r t h e r e i s a tendency t h a t the fundamentals i n the  'Aj  s t a t e have h i g h e r energy t h a n those i n the  1  state.  T h i s behaviour has been a l s o observed i n naphthalene ( 4 6 ) . Table 8 The Fundamentals  o f Anthracene i n the  '/\| Ground and the  ' ^ i u Upper S t a t e  Remark 394  510 629 759  874 1020 1163  1267  1340 1409  1568 3018 911 1045  1180 1639  1660  c m  o r * "  389 590 663 744 1030  1057 .1247 1338 1399 1503 894 926  1166 1464  3119  c m  1  certain probable probable certain doubtful certain  389+663+5, FR'/' ?  certain probable ^ 590+744+4: i n 'B, certain certain C-H s t r e t c h " ? certain possible certain certain certain C-H s t r e t c h ? ?  u  state only  401  F e r m i Resonance P o s s i b l e examples summarized  of Fermi resonance i n a b s o r p t i o n a r e  i n T a b l e .9. Table 9  P o s s i b l e Examples o f Fermi Resonance i n t h e A b s o r p t i o n of Anthracene  set  C-  a  V, u  C  A  u.  e  1  l i n e i n n-•heptane, a t 4.2°K No.  i n f l u o r e n e , a t 4.2°K  65  1030, ag  1028, ag  66  1057 = 389+663+5  1062 = 387+657+18  82  1338 = 590+744+4  84  1374 = 590+2x389+6  85  1399,  ag  1396,ag  86  1418 = 389+1030-1  1422 = 392+1028+2  89  1464, b3g  1462, b3g  90  1480 = 590+894-4  1495 = 585+891+19  105  1788 = 389+1399  1783 = 392+1396-5  107  1822 = 663+1157+2  1814 = 652+1169-7  144  2734 = 590+744+1399+2  145  2798 = 2x1399  150  2954 = 389+1157+1399+7  2445 = 392+1169+1396-12  151  2991 = 2x744+1503  2978 = 2x733+1498+14  A l l o f these examples show a more pronounced  Fermi  resonance i n t h e f l u o r e n e m a t r i x ; t h i s was t h e tendency i n  42 fluorescence also.  The  s e t s i n the f l u o r e n e m a t r i x a, c and  f show good examples of the e f f e c t b o t h i n terms of the energy s h i f t and i n t e n s i t y t r a n s f e r .  The  other sets i n  f l u o r e n e and a l l the s e t s i n n-heptane show o n l y an transfer.  I n set b the s t r o n g  intensity  fundamental a t 1399  cm"*  1  seems to share the i n t e n s i t y among .'e.Everal nearby combinations.  However, s i n c e t h e r e must be some e r r o r i n  e s t i m a t i n g i n t e n s i t i e s from the photographic p a r t i c u l a r l y near the s t r o n g l i n e a t 1339  prints,  cm , -1  actual  F e r m i resonance might occur o n l y between the l i n e s 85  and  86. Although anharmonicity  i n c r e a s e s i n the h i g h e r energy  r e g i o n , no F e r m i resonances were i d e n t i f i e d because of the d e c r e a s i n g i n t e n s i t y of the l i n e s w i t h a consequent i n c r e a s e i n the measurement e r r o r due t o l i n e b r o a d e n i n g . two m a t r i c e s a lower r e s o l u t i o n  I n the  other  of the s p e c t r a d i d not a l l o w  Fermi resonance to be i d e n t i f i e d . From t h e measurement of the e n e r g i e s of the fundamentals and t h e i r v a r i o u s combinations and of t h e r e l a t i v e i n t e n s i t y d i s t r i b u t i o n amongst them, i t i s seen t h a t the potential  energy s u r f a c e of the  s u r p r i s i n g l y harmonic.  T h i s f a c t may  electronic  state i s  a l s o account f o r the  s m a l l numbers of examples of Fermi resonance i n the a n t h r a cene s p e c t r a .  Other L i n e s The l i n e s which c o u l d not be a s s i g n e d i n terms of the observed  and  the f o l l o w i n g  types:  1.  fundamentals may be s e p a r a t e d i n t o  l i n e s which appeared i n o n l y one of the f o u r  m a t r i c e s , ( a ) i n n-heptane, and (b) i n f l u o r e n e 2.  l i n e s which appeared i n more than one m a t r i x .  Type 1 ( a ) : i n n-heptane.  Some weak l i n e s were  grouped around the o r i g i n and o t h e r s t r o n g CX| modes of the 1  &io e l e c t r o n i c s t a t e , as summarized i n T a b l e 10.  