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UBC Theses and Dissertations

Study of the 2700A absorption of molecular iodine. Mintz, Kenneth Jose 1967

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A STUDY OF THE 2700A ABSORPTION OF MOLECULAR  IODINE  toy  KENNETH JOSE MINTZ B . S c . ( H o n . ) , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1965  A THESIS SUBMITTED IN'PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE 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 a s c o n f o r m i n g required standard  t o the  THE UNIVERSITY OF B R I T I S H COLUMBIA DECEMBER,  1967  In  presenting  advanced  Library  agree  this  degree  shall  that  purposes  at  make  the  be  tatives.  It  financial  gain  University  for  granted  is understood  shall  not  gcW  of  be  the  Head  that  //  /9  British  allowed  Columbia  /?  for  of  my  the  of  this  Department  or  without  requirements  Columbia,  reference  copying  copying  nf  .  f u l f i l m e n t of  available  extensive  by  The U n i v e r s i t y of B r i t i s h V a n c o u v e r 8, Canada  Date  in p a r t i a l  i t freely  permission  may  Department  thesis  and  study.  thesis  or  publication  my  I agree  written  by  of  for  that  I  the  further  for  scholarly  his  represen-  this  thesis  permission.  an  for  ii  ABSTRACT  A weak a b s o r p t i o n by  earlier  i n iodine  t o t h e d i m e r I4.  The u l t r a v i o l e t  of  iodine  on  a more q u a n t i t a t i v e b a s i s .  v a p o u r was r e i n v e s t i g a t e d  c o e f f i c i e n t s have been  concentration  of iodine  broadening).  The e x t i n c t i o n  5  -  2  t o 10  M), p r e s s u r e  f o r the usual  strength  temperature  continmim  (maximum  2694±  4.98 ± . 05 x 1 0 ~ ) must 4  due t o a t r a n s i t i o n i n -the f r e e m o l e c u l e t o a 2 2  repulsive  state  ?  c o r r e l a t i n g with  either  +  ^3/2  2 P3/2 "'"  upper  state  p  l / 2 atoms. involved  The i d e n t i f i c a t i o n  of the  and o f t h e mechanism  allowing  t r a n s i t i o n t o o c c u r were n o t p o s s i b l e  with the  available of  (10  The absorption  3 A; o s c i l l a t o r  the  study  an i n e r t g a s (up t o 1 a t m ) , and t e m p e r a t u r e  (25°C t o 2 2 0 ° C , e x c e p t  or  in this  spectrum  f o u n d t o be independent, o f -  be  reported  w o r k e r s t o n o t obey B e e r ' s Law, and was  attributed  of  v a p o u r was  evidence.  The p r e v i o u s  identification  I4 i n s o l u t i o n and o f .Br4 i n t h e v a p o u r phase',  d e t e r m i n e d by s i m i l a r u l t r a v i o l e t discussed  continua,  are  i n relat.ion to the lack of evidence f o r  1. i n t h e v a p o u r p h a s e  found  in this  study.  i i i  TABLE OF CONTENTS  INTRODUCTION E l e c t r o n i c A b s o r p t i o n Spectrum p f Iodine Vapour... 2700A Continuum o f Iodine Vapour . . Iodine i n S o l u t i o n . Purpose o f t h i s Study  EXPERIMENTAL Optical Cells Chemical s Spectroscopy Slit-width Corrections Measurement o f C o n c e n t r a t i o n . . . „  RESULTS V i s i b l e Spectrum 2700A Continuum  DISCUSSION I n t e r p r e t a t i o n o f the 2700A Continuum. Comparison w i t h S o l u t i o n . . . Comparison w i t h Bromine  BIBLIOGRAPHY  Page 1 4 6 .9  ......10 13 . .14 17 .....20  23 ...32  44 52 58 . 62  iv TABLE O F FIGURES  1.  The V i s i b l e  Absorption  2.  Log Absorbance v e r s u s Absorption  Spectrum o f I o d i n e Vapour x  3.  4.  {  v  - v„  )  2  . . f o r the V i s i b l e 30  Absorbance versus Absorbance Spectrum The U l t r a v i o l e t  a t 4400A f o r t h e V i s i b l e 33  Spectrum o f I o d i n e Vapour  5 6. Absorbance 63°C  i n the U l t r a v i o l e t ..  versus  7,8. A b s o r b a n c e  i n the U l t r a v i o l e t  versus  f  Concentration  Coefficient  10. C o n s t r u c t i o n o f P o t e n t i a l  Concentration  Coefficient  versus  Energy Diagram  versus  at  C o n c e n t r a t i o n . . . 40  Energy Curve.,  12. D i f f e r e n c e b e t w e e n U l t r a v i o l e t at D i f f e r e n t Concentrations... 13. P o t e n t i a l  at  .39a,b  Apparent E x t i n c t i o n  11. E x t i n c t i o n  ....35  37, 38  220°C 9.  Page 24  Concentration Spectra  43 ,.46  Measured  of Iodine......  47 .53  V  ACKNOWLEDGMENTS  The to  author  D r . E . A. O g r y z l o  direction  The to  wishes  o f this  author  assistance  during  h i ssincere  f o rh i s p a t i e n t  and  gratitude  knowledgeable  research.  would  D r . A. V . B r e e  t o express  also  like  ' a n d D r . D.  t o express  P. C h o n g  Dr. Ogryzlo's  h i s appreciati  f o radvice and  Sabbatical  Leave.  - 1 INTRODUCTION  The and  absorption  i n solution  early  days  spectrum by  now,  spectrum  has been  of iodine  extensively  o f spectroscopy„  encompassing well  The  the near  understood  mainly  i n the gas  studied  low-energy  infrared due  phase  since  the  electronic  and v i s i b l e a r e ,  t o the  theoretical  1—3  studies s t i l l  by Mullikerio '  disagreement  ultraviolet with  spectrum„  A  a t about b r i e f  iodine  absorption  a r e most  continuum  o f the apparent  with i t s  o  o f the electronic  w i l l  there i s  the interpretation  Contradictions  2700A  survey  vapour  the other hand,  regarding  r e s p e c t t o a weak  maximum  of  On  be  presented  absorption  f i r s t  spectrum  f o r background  information.  (a)  Near  Infrared.  Brown^ system .its  maximum  Rees^, of  from  this  has observed 9300  t o 8360A,  a t 7 320A  1  cm*"  1  leading  a t 50°C  continuum  30 1 m o l e "  and analyzed a v e r y  o  to a  continuum  with  According t o Mathieson  h a s i t s maximum  a t 6950A  weak'band  a t 120°C.  extinction This  and  coefficient  system  has  been  assigned (b)  t o the A  3  violet  1  colour,  with  the continuum  7500A  rotational  partially  transition. ' ' '  +  3  4  5  absorption  extending  structure by  by  l a t e r workers by to broaden  There  at  used.  the l i n e s .  and  at a l . ^  because  1  i s no  cm"  This  g i v e n by  coefficients  a maximum e x t i n c t i o n 1  a t about  doubt  that  t o the B TT(0 +) 3  i s some q u e s t i o n  u  was  pressure  5200A a t  the band X  eliminated o f an  Wood range  coefficient 20°C.  system  i s due  transition.  about a possible  underlying  +  (0  i n the  inert  )  1  £  100%  lines  ft R a b i n o w i t c h and  '  early  of nearly  error  a high 7  4990A,  been r e s o l v e d  coefficients  using  finding  1 mole"  entirely  limit  4000A.  partly  have p r e s e n t e d e x t i n c t i o n  There  ranging  a t t h e maxima o f t h e r o t a t i o n a l  the low pressures  820  has  bands  down t o a b o u t  Steinfeld  i n error,  at  4400-6000A,  i t s characteristic  of discrete  of extinction  w o r k e r s were  iodine  to i t s convergence  analyzed  Values  gives  consists  about  of  +  u  system, which  from  gas  (l )<&-X 5 : ( 0 g )  Visible This  The  TT  + g  7  continuum,  however.  3  3  Mulliken  has  extrapolation  o f the c h l o r i n e and  spectra,  the  would  that  of  it.  and  more (c)  2  with  an  that  absorption  u'^  ^  a  r  e  e  +  (°  e  c  g  +  of l e s s than  t e d  t o be  )  X  states i n this P  x  g  o f t h e B <&•  intensity  from  1%  region  much  forbidden. Ultraviolet Various  from  about  can be  weak d i s c r e t e b a n d s h a v e b e e n  3500A  to shorter wavelengths.  observed only  200°C., b u t w i t h toward' l o n g e r converge  below  wavelengths  until  high  (d)  These bands and  vibrational  Vacuum  Iodine  bands  they  at  they  3413A.^  levels  have been  the  reported  "continuum"  of the ground  below  spread  This  a series of overlapping  extinction coefficients  system.  These  a t 1 1 0 0 °C  continuum  i s actually  reported  2200A a t t e m p e r a t u r e s  i n c r e a s i n g temperature  to. an'apparent  "continuum" No  x l  Transitions to other  ( ^TT (Ou,  bromine  transitionVrdu) ^  h a v e a maximum n e a r  transition  estimated,  must  bands.  for  this  involve  state.  Ultraviolet  vapour  2000A  to shorter  about  1850A.  shows s t r o n g banded  wavelengths  Cordes ^ 1  rising  measured  absorption  t o a maximum  from at  a l a r g e number o f b a n d s  i n the  range  1950-1540A  These  bands  may  u l t r a v i o l e t Cordes,  1  i s a  be  bands  low  and  temperatures  part  of  the  discussed  Mulliken,  0  Mathieson i t  at  Psees,  2  5  same  above  and  system  as  Nobs  and  Venkateswarlu  system  and  as  the  suggested  and  separate band  and  pressures.  Wieland. 1  2  analyze  1  weak  by  However,  1  claim  that  i t on  that  basis.  2700A  The  Continuum  of  Iodine  Vapour  13 Butkow f i r s t  to  and  Wojchiechowska  observe  that  i t d i d not  have  measured  this obey  the  absorption Beer s  extinction  concentrations  confirmed  that  with  increasing  absorption  was  dimer  They  at was  I^.  