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UBC Theses and Dissertations

Studies in radiation chemistry Shaede, Eric Albert 1971

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STUDIES IN RADIATION CHEMISTRY by ERIC ALBERT SHAEDE  B.Sc.,  U n i v e r s i t y o f B r i t i s h Columbia, 1966  M.Sc,  U n i v e r s i t y o f B r i t i s h Columbia, 1968  M.C.I.C., Chemical I n s t i t u t e o f Canada, 1969  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of Chemistry  We a c c e p t t h i s t h e s i s as conforming t o the required standard  The U n i v e r s i t y o f B r i t i s h A p r i l 1971  Columbia  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  the  requirements f o r an advanced degree at the U n i v e r s i t y  of  B r i t i s h Columbia, I agree t h a t  the L i b r a r y s h a l l make i t  f r e e l y a v a i l a b l e for reference  and  study.  I further  t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s s c h o l a r l y purposes may  be g r a n t e d by the Head of my  or by h i s r e p r e s e n t a t i v e s .  I t i s understood t h a t  or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n be  allowed w i t h o u t my  written  permission.  Department of Chemistry The  U n i v e r s i t y of B r i t i s h Columbia  Vancouver 8,  Canada  Date: A p r i l 7,  1971  agree for Department  copying shall  not  (ii)  ABSTRACT  The  e x p e r i m e n t a l work presented  consists  o f two s e p a r a t e  reaction  of hydrated  reported. effects pylene and  Hydrated  at icant  of  t h e gas space  the radiation  agents,  <  on d i s s o l v e d  i t i s unable  rate  An upper  t o cause limit  arose  through  N^.  Although  18  e l e c t r o n s t o H atoms  t h e ammonia  reduce  In propylene electrons.  yield,  of  i t was  "direct  shown action"  the hydrated  and r e a c t i v e  M~"^s~"'" w a s  i n acid  Signif-  completely  reduction fixation  of  °K,  y~radiolysis  atm p r e s s u r e ) .  constant of the reduction reaction.  the hydrated  a t 77  and a l s o c o n t a i n i n g  above t h e s o l u t i o n  i s one o f t h e most p o w e r f u l  nitrogen.  to  (200  by  were o b t a i n e d , but by  o f ammonia  M  of the  are presented.  yields  t h e m a j o r i t y o f t h e NH^  affect  a n d 0H~  state  t o 0.1  electron  the  c o n t a i n i n g H^  nitrogen i s  solvent, pro-  c o n c e n t r a t i o n s up  eliminating that  temperature,  e l e c t r o n s were generated  solutions  of the  o f an i n v e s t i g a t i o n  on t h e p o l a r a p r o t i c  a t room  dissertation  a study  (a) i n t h e g l a s s y s o l i d  (b) a s a l i q u i d  aqueous  the results  ^-radiation  carbonate;  Firstly,  electrons with molecular  Secondly,  of  parts.  i n this  reducing of  molecular  estimated f o r Conversion  solution  i m p l y i n g t h a t H atoms  of  d i d not  are also  unable  nitrogen.  the glassy s o l i d carbonate  state  produced  They were  a t 77  °K,  ^-irradiation  species identified  characterised  by a narrow  as (AH  of  trapped = 4.5  G),  (iii)  G a u s s i a n shaped ESR l i n e a t g = 2 . 0 0 2 8 and an o p t i c a l t i o n band wi t h X  "  3 7 0 nm .  absorp-  The e l e c t r o n s were u n s t a b l e  max a t 7 7 °K and decayed v i a a non-homogeneous p r o c e s s b e l i e v e d to be r e a c t i o n w i t h p o s i t i v e i o n s .  A l s o formed by the  *y - r a d i a t i o n were f o u r u n i d e n t i f i e d trapped r a d i c a l s , a l l c h a r a c t e r i s e d by d o u b l e t ESR s i g n a l s c e n t e r e d a t g = 2 . 0 0 2 3 and w i t h h y p e r f i n e s p l i t t i n g s o f 4 2 , 5 8 , 8 3 , and 1 2 4 G . U l t r a v i o l e t p h o t o l y s i s o f the i r r a d i a t e d g l a s s e s a t 7 7 °K new r a d i c a l s i d e n t i f i e d as C O j , HCO and C H 3 . The  produced CO^"  r a d i c a l gave a s i n g l e ESR l i n e a t g ^ 2 . 0 1 5 and a broad  v i s i b l e o p t i c a l a b s o r p t i o n band w i t h  X  ^  6 0 0 nm .  HCO was  i d e n t i f i e d by i t s asymmetric d o u b l e t ESR s i g n a l w i t h o f about 1 3 0 G and a m u l t i - l i n e  fine splitting  a b s o r p t i o n spectrum  i n the 5 0 0 -  hyper-  vibronic  7 50 nm r e g i o n .  The methyl  r a d i c a l s were u n s t a b l e i n the m a t r i x and were i d e n t i f i e d by their characteristic 1 : 3 : 3 : 1  q u a r t e t ESR spectrum  with  hyper-  f i n e s p l i t t i n g o f about 2 1 G . * y - r a d i o l y s i s o f l i q u i d p r o p y l e n e carbonate B.^ , CO and C 0  produced  products with y i e l d s : and  G  Q Q  = 2  secondary  2  ~ 0-3 .  2  as the major gaseous  "molecular"  = 0.75± 0.05,G  = 1.2 - 0 . 1 ,  G^  0.02 .  c 0  Methane was a l s o produced  p r o c e s s i n v o l v i n g methyl  G(CH ) = 0 . 2 0 -  at 2 5 °C  viaa  r a d i c a l s with a y i e l d :  Scavenger experiments  with N 0 , 2  I ,  methanol and a c i d i n d i c a t e d t h a t an a n i o n i c r e d u c i n g s p e c i e s was formed by the r a d i a t i o n w i t h a y i e l d o f G - = 2 . 0 -  0.2 .  T h i s s p e c i e s was p r o b a b l y a s o l v a t e d e l e c t r o n although the p o s s i b i l i t y o f i t being a r e a c t i v e m o l e c u l a r a n i o n c o u l d not  ~ (iv) be e x c l u d e d on the b a s i s o f the steady s t a t e r a d i o l y s i s  data.  A t r a n s i e n t o p t i c a l a b s o r p t i o n a t 630 nm was observed on p u l s e r a d i o l y s i s of propylene carbonate w i t h o f 0.5 MeV the  C 0  3~  electrons.  However,  3 nsec  pulses  e i t h e r solvated electrons or  r a d i c a l i o n c o u l d have been r e s p o n s i b l e f o r the  absorbance.  (v)  TABLE OF CONTENTS  CHAPTER I.  PAGE  INTRODUCTION TO RADIATION CHEMISTRY A.  I n t e r a c t i o n o f High Energy R a d i a t i o n w i t h matter  B.  1.  Electromagnetic  r a d i a t i o n (X o r ^ - r a y s )  2.  High energy e l e c t r o n s  Chemical Consequences o f the A b s o r p t i o n Energy R a d i a t i o n  C.  II.  1  . . .  2 3 6  o f High 10  1.  Polar liquids  11  2.  F r o z e n p o l a r systems  15  3.  R a d i a t i o n chemical  17  u n i t s and terms  Stabilized Electrons  18  1.  E l e c t r o n s o l v a t i o n process  19  2.  E l e c t r o n t r a p p i n g i n f r o z e n systems  22  3.  Properties of s t a b i l i z e d electrons  23  4.  Yields of s t a b i l i z e d electrons  23  AN ATTEMPT AT NITROGEN FIXATION UTILIZING HYDRATED ELECTRONS . . A.  B.  c  Introduction  28 28  1.  Background t o the problem  28  2.  L i t e r a t u r e survey  29  3.  The chemical  31  system  Experimental  33  1.  Reagents  33  2.  R a d i a t i o n source  34  3.  Apparatus and techniques  34  (vi)  II.  (CONTINUED) 4.  Analytical  procedures  42  C.  Results  43  D.  Discussion  43  E.  Suggestions  III.  f o rFurther  Study  48  A S P E C T S OF T H E R A D I A T I O N C H E M I S T R Y OF  PROPYLENE  CARBONATE PART  I.  50  RADIOLYSIS  OF P R O P Y L E N E C A R B O N A T E  I N THE  SOLID STATE A.  Introduction  B.  Experimental  C.  53 ,  53 55  1.  Reagents  2.  Radiation  3.  Sample p r e p a r a t i o n  4.  E l e c t r o n s p i n resonance measurements  5.  Optical absorption  6.  Light  Results 1.  2.  55 source  sources  55 and i r r a d i a t i o n  56 . . . .  measurements  60  f o rphotobleaching  experiments  and D i s c u s s i o n  The t r a p p e d  61 62  electron  62  (a)  E l e c t r o n s p i n resonance  (b)  Optical absorption  (c)  Summary  Trapped  57  observations  . . .  spectrum  62 82 87  radicals  i n irradiated  PC  (a)  Radicals  formed  during  (b)  Radicals  formed  b y UV p h o t o l y s i s o f t h e  irradiated  PC g l a s s e s  radiolysis  89  a t 77 °K  a t 77 ° K  89  96  (vii)  CHAPTER III.  PAGE  (CONTINUED)  PART I I .  RADIOLYSIS OF PROPYLENE CARBONATE I N THE LIQUID PHASE  105  A.  Introduction  105  B.  Experimental  107  1.  Reagents  107  2.  R a d i a t i o n source  107  3.  Apparatus  108  and t e c h n i q u e s  (a)  Sample c e l l and sample p r e p a r a t i o n . . . .  (b)  Gaseous p r o d u c t a n a l y s i s  (c)  Vacuum t e c h n i q u e s and d e t e r m i n a t i o n o f the s o l u b i l i t y  C.  D.  108  I l l  of nitrous oxide  114  Results  118  1.  Pure PC - gaseous r a d i o l y s i s  2.  Scavenger  products . . . .  experiments  Discussion  PART I I I .  118 118 123  GENERAL CONCLUSION AND SUGGESTIONS FOR FURTHER STUDY OF THE RADIATION CHEMISTRY OF PROPYLENE CARBONATE  BIBLIOGRAPHY APPENDIX 1.  133 . 136  FERROUS SULFATE DOSIMETRY  141  A.  Theory  141  B.  Procedure  142  C.  Results  143  1.  Nitrogen fixation  experiments  143  2.  R a d i o l y s i s o f l i q u i d PC  144  3.  Dose c o r r e c t i o n p r o c e d u r e - computer program  145  (viii)  CHAPTER  PAGE  APPENDIX 2.  INDOPHENOL BLUE AMMONIA ANALYSIS  A.  Theory  B.  Experimental Procedure  C.  149 . 149  1.  Reagents  149  2.  A n a l y s i s procedure  151  Results  APPENDIX 3.  B a s i c Theory  B.  A p p l i c a t i o n o f ESR t o amorphous systems  APPENDIX 4.  156 156 . . . .  159  PURIFICATION AND ANALYSIS OF PROPYLENE CARBONATE  APPENDIX 5.  153  ELECTRON SPIN RESONANCE  A.  VITA  149  GAS CHROMATOGRAPHIC ANALYSIS SYSTEM  161 . . . 169  (ix)  L I S T OF TABLES  TABLE 1.  PAGE  Approximate time s c a l e f o r the r a d i o l y s i s o f l i q u i d water  2.  13-14  Selected properties of s t a b i l i z e d electrons formed by r a d i o l y s i s  24  3.  Summary o f n i t r o g e n f i x a t i o n e x p e r i m e n t s  44  4.  Characteristics  of electrons trapped i n propylene  c a r b o n a t e g l a s s e s a t 77 °K 5.  Summary o f second s c a v e n g e r e x p e r i m e n t a l r e s u l t s  88 . 124  (x)  LIST OF FIGURES  1.  Scheme o f r e a c t i o n s i n r a d i a t i o n c h e m i s t r y  . . . .  2.  D i s t r i b u t i o n o f s p u r s and p r i m a r y e v e n t s a l o n g t h e track of a fast electron i n a l i q u i d  3.  10  P r i m a r y p r o c e s s e s i n t h e a c t i o n o f r a d i a t i o n on matter  4.  12  Q u a l i t a t i v e r e p r e s e n t a t i o n of the p o t e n t i a l o f an e l e c t r o n as a f u n c t i o n o f time a f t e r  energy local-  ization i n a liquid 5.  1  21  Y i e l d of r a d i o l y t i c a l l y generated free ions  ( £^) G  as a f u n c t i o n o f t h e s t a t i c d i e l e c t r i c c o n s t a n t (D ) s of a l i q u i d 6.  Photograph  26 o f t h e m o d i f i e d 50 ml a l l - g l a s s s y r i n g e  and a t t a c h m e n t s 7.  Photograph  36  of the s t a i n l e s s s t e e l high pressure  c e l l used t o p r e s s u r i z e t h e s y r i n g e s  37  8.  S c h e m a t i c diagram o f t h e h i g h p r e s s u r e system . . .  38  9.  Diagram o f t h e a p p a r a t u s used t o f i l l with  gas and l i q u i d samples,  the syringes  shown w i t h a s y r i n g e  attached  40  10.  One o f t h e s t e r e o i s o m e r s o f p r o p y l e n e c a r b o n a t e  .  11.  V a r i a b l e t e m p e r a t u r e ESR dewar  12.  ESR spectrum o f ' y - i r r a d i a t e d g l a s s y PC i m m e d i a t e l y  50 58  f o l l o w i n g the i r r a d i a t i o n u s i n g the lowest operable microwave power (about 0.5 mW)  c  (Dose ^0.8 Mrad) .  63  (xi) FIGURE 13.  PAGE  ESR spectrum  o f t h e same sample as F i g u r e 12  o n l y a t about 10 mW microwave power 14.  H i g h r e s o l u t i o n ESR s c a n o f l i n e  64  "A" o f F i g u r e 12.  T h i s l i n e i s a t t r i b u t e d t o t r a p p e d e l e c t r o n s i n PC 15.  H i g h r e s o l u t i o n ESR s c a n o f t h e t r a p p e d  65  electron  l i n e showing t h e n o r m a l i z a t i o n method o f l i n e shape a n a l y s i s . 16.  ESR s p e c t r u m  •=Gaussian,  x=Lorentzian . . . .  o f ^ - i r r a d i a t e d g l a s s y PC a t 77 °K  c o n t a i n i n g 0.02 M i o d i n e 17.  ESR spectrum  ^ - i r r a d i a t e d g l a s s y PC a t 77 °K as f o l l o w e d by  ESR.  (Data a r e a r b i t r a r i l y n o r m a l i z e d a t "0"  time.)  73  F i r s t order k i n e t i c analyses of the trapped e l e c t r o n decay d a t a from F i g u r e 18  20.  75  Second o r d e r k i n e t i c a n a l y s e s o f t h e t r a p p e d e l e c t r o n decay d a t a from F i g u r e 18  21.  71  I s o t h e r m a l spontaneous decay o f t r a p p e d e l e c t r o n s in  19.  70  o f y - i r r a d i a t e d g l a s s y PC a t 77 °K  c o n t a i n i n g 0.1 M n a p t h a l e n e 18.  67  ESR spectrum  76  o f y - i r r a d i a t e d g l a s s y PC a f t e r  v i s i b l e p h o t o l y s i s t o remove most o f t h e t r a p p e d electrons 22.  81  O p t i c a l a b s o r p t i o n s p e c t r a o f y ~ i r r a d i a t e d PC a t 77 °K (sample p a r t i a l l y c r y s t a l l i n e ) i n a 1 cm cell.  Curve 1 was o b t a i n e d i m m e d i a t e l y a f t e r t h e  i r r a d i a t i o n and c u r v e 2 was o b t a i n e d 24 hours later.  ( D o s e ~ 1 . 3 Mrad)  83  (xii) FIGURE 23.  PAGE  A b s o r p t i o n spectrum a t t r i b u t e d to electrons  i n PC  subtraction 24.  ESR  a t 77  °K  trapped  as c o n s t r u c t e d  by  of c u r v e 2 from c u r v e 1 o f F i g u r e 22 y - i r r a d i a t e d glassy  spectrum of  a f t e r t h e r m a l decay o f the  PC a t ~110  trapped electrons  . °K  and  other radicals 25.  ESR  90  spectrum of y - i r r a d i a t e d g l a s s y  a f t e r p a r t i a l UV responsible 26.  