structure  This  might be found i n the h i g h e r quantum r e g i o n , but  i t s i d e n t i f i c a t i o n i s i m p o s s i b l e because of the appearance of much s t r o n g e r combinations of the fundamentals. weak l i n e s have two p o s s i b l e i n t e r p r e t a t i o n s .  These  Firstly  these may be a number o f s p e c i a l s i t e s i n the l a t t i c e ,  each  s i t e : ; h a v i n g a d i f f e r e n t environment and g i v i n g r i s e t o a d i f f e r e n t "solvent s h i f t " .  Thus f o r each d i f f e r e n t  environ-  ment a s e p a r a t e s h i f t e d spectrum s h o u l d be observed; the i n t e n s i t y of each " s h i f t e d " spectrum would depend on the number of anthracene molecules o c c u p y i n g t h a t type of s i t e . The d i f f e r e n t p o s s i b l e s i t e s t h a t might be c o n s i d e r e d a r e s u b s t i t u t i o n a l s i t e s , i n t e r s t i t i a l s i t e s , s i t e s next t o a vacancy, or next t o o t h e r anthracene molecules ( e i t h e r or more) ( 4 7 ) .  one  10  Table  S i m i l a r i t y o f t h e S t r u c t u r e A r o u n d Some S t r o n g A b s o r p t i o n - A cra-1  127 112 :. ,92 d  e  A e d e  153 236 l& i5i 628  135  127 110  133±  "~  262 279  w:  w  -  73 k-9 316 3k0 69 51  521 539  131+  116± 92 76 70 663 687 703 709 91 78 71 h8 127 I l k  VW-7  vvw W  ~*  153  116 k%  90 299  73 k-3  80  VVW vvw  w  vw  a  V cra-1 0-0  + 4 cm~l  9  MS  389  vvS  590 S 779 MS  c.  Lines  25  14,7  70  85 133  21 h7 75 95 k l O k36 k6k k8k 26 73 97 616 663 687 19 kk 78 92 798 823 857 871 23 k6 7k 92 S  MW  w  W  132 521 -  H4-6  178  l k 2 16k 177  531  -  553  1391' l k 7 f 162 176 918 926 9 k l 955 135 1^5 163 177 VW  VW  VW  a.  t h e c e n t e r s o f t h e s t r u c t u r e : t h e o r i g i n and ag fundamentals  b.  average energy d i f f e r e n c e from  c.  s : s t r o n g , MW: medium weak, W: weak, VW: v e r y weak, VVW: v e r y v e r y weak, MS: medium s t r o n g , VVS: v e r y v e r y  566  -  strong  d.  t h i s r o w shows t h e d i f f e r e n c e o f e n e r g y v a l u e f r o m V» i n cm"*-*-  e.  this  r o w shows t h e d i f f e r e n c e o f e n e r g y v a l u e f r o m t h e o r i g i n  i n cm~l  W  4§ Another p o s s i b i l i t y which must he c o n s i d e r e d i s t h e f o r m a t i o n o f c l a t h r a t e compounds.  I t has a l r e a d y been sug-  gested by C i a i s (48) and S h p o l ' s k i i (49) t h a t s a t u r a t e d normal p a r a f f i n molecules form a cage about the s o l u t e molecule.  Evidence f a v o u r i n g t h i s p o i n t of view i s found i n  the f o l l o w i n g experiment ( 5 0 ) .  3.4 - benzpyrene i n c y c l o -  hexane gave a d i f f u s e spectrum a t 77°K. n - o c t a n e was  A d d i t i o n o f 10%  s u f f i c i e n t t o p r o d u c e t h e sharp s p e c t r u m a t  77°K t y p i c a l of the S h p o l ' s k i i e f f e c t .  I f the assumption  i s t r u e t h a t c l a t h r a t e compounds a r e formed, t h e n the molecule may undergo f r e e or h i n d e r e d r o t a t i o n .  This allows  an a l t e r n a t e e x p l a n a t i o n f o r the c l o s e l y spaced weak l i n e s t o the b l u e of the o r i g i n .  However t h e r e a r e c l o s e l y spaced  l i n e s of about the same i n t e n s i t y t o t h e r e d of the o r i g i n , and t o e x p l a i n the presence of t h e s e l i n e s i t i s n e c e s s a r y t o assume t h a t the molecules r o t a t e i n the ground  state.  T h i s i s not p o s s i b l e a t the low temperature used and so t h i s e x p l a n a t i o n i s not p r e f e r r e d . The s t r o n g e r l i n e s about 200 cm"  1  t o the b l u e o f  t h e o r i g i n a r e hard t o account f o r . However, i f t h e symmetry o f t h e c r y s t a l f i e l d a t t h e s i t e o c c u p i e d by the anthracene molecule i s lower t h a n t h e m o l e c u l a r p o i n t group then i n t r a m o l e c u l a r v i b r a t i o n s o t h e r than ftj o r 1>SJ modes may  appear.  The i n t e n s i t i e s o f t h e s e e x t r a l i n e s would depend on the s t r e n g t h o f the c o u p l i n g between the molecule w i t h i t s environment.  