different actually  maximum was  of  iodine  extinction  to  a  d i d not  reported  and  and  attempt  observe  to  determine or  not-  2670A by  both  They increased  postulated  to  that  the  the  the  spectrum  whether The  note  three  3 4 0 °C.  coefficients  to  Friedheim  for  involving  complex as  at  the  and  transition  temperatures a bound  Kortum  coefficients  concentration due  continuum  Law.  1  different  the  a p p a r e n t l y were  the  I4  absorption  groups  of  workers. Sumner^  also  observed  the  2700A  continuum  but  at  -  5 -  somewhat lower temperatures. vapour and t h e r e f o r e was  He used  unable to change the  c o n c e n t r a t i o n independently o f the The absorbance  saturated  a t 2700A was  temperature.  then found to be  p r o p o r t i o n a l to between the f i r s t and second power o f the c o n c e n t r a t i o n .  (It should be noted t h a t i n  h i s experiments h i g h e r c o n c e n t r a t i o n a l s o corresponded to h i g h e r temperature.)  Since the absorbances were  measured a t d i f f e r e n t temperatures, he assumed t h a t the absorbance was  a c t u a l l y p r o p o r t i o n a l to the  square o f the c o n c e n t r a t i o n , and the d e v i a t i o n the square dependency was I4  due t o the d i s s o c i a t i o n o f  a t h i g h e r temperatures.  bond energy f o r I  4  o f 6.2  from  T h i s method y i e l d e d a Kcal/moie.  However,  Sumner a l s o obtained evidence which seemed t o contradict h i s hypothesis.  A f t e r h e a t i n g the i o d i n e  above i t s b o i l i n g p o i n t , the 2700A continuum  d i d not  change upon f u r t h e r h e a t i n g up to the maximum temperature o b t a i n e d (380 t h i s l a s t e f f e c t was McConnell continuum  1 6  i s due  °C).  No e x p l a n a t i o n o f  given.  has suggested t h a t the 2700A to a t r a n s i t i o n  in a  "self-  i n t e r m o l e c u l a r c h a r g e - t r a n s f e r complex with the  formula  I4."  The  charge-transfer various gas  1  and  7  existence  donors  observed  i n the  equation  given  that  charge-transfer  same  at  rules  as  phase  into  the  by  absorption  ultraviolet.  the  experimental  on  the  work, weak  claimed  Iodine  to  some  brown  hand,  Kortum  that  I4  of  w i l l  free  1  I4  be  follow  i n  s l i g h t l y  the  further  value  for  well  and  with  Friedheim.  Rees,  Friedheim's  the  This  reasonably;  Kortum  predicts  8  should  i n solution;  absorption  i n the  P i a t t  M a t h i e s o n and and  the  external  of  are  again  semiquantitative  arises  from  molecule which  a  i s  very extremely  perturbations.  i n Solution,  Iodine, in  of  transition  sensitive  results  and  predicted  maximum, a g r e e s  other  the b a s i s  would  The  absorption  complexes.)  f o r I4  i n both  semi-empirical  absorption  donor  i s actually  absorption  A  (assuming  and  transitions  M c C o n n e l l , Ham  2820A  the  On  Unique  8  ultraviolet.  iodine  the  1  iodine  established  charge-transfer  about  prediction gas  to  intermolecular  between  i n s o l u t i o n .  due  occur  of  i s well  continua  the  -  complexes  electron  phase  6  as  solvents  colour  i s well and  known,  brown  i s usually  forms  solutions  attributed to  v i o l e t  solutions  i n others. 1:1  The  complexes  -  of  iodine  yield  with  violet  carbon  the  solutions  solvents,  closely  resembles that  and  solvent  Doubt  has  been  found  ultraviolet  n-heptane  iodine,  and  was  due  between spectrum closely  iodine  as  and the  iodine  was  truly  of that  iodine of  to  iodine  an  a weak  or  gaseous  the  that  solvent  may  s t i l l  complexes  with  iodine,  and  have  different  ultraviolet  spectrum  form a  from  of  v i s i b l e resembles  "violet" charge-transfer  considerably that  of  gaseous  iodine.  Evans  19  • also  found a  low  an  complex  i f the  ( i . e . a  solvent),  towards  below  particular solvent iodine  ether.  existence  c o l l i s i o n a l Even  i n  solvents:  transition  n-heptane. i n a  dissolved  inert solvent  indicate  by  between  di-perfluorohexyl  charge-transfer  and  interpretation  fluorinated  and  able  this  d e f i n i t e difference  i n two  to either  iodine  on  (PFH)  PFH  intermolecular 2 6 0 0 A  gaseous  to  spectrum  i s formed between  cast a  that  that he  hydrocarbons,  referred  the v i s i b l e of  that  aliphatic  usually  spectrum of  perfluoroheptane Assuming  as  solvents  molecules.  E v a n s . H e the  since  complex  The  (such are  "inert"  no  -  solvents.  tetrachloride)  presumably  7  absorption  maximum  - 8 at  about  and  a  2800A  smaller  n-heptane. and  maximum  Both  nearly  were  to  Keefer  Allen  i n carbon  dissolved 2850A  the  I4  20  proven  i n  obey  chloroform.  and  deMaine  the existence  the  the  £ € K  The  n-hexane, The  of  two  the  dimer  deMaine  and  are  extinction C  a  p  c-hexane,  i n f a i r l y Both  2  good  +  2  i n  agreement  decompose  0 )  and  dissolved  the  coefficient, £  =  p  include  according  £ K(l ) 4  apparent  2  2  2  i s  the  extinction  coefficient  of  I2  4  i s  the  extinction  coefficient  of  I4  i s  the  equilibrium  extinction  close  have  to  f o r iodine  workers.  molar  work  n-heptane,  results  equation:  where:  21  deMaine,  extended this  tetrachloride  (observed) to  These  dimer.  tetrachloride.  have  solvents  between  Law  -  McAlonie '  carbon  i n  Beer's  d i l u t i o n .  22  as  chloroform  f o r iodine  d i d not  a t high  attributed  and  at  peaks  vanished  independently 14  for iodine  coefficients  of  I2  constant  and  1^  I4  have  maxima  together:  Keefer  and  A l l e n  2  0  :  €  a  t  2  2800A,  £  4  at  2880A;  2775A,  £  4  a t  2925A.  21 deMaine  :  ^  a t  -  The  decrease  was  interpreted  (I4) The be  as opposed heat  1  -  Purpose  The region as  a  This at  with  4  increasing  as evidence  f o r a hound  to a colliding  pair  species  of molecules. calculated  2 Kcal/mole,  the  of this  depending  on  extinction c o e f f i c i e n t s i n the of iodine  function should  vapour  vapour  a r e t o be  of concentration  c l a r i f y  the nature  I t should phase degree  then  solvent.  spectrum  with  of certainty.  some  i n t e r e s t t o determine as w e l l  as  ultraviolet  determined  and  of the  transition to  correlate  the solution I t i s also  whether  i n various  accurately  temperature.  be possible  some  gas phase  t o  Study  with  the  temperature  o f d i s s o c i a t i o n o f I4 w a s  2700A.  the  i n K £  9 -  I4  spectra of  exists i n  solvents.  - 10  -  EXPERIMENTAL  Optical  Cells.  The weak.  2700A  In  where  order  iodine  sufficient three  part  of  of  has  path  exact the  through  a  fused  graded s i l i c a  s i l i c a  under  vacuum.  in  could  order  be  to  convection  onto  a  length  c e l l  on  tubing.  earlier  when  c e l l , two the  entire  the  inner  used  s t i l l  have  results,  a  The  c e l l  a  at  a  v/indows  5  then  cm. sealed  First,  optical  windows.  these  length  onto  purposes. inner  joined  short  v/as  major  the  windows  constant prevented Therefore,  windows,  thus  measurements.  fused  However,  ultraviolet  a  which  double  on  and  tube  blown  absorption  tube.  pyrex  was  condense  c e l l  a  This  the  very  temperatures  cm.  to  beyond  with  298.5  end  heated  i s  constructed.  each  achieved  the  low  accurate  was  of  at  above,  pressure,  was  This  not  work  obtain  consisted  cooling of  pyrex  to  length  seal  mentioned  vapour to  Secondly,  could  fluoresce  able  low  maintain  interfering  An  a  as  spectroscopic  temperature.  iodine  be  path  c e l l  fused  c e l l  to  absorbance  meter  The  continuum,  the  light  s i l i c a cement was  windows  cemented  appeared  shone  on  to  i t ; also  the  cement  iodine. could  discoloured  Therefore,  n o t be  An  inlet  leak up  heating  Tygon  for  a  from  absorbing during  the  tubing  vacuum  t h e vacuum tygon  t o be  the c e l l ,  concentration pumping to  a s was  whose  containing  this  c e l l  Iodine  never  new  t h e stem  i t d i d not (lasting  occurred  between  Flexible  the needle  valve  tubing  used  the alignment  and also  quickly.  Iodine  i n the c e l l inert  absorption  v/as b e i n g  the the  c e l l  discoloured i t was  was n o t c o n t a m i n a t e d  introduced  the tygon  was used.  with  Therefore,  the c e l l  tubing  was  t o isolate  was a l w a y s  When  results  •  t o connect  through  o f iodine  vapour,  reaction  vibrations.  rather  Although  o f a  shown b y r e p r o d u c i b l e  system.  easier,  consisted  o f measurements  the c e l l .  o u t some o f i t .  the c e l l ,  iodine  chemical  certain that  any impurity.  into  series  t o make  pump  tubing  a  valve.  iodine  was used  connection  necessary by  No  and cooling  spectrophotometer from  using  i n the cell  needle  and iodine  small  this  midway  teflon  few days).  teflon  with  r e s u l t s obtained  about  appreciably  t o a  the on  pink  the c e l l  used.  