ESR  photolysis  ESR  a t ~110  °K  radical  s p e c t r u m of  a f t e r b r i e f UV  92  y - i r r a d i a t e d glassy  a f t e r s t a n d i n g f o r 200 27.  o f the  PC  f o r d o u b l e t "D"  spectrum of  PC a t 77  °K  hours i n the d a r k  y - i r r a d i a t e d glassy photolysis.  93  PC a t 77  °K  Samples dark b l u e  i n colour 28.  97  A b s o r p t i o n s p e c t r u m i n the for  y - i r r a d i a t e d PC  500  - 7 50 nm  a f t e r b r i e f UV  region  photolysis.  Spectrum a t t r i b u t e d t o a c o m b i n a t i o n o f  29.  HCO  and  ESR  spectrum of  c  0 ~ 3  the  a b s o r p t i o n bands  98  y - i r r a d i a t e d glassy  a f t e r 20 m i n u t e s o f i n t e n s e UV Samples v i r t u a l l y c o l o u r l e s s .  PC a t 77  °K  photolysis. Arrows  indicate  m e t h y l r a d i c a l , (compare w i t h F i g u r e 27) 30.  ESR  85  spectrum of  y - i r r a d i a t e d glassy  a f t e r 50 m i n u t e s o f i n t e n s e UV  PC  101 a t 77  °K  photolysis.  Arrows i n d i c a t e m e t h y l r a d i c a l q u a r t e t  102  (xiii) FIGURE 31.  PAGE  ESR spectrum o f UV p h o t o l y s e d , ^ - i r r a d i a t e d o PC samples a t 77 ysis.  Showing  (arrows). 32.  K; about 4 hours a f t e r p h o t o l -  t h e decay o f t h e m e t h y l r a d i c a l s  (compare w i t h F i g u r e 30)  104  P h o t o g r a p h o f t h e sample c e l l used f o r t h e l i q u i d phase r a d i o l y s i s o f PC  33.  109  S c h e m a t i c d i a g r a m o f t h e vacuum system used t o add n i t r o u s o x i d e t o t h e PC samples i n t h e "bubbler" c e l l C o n c e n t r a t i o n o f d i s s o l v e d n i t r o u s o x i d e i n PC a t  34.  115  room t e m p e r a t u r e (20 - 25 °C) as a f u n c t i o n o f the 35.  n i t r o u s oxide pressure i n the "bubbler" c e l l  . 117  Y i e l d s o f gaseous r a d i o l y s i s p r o d u c t s from PC ^ - i r r a d i a t e d a t 25 °C, as a f u n c t i o n o f dose . . 119  36.  N i t r o g e n y i e l d as a f u n c t i o n o f accumulated sample dose f o r a c o n s t a n t n i t r o u s o x i d e c o n c e n t r a t i o n (0.05 M)  37.  G  ( 2^ N  a s  at 38.  a  f  i°  u n c t  c o n s t a n t dose  n  120  of nitrous oxide concentration 18 l (about 5 x 10  eV g  122  D a t a from F i g u r e 37 p l o t t e d as 1/G(N,,) v e r s u s 1/ [N 0]  128  2  39.  )  P l o t o f 1/G(N ) v e r s u s 2  [N 0] = 0.077 M 2  [l ]/[N Q] f o r 2  2  130  (xiv) FIGURE  PAGE +3  Al-1.  P l o t o f the absorbance  o f Fe  a t 304 nm as a  f u n c t i o n o f F e ^ c o n c e n t r a t i o n a t 25 °C +  Al-2.  ....  146  Ferrous s u l f a t e dosimetry r e s u l t s f o r the " b u b b l e r " c e l l used i n t h e l i q u i d phase r a d i o l y s i s o f PC  A2-1.  147  A b s o r p t i o n spectrum o f t h e i n d o p h e n o l b l u e dye i n a l k a l i n e aqueous s o l u t i o n  A2-2.  150  T y p i c a l c a l i b r a t i o n graph f o r the indophenol b l u e ammonia a n a l y s i s p r o c e d u r e  A3-1.  154  T h e o r e t i c a l ESR d e r i v a t i v e l i n e shapes f o r amorphous samples when t h e r a d i c a l i s c h a r a c t e r i z e d by:  (a) an a x i a l l y symmetric g - t e n s o r  no h y p e r f i n e s t r u c t u r e ,  (b) an  and  asymmetric  g - t e n s o r and no h y p e r f i n e s t r u c t u r e , and  (c)  a x i a l l y symmetric g- and A - t e n s o r s w i t h t h e same symmetry axes and a l a r g e h y p e r f i n e s p l i t t i n g o f a s p i n % nucleus A4-1.  160  S t o r a g e - d i s p e n s i n g f l a s k used t o keep t h e p u r i f i e d PC under a h e l i u m atmosphere  A4-2.  Mass spectrum o f d o u b l y d i s t i l l e d carbonate  A4-3.  164  propylene  (PC)  165  U l t r a v i o l e t a b s o r p t i o n s p e c t r a o f Eastman Kodak p r a c t i c a l grade PC and i t s s i n g l y and distilled  fractions  doubly 166  (xv)  FIGURE A4-4.  PAGE 60 MHz n u c l e a r m a g n e t i c resonance spectrum o f d o u b l y d i s t i l l e d PC  A4-5.  167  I n f r a r e d a b s o r p t i o n spectrum o f d o u b l y d i s t i l l e d PC  A5-1.  168  Schematic diagram o f the m o d i f i e d V a r i a n A e r o g r a p h gas chromatography  A5-2.  system  170  T y p i c a l chromatogram produced by t h e GC system shown i n F i g u r e A5-1 f o r a h y p o t h e t i c a l sample c o n t a i n i n g N , C H , CO and C 0 2  A5-3.  4  D e t e c t o r r e s p o n s e t o N , CO, C H 2  173  2  4  and C 0 f o r  t h e GC system shown i n F i g u r e A5-1  2  174  (xvi)  ACKNOWLEDG EMENT S  The Dr.  author would  D. C. W a l k e r .  their  and  Special in  sions  regarding  discussions ESR  data In  their  D r . F . G. H e r r i n g  Enlightening  i n connection  a d d i t i o n , t h e author would  like  with the  t o t h a n k t h e U.B.C.  shops and t h e  excellent craftsmanship  i n designing  i n this  glassblowers and constructing  research.  support by t h e Chemistry Department assistantships  i sthe receipt of a National  postgraduate  discus-  acknowledged.  some o f t h e a p p a r a t u s u s e d  as  f o r guidance  and h e l p f u l  interpretation of the spectra.  are also  form o f teaching  availablefor  a r e d u e t o M r . N . S. D a l a i  o f t h e ESR s p e c t r o m e t e r  with  Financial  t o pursue  advice.  Chemistry Department mechanical for  students  i n t e r e s t s a n d was a l w a y s  thanks  the operation  t o express h i sgratitude t o  He e n c o u r a g e d h i s  own r e s e a r c h  consultation  like  scholarship.  i n the  i s g r a t e f u l l y acknowledged, Research Council  o f Canada  (xvii)  I n l o v i n g memory o f my  father,  ERIC ALBERT KURT SHAEDE (1904 - 1969) and a v e r y d e a r f r i e n d , WILLIAM LYLE MACKEN  (1883 - 1967).  CHAPTER I INTRODUCTION TO RADIATION CHEMISTRY  "Fundamental s t u d i e s i n r a d i a t i o n c h e m i s t r y aim t o i d e n t i f y t h e v a r i o u s SPECIES formed i n p a r t i c u l a r systems and t o u n d e r s t a n d t h e PHYSICAL PROCESSES by w h i c h t h e y a r i s e .  The  AMOUNTS formed f o r a g i v e n dose o f r a d i a t i o n a r e measured. Then t h e CHEMISTRY o f t h e s p e c i e s i n t h e i r r e a c t i o n s w i t h each o t h e r and o t h e r compounds p r e s e n t i s s t u d i e d .  This involves  i n v e s t i g a t i o n s o f r e a c t i o n k i n e t i c s and mechanisms, and o f i n t e r m e d i a t e s t h r o u g h t o t h e f i n a l , s t a b l e end p r o d u c t s . " ^ Thus t h e g e n e r a l scheme o f r a d i a t i o n c h e m i c a l  investigations  may be r e p r e s e n t e d by F i g u r e 1.  