T h i s c o u p l i n g i s weak i n such a m o l e c u l a r  46  c r y s t a l and so p e r t u r b a t i o n t h e o r y may be a p p l i e d .  The  i n t e r a c t i o n s between s o l v e n t and s o l u t e molecules a r e o f two k i n d s .  There i s a m i x i n g o f e l e c t r o n i c wave f u n c t i o n s  of s o l v e n t and s o l u t e m o l e c u l e s g i v i n g r i s e t o a s o l v e n t s h i f t (20); we a r e not concerned w i t h t h i s e f f e c t here. There i s a l s o an i n t e r a c t i o n between t h e v i b r a t i o n a l s t a t e s of t h e anthracene molecule w i t h t h e v i b r a t i o n a l s t a t e s o f the environment which occurs i n t h e f o l l o w i n g way.  The  anthracene molecule i s s l i g h t l y b i g g e r i n t h e e x c i t e d s t a t e ; t h i s b e h a v i o u r has a l r e a d y been observed i n benzene (51) and naphthalene (46).  The evidence i n support o f t h i s con-  c l u s i o n i s t h a t t h e o r i g i n i s not t h e s t r o n g e s t l i n e i n t h e spectrum, r a t h e r t h e l i n e a t 1399 cm"  1  i s . That i s , t h e  Franck-Condon o v e r l a p f a c t o r i s g r e a t e s t t o t h e e x c i t e d e l e c t r o n i c s t a t e w i t h one quantum o f t h e 1399 c m  - 1  funda-  mental and so t h e r e i s an expansion i n t h e c o r r e s p o n d i n g normal c o o r d i n a t e .  However, t h e expansion o f t h e a n t h r a -  cene molecule i s f e l t by t h e s u r r o u n d i n g  molecules,  lattice  mations r a t h e r than i n t r a m o l e c u l a r v i b r a t i o n s o f t h e s o l u t e molecule tend t o be e x c i t e d , because t h e r e s t o r i n g f o r c e s are much weaker between t h e m o l e c u l e s o f t h e l a t t i c e t h a n between t h e s t r o n g l y bonded atoms o f t h e m o l e c u l e .  Thus  t h e r e i s an i n t e r a c t i o n between t h e i n t e r n a l v i b r a t i o n s o f anthracene and l a t t i c e v i b r a t i o n s .  A p p l i c a t i o n of f i r s t  order p e r t u r b a t i o n t h e o r y l e a d s d i r e c t l y t o t h e r e s u l t t h a t t h e m i x i n g o f t h e s t a t e s i s g r e a t e s t when t h e energy s e p a r a -  4? t i o n between them i s s m a l l e s t .  But t h e f r e q u e n c i e s o f  l a t t i c e modes a r e u s u a l l y l e s s t h a n 100 c m .  Hence t h e  -1  low energy v i b r a t i o n a l s t a t e s o f anthracene w i l l be most effected.  I n t h i s way l o w energy anthracene fundamentals  of symmetry o t h e r t h a n  or  may appear.  Naphthalene  has l o w energy fundamentals o f symmetry b i j , b a j and bsu (52).  The l i n e a t 420 cm"  1  i s i n t e r p r e t e d as t h e overtone  of t h e 211 cm"" fundamental g a i n i n g i n t e n s i t y from t h e s t r o n g 1  (Xgfundamental a t 389 c m  - 1  by Fermi .resonance.  Type 1 (b) i n f l u o r e n e .  Most o f t h e l i n e s i n t h i s  spectrum can be r e a d i l y i n t e r p r e t e d i n terms o f t h e a n t h r a cene fundamentals and t h e i r c o m b i n a t i o n s .  In fluorene the  l i n e s a r e b r o a d e r than i n n-heptane even a t 4.2°K.  This  i s e s p e c i a l l y t r u e i n h i g h e r energy r e g i o n s where c l o s e l y spaced combinations have not been r e s o l v e d .  No evidence f o r  the  presence of i m p u r i t i e s ( l i k e c a r b a z o l e w h i c h i s known  to  form a s o l i d solution;: i n f l u o r e n e (40)) has been found. The a b s o r p t i o n spectrum of f l u o r e n e i t s e l f was  observed above 31000 c m . -1  W h i l e t h e d e t a i l o f t h i s spectrum  i s not u n d e r s t o o d , i t i s apparent t h a t t h e f i r s t group o f l i n e s i s polarized along C a x i s .  Thus, t h e l o w energy  t r a n s i t i o n i n fluorene i s polarized along the long axis of the  molecule. Type 2.  