Fischer-Porter turned  upon h e a t i n g  directly  tubing.  The  was changed gases  were  Therefore, studied  by added  the  a t any  time  -  had  never  and  the  been  12  -  i n contact with  p o s s i b i l i t y  of  the  tygon  tubing,  contamination of  the  sample  was  eliminated.  The and  c e l l  thus  prevent  length.  of  c e l l ,  and  more  wrapped  volt  The  onto  model  50°C),  glass  temperature  for  c e l l  the  middle.  between be  the  the c e l l .  for insulation  for heating  A  voltage  from  applied  through  the  up  c e l l  up  to  was  At  to  160  the  1  yielded  °C.  t h e r e was  ends  up  to  On a  a  65  few  f o r the  are  those  middle  maintained  and at  as  °C,  °C).  at  ends.  In  constant  other  degrees high  measured  various  cemented (below  same  temperature  Temperatures given  the  were  nichrome  measured  the  the  a  lower.temperatures  thermocouples  to A  asbestos  the  about  c e l l  wire  for temperatures  tubing.  within  with  measurements  the  path  nichrome  c e l l .  of  reflections  optical  around  along  temperatures  temperatures  the  could  model  eliminate  copper-constantin thermocouples  a l l the  higher  of  the  temperature  using  the  layers  around  volt  wrapped  variations  paper,  to  i n effective  was  t r a n s f o r m e r v/as  (120  places  error  f o i l  asbestos  variable  240  an  temperature  layer  wire  painted black  Aluminum  prevent  then  was  h a n d , at drop  along  warmer  than  temperature half-way  a l lcases, conditions  the for  c e l l as  long  as  necessary  For ments,  a  because to  higher  measure  constructed was  to  had  vacuum. as  case,  a  The. the  cell  A  concentration by the  amount  of  had  three meter  c e l l .  purposes,  The  was  be  11.8  cm.  c e l l ,  made  entirely  c e l l was  sidearm  was  left  varied  at  temperature insulation  on  one  -heated  i n  of  the  i n  c e l l  constant sidearm  this  fused  being  unwrapped  the  c e l l  of  described above.  sealed  high  spectrophotometer  outer  and  too  Originally  14  the  used  r e g i o n was  Cary  wrapped  c o u l d be  this  to  the  jacket,  iodine  v a r y i n g the  c o n c e n t r a t i o n measure-  2700A  three meter  small  and  the  double  however,  vacuum.  i n  f i tinto  compartment.  s i l i c a ,  way  the  hours).  length cell  for other  designed  c e l l  path  absorbance i n  two  temperature  shorter the  (about  the  a same  In  this  under and  the  temperature by  varying  sidearm.  Chemicals.  Mallinkrodt iodine of  was  used  impurities  1008  resublimed  in a l l e x p e r i m e n t s .  specified  Br-0.005%,  nonvolatile  absorption  measurements  on  phase,  the  gas  analytical  by  the  matter i n  -  this  nonvolatile  reagent  The  maximum  supplier  are:-CI  0.10%. work  and  Since a l l  were  impurities  limits  carried are  out  unimportant.  -  Therefore,  no  1 4  -  further purification  degassing  the  s o l i d , v/as  nitrogen,  oxygen  and  carried  carbon  other  out.  than  Commercial  d i o x i d e were  used  grade  without.  p u r i f i c a t i o n .  Spectroscopy.  Since f i t  into  beam be  the  the  long  c e l l  path  length  compartment  spectrophotometer,  used.  involved  A  This  was  more  of  a  c e l l  of  any  course  less  not  double-  instrument  convenient  to  had  to  use  and  calculations.  Beckmann  DU  spectrophotometer  The  electronics  p h o t o m u l t i p l i e r tubes  and  c e l l  compartment  v/as  used  and  the  were  only  as  a  original  removed  from  instrument.  A  holder  constructed the  exit  power  for  and  s l i t .  supply  v/as  The  current a  a  RCA  IP28  attached A  photomultiplier  by  could  automatic  single-beam  monochromator.  the  obviously  to  Kepco used  apply  (900  produced  by  the  monochromator  regulated  to  tube.  p h o t o m u l t i p l i e r tube  the  a  voltage  volts  necessary  v/ere to  small use  (10~^  very  to  short  gave  against  voltage  to  optimum  10  Since ^  leads  amp.), to  the i t  DC  the  p h o t o m u l t i p l i e r v/as  K e i t h l e y micromicroammeter.  produced  variable  was  conditions). measured  currents was  eliminate  stray  - 15  -  currents.  The for  the  light  sources  v i s i b l e  region  hydrogen  lamp  region.  A  keep  the  light  The  monochromator  pressure the  wavelength  The  DU  c e l l  the (I ) Q  were the  made  or  The  2000A  (as  by of  the  c e l l  calculated  eliminate of  of  I  the  the  the D  The  accuracy  absorbances  of  depending  the  on  tolerance  and  current  transmitted  by  iodine  equation: the  A  whole of  a  varies factors:  at =  the  under  concentration  absorbance  i n  i n  the  (I)  each log  .  spectrum change  intensity  photomultiplier  three  given  by  emission  of  low  measured  p o s s i b i l i t y  c e l l ,  a  6000A.  over  sensitivity  wavelength,  using  to  to  at  -The  by  used  6A  temperature  separately.  ultraviolet  constant.  containing  transmittance  lamps  at  was  lamp  Beckmann  instructions  manual.  light  remeasurements to  calibrated  the  the  and  measured  Frequent  for  tube)  must  was  of  and  lamps  to  tungsten  photomultiplier  conditions  wavelength  supply)  according  1A  small  spectrum,  these  was  from  varying be  a  transformer  instruction  ranges  by  from  lamp  intensity  produced  the  voltage  output  mercury  of  were  i t s power  constant  Beckmann  empty  (with  used  i n of.the  -tube.  considerably emission  of  with  - 16 -  the  lamp  used,  dispersion was  used  between in.a  region  0  The of  which  of  the  the  absorbs  rises  very  region  wavelength  range  6000-2500A,  compressed),  there  due  to  a  at  2200A.  i s changing i n the  w i l l slight  be  an  absorbance and  Under  rapidly  v i s i b l e an  0.008  7000-2200A.  0.02,  absorbance  lamp  slightly.  i s about  about  at wavelength  lamp  some, o v e r l a p  to  1.0  the  hydrogen  only  wavelength  and  tungsten  allowed  i n absorbances  (especially  uncertainty  The  3400A; This  iodine  i n the  uncertainty  v/avelength is  where  i n the  and  2100A.  uncertainty  absorbance in  7000  and  absorbance  2.5  response,  the monochromator.  between. 4000  The at  of  photomultiplier  where  increase  uncertainty  at  an  conditions  with the  of  spectrum  the  i n the v/avelength  position.  As  mentioned  recording  above  operating  This  instrument yields  only the  the  at higher  number  necessary to empty  Cary  s p e c t r o p h o t o m e t e r v/as  c e l l  reducing  the  t  c e l l  14 used  f o r the  temperatures  absorbances  subtract to  o f f the obtain  and  involved. absorbance  the  smaller  pressures.  directly,  of. c a l c u l a t i o n s  i n order  double-beam  iodine  therefore I t v/as due  to  spectrum.  -  According  to  17  the  -  manufacturer,  the  accuracy  + ranges to  -  from  .008  -  at  .002 2.0  measured  on  slippage  and  by  0.005  about  Slit-Width  A  absorbance  absorbance  this  instrument).  contractions  width  of  0.4  using  This  narrowest  the  have  the  sufficient  photomultiplier  tube  different  absorbances  concentrations  of  in to  Errors the  across for  the  A(X)=  the  due  s l i t  true  log  the  can  chart this  of  the  rather  _ |  the  be  paper  error  could  used  the  and  the accurate  width  considerably  gave  (when but  measure  high  only  ultraviolet.  i t was  of  reasonably  to  true  be on  v i s i b l e  the  most  spectrophotometer.  were' u s e d ) ,  Since  the  obviously  s l i g h t l y the  concentration  of  prime  absorbances.  finite  light than  s l i t  width  distribution  the  slope.  depend curve  The  equation  i s :  f oi\)- K F  o g  s l i t  a  for  intensity  used  using  absorbance  f<j> (\)\ 0  i n  c e l l ,  to  curvature the  i n  used  that  yield  i n  was  know  was  s l i t  iodine  absorption  iodine  that  increase  Beckmann  the  absorbances  importance  on  of  mm.  to  Increasing  v i s i b l e  absorbance  units.  light  results.  different  0  maximum  Errors  w i l l  absorbance  measurements  s t i l l  (the  at  Correction.  s l i t  was  units  L\ F (\) 2  0  +  L A , F ( \ , + ... 4  0  -  where:  18 -  Q refers  thesubscript  t o no sample  i n the light  beam. <J> f x )  i sthetrue  F fx)  i st h eobserved  light  i n t e n s i t y a t wavelength  K and L a r econstants  which  depend  values they K  o f t h eentrance  a r eequal,  A F 4  c  as  widths.  When  spectrophotometer,  200A  were  t h ev a l u e s  varies  2  Fa)  2  s l i t  band  width  width)  (equal  expressed  t o t h e Beckmann  f o ra mechanical a t 7000A  Since generally  -  t o one-half i n t h e same  units  X .  from  with  every  was approximated adjacent  o f 0 . 4 mm.  varied  a n d 4A a t 2000A.  \  o f light  intensity  These  were  5 0 A ( f o rc o n v e n i e n c e ) ,  wavelength, (  width  the spectral  i nthecalculations.  