Radiation _  CHEMICAL SYSTEM — W W  l^tV.nn  ^ WHAT S P E C I E S ? HOW M A N Y ? chemical r e a c t ions  STABLE P R O D U C T S -  t  INTERMEDIATE  SPECIES  F i g u r e 1. Scheme o f r e a c t i o n s i n r a d i a t i o n c h e m i s t r y . ( a f t e r F i g u r e 1.1, O'Donnell and S a n g s t e r , r e f e r e n c e 2, page 2)  -2-  This  t h e s i s i s concerned w i t h s e v e r a l o f t h e funda-  mental a s p e c t s o f r a d i a t i o n c h e m i s t r y o u t l i n e d above. ically,  Specif-  the c h e m i c a l r e a c t i o n o f the h y d r a t e d e l e c t r o n , an  important p r i m a r y s p e c i e s molecular nitrogen  was s t u d i e d .  of the primary species organic l i q u i d  i n the r a d i o l y s i s o f water, w i t h In a d d i t i o n an i n v e s t i g a t i o n  formed by ^°Co ^ - r a d i a t i o n i n a p o l a r  (propylene carbonate) was conducted both d i r -  e c t l y , i n the s o l i d s t a t e , by e l e c t r o n s p i n resonance and o p t i c a l s p e c t r o s c o p y ; and i n d i r e c t l y , i n the l i q u i d phase, by competition k i n e t i c studies  i n v o l v i n g scavengers and a n a l y s i s  o f t h e f i n a l s t a b l e p r o d u c t s o f the r a d i o l y s i s . Understanding r a d i a t i o n c h e m i c a l phenomena r e q u i r e s  a  b a s i c knowledge o f the p r o c e s s e s by which r a d i a t i o n i n t e r a c t s w i t h matter s i n c e the c h e m i c a l e f f e c t s a r e a d i r e c t consequence o f the a b s o r p t i o n A.  o f energy from the r a d i a t i o n .  INTERACTION OF HIGH ENERGY RADIATION WITH MATTER S i n c e the m a j o r i t y  i s t r y involve  of investigations  i n r a d i a t i o n chem-  the use o f h i g h energy photons o r e l e c t r o n s as  the r a d i a t i o n s o u r c e , the p r e s e n t d i s c u s s i o n w i l l be l i m i t e d to the i n t e r a c t i o n s o f these r a d i a t i o n s w i t h matter. e r a l the p h y s i c s  In gen-  and c h e m i s t r y o f the i n t e r a c t i o n s o f o t h e r  types o f r a d i a t i o n , namely neutrons and charged p a r t i c l e s such as p r o t o n s , a l p h a p a r t i c l e s and f i s s i o n fragments, a r e s u b s t a n t i a l l y d i f f e r e n t to that of electrons complete d i s c u s s i o n  (and photons) and a  o f a l l o f the i n t e r a c t i o n s i s beyond the  scope o f t h i s t h e s i s .  -3-  1.  E l e c t r o m a g n e t i c R a d i a t i o n (X o r ^ - r a y s )  E l e c t r o m a g n e t i c r a d i a t i o n i s absorbed by m a t t e r v i a four p r i n c i p a l processes: (b) t h e Compton p r o c e s s , n u c l e a r r e a c t i o n s . The  (a) t h e p h o t o e l e c t r i c e f f e c t , (c) p a i r p r o d u c t i o n , and  (d)photo-  i m p o r t a n c e o f each o f t h e f o u r r e a c t -  i o n s depends p r i m a r i l y i n t h e energy o f t h e i n c i d e n t photon and depends t o a l e s s e r e x t e n t on t h e a t o m i c number o f the absorbing m a t e r i a l . S i n c e X o r ^ - r a y s obey a b s o r p t i o n laws common t o o t h e r e l e c t r o m a g n e t i c r a d i a t i o n (such as v i s i b l e l i g h t ) , t h e y n o t c o m p l e t e l y a b s o r b e d by a f i n i t e t h i c k n e s s o f  are  absorber.  Thus a beam o f h i g h e n e r g y photons o f i n i t i a l i n t e n s i t y , I , Q  w i l l have a f i n a l i n t e n s i t y , I , a f t e r p a s s i n g t h r o u g h t h i c k n e s s , x, o f a b s o r b i n g m a t e r i a l as g i v e n by t h e  a equation  (i), I = l  Q  • e"^  (i)  X  where jX i s the t o t a l l i n e a r a t t e n u a t i o n c o e f f i c i e n t e q u a l t o t h e sum  o f t h e i n d i v i d u a l c o e f f i c i e n t s f o r each o f the f o u r  i n t e r a c t i o n p r o c e s s e s mentioned above.  This equation i s  a n a l a g o u s t o t h e Beer-Lambert law f o r the a b s o r p t i o n o f The  light.  range o f e l e c t r o m a g n e t i c r a d i a t i o n i s o f t e n d i s c u s s e d i n  terms o f t h e " h a l f t h i c k n e s s " o f an a b s o r b e r ,  i . e . the  ness r e q u i r e d t o r e d u c e t h e o r i g i n a l i n t e n s i t y by one F o r 1 MeV  thickhalf.  photons t h e h a l f t h i c k n e s s i n w a t e r i s about 10 cm .  The p h o t o e l e c t r i c e f f e c t i s t h e i n t e r a c t i o n o f e l e c t r o m a g n e t i c r a d i a t i o n w i t h an atom or m o l e c u l e  which r e s u l t s i n  t h e complete a b s o r p t i o n o f the photon and s i m u l t a n e o u s  ejection  - 4 -  of  an  e l e c t r o n w i t h k i n e t i c e n e r g y , E, E = hj/  where hV of  the  i s the  aratively  low  increasing  An bound o r results  (ii)  This  process  photon energies  atomic  elastic  electron.  i s the  collision  transfer  i s important  (<  0.1  MeV)  only  and  energy"  for  comp-  increases  b e t w e e n a p h o t o n and known as  of  some o f  Conservation of  the the  Compton  with  to  the  momentum r e q u i r e s  electron,  E,  a  loosely  process,  photon's energy to  must change d i r e c t i o n , i . e . i s s c a t t e r e d , energy transfered  "binding  number.  unbound e l e c t r o n , i n the  equation ( i i ) ,  <f>  -  p h o t o n e n e r g y and  electron.^  g i v e n by  and  that  the  the  photon  amount  i s g i v e n by  the  the  of  equation  (iii) / E = hi/ where hi/ gies  and  hi/'  respectively.  is  related  by  the  to  - hi/' are  the  The  energy of  its original  o  c  important equation the  and  the  scattered  scattered  e n e r g y and  the  photon  ener-  p h o t o n , hi/  ,  angle,Q,  scattering  hi/ 1 +  as  incident  relationship (iv),  ,,/_ hV =  where m  (iii)  2  i s the aspects  (iv) are:  scattering  (J^_) m c^ o  ,. v (iv)  (  cosQ)  1 -  r e s t mass e n e r g y o f of  the  electron.  Compton s c a t t e r i n g w h i c h a r e (a)  the  angle $  energy  lost  increases,  (b)  by  The  evident  a photon  the  o  energy  from  increases• loss  for  -5-  a g i v e n s c a t t e r i n g a n g l e i n c r e a s e s w i t h i n c r e a s i n g photon e n e r g y , and (c) t h e e n e r g y o f a photon s c a t t e r e d a t t h e m a x i mum  angle  ($=180) approaches a l i m i t i n g v a l u e o f 0. 256 MeV  ( i . e . % m c ^ ) as t h e i n i t i a l photon e n e r g y i n c r e a s e s . o  Since  i n t e r a c t i o n w i t h e l e c t r o n s i s i n v o l v e d i n t h e Compton p r o c e s s , i t s effectiveness increases with increasing "electron density" ( i . e . r a t i o o f a t o m i c number, Z, t o a t o m i c mass, A) o f t h e a b s o r b e r . Photons w i t h energy i n t h e range 0.2 t o 5 MeV a r e a l m o s t e x c l u s i v e l y absorbed  by t h e Compton p r o c e s s f o r l o w  a t o m i c number m a t e r i a l s . P a i r p r o d u c t i o n r e s u l t s when a h i g h e n e r g y photon i s a n n i h i l a t e d i n t h e r e g i o n o f an a t o m i c n u c l e u s w i t h t h e c o n comitant production  o f an " e l e c t r o n " p a i r —  a p o s i t i v e and a  negative electron.  