The l o w f r e q u e n c y i n t e r v a l s (about 25 c m ) , - 1  b u i l t on a l l s t r o n g l i n e s , a r e common t o t h e s p e c t r a i n a l l matrices. the  These a r e due t o l a t t i c e modes which c o u p l e t o  i n t e r n a l modes of anthracene as e x p l a i n e d e a r l i e r .  It  48 i s not unexpected t o f i n d t h e l a t t i c e modes o f d i f f e r e n t m o l e c u l a r c r y s t a l s b e i n g about t h e same energy, s i n c e t h e f r e q u e n c y (V) o f a v i b r a t i o n i s r e l a t e d t o t h e f o r c e cons t a n t (k) and t h e reduced mass o f t h e system (/*) by  V  (<//0*  = w  The f h r c e c o n s t a n t (k) i s d i r e c t l y r e l a t e d t o bonding between t h e m o l e c u l e s which i n t u r n i s g i v e n by t h e heat o f sublimation. are  The heats o f s u b l i m a t i o n f o r m o l e c u l a r c r y s t a l s  o f t h e same o r d e r of magnitude,  e.g. f o r f l u o r e n e (53)  i t i s 19.8 k c a l / m o l e ; b i p h e n y l ( 5 4 ) , 17.9 k e a l / m o l e ; naphthalene  ( 5 3 ) , 17.3 k c a l / m o l e ; n-octadecane  ( 5 5 ) , 36.8  kcal/mole.  No d a t a i s a v a i l a b l e f o r t h e heat o f s u b l i m a t i o n  of n-heptane but we w i l l assume t h a t i t i s about t h e same as f o r n-octadecane.  The heat o f s u b l i m a t i o n i s temperature  dependent and t h e v a l u e s g i v e n above were measured around room temperature.  I f i t i s assumed t h a t t h e h e a t s o f  s u b l i m a t i o n a t 4.20K f o r a l l t h e m a t r i c e s a r e n e a r l y e q u a l (and l a r g e r t h a n t h e room temperature v a l u e ) , t h e n we can  •9, conclude t h a t t h e f a r c e c o n s t a n t s a r e a l s o w i t h i n t h e same o r d e r o f magnitude.  Because t h e molecules c o n s i d e r e d have  about t h e same m o l e c u l a r weight ( f l u o r e n e , 166; b i p h e n y l , 154; naphthalene, 128; anthracene, 178; n-heptane, 100), t h e reduced masses of t h e systems a r e n e a r l y enough t h e same. T h e r e f o r e the f r e q u e n c i e s of t h e l a t t i c e modes should be v e r y s i m i l a r ( f l u o r e n e , 29 c m ; n-heptane, 25 c m ; -1  naphthalene  ( 3 0 ) , 26 c m ) . - 1  -1  Thus t h e s e low f r e q u e n c y  49 intervals  a r e a s s i g n e d as l a t t i c e modes.  In one sample o f anthracene i n f l u o r e n e a weak l i n e at 73 cm"  1  t o t h e r e d of the o r i g i n was observed.  t a k e n t o r e p r e s e n t t h e presence o f a ground  This i s  state.phonon.  The i n t e n s i t y o f t h i s l i n e was about one t e n t h t h a t o f t h e o r i g i n and so t h e temperature o f t h i s sample was about 50°K. The l i n e was measured i n an e a r l i e r spectrum i n which t h e c r y s t a l was cemented t o t h e h e l i u m can w i t h s i l i c o n e g r e a s e . T h i s i s f u r t h e r evidence t h a t s i l i c o n e grease p r o v i d e s poor t h e r m a l c o n t a c t a t low temperature. S h i f t of t h e O r i g i n s o f The energy o f t h e  'flf *- 7*3 t r a n s i t i o n showed a r e d  s h i f t as the m a t r i x was changed from n-hexane, biphenyl to fluorene.  n-heptane,  And a s h i f t was a l s o observed i n n-  heptane as t h e temperature was lowered as seen i n Table 5. A c c o r d i n g t o McClure (20) d i s p e r s i o n f o r c e s between host and guest m o l e c u l e s causes t h e energy s h i f t , and h i s c a l c u l a tions f o r the ' B i o " *  -  'Ag t r a n s i t i o n o f anthracene i n the  vapour phase and i n s o l i d m a t r i c e s o f naphthalene and phenanthrene  show f a i r l y good agreement w i t h experiment ( 3 0 ) .  S i n c e t h e f l u o r e n e molecule i s s l i g h t l y p o l a r , t h i s i n t e r p r e t a t i o n g i v e s r e a s o n a b l e agreement w i t h our r e s u l t .  50  BIBLIOGRAPHY  1  D.P. C r a i g and P.O. Hobbins, J . Chem. Soc. 1955. 5 3 9 .  2  S . I . Weissman, J . Chem. 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