measurements  taken  s l i t  DU m a n u a l ,  t o 85A a t 5000A  used  A +c) a n d F  manner:  F U - c )  2  spectral  width  two  +  2  band  F  s l i t  CM = A F ( A + c ) •+ A F a - c ) - 2 A. F(X)  According  (  and exit  as a linear  measurements  and  i twas n o t p o s s i b l e  ~c) f o reach  X  .  function  ( 5 0 Ar a n g e )  x  on t h er e l a t i v e  a s i n t h e Beckmann  i sthespectral  the  F  X  i n t e n s i t y a t wavelength  = 1/12, L =1/90 £?F ( A ) - - F t t + c )  "c"  light  o f  since  t o measure  Therefore x  between  i nthe following  -  A F(X)  =A F'(X)  2  +  2  -  19  fract^){A F"(X)a  A^F'CA) = F ( X + 50 int/j^)  +  F ( X - 50 i n t f ^ ) - 2 F ( X )  A F " ( X ) = F ( X + 50 i n t f ^ H s o ) + F.(A + 50int^)+. SO) -  2f(\)  2  where:  i n t (c/50) means fract  ratio. A  thei n t e g r a l  (c/50) means X  c and similar  part  thefractional  was d e r i v e d  part  ratio  o f that  i n Angstroms a  a r e measured  equation  o f that  A  f o rthe  4  term.  F  4 It  was found  that  to  the  A  The  2  above equations  spectrum  0.4,  1 . 0 , a n d 1 . 5 mm.  considerably different  a t three  were  correct  thecorrected  within experimental  f o rs l i t - w i d t h  extrapolated  t o zero  absorbance.  This  widths,  and would  Therefore,  neglected.  absorbances  slit  absorption)  absorbances  errors. width  were for the  agreed  c a n be used  Absorbances  t o obtain require  considerably  t h e former method was u s e d .  c a n be  the true  that  a t each wavelength  involve  widths:  error.  e m p i r i c a l method  method would  i n t e n s i t y be measured  compared  tested by measuring the  The u n c o r r e c t e d  widths;  small  d i f f e r e n t (mechanical) s l i t  An a l t e r n a t e p u r e l y to  i t was  d i f f e r e n t ( f o rt h e v i s i b l e  slit  other  F term was v e r y  Fterrn; t h e r e f o r e  same  each  A  the  the'light  a t a few s l i t  more  work.  with  -  The  Cary  resolution The  width  Beckmann  for  i n  the  square  of  means  iodine  obeys c,  of  the  measurements  The  be  of  Since  better  Beckmann  that  that  s l i t  no  Cary  in  this  the  used  width  DU.  spectral with  the  errors  depend  c o r r e c t i o n s were  necessary  spectrophotometer.  study  spectroscopic. Law  between  determined  A  i s  the  £  i s the  length.  Since  5000  from  to  and  this  measure  the  the  v i s i b l e  4000A,  7  '"  14  the  concentration absorption concentration,  equation:  A ~ £ I absorbance molar  at  any  particular  wavelength  extinction coefficient  at  that  wave-  . I  i s the  Extinction iodine  the  the  such  1/50  width,  considerably  Concentration  C  where:  s l i t  than  set  about  using  chosen  was  Beer's  can  c o n t r o l was  5 0 0 0 A was  has  region  spectrophotometer.  Measurement  of  v i s i b l e  s l i t  at  -  spectrophotometer  the  automatic  band  on  14  20  are  optical  path  coefficients  available in  the  length.  for  the  visible  literature.  7  '  14  absorption '  23  Since  of  i t i s  -  necessary and. t h a t  that the  the  rigorously,  was  carried  Three  method  especially (2)  The  device  (3)  have  separate  there c e l l  are  accurate  indeed, obey  Beer's  the  spectrum  v i s i b l e  of  without  be  concentrations  be  vapour  very  to  in  to  measure  used  and  pressure  r i g i d  the  the  the  concentrat-  curve  temperature  be  low  c e l l  condensation, at  the  could  the  of  iodine.  control,  of  be  pressure  temperature  pressures,  of  the  i o d i n e and  the  such  a  measuring  measured measuring c e l l . necessity device  would  d i f f i c u l t i e s .  be  sealed  into  chemically.  for  each  I t would  accurately.  a  c e l l , This  different  d i f f i c u l t i e s  loss.  used  c e l l :  could  known  iodine  analyzed sample  be  temperatures.  design  could  would  the  corrosive nature  very  major  i n  require  prevent  the  later  the  higher  To  Iodine  ized, a  of  of  could  i o d i n e vapour from  at  measuring  present  iodine  would  would  Because  does  reinvestigation  pressure  directly.  of  of  determined  This  absorption  a l t e r n a t e methods  Saturated  ion  a  coefficients  out.  concentration (1)  extinction  v i s i b l e  Law  -  21  method  very  would  concentration.  transferring be  completely  the  iodine  d i f f i c u l t  to  vapourrequire Also from  measure  the low  -  22  -  The s p e c t r o s c o p i c m e t h o d was u s e d i n t h i s it  i s e a s i e s t and c a n b e u s e d w i t h  a b o u t t h e same  a t a l l t e m p e r a t u r e s and c o n c e n t r a t i o n s . most i m p o r t a n t of  factor of observing  i o d i n e v a p o u r i n t h e l i g h t beam.  tions with  adsorption  study  T h e r e a r e no  extinction coefficients.  control. culated It  values  Therefore,  o f t h e i o d i n e vapour pressure i  b e assumed a t some t e m p e r a t u r e i n o r d e r  then there  complica-  o f i o d i n e on t h e w a l l s , e t c .  o f e x t i n c t i o n c o e f f i c i e n t s can be determined. l i t e r a t u r e value  i s the  the concentration  However, s p e c t r o s c o p i c a l l y o n l y t h e r e l a t i v e  the  accuracy  Also, there  directly  because  had t o  to find the actual  Room t e m p e r a t u r e was u s e d b e c a u s e  c o u l d b e no e r r o r s i n v o l v e d w i t h  temperature  The v a l v i e s u s e d f o r t h e v a p o u r p r e s s u r e from t h e equation  were c a l 25 and F r a s e r .  given by G i l l e s p i e  i s p o s s i b l e t o d e t e r m i n e t h e c o n c e n t r a t i o n by measur-  i n g t h e absorbance a t o n l y one w a v e l e n g t h i n t h e v i s i b l e continuum. the  However, o v e r a w i d e range o f c o n c e n t r a t i o n ,  absorbance a t any p a r t i c u l a r v/avelength  w i l l , become t o o  l a r g e o r t o o s m a l l t o be .accurately measured. the  u s e o f a number o f p o i n t s w i l l  involved.  In addition,  r e d u c e t h e random e r r o r  -  23  -  RESULTS  Visible  Spectrum  Curves  (a) a n d (b) o f F i g u r e 1 show t h e a b s o r p t i o n  spectrum o f i o d i n e vapour w i t h o u t (1  atm.).  Saturated  e f f i c i e n t s represent  and w i t h a d d e d i n e r t g a s .  v a p o u r v/as u s e d : t h e e x t i n c t i o n c o an a v e r a g e o f t h r e e m e a s u r e m e n t s  at d i f f e r e n t times w i t h the 3-meter c e l l of  2 5 - 2 7  °C  2 x 10~^M). be  (corresponding During  h e l d t o with i n  a t a temperature  t o a c o n c e n t r a t i o n o f about  any one o f t h e s e 0 . 2 ° C ,  taken  spectra, the c e l l  corresponding  could  t o a maximum e r r o r  of 2 % i n the concentration o f iodine.  The t e m p e r a t u r e was  measured n o t o n l y w i t h t h e thermocouples, b u t a l s o w i t h a mercury thermometer o u t s i d e t h e c e l l being  h e l d a t room t e m p e r a t u r e ) .  agreed w i t h each o t h e r w i t h i n  ( s i n c e t h e c e l l was  The t e m p e r a t u r e s m e a s u r e d The a v e r a g e d e v i a t i o n  0 o 2 ° C .  i n e x t i n c t i o n c o e f f i c i e n t s w a s l e s s t h a n 2% i n t h e r a n g e 4 3 0 0 - 6 5 0 0 A .  The  d i f f e r e n c e between curves  6 3 5 0 - 4 9 5 0 A  (a) a n d (b) i n t h e r e g i o n  i s d u e t o more c o l l i s i o n a l  rotational lines  broadening o f the  a t the higher pressures.  i s the high pressure  spectrum,  7 8 ' curve  The " t r u e " spectrum (b).  No d i f f e r e n c e  -  was  found  (or  absorption A  3  at  ^ i u "= £  tions the  near  —  about  b y Rabinowitch  a spectrum  considerably  to  t o t h e 2 9 8 . 5  smaller  A  than  a n d Wood  that  done  good  here  into  t h ec e l l  a n d Wood  a t 20°C.  iodine  due t o transi-  respectively, o f  was found  i nc e l l  that  agreement  temperature  from  using  o f t h e  (not  shown  here).  spectra was i s probably  ( 1 2 cm. a s o p p o s e d i st h e consider-  error  w a s 2%, a n d t h a t  two d i f f e r e n t i na manner Iodine held  using  instruments.  similar t o  was  introduced  a t 19°C. The  o f t h es a t u r a t e d  container,  pre-  coefficients.  a container  t obe that  also  This  problem  their  a t room .temperature.  was assumed  here.  lengths.  was determined  a t 20°C  They  vapour  i ne x t i n c t i o n state  spectrum  andlowpressure  much m o r e ' s e r i o u s  concentration  pressure  and 2,  noticeable  i st h ehigh-pressure  t h eh i g h  difference  obtained  Their  the  between  cm).  Rabinowitch they  1  o f t h epure  (20%) d i f f e r e n c e  able  certainly 1  levels  The  due t o t h e  The shoulders  a r ealmost  ( c )i nF i g u r e  difference  due  largely  6350A.  state.  Curve  The  o r above  4950A  t r a n s i t i o n . ^  t h evibrational  ground  sented  below  and 5750A  5500  -  i s probably  6500A  ' 21 g  x  from  obtained  expected)  25  vapour a t  t h evapour  pressure  curve  given  by Baxter,  Hickey  and Holmes.  