T h i s p r o c e s s has a t h r e s h o l d e n e r g y o f  1.02 MeV, t h e energy r e q u i r e d t o produce two e l e c t r o n r e s t masses, and t h e r e f o r e t h e n e t k i n e t i c energy o f t h e e l e c t r o n s , E  P  + E  e  , i s g i v e n by e q u a t i o n ( v ) , Ep + E e  = YiV  - 2m c  o  where hi/ i s t h e p h o t o n energy.  2  = hi/-  1.02 MeV  (v)  P a i r p r o d u c t i o n becomes an  i m p o r t a n t a b s o r b i n g p r o c e s s o n l y f o r v e r y h i g h photon e n e r g i e s ( > 1 0 MeV) . P h o t o n u c l e a r r e a c t i o n s a l s o r e q u i r e v e r y h i g h photon energies i n order t o e j e c t neutrons nuclei.  o r p r o t o n s from  atomic  The photon energy must exceed t h e " b i n d i n g " e n e r g y  o f a n u c l e a r p a r t i c l e and t y p i c a l l y i s i n t h e range o f 6 t o 18 MeV.  However t h i s p r o c e s s makes a n e g l i g i b l e c o n t r i b u t i o n  -6to the t o t a l l i n e a r attenuation c o e f f i c i e n t f o r electromagnetic r a d i a t i o n s n o r m a l l y used i n r a d i a t i o n c h e m i c a l s t u d i e s . I n summary, t h e most i m p o r t a n t 60 o f moderate energy (e.g. i s t h e Compton p r o c e s s .  i n t e r a c t i o n f o r photons  Co ^ - r a y s a t 1.17 and 1.33 MeV) Because t h i s a b s o r p t i o n e s s e n t i a l l y  r e s u l t s i n t h e c o n v e r s i o n o f h i g h energy photons t o h i g h energy e l e c t r o n s , i t i s n e c e s s a r y  t o consider i n d e t a i l the  i n t e r a c t i o n o f h i g h energy e l e c t r o n s w i t h m a t t e r s i n c e they are the species d i r e c t l y r e s p o n s i b l e f o r r a d i a t i o n  chemical  effects. 2.  H i g h Energy E l e c t r o n s  U n l i k e e l e c t r o m a g n e t i c r a d i a t i o n , e l e c t r o n s have a f i n i t e range i n an a b s o r b i n g m a t e r i a l .  They l o s e t h e i r energy  v i a two i m p o r t a n t p r o c e s s e s , namely r a d i a t i o n (Bremsstrahlung)  emission  and i n e l a s t i c c o l l i s i o n s w i t h o t h e r e l e c t r o n s  i n t h e medium. When a h i g h energy e l e c t r o n p a s s e s c l o s e t o an atomic nucleus  i t i s d e c e l e r a t e d by t h e e l e c t r i c f i e l d . , A c c o r d i n g t o  c l a s s i c a l p h y s i c s t h i s means t h a t t h e e l e c t r o n must r a d i a t e e l e c t r o m a g n e t i c r a d i a t i o n (Bremsstrahlung)  i n order that the  system conserve  The r a t e a t w h i c h  b o t h energy and momentum.  0  2  2  the e l e c t r o n l o s e s energy, -dE/dx, i s p r o p o r t i o n a l .to e Z /m where e,Z a r e t h e e l e c t r o n i c and n u c l e a r charges r e s p e c t i v e l y and m i s t h e e l e c t r o n mass.  Bremsstrahlung  emission i s n e g l -  i g i b l e f o r e n e r g i e s below about 100 keV and becomes s i g n i f i c a n t o n l y above 1 MeV.  Of course t h i s e l e c t r o m a g n e t i c  radiation  -7-  w i l l t h e n be p a r t i a l l y r e - a b s o r b e d i n t h e medium by t h e p r o cesses discussed i n the previous s e c t i o n . The predominant mechanism f o r energy l o s s by e l e c t r o n s w i t h energy l e s s t h a n 1 MeV i s t h r o u g h i n e l a s t i c  Coulombic  i n t e r a c t i o n s with the electrons of the absorbing m a t e r i a l . I n t e r a c t i o n s o f t h i s t y p e produce t h e i o n i z a t i o n and e x c i t a t i o n w h i c h l e a d s t o c h e m i c a l change i n t h e system. The r a t i o o f energy l o s s by r a d i a t i o n e m i s s i o n t o t h a t l o s t by c o l l i s i o n i s g i v e n a p p r o x i m a t e l y by t h e f o r m u l a ( v i ) , (dE/dx)  r a d  (dE/dx)  c o  EZ  Z n  (vi) 1600  mc Q  z  where E i s t h e e l e c t r o n energy and Z i s t h e a t o m i c number o f 3 the m a t e r i a l . A t h i r d p r o c e s s w h i c h a f f e c t s t h e range o f e l e c t r o n s i n an a b s o r b e r i s t h e i r d e f l e c t i o n by t h e Coulombic f i e l d s o f the atomic n u c l e i .  T h i s r e s u l t s o n l y i n a change i n d i r e c t i o n  and i s g r e a t e s t f o r l o w e l e c t r o n e n e r g i e s and h i g h a t o m i c number m a t e r i a l s . Thus e l e c t r o n s l o s e t h e i r energy and a r e d e f l e c t e d as t h e y pass t h r o u g h a medium.  The t o t a l i n i t i a l energy and t h e  r a t e o f energy l o s s c o n s e q u e n t l y d e t e r m i n e t h e range o r p e n e t r a t i o n distance of the e l e c t r o n .  For monoenergetic e l e c t r o n s ,  a g r a p h showing t h e number o f e l e c t r o n s t r a n s m i t t e d a t a g i v e n d i s t a n c e w i t h i n t h e bombarded m a t e r i a l , as a f u n c t i o n o f d i s t ance, i s n e a r l y l i n e a r w i t h a n e g a t i v e s l o p e and f i n i s h i n g i n  -8a small t a i l .  The e x t r a p o l a t e d o r p r a c t i c a l r a n g e , R ,  is  p  found by e x t r a p o l a t i n g t h e l i n e a r p o r t i o n o f t h e c u r v e . maximum r a n g e , R ,  i s t h e p o i n t where t h e t a i l  Q  merges w i t h t h e background. electrons  F o r a beam o f  of the curve  non-monoenergetic  ( e . g . ^ - p a r t i c l e s o r Compton e l e c t r o n s ) t h e c u r v e  does n o t have a l i n e a r r e g i o n and o n l y a maximum r a n g e , can be d e t e r m i n e d .  between 0.01  R, Q  The range o f e l e c t r o n s has been e m p i r i c a l l y  r e l a t e d t o t h e i r energy f o r aluminum a b s o r b e r s .  mum  The  and 2.5 MeV  For energies  t h e range o f ^ - p a r t i c l e s w i t h m a x i -  e n e r g y , E, o r t h e e x t r a p o l a t e d range o f m o n o e n e r g e t i c  e l e c t r o n s o f e n e r g y , E, i s g i v e n by e q u a t i o n ( v i i ) , Range = 412 E 1-265  - 0.0954 l n E  where t h e r a n g e i s g i v e n i n mg cm~^.  3  ( v ± i )  T h i s f o r m u l a can a l s o  be a p p l i e d t o most o t h e r low a t o m i c number m a t e r i a l s the  range e x p r e s s e d i n u n i t s o f mg cm~*  w i t h a t o m i c number.  Thus t h e range o f 1 MeV  c a l c u l a t e d from e q u a t i o n ( v i i ) to  varies only  a t h i c k n e s s o f 0.41  i s 412 mg cm~2  since slightly  e l e c t r o n s as which corresponds  cm f o r w a t e r .  The n e t r e s u l t o f t h e passage o f a h i g h e n e r g y  electron  t h r o u g h a condensed medium i s an i r r e g u l a r d i s t r i b u t i o n o f i o n i z e d and e x c i t e d m o l e c u l e s .  The p a t h o f t h e p r i m a r y e l e c t r o n  is  r e f e r r e d t o as i t s " t r a c k " , w h i c h i s g e n e r a l l y near  at  h i g h energy b u t d e f l e c t i o n s become more common as t h e e l e c t -  ron  s l o w s down.  linear  I o n i z a t i o n s and e x c i t a t i o n s w h i c h o c c u r a t  i r r e g u l a r i n t e r v a l s along the t r a c k are c a l l e d "primary events". The p r i m a r y i o n i z a t i o n s w i l l produce s e c o n d a r y e l e c t r o n s w i t h s u f f i c i e n t energy t o escape r e c o m b i n a t i o n w i t h t h e i r  positive  -9-  ion  and t h e y may  be c l a s s i f i e d i n t o two energy c a t e g o r i e s ;  the  low energy s e c o n d a r y «  secondary e l e c t r o n s  100 eV) and t h e h i g h energy  ( > 100 e V ) .  The low energy s e c o n d a r y  e l e c t r o n s w i l l s u f f e r l a r g e d e f l e c t i o n s and form a r e g i o n o f t e r t i a r y i o n i z a t i o n and e x c i t a t i o n c a l l e d a " s p u r " / w h i c h t o a f i r s t a p p r o x i m a t i o n may  be r e g a r d e d as s p h e r i c a l i n shape.  Each s p u r w i l l t h u s i n i t i a l l y c o n t a i n a number o f e x c i t e d m o l e c u l e s , p o s i t i v e i o n s and v e r y low e n e r g y e l e c t r o n s w i t h an average o f somewhat l e s s t h a n 100 eV d e p o s i t e d i n t h i s  area.  The more e n e r g e t i c s e c o n d a r y e l e c t r o n s have s u f f i c i e n t range t o form s h o r t t r a c k s o f t h e i r own,  called  "S-rays", and  t h e s e e l e c t r o n s can be f u r t h e r c l a s s i f i e d i n t o two The most e n e r g e t i c s e c o n d a r y t r a c k o f t h e i r own  §-electrons w i l l  form a t r u e  a l o n g w h i c h t h e r e w i l l be f u r t h e r  and t h e f o r m a t i o n o f s p u r s .  ionization  Known as a "branch t r a c k " , t h e  average s e p a r a t i o n o f s p u r s a l o n g i t s p a t h w i l l be so t h a t t h e r e w i l l be no o v e r l a p p i n g . energetic  sub-groups.  sufficient  In c o n t r a s t , the l e s s  ^ - e l e c t r o n s w i l l have o n l y enough energy t o form  a v e r y s h o r t t r a c k and t h e s p u r s a l o n g i t w i l l o v e r l a p t o form a k i n d o f "super s p u r " w h i c h i s sometimes r e f e r r e d t o as a "blob". the  F o r a 1 MeV  e l e c t r o n s t o p p e d i n w a t e r about 6 7 % o f  energy i s d e p o s i t e d i n i s o l a t e d s p u r s , 2 2 % a l o n g t h e  b r a n c h t r a c k s , and 1 1 % i n b l o b s . 1 From t h e above d i s c u s s i o n s i t i s c l e a r t h a t t h e p h y s i c a l e f f e c t o f r a d i a t i o n i s t o produce an inhomogeneous d i s t r i b u t i o n of  i o n i z e d and e l e c t r o n i c a l l y e x c i t e d m o l e c u l e s and v e r y low  -10e n e r g y e l e c t r o n s i n t h e medium as may be d e p i c t e d b y F i g u r e 2.  F i g u r e 2. D i s t r i b u t i o n o f s p u r s and p r i m a r y e v e n t s a l o n g t h e t r a c k o f a f a s t e l e c t r o n i n a l i q u i d , ( a f t e r F i g u r e 2-8, H e n l e y and Johnson, r e f e r e n c e 2, page 31) The  f a t e o f t h e s e p r i m a r y s p e c i e s governs t h e subsequent  c h e m i s t r y i n t h e system. B.  CHEMICAL CONSEQUENCES OF THE ABSORPTION OF HIGH ENERGY RADIATION " I n g e n e r a l , most o f t h e r e a c t i o n s w h i c h o c c u r i n r a d i ~  a t i o n chemistry are ordinary thermal chemical r e a c t i o n s , a l t h ough some i n v o l v e r a t h e r u n u s u a l c h e m i c a l s p e c i e s .  I n some  cases r e g i o n s o f excess e n e r g y - "hot s p o t s " - may be p r e s e n t , and t h e s e r e g i o n s c a n p r o v i d e a c t i v a t i o n e n e r g i e s g r e a t e r t h a n those a v a i l a b l e t h e r m a l l y .  However, t h e s e r e a c t i o n s a l s o obey  c h e m i c a l l a w s , and t h e r e i s no need t o t r e a t r a d i a t i o n  chemistry  as a domain beyond t h e realms o f c h e m i s t r y because o f t h e v a s t energies  available.  F o l l o w i n g the a b s o r p t i o n o f h i g h energy r a d i a t i o n , the e x c i t e d molecules  and i o n s formed by t h e p h y s i c a l p r o c e s s e s  described i n the previous s e c t i o n and r e a c t i o n s .  undergo a v a r i e t y o f changes  The i o n s may recombine, t h e e x c i t e d m o l e c u l e s  may d i s s o c i a t e o r l u m i n e s c e  and many o t h e r r e a c t i o n s may o c c u r  as t h e s p e c i e s d i f f u s e and become homogeneously d i s t r i b u t e d  -11t h r o u g h o u t t h e medium.  A general o u t l i n e of these chemical  processes which occur f o l l o w i n g the p h y s i c a l stage of the r a d i o l y s i s i s s c h e m a t i c a l l y i l l u s t r a t e d i n F i g u r e 3. The  t i m e s c a l e s on w h i c h t h e s e e v e n t s o c c u r , and i n d e e d  whether t h e y o c c u r ,  depend t o a l a r g e e x t e n t on t h e p o l a r i t y  o f t h e medium and i t s p h y s i c a l s t a t e gas).  ( i . e . s o l i d , l i q u i d , or  The f o l l o w i n g d i s c u s s i o n w i l l be r e s t r i c t e d t o t h e  condensed p h a s e s , s p e c i f i c a l l y l i q u i d and f r o z e n p o l a r systems w h i c h w i l l be t r e a t e d 1.  Polar  separately.  Liquids  An i n d i c a t i o n o f t h e p r o b a b l e time s c a l e f o r t h e r a d i a t i o n events i n a t y p i c a l d i e l e c t r i c l i q u i d , water, i s g i v e n i n T a b l e 1. During the physiochemical which begins w i t h i n 1 0 s e c o n d s  stage o f the r a d i o l y s i s , a f t e r the incidence of the  r a d i a t i o n ; ion-molecule reactions occur,  electronically  e x c i t e d m o l e c u l e s a r e i n v o l v e d i n energy t r a n s f e r p r o c e s s e s o r e l s e d i s s o c i a t i o n , and r a d i c a l d i f f u s i o n b e g i n s . ion  t h e low e n e r g y e l e c t r o n s become t h e r m a l i z e d ,  have e n e r g y e q u i v a l e n t  In a d d i t -  that i s they  t o kT o r '•'0.025 eV, and may e n t e r  i o n - m o l e c u l e r e a c t i o n s o r e l s e become s o l v a t e d by c a u s i n g p o l a r i z a t i o n of the s o l v e n t d i p o l e s Solvated  into a  (dielectric relaxation).  