26  This  curve  i s  25 a b o u t 2% o f t h a t  within  temperature Curve efficients Wieland that  (d) i n F i g u r e calculated  (seebelow).  - 1  here  especially  Harris cm  This  curve  and W i l l a r d  a t 5200A.  This  of  of Rabinowitch  extinction  Rabinowitch  concentration  the  different  27  found  value  + o f 780- 40  1  '  and t o  and  mole  -1  at the absorption  i s within experimental  values) 7  Sulzer  maximum.  a n d Wood, b u t n o t o f  of iodine,  by  by Rabinowitch  a value  coefficient  given  co-  generally closer  obtained  coefficients  and Wood's  the  that  l i e s  the absorption  maximum  The  i n this  the extinction  the equation  than  near  1 represents  from  f o r the extinction  that  and Fraser  range.  obtained  Wood,  of Gillespie  o f iodine  have  been  ours.  vapour  used  27 t o compare  error  t o  (usually measure  the spectra of  3 halogen  molecules,  and t o d i s c u s s d i f f e r e n c e s 28  between  iodine  results  and arguments would have  the  extinction The  large  i n t h e gas phase  coefficients  this  study  careful  measurements  here  made  were  quite  here.  Some  somewhat i f  are correct.  i n extinction  and others were  t o be revised  found  discrepancies  between  and i n s o l u t i o n .  A  coefficients  unexpected. large  excess  Very o f  solid  -  iodine  was  l e f t  equilibrium was be  be  assumed  As  mentioned  equation  f o r a  molecule. curve  the  b u t no  two hours.  that  could  the extinction t o be  Sulzer  continuous  area  change  i n  There  falsify  t o come t o absorbance  does  n o t seem t o  our results  coefficients  obtained  and Wieland  have  absorption spectrum  simplifying  o f constant  days  by here  correct.  above,  Under  coefficient  about  o f error  Therefore,  w i l l  for,several  t h e vapour,  after  any source  20%.  i n the cell  with  observed  27 -  assumptions  of a  (such  as a  f o r the absorption), the  a t temperature  T  and frequency  v  derived  an  diatomic gaussian  extinction  i s given  by  equation:  where:  co  £  i s t h e fundamental  Q  m  a  x  i s  the extinction  vibrational  coefficient  frequency.  a t t h e maximum  a t  0°K Av*  i s the half-width  o f t h e absorption continuum  0°K v this  0  i s the frequency  equation,  i ti s necessary  o f t h e maximum. t o measure  According  t h e spectrum  to  a t  a t  -  only  one temperature ,  £4  and  the. f r e q u e n c y , not  cm  calculation was  to find  parameters; and Wieland  o f the v i s i b l e  o f the temperature,  above  estimated  a l l three  For iodine, Sulzer  a t 423°K  - 1  -  o f t h e maximum  independent  19,250  at  .  28  t o 18,750  f o rFigure  i  cm  , &i><?  found  that  a b s o r p t i o n v/as  but varied  from  a t 1325°K.  - 1  €™*"  For the  ( d ) ,t h e a b s o r p t i o n  by e x t r a p o l a t i o n t o be  maximum  a t 19,500  cm"  constants  i n the Sulzer-  1  (5130A)  25°C.  An  attempt  Wieland  was made  equation  closer.  that  According  t o find  would  new  f i tthe experimental  t o the equation,  results  a t any temperature  the  2 plot  of l o g €  versus  line  of slope  (AV*)  spectrum  of iodine  inert  gas).  5115-  5A.  The  experimental  in  differs  I f lines o f 2050  contrast  Wieland  This  a t 6 5 °C  I t can be  peak  widths"  .  1  seen  that  t o t h e 2060  equation.  plot  the long from  yield  i s shown  50 t o r r  obviously  a r e drawn and 2490  should  maximum was  considerably results  )  (v/ith  The a b s o r p t i o n  the  line.  ( v - *>„  CO2  added  on a  a s shown,  from  f o r a  as an  side of  wavelength  do n o t f a l l  calculated  2  to be a t  v/avelength  cm""'', r e s p e c t i v e l y , cm  straight  i n Figure  found  the short  approximately,  a  side.  straight "half-  are obtained the Sulzer-  -  Obviously, a  good  29  -  the Sulzer-Wieland  f i tof the experimental  equation  data  does  not  provide  f o r the v i s i b l e  absorption  29 of  iodine.  find  a  In contrast,  s e t o f parameters  experimental halogens. to  on  The p o o r  the p a r t i a l  vibrational in  data  Seery that  would  the v i s i b l e  .were  adequately  absorption  f i t f o r iodine  separation  levels,  and B r i t t o n  noticeable by  from  to  f i t their  spectra  i s at least  of absorption  able  of  partly  other due  the various  the presence  of  shoulders  Figure 1(b).  29 Gibson and  and B a y l i s s  B a y l i s s ^  absorption  curve  vibrational with ever, even  f o rbromine,  0  into  levels.  temperature  f o r chlorine, have  separated  c o n t r i b u t i o n s from This  of t h e absorbance  first'two involve  temperature,  vibrational  such  a  long  the  12%  a t each  levels  This  experimental  the  much  method  two variation  wavelength. closer  of the molecules  levels.  Aicken,  the f i r s t  involves measuring  iodine has i t s vibrational a t room  and Acton,  together,"  are not i n the  would  e x t r a p o l a t i o n a s t o make  How-  the  therefore results  meaningless. Since i t  absorption  continua  i s not possible t o calculate  change  shape  with  the concentration  temperature, of  iodine  2.0r  FIGURE  2:  Log  Absorbance  (a)  short  (b)  long  versus  wavelength wavelenght  (£/-£>„ side side  )  for the  Visible  Absorption  - 31 -  directly not  from  t h e absorbance  a t t h e same  efficients  temperature  had been  experimental  absorption  at different  correction  could  curve  temperature.  in  this  very  study  crude  From  of  the vibrational  be  Since  levels  w i l l  then  t o cancel  allow  It  should be  noted  a t any p a r t i c u l a r  yielded  side  population  The  Boltzmann  of the correction temperature.  a t a number  n e c e s s a r y was consistent  the relative  temperature  to use a  can be estimated  of increasing  fairly  used  equation, the  respectively.  the calculation  that  range  wavelength  maxima  the absorbance  a  correction.  the Boltzmann  the correction They  so that  of the relative  out the effect  was measured,  t o f i t the  i t v/as p o s s i b l e  vibrational  4200A,  co-  i n the absorption  the temperature  large,  using  four  4400,  each'wavelength.  iodine  Since  at.a l l t e m p e r a t u r e s  lengths at  f o rthe variation  and t h e c a l c u l a t i o n  5100, 4700,  necessary  made  t o estimate the necessary  of the f i r s t  distribution  were  t h e s h o u l d e r s p r e s e n t on t h e long  t h e peak,  to  attempts  i s  an e q u a t i o n which i s  temperatures  was n o t v e r y  of  position  into  i fthe c e l l  the extinction  The above  curve  b e made  method  at which  measured.  applicable  with  i n the v i s i b l e  o f wave-  calculated results.  concentrations  are s t i l l  accurate t o  of  about by  2%,  but the absolute  as much  Figure  3  wavelengths at  4400A  that  5%  as  at the higher  shows  a plot  i n the v i s i b l e  a t 63-  concentration  2  the v i s i b l e  C.  of  the absorbance  continuum  had been  proven  ion  used  that  was  Absorption concentrations 25°C,  160°C  photometer 14  using and  spectrophotometer.  were  obtained  plotted  2 700A  slopes  when  against  were  '  ).  cell  obtained  The  and  other  t h e 11  at different  the absorbance  which  Beer's  maximum  at  show  Lav;  concentrat-  different  temperatures:  t h e Beckmann cm.  In a l l cases,  absorbances  absorbance  vapour.  at various  t h e 3m.  various  the  i n the v i s i b l e  a t 220°C u s i n g  (with: d i f f e r e n t  cell  similar  and  Spectro-  the  straight  temperatures  at various  DU  of  lines  course)  wavelengths  at a particular  Cary  were  wavelength.  Continuum  Figure at  made  at  13  saturated  measurements were  i n error  i s consistent with  previously  of the  versus  lines  7 (as  be  temperatures.  Straight  continuum  may  various  apparent  4  shows  the u l t r a v i o l e t  temperatures.  molar  The  spectrum  vertical  extinction coefficient  axis  of  iodine  i s called  because  vapour the  these extinction  FIGURE  3:  Absorbance versus V i s i b l e Spectrum.  Absorbance  a t 4400A  f o r the  -  coefficients  have been  34  -  r e p o r t e d t o change  with  concentra-  3 4 tion."  At low temperatures,  completely  separated  temperature, overlap  curve of  because  increase  higher  lengths,  out to  peak.)  near  An  be  • i n  * cm""" ". 1  i n  each  However,  extinction  a l l too high  t h e maximum  temperature.  due t o o v e r l a p  i s no doubt  of molecules  ^crr,  1 mole  (d) may  increasing  This  coefficients  or  5%.  i s probably  at higher  since .this  increasing  i n concentration, the  (c) and  temperatures.  continuum  With  1 mole  0.2  coefficients  with  a t 220°C  percentage  i s v i r t u a l l y  absorption spreads  0.5  (d) t o about  an a d d i t i o n a l  extinction  u l t r a v i o l e t  at  (c) ,  t o decrease  peak.  of the extinction  t o about  i n curves  too low by  The  the  values  of the uncertainty  coefficients  seen  ultraviolet  (a) a r e a c c u r a t e (b) ,  any other  continuum  continuum.  