e l e c t r o n s and t h e i r p r o p e r t i e s w i l l be d i s c u s s e d i n  detail i n a later section. The  d i s t i n c t i o n between t h e p h y s i o c h e m i c a l  and t h e t r u e  (HIGH ENERGY PHOTONS) Compton ^ process  FAST ELECTRONS  Physical stage  Excitation  Ionization, *  POSITIVE IONS  M Chemical stage  •  SLOW ELECTRONS fc— '  +  Ion-molecule reactions  I MH + R+  Pre-formed traps in solids  Geminate "" Ionic =  EXCITED MOLECULES  M*  recombination dissociat ion  Dielectric relaxation in liquids  h-9  uminescenc  diationless Dissociation H transitions  I  STABILIZED ELECTRONS Ion-molecule reactions MH*,M or S  >  RADICALS fV  STABLE PRODUCTS  Figure 3.  P r i m a r y p r o c e s s e s i n t h e a c t i o n o f r a d i a t i o n on m a t t e r .  M  TABLE 1 APPROXIMATE TIME SCALE FOR THE RADIOLYSIS OF LIQUID WATER (adapted from T a b l e 8.3, r e f e r e n c e 1, page 252-3) Time (sec) 10-18  E l e c t r o n o f 1 MeV energy molecule  t A  10 -15  10 -14  10 -13 Physiochemical stage  Present  traverses H 0-*<M*H 0  2  Physical stage  Species  Reactions  Events  Thermal e l e c t r o n (0.025 eV) t r a v e r s e s a m o l e c u l e . Time between s u c c e s s i v e i o n i z a t i o n s by a MeV electron. Time f o r " v e r t i c a l " e x c i t a t i o n t o an e l e c t r o n i c e x c i t e d state.  H  10~11  R e l a x a t i o n time f o r t h e o r i e n t a t i o n o f t h e water d i p o l e s .  n  > 0 —*AA>W-" H  2  2  H 0 (localized i n spurs o r t r a c k zone)  O  2  J  J  H 0 + H 0 -*H 0 +OH+  +  2  2  3  iH-  H O* 2  Secondary e l e c t r o n s reduced t o t h e r m a l energy. Electron capture. I n t e r n a l c o n v e r s i o n from h i g h e r t o lowest e l e c t r o n i c s t a t e . R a d i c a l moves one "jump" i n  2  >  Ion m o l e c u l e r e a c t i o n s . Period o f molecular v i b r a t i o n . Dissociation of molecules e x c i t e d t o r e p u l s i v e states.  10 -12  H„O 2  +  +  OH«  + OH* ?  •H 0+H*  H 0-+  H«  2  3  diffusion.  ( e  e~ _ +  H  2  0  *- e^q ^ . H  +  o  i  r  H* OH' ,e"" H o*(?) ' a  )  2  (... c o n t i n u e d on page 14)  q  l  TABLE 1  o  n  t  -  Events  Time (sec)  10 -10  c  Reactions  Minimum time f o r d i f f u s i o n c o n t r o l l e d reactions i n the bulk of the l i q u i d .  H*  +  H-  OH* *  10 -9  10 -8  Electron with i n i t i a l comes t o " r e s t " .  energy  2  OH*  2  H*  >  2  e"  » H  aq  J  10  -5  Chemical stage  10 - 4  —  Reaction time f o r r a d i c a l s with solutes i n molar concentrations. Lifetime of the hydrated electron.  H  H y  H  9  Present  0H«  c  2 °  2 ° 2  H  o f 1 MeV  Radiative lifetime of singlet excited states. Formation of molecular prod u c t s c o m p l e t e i n 'V-ray s p u r s .  Species  H  2  2  0 * ( ? ) , 0  or  + 2 0 H "  H  2  ,  - ( a l l i n  2  near  and  ^  aq'  spurs  track)  J  R*  + S  products  i  Time r e q u i r e d f o r a r a d i c a l t o . d i f f u s e the inter-spur distance i n t h e t r a c k o f a n MeV e n e r g y e l e c t r o n .  10"  Radiative states.-  10  Chemical  lifetime of triplet  excited  H o ,  reactions  complete,  H  2  0  2  and  products of r a d i c a l reactwith solutes.  -15c h e m i c a l s t a g e s o f t h e r a d i o l y s i s i s g e n e r a l l y drawn a t about —9  10  seconds, w h i c h a l s o happens t o be the time r e q u i r e d t o  s l o w a 1 MeV e l e c t r o n t o t h e r m a l v e l o c i t y .  During the chemical  s t a g e , t h e r a d i c a l s and i o n s formed i n t h e s p u r s d i f f u s e o u t ward and t h o s e w h i c h escape r e c o m b i n a t i o n e v e n t u a l l y become homogeneously d i s t r i b u t e d t h r o u g h o u t t h e l i q u i d . these " p r i m a r y " s p e c i e s w i t h s o l u t e  Reactions of  (scavengers) o r s o l v e n t  m o l e c u l e s c a n t h e n o c c u r t o form s t a b l e " p r i m a r y " r a d i o l y s i s products.  Those s p e c i e s w h i c h r e a c t w i t h i n t h e s p u r s t o form  s t a b l e m o l e c u l e s , termed " m o l e c u l a r p r o d u c t s " , a r e g e n e r a l l y not s c a v e n g e a b l e  a t normal s o l u t e c o n c e n t r a t i o n s ( i . e . 10  M) ,  however i f v e r y h i g h s o l u t e c o n c e n t r a t i o n s a r e used  ( i . e . 1 M)  t h e p r e c u r s o r s o f t h e s e " m o l e c u l a r p r o d u c t s " may be  scavenged.  When v e r y l a r g e r a d i a t i o n doses a r e g i v e n , t h e " p r i m a r y " p r o d u c t s may become i n v o l v e d i n r e a c t i o n s w i t h t h e p r i m a r y r a d i c a l s p e c i e s t o form d i f f e r e n t "secondary" s p e c i e s and products  ( e . g . i n w a t e r , H2°2  a  m  °l  e c u  l  a r  product, e v e n t u a l l y  r e a c h e s s u f f i c i e n t c o n c e n t r a t i o n t o r e a c t w i t h e~ , OH*, and H* t o form 0H~ + OH- , H- + H-,0, and OH* + H?0 r e s p e c t i v e l y ) . aq ^ z  2.  F r o z e n P o l a r Systems  By f r e e z i n g a l i q u i d and l o w e r i n g t h e temperature sufficiently, of  i t i s p o s s i b l e t o s l o w down t h e c h e m i c a l s t a g e s  r a d i o l y s i s l i s t e d i n T a b l e 1.  fies  I n many systems t h i s  simpli-  t h e r e a c t i o n s w h i c h c a n o c c u r and i n some c a s e s , a l l o w s  d i r e c t o b s e r v a t i o n o f t h e p r i m a r y s p e c i e s and i n t e r m e d i a t e s involved. R a d i c a l s formed e i t h e r d u r i n g t h e p r i m a r y r a d i o l y s i s  -16processes as H may  also  an  radical,  the p o s i t i v e molecule  and  are  o f t e n trapped  electronic  polarization  ilize  themselves  occur  to form  radicals  observed  by  a  of  electron  spin  a l s o may  be  i o n s by  used  the o v e r a l l  These  particular,  positive  "holes"  quickly  induce and  dipole relaxation trapped  and  negative  t h e r e f o r e may  spectroscopy.  in identification  be  detected  stabcan  ions be  Optical  of  the s p e c i e s .  the b a s i c o b j e c t i v e s of  radiolysis  (b) What r e a c t i o n s do these  In  of f r o z e n systems i n the  (a) W h i c h s p e c i e s may to  becoming  the s o l v e n t d i p o l e s are  i o n s may  resonance  summarized  the r a d i o l y s i s  formation  the s u r r o u n d i n g m o l e c u l e s  "deeper" t r a p .  Ions  transferring  resulting  i n "pre-formed" the  such  matrices.  i o n s by  negative  i n t h i s manner u n t i l  Kevan^ has  do  with  are o f t e n paramagnetic  spectroscopy  how  the  Alternatively,  species  temperature  o r i e n t e d to provide s t a b i l i z a t i o n .  t h e medium.  relate  primary  i n d e f e c t s i n t h e m a t r i x where  electrons  into  i n low  to a neighbouring  suitably  and  r e a c t i o n s of mobile  become s t a b i l i z e d ;  additional  trapped  in  from  atoms, become t r a p p e d  a proton of  or  research  f o l l o w i n g manner:  and  how  do  their  yields  mechanism?  