realative  curves  a l l  the main  t h e 2700A  The  from  t h e 2700A  (The from  can also  over  i ti s not as noticeable.  t h e main  vibrational  increase i n the t a i l s  increase i s spread  apparent  due t o t h e decrease  i n the lowest  temperatures  can be  level  of the  be observed,  a larger  i n  but  range  o f wave-  F o r t h e change  i n shape  to  be  due  to  temperature broadening,  a s v/e b e l i e v e ,  integrated  a b s o r p t i o n must remain  within  error limits  the  The was at  absorbance  2°C.  as  the  shown  going  prove  that  these  concentrations.  from the  through  the  B e e r ' s Law  straight  the  origin  ultraviolet  6.  Quite  straight to  i s obeyed w i t h i n experimental  error  at  at  were obtained.  good  taken  seems  appears  the  region  results  i n the  f o r measurements  5 and  t o be  some d e v i a t i o n  shorter wavelengths.  i s l a r g e r because the  p h o t o m u l t i p l i e r decreases  Similar  i s true  This  There  line  random e r r o r i n t h i s of  concentration  in Figures  lines  This  above.  at various wavelengths  plotted against 63-  noted  constant.  the  rapidly  m e a s u r e d on  the  towards  Cary  14  The sensitivity  200QA.  spectrophoto-  + meter  at  fairly  220-  good  5°C  straight  somewhat more ents  were  of  a plot  sloped  shown i n F i g u r e s lines  scatter.  actually  A = £, 1 then  are  2  of  were o b t a i n e d ,  I f the  composed of  (i ) £  . T h i s  +  €  2  1 ( I  versus plot  7 and  observed linear 2  )  8.  Again,  although  extinction  and  quadratic  there  is  coefficiterms:  2  would  give  a  straight  i s shown - i n F i g u r e  9  for  three  line  -  FIGURE  5:  Absorbance a t 6 3 °C.  in  37  the  -  Ultraviolet  versus  Concentration  -  38  -  -  wavelengths. can  to  The s c a t t e r  n o t be decided  actually  be increasing £  wavelengths higher  l i m i t  certainly  cannot  quadratic  term.  than and  that  When no  stem  slight  oxygen c e l l  below  era"  2  2800A.  1  vapour  An  upper  This  a  progressively  i san upper f o ra  containing  l i m i t and  non-zero  iodine  p r e s s u r e v/as v a r i e d  a t less  between  slightly  This  v/as p r o b a b l y less  w a s made  iodine  a thigher  o f t h ep e a k  with  increasneedle  temperatures. i n concentration,  v/as o b s e r v e d  a t higher  25  i t was  due t o t h eT e f l o n  f o r t h echange  i n t h e 2700A c o n t i n u u m  appear  c a nb e e s t i m a t e d f o r  as evidence  o f t h ec e l l  absorbing  discussed  except  temperatures,  f o r a as  above.  effect  studied.  wavelength.  t h ec o n c e n t r a t i o n increased  broadening  The  -  t h eslope would  absorption,  a correction  change  mole  so that i t  B y r e f e r e n c e t o t h ev i s i b l e  temperature.  valve  However,  large  o r notthere i s  3200 a n d 2800A, w i t h  temperature  65 °C.  2  whether  shorter  be taken  i t s saturated  found ed  towards  between  upper  The  slope.  o f 100 I  2  i ss u f f i c i e n t l y  definitely  a positive  l i m i t , f o r  39 -  o f inert  About  were  each  v/as h e a t e d  g a s o n t h e 2700A c o n t i n u u m  50 t o r r  o f carbon  added  t o t h ec e l l  dioxide,  also  nitrogen, and  containing  t o 63 °C a n d t h e s p e c t r u m  was  iodine.  taken.  The  None o f  - 39a -  -  FIGURE  8:  ' Absorbance a t 2 2 0 °C.  i n  39b-  the  Ultraviolet  versus  Concentration  FIGURE 9:  Apparent E x t i n c t i o n at 220 °C.  Coefficient  versus Concentra  - 41 -  these  gases  caused  spectrum.  One  containing  excess  were  measured  atmosphere  results  present.  An  upper  iodine  obtained o f 20  used a  at 2700a  with  could  be  maximum  observed  3a.  the wavelength  than  because  this  The  of  oscillator  calculated  from f  »  .0s)x has  an  oscillator  our  work).  of  n o t be  X I0"  9  '.  strength  no a i r  true  continuum.  width  0.05  of  This  The  much  estimated  (Ip) (Inert g a s ) .  mm  corresponds  absorption  possible  to  more, e i c c u r a t e l y  o f t h e maximum.  f o r the 2700a  equation:  10  a  s l i t  Virtually  . can be  at 250ga.  the broadness  4.31  a  t h e maximum  strength  the  t o be  C.  with  1  cell  coefficients  spectrophotometer.  I t would  determine  iodine  mole^cm  when  to the  t o 63  up  ultraviolet  added  of the term  of 2.5a  width  i s at 2694^  using 1  the  extinction  appears  t h e Backmann  s p e c t r a l band  and  on  also  temperatures  limit  absorption  structure  v/as to  were  effect  o f a i r was  the e x t i n c t i o n coefficient  The No  solid  at various  identical  for  any observable  continuum  was  32  j €. c/^  The  v  visible  o f about  9.5  absorption, x  10  by  contrast  (according  to  -  If is  due  i t i s assumed  to a transition  potential  energy  transition wave  of  over  molecules  the  harmonic  the  f i r s t  on  are  plotted  Flerzberg onto upper  nearly  a  The  function  state square  functions  a t 63°C.  The  axis  taken  resultant  as curve  o f each  the vertical that  w i l l  be  In this  w i l l  reflect  the potential case,  since  the potential  straight  line.  level  (b).  only  f o r the  i s plotted  10. by  Here,  with  account  distribution  as curve  that  distribution  were used into  The  the  frequency  According  one o f these  curves  energy  of the  both energy  curve  curves curve -  the  v i b r a t i o n a l  distance.  (a) o f F i g u r e  axis  i n  i n that  the  extinction c o e f f i c i e n t s divided on  then  involved  of internuclear  wave  a t 2 700A  molecule,  the fraction o f molecules  v i b r a t i o n a l levels  i n shape, a  iodine  o f t h e upper  o s c i l l a t o r  the other  gaussian is  as  , a curve  state.  continuum  a l l v i b r a t i o n a l levels yields  the horizontal  experimental  the absorption  constructed.  times  four  calculation  -  i n the free  curve  can be  function  summed  that  42  are  to  nearly  i n this  region  O  • can  • •5=  to  > o OS  l.nternuclear FIGUP.E 1 0 :  distance  C o n s t r u c t i o n of P o t e n t i a l Energy Curve.  DISCUSSION  Interpretation  The  of  above very  in  I t does  ure,  or  quite is  2 700A  results  behaves I2.  the  much  indicate  l i k e  not  a  necessary  to  interpreted  that  "normal",  seem  concentration.  different  Continuum  t o be  2700A  although  affected  However,  by  previous  results.  To  show  the other  that  the  make  our  continuum  weak,  transition  temperature, workers  results  results  press  have  found  acceptable,  may  have  i t  been  incorrectly.  14 Kortum tion 2.6  spectrum x  that  and  10"  M)  monomer  and  extinction straight  as  at  shown  I f the  If  absorption  t o the dimer,  i n Figure  does  versus  type  However, 11  not provide.a  analysis  not  temperature  coefficients  This  of we  f o r a  good  v  (9.2 x  10~ ,  (340°C).  They  increased with were then  due  analysis made  such  was  of  of  few wavelengths.  be  the data.  A  10~  the  apparent yield by  their  a  Kortum results  straight  Therefore,  line'  this  true.  i n extinction  coefficients  3  observed  to  n o t done  a plot  x  increasing  partly  a plot  absorp5.6  4  concentration would  f i tof  appear. to  the increase  the u l t r a v i o l e t  concentrations  coefficient  line.  measured  a higher  partly  Friedheim.  does  at three  the extinction  concentration.  and  Friedheim  were  actually  due  t o the 2700A continuum, then there should be a l a r g e r  i n c r e a s e i n the e x t i n c t i o n  c o e f f i c i e n t with  concentration  at 2 700A than a t e i t h e r h i g h e r or lower wavelength. (a) o f F i g u r e 12 shows the d i f f e r e n c e c o e f f i c i e n t s between t h e s p e c t r a  i n the e x t i n c t i o n  measured by Kortum and  F r i e d h e i m a t 5.6 x 1 0 " and 9.2 x 10" M; curve 3  4  measured a t 2.6 x 10 " and 9,2 x 10" M. F i g u r e 12 t h a t  Curve  (b) that  i t i s obvious from  the i n c r e a s e i n e x t i n c t i o n  c o e f f i c i e n t s with  c o n c e n t r a t i o n i s not due t o the 2700A continuum, b u t r a t h e r to some a b s o r p t i o n f u r t h e r  There has been l i t t l e  i n t o the u l t r a v i o l e t .  quantitative  work done on the  vacuum u l t r a v i o l e t a b s o r p t i o n spectrum o f i o d i n e . and  Sullivan  54,000 cm"  1  J  Bayliss  observed the spectrum between 46,500 and  (2150 t o 1850A), and r e p o r t e d e x t i n c t i o n  coeffic-  i e n t s o f 29,000 a t 49,000 cm" , 130,000 a t 51,000 cm" , and 1  150,000 a t 53,000 cm" . 1  1  An o s c i l l a t o r s t r e n g t h o f 2.29 was  a l s o r e p o r t e d , although i t i s d i f f i c u l t was  measured s i n c e  the maximum of the peak i s beyond the l i m i t  of t h e i r measurements. 1000  t o understand how t h i s  Our e x t i n c t i o n c o e f f i c i e n t s are about  times s m a l l e r a t 2150A.  A more d e t a i l e d comparison i s  i m p o s s i b l e t o made because the temperature a t which t h e i r spectrum was taken was not s p e c i f i e d .  - 46 -  - 47 -  - 48 Grover of  and W i l l a r d  iodine  the  vapour  maximum  1849.58A. argon  1849A, and  This  increase  was  absorption  line."  that  to the  to  a t  o f  50,000  to  "pressure  the iodine  i ti s the than  coefficient  overlap  bands  i n the region  rather  i n extinction  of 100% absorption  from  between  Actually  close  o f 600 t o r r  bands  are broadened  due t o t h e i n c r e a s e d  elimination  absorption  coefficient  attributed  coefficient  a t 1849.68A  the addition  the overlap  mercury  The i n c r e a s e  just  that  line  intense  the extinction  lines  the extinction  the mercury  found  increasing  t h e 1849A  .bands.  using  measured  0  of the iodine  thus  rotational  not  They  increased  broadening  0  o f one o f t h e most  1 0  200,000.  36  of  band  individual  the  vibrational  i s probably  but also  to the  at. t h e c e n t e r s  of the  rotational  lines.  Although would  Grover  appear  Bayliss  t o be  and W i l l a r d ' s i n fair  and S u l l i v a n ,  measuring  different  were  measuring  very  band  using,  hand, s l i t  average  covered  extinction  noted  a very  narrow  were  using  several  coefficient  bands  over  coefficient  those that  Grover  t o t h e maximum  and S u l l i v a n  (10A) w h i c h  be  with  quantities.  close  i n effect,  Bayliss  agreement  i tshould  were  extinction  t h e two and  o f an  s l i t .  measured  On  absorption the other  and y i e l d e d bands.  groups  Willard  a comparatively  those  by  wide  an This  should  -  be  much  smaller  maximum.  than  were  these  authors  both  latter Grover  Sullivan's ably  measurements  Therefore,  coefficients  -  49  made  near  t h e band  B a y l i s s and S u l l i v a n ' s e x t i n c t i o n  not confirmed apparently  and W i l l a r d ' s work  by Grover  and W i l l a r d as  believe.  On  and ours,  extinction coefficients  the basis  o f  B a y l i s s and  appear  to be  consider-  too large.  An seems  interesting quite  pressure  point  possible  i n a  i s the pressure  that  similar  the Cordes  manner  broadening.  bands  I t  are affected by  to the v i s i b l e  bands.  As  shown  7 by  Rabinowitcb  not  obey  a n d Wood,  Beer's  Lav/ b e c a u s e  at  the rotational  in  the ultraviolet,  Figure Law  12, which  towards  test  atmosphere  lines,  spectrum  easily  markedly  similar  Sumner's  should  to that  results  t h e case  easily from  explained, Beer's  our hypothesis.  containing  iodine  the individual  the absorption,  o f Kortum's  possibly  i s indeed  A  The a d d i t i o n o f an  broaden  increase  do  absorption  departure  supports  b e made.  apparently  complete  can be  increasing  gas to a c e l l  a t 340 C  I f this  results  wavelengths,  of inert  thus  centers.  an  bands  of v i r t u a l l y  Kortum's  shows  could  concentration al  line  shorter  of this  the visible  can be  high  a t a low rotation-  and g i v e  concentration  explained  i n a  a  sample.  similar  -  manner.  He  used  a  absorption  the  2700A c o n t i n u u m was,  shoulder  ially tion  due  higher  shape w i t h  Sumner  found  c a n n o t be  identification  transition  does present  energy curve because  the  probable, with  this both  system.  can  occur;  underlying  to  20%  outside  only espec-  absorp-  temperature  considered  Since  temperature,  errors  a b o u t 10  either  one  absorption  on  ground 2  excited  { P^/2)  those  at too (a)  energy) 2 (1  3  3  A  £  the  upper  of  "g" are  state  some p r o b l e m s . i n the  and  quadratic his  limits  state  Because  i t would  that  the  atom.  symmetry  and  The  in  the  the  potential  investigated,  and  seem m o s t  state  2 ( P-s/^) a t o m s o r  state  the  involved  range  i s continuous,  a qualitative basis, two  low  of  i s almost l i n e a r  (rejecting  correlates  one  ground  possible  states  those which would l i e  following:  U'  +  0-u<  °u)  (o )  (c) All  the  off  error.  The  (b)  at  that  changing  subtracting  main u l t r a v i o l e t  when i t i s c o n s i d e r e d  dependency; t h i s  and  the  large  be  this  concentration.  of  to  method of  system,  may  to  -  subjective  the  a  50  u  these  states  arise The  from the iodine  electron molecule  configuration is fairly  close  to  -  Hund's types in  case of  (c)  (  symbols  brackets  J l  for  (case  -  51  -  _n_  ) -coupling.  the  states  )  probably  (c)  are  Therefore  given,  giving  a  with  both  the  better  ones  represent-  ation.  According rigorous  to  both  cases  selection rule.  (a)  and  (C),L\>%=  Therefore,  0,-  1  transitions  i s  a  to  3  A  (2 ,  3 )  U  states  U  are  forbidden.  5 Mathieson correlate do  so  and  with  i s one  Again  0  h  and  Rees  ground  of  the  0  "S^*.-o~ i s a  Y2~  £ ] « ^ 3 »  f°  r  c  a  s  suggest  state  U  atoms.  states?  rigorous ( )  e  a  that  •  A  the  The  which  state  only  one  involved  state  i s not  that  yet  w i l l  certain.  selection rule  for  case  transition  ^  (Oy)  to  must  (c)  5 i s  forbidden  that i s  although  the  either  case.  transition  rigorously forbidden  absorption A  occur  to  for  to  i n  this of  and  Rees  consider  (Q~) case  coupling  strength  (c)  coupling,  i s not  complete.  i n t e r p r e t a t i o n from the  2700A  weak  continuum  the being  ti  i n f r a r e d transition.  case  Mathieson  pure  i f the  arises  o s c i l l a t o r  comparable near  may  d i f f i c u l t y  observed  in  for  (c); therefore  This  would  be  latter  transition  expected  to  be  i s  allowed  considerably  stronger  than  Therefore, 3  either the  the  3  £  +  the p o s s i b i l i t y  £2*or  upper  3  X  (0~) that  a l  'L ( g) +  u  state  ^3/2  /J^ ) correlating with u  state  of,"the  2700A continuum  t r a n s i t i o n .  0  (a component +  ^ l/2 p  appears  a  t  o  i  n  of J-  s  s  not  unreasonable.  Figure in  13  question  dotted  shows t h e p o t e n t i a l  energy  i n r e l a t i o n t o t h e more  l i n e s  show  the.very  curve  o f the.  established  approximate  state  states.  potential  The  energy  curve  3v—> -v-  i f  the state  portion taken  were  either  o f the 0 ~  state  U  from  of a  between  t h e two c h o i c e s  (°u  at large  the potential  Because  can  a  energy  scarcity of data  '  r  a  s  internuclear  diagram  on  o  these  t  a  t  e  '  The  distance  of Steinfeld, curves,  f o r the identification  a  i s '  decision  of the  state  n o t be. made.  Comparison  As been  With  Solution  mentioned  done on  Work  i n the Introduction,  the ultraviolet  spectrum  considerable o f iodine  work  has  i n solution.  20 Of  interest especially 2.1  deMaine  i s t h e work  of Keefer  and A l l e n  I t should  be  and  22  ''  of  a l l that  of  papers  on  the iodine  deMaine  when  makes  presenting  dimer. a gross  error  the extinction  noted  throughout  a  f i r s t number  coefficients of  I4.  -  They  are  a l l a  Monomeric  The  factor  19  1  extinction  cm"  1  coefficients two-body  £ _  This  ~  better We  ( i  2  due  )  J  1  the  to  course,  only  the  a  a  value  crude  would  only  the  greater  -2  l^mole than  absorption could  arise  intensities solvent. to  solution  cm  i n  the  due  .  Since  gas the  to  100A  could  at  found  here  difference i n the and  extinction  solvent  same  the  about  become lower  shift be  upper  value  i n  i n  transition,  of  caused  the by  2.5  1  mole"'"cm"" ". 1  since  value  very  but  o f Cj.  of  £ °  limit  in  i s  solution,  any  _cc]  -  ' I - I n e r t T  2  much the  solution  at  with  difference i n  the  peak a  molecules,  important,  the  limit  induction of  from  (Solvent),  approximation  and  at of  transition  1  this  2700A  carbon  i t s maximum  value  of  upper  corresponding  from  The  2  -1  the  i n  I  £  9 20  at  - 1  iodine  collisions  previously estimated  be  phase  solvent  ha\'e  approximation  cm  1  induction of  £  higher-order  monomeric  I f the  between +  mole"  J  to  small.  of  gas  2700A.  would  ^ -4  L,  i s , of  solution  at  1  collisions  i  46  with  were  =.e l  2  too  4  coefficient  i s about  compared  2 0  mole"  i.e.. A  10  Absorption  tetrachloride 2800A,  of  54  the  transition  maximum small  going  2800A  by  the  from  perturbation  gas of  gas,  -  the  iodine  curve  molecule  o f t h e upper  internuclear be  i f  an  could  t o cause  this  on  this  be  i n t h e gas phase.  heated  would  Since  pressure be  much  markedly  could  be  would  continuum However,  inert t o iodine  of the absorption  transition,  increase  at the equilibrium  a change o f 0.02A  t h e 2700A  c e l l  energy  would  be  by  achieved  inert  a very that  gases  long  could  path  be  required.  i s , according  induced  steep  hypothesis  e f f e c t on  found  The p o t e n t i a l  shift.  inducing  high  This  i s very  of iodine:  confirmation  length  2800A  the solvent.  state  distance,  sufficient  Some  by  55 -  of iodine  to our hypothesis,  due  i n solution at to the  the extinction c o e f f i c i e n t s  with  achieved  increasing by  using  density  a cell  should  of the  which  solvent-  solvent.  compresses 38  the  solution,  similar to the cell  constructed  by  Ham.  2? deMaine dissolved spectra  i n other  of I  comparisons. intensity solvent.  has studied  2  inert  the ultraviolet solvents.  spectrum  Unfortunately,  are not of sufficient  accuracy  I f t h e above  i s correct,  of the absorption  analysis of  "1' " s h o u l d 2  of h i s  t o make  vary  iodine  any  the with  the  -  Dimeric  evidence  rate,  there  transition in  seems i s  about  wavelength  a  molecule,  to  the  same  be  a  2880A.  transition,  but  i s  Introduction).  ,2  .,  1  -2  -1  than  1000 the  iodine are  zt>  molecules  solvent  a  K  could  a  coincidence to  that  has  the  "free"  they  transition  are  due  cannot  charge-transfer  determined  (see  to  ( i . e .  be  small  C^K.  Since  would  appear  £ K  =  4  2000  .  e f f e c t i v e at the  dimer  inducing  and  iodine An  Therefore the  a  and  iodine  perturbation  inducing  the  to  be  to  direct  transition  the  at  transition  i n t e r a c t i o n s between  nature.  stronger  at  be  >  iodine  the  due  at  transition.  i s believed  20,21,  molecule.  effectiveness  1^  which  close  that  induced  "E^K"  d i f f e r e n t in  cause  an  However in  the  the  solution,  complex  probable  so,  c  more  solvent.  w i l l a  at  of  therefore  d  „,.<>  times  somewhat  dimer w i l l  cm  n  1^  in  self-intermolecular  only  a  that  and  quite I f  However,  ^ 2 ^ '  mole  least  the  <  bound  peak  simply  Experimentally  <  this  transition. or  clear  Because  i t seems  simultaneous  I  fairly  weakly  between  iodine  ( 4)  -  Absorption  The any  56  two  solvent  molecule  in  i t s 'partner comparison between  the  a than of  -  dimer  and  It of gas  the  c o l l i d i n g  main  u l t r a v i o l e t  problem  i n the Only  enough  Both  the  forbidden  f o r the  much  can  and  the  to  be  i s correct,  I4 not  of  inert the  and  not  allow  should as  than  coefficient  the  upper  e x p l a i n e d i n one 1^  complex  formed  of  l i m i t  two  i n a  ways: large  observed. i n the  gas  p>hase  observed of  I ^  at  the  exists.  2800A i s  solvent  i s  necess-  occur.  the  I f p o s s i b i l i t y of  out  extinction  interaction  compressing  coefficients  spread  larger  transition  transition  Again, question.  the  I4,  that  concentrations required,  would  i s the  solution  for  and  to  effectiveness  Unfortunately, at  quadratic  being  phase  because  molecules  the  observed.  solution  i n  valid.  compare  phase).  c o n c e n t r a t i o n t o be  However,  (1)  of  gas  i n  gas  system  be  to  iodine  temperatures  to  s t r i c t l y  interest  ( i n the  high  -  i s not  of  i n solution  found  ary  of  pairs  2700A p e a k  found  (2)  be  molecules  The  (1)  solvent  would  extremely t h e  the  57  solvent  (2)  help  i s correct,  increase  great  may  a  then  markedly;  change  decide  would  the  i f be  this extinction  p o s s i b i l i t y expected.  -  58  -  We h a v e assumed above, that  i n common w i t h  C C l ^ a c t s as an " i n e r t " . s o l v e n t .  a l l other  This  authors  assumption  may  19 not be v a l i d . (PFK)  Evans  h a s shown t h a t  and d i p e r f l u o r o h e x y l e t h e r  "inert"  towards i o d i n e  hydrocarbons. iodine  This  i n PFK b e i n g  to the  more  or the p a r a f f i n  i s shown b y t h e u l t r a v i o l e t  spectrum o f  c l o s e r t o t h a t o f vapour phase 22  iodine i n chloroform  Since  deMaine  iodine  has found  has a s i m i l a r , u l t r a v i o l e t  spectrum  t h a t o f i o d i n e i n c a r b o n t e t r a c h l o r i d e , C C l ^ may n o t b e ideal  inert  solvent  f o r studying  Evans noted t h a t the a b s o r p t i o n was  slightly  but  apparently  considerable I4  are considerably  than are c h l o r o f o r m  than i s i o d i n e i n chloroform. that  perfluoroheptane  absorption  different  interest  i n the f l u o r i n a t e d solvents  i t in detail.  I t would be o f  t o determine whether t h e r e  i n these  spectrum.  o f i o d i n e i n t h e gas phase  from t h a t  d i d not study  the iodine  i s any  s o l v e n t s or whether a l l a b s o r p t i o n  o b e y s B e e r ' s Lav/ as i n the. g a s p h a s e . Comparison w i t h Bromine 39  Recently  two g r o u p s o f w o r k e r s  ly  i n d i c a t e d the existence  of  a weak a b s o r p t i o n  40 '  have  independent-  o f B r ^ i n t h e g a s p h a s e b y means  continuum  a t a b o u t 2100A:. The a p p a r e n t  extinction  coefficient  independent tration did  o f and a term  o f bromine.  not vary  was f o u n d  t o be composed o f a  linearly  . The t e r m  dependent on t h e concen-  independent  which This  term was a t t r i b u t e d would  then have  transition  eous,  of concentration  appreciably with temperature;  decreased, c o n s i d e r a b l y w i t h i n c r e a s i n g latter  term  the other  temperature.  to a transition  a bond energy  The  i n t h e B r ^ dimer,  o f about  was n o t i d e n t i f i e d ,  term  2  Kcal/mole.  b u t must be a s i m u l t a n -  charge-transfer, or induced  transition.  39 According Br^  t o Ogryzlo  has a d e f i n i t e  and S a n c t u a r y ,  t h e peak due t o  2100A,  maximum a t a b o u t  According to  40  Passchier  et a l ,  t h e B r 4 p e a k h a s i t s maximum a b o u t  However,  examination  may w e l l  l i e below  appears groups  t o have used  virtually of  2000A  data  (their  shows t h a t  lower  tube.  falls  The B r  5  peak  Both  t h e RCA 1 P 2 8  According t o i t s specifications, the below  below 2I00A,  can not be stated  two f e a t u r e s have been  2200A, and i s  Therefore, the position  t h e m a x i m u m o f the. q u a d r a t i c t e r m  only  limit),  containing  o f fvery rapidly  insensitive  coefficient  t h e maximum  i t s maximum b e t w e e n 2 1 0 0 a n d 2 300A.  spectrophotometers  photomultiplier sensitivity  of their  2050A.  of the extinction  t o have been  shown  found.  convincingly:  We  believe  -  (1)  a  continuum  (2)  Some  v i o l e t with  is  does  at  2  with  not  obey  Beer's  There  good  to  the  The  of  to the  Br^  ;  careful  of  I  1/4.)  0  transition  at  2  On  dimer  study  complete  p o s s i b i l i t y as  2700A.  the  other  cannot  i n the  absorption  be  into  and  which  that  the  B r  we  found of  Br  (The  ratio  hand,  the  identified  vacuum  furfh er  law  extinction coefficient  that  about  same  2200A  i t s maximum  temperature.  i s a  -  about  increasing  2700A.  is  B r  absorption  which  due  1/6  of  60  absorption  2  at  of  2100A  the  such has  at i s  about  v i s i b l e  absorption  ultraviolet  u l t r a -  decreases  i n iodine  2  as  the  peaks  attributed  u n t i l  a  determined  the  continuum.  41 Evans bromine  has  dissolved  although  the  we  cannot  phase and  and  no  the  ultraviolet  i s similar  from  Beer's  q u a n t i t a t i v e work  spectrum  compare  that  i n PFH  deviation  Unfortunately, u l t r a v i o l e t  noted  the  of bromine  to Law  the  that  has  been  i n inert  of  gas  i s more  phase  done  bromine  iodine  of spectrum,  marked. on  solvents,  d i f f e r e n c e between  i n solution with  spectrum  i n the  so  the that  i n the gas  phase  i n solution. Earlier,  solution),  the  v/e p o s t u l a t e d transition  at  that  i n the  2800A  due  iodine to  dimer  gas  ( i n  i s actually  - 61 -  just its  the  2700A  partner.  between  gas  I n gas  iodine  transfer  and  in  2700A a  data.  The  would  induced band,  the  with  the  excited  only  one  band  gaseous  can  transition  to  the  and  on  diethyl  iodine  ether-  t o be  as  t o be  the  character  transition.  complexes i n inert  between solvents  problem.  0  band.  there of  Further iodine may  of  since  s t a t e may  case,  the  separate  charge-transfer  that  of  lack  observed  charge-transfer  having  a  of  1 7  induced  the magnitude  may  In  (diethyl  2 340A).  because  small  charge-  2700A.  expected  occur  by  complexes  estimated  state.  induced  be  However  strong  excited  iodine  and  too  induced  the observed  f a r from  would  not be  charge-transfer  molecules  very  complex.  observable  charge-transfer  this  i s not  possibly  l i eclose  Alternatively,  molecules,  transition  transition  strongly  charge-transfer  benzene-2680A,  iodine  absorption i t  phase  charge-transfer  induced  transition  donor  transition  sulphide-2900A; The  phase  mix may  be  both work and  help  on donor  c l a r i f y  -  62  -  BIBLIOGRAPHY  1.  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