trapped  i n t e r m e d i a t e s undergo  r e a c t i o n s compare t o t h o s e  o c c u r i n g i n the  and  liquid  phase ? (c) What i s t h e various  nature  of  and  how  (e) A r e in  trapping sites  of  the  species? (d) What i s t h e s p a t i a l  iates  the  does new  i t affect types  f r o z e n s y s t e m s due  distribution  the  chemistry  of  i n the  of species generated  to matrix  the  stabilization?  intermedsystem?'  radiolytically  -17 -  ( f ) I s energy s t o r e d i n i r r a d i a t e d f r o z e n systems?  If  so, how e f f i c i e n t i s t h e p r o c e s s and c a n e n e r g y be s e l e c t i v e l y t r a n s f e r r e d from s i t e t o s i t e ? Thus s t u d i e s on f r o z e n systems a r e o f t e n c o m p l i m e n t a r y t o l i q u i d phase i n v e s t i g a t i o n s and h e l p i n s o l v i n g t h e o v e r a l l r a d i o l y s i s mechanism. 3.  R a d i a t i o n C h e m i c a l U n i t s and Terms  The  y i e l d o f a s p e c i e s o r p r o d u c t formed by r a d i o l y s i s  i s known as t h e "G v a l u e " . molecules,  I t i s d e f i n e d as t h e number o f  i o n s , atoms o r r a d i c a l s w h i c h a r e formed ( o r disr-  apear) f o r e v e r y 100 eV o f energy d e p o s i t e d i n t h e system.  For "primary"  the n o t a t i o n " G  species or "molecular"  " i s g e n e r a l l y used and G  the range o f 0-10 .  by t h e r a d i a t i o n  normally  products is in  Y i e l d s o f p r o d u c t s w h i c h a r e n o t formed  s o l e l y from a p r i m a r y p r o c e s s a r e i n d i c a t e d by " G(X) ". F o r secondary processes i n v o l v i n g chain r e a c t i o n s i t i s not unusual f o r a G v a l u e t o exceed 10. In order  t o o b t a i n an a b s o l u t e measure o f t h e G v a l u e  o f any s p e c i e s formed by r a d i a t i o n i t i s n e c e s s a r y t o know t h e t o t a l amount o f e n e r g y absorbed by t h e medium.  This  quantity  i s termed the "absorbed dose" and i t i s e x p r e s s e d i n many d i f f e r e n t u n i t s , t h e most common o f w h i c h i s t h e " r a d " . One r a d i s d e f i n e d as t h e d e p o s i t i o n o f 100 ergs g ~ l . sometimes c o n v e r t e d  This u n i t i s  t o a more c o n v e n i e n t q u a n t i t y , i . e . eV g~^, 13  by t h e f a c t o r 6.24 x 10  -1 eV g  - l rad  , since G value  r e q u i r e knowing t h e t o t a l dose i n u n i t s o f eV.  calculatxons  There a r e  -18-  numerous methods used t o d e t e r m i n e dose ( d o s i m e t r y ) .  They  v a r y from c h e m i c a l r e a c t i o n s w i t h a c c u r a t e l y known y i e l d s + 2  (e.g. o x i d a t i o n o f Fe  i n 0.8N  G ( F e ) = 15.5  'X-rays) t o e l e c t r o n i c d e v i c e s  for  + 3  6 0  Co  s u l f u r i c a c i d s o l u t i o n has capable  o f m e a s u r i n g the number o f c h a r g e d p a r t i c l e s o r i o n s produced and  c a l o r i m e t r i c methods d e s i g n e d t o measure the energy  when i t i s a l l c o n v e r t e d t o h e a t . C.  STABILIZED ELECTRONS I n the previous  deposited  3  5  s e c t i o n s i t has  been shown t h a t  the  i n t e r a c t i o n o f i o n i z i n g r a d i a t i o n w i t h m a t t e r produces h i g h e n e r g y e l e c t r o n s w h i c h t h r o u g h a cascade o f p r o c e s s e s g i v e r i s e t o numerous low e n e r g y e l e c t r o n s . 1 MeV  e l e c t r o n may  electrons.)  produce between 10  These low energy e l e c t r o n s  and  eventually  (In f a c t a s i n g l e IO  (<10  3  secondary eV)  l o s e most o f  t h e i r r e m a i n i n g energy by e x c i t a t i o n o f e l e c t r o n i c t r a n s i t i o n s and  v i b r a t i o n a l s t a t e s o f the medium.  o r drops below ^0.5 thermalized, 7 **10  the  " s u b - e x c i t a t i o n " e l e c t r o n s become  w h i c h means t h a t t h e i r v e l o c i t y d e c r e a s e s t o  -1 cm s  ( a t room temperature) and  r e d u c e d to**»0.03 eV. c a t i o n s and  The  t h e i r energy i s f u r t h e r  s e p a r a t i o n d i s t a n c e between the  electrons increases  e n e r g y l o s s and and  eV,  When t h e i r energy r e a c h e s  the t h e r m a l i z e d  d u r i n g the l a t t e r s t a g e o f e l e c t r o n may  leave i t s spur  p o s s i b l y overcome the Coulombic f i e l d o f the c a t i o n s . Charge  n e u t r a l i z a t i o n does e v e n t u a l l y o c c u r however i f the  electron  i s u n a b l e to escape the i n f l u e n c e o f i t s p o s i t i v e i o n and p r o c e s s i s c a l l e d "geminate r e c o m b i n a t i o n " . t h a t the t h e r m a l i z e d  this  The p r o b a b i l i t y  e l e c t r o n s w i l l escape from the  influence  -19o f the Coulombic f i e l d depends on the p o l a r i t y o f the medium ( i t s d i e l e c t r i c . c o n s t a n t ) , i t s degree o f o r d e r  (liquid,  c r y s t a l l i n e o r g l a s s y amorphous s t a t e ) , and t h e t e m p e r a t u r e (viscosity) . I f t h e t h e r m a l e l e c t r o n s do escape geminate  recombin-  a t i o n t h e n they may be s t a b i l i z e d by the s u r r o u n d i n g medium, e i t h e r t h r o u g h a s o l v a t i o n p r o c e s s i n p o l a r l i q u i d s o r by t r a p p i n g i n pre-formed " h o l e s " i n f r o z e n systems.  An a l t e r n -  a t i v e , f a t e f o r these thermal e l e c t r o n s i s o f course t o r e a c t w i t h a s o l v e n t m o l e c u l e and t h i s r e a c t i o n w i l l depend on t h e e l e c t r o n a f f i n i t y o f the s o l v e n t . 1.  E l e c t r o n S o l v a t i o n Process  D u r i n g the e a r l y i n v e s t i g a t i o n s o f the r a d i a t i o n chemi s t r y o f w a t e r , by f a r the most t h o r o u g h l y s t u d i e d system t o d a t e , s e v e r a l t h e o r i e s were advanced t o a c c o u n t f o r t h e o b s e r v e d c h e m i s t r y , and p a r t i c u l a r l y the p r o d u c t i o n o f hydrogen. and Magee moderated still  Samuel  proposed t h a t the s u b e x c i t a t i o n e l e c t r o n s would t o t h e r m a l e n e r g i e s w i t h i n 10""13 seconds and  i n the Coulombic f i e l d o f the p a r e n t i o n s .  d i e l e c t r i c r e l a x a t i o n time o f w a t e r i s 1 0 ~ H  be  while  S i n c e the  s e c o n d s , the  d i p o l e s would not be a b l e t o r e o r i e n t t h e m s e l v e s q u i c k l y enough to s o l v a t e the e l e c t r o n .  T h e r e f o r e geminate r e c o m b i n a t i o n  would o c c u r t o produce an e x c i t e d w a t e r m o l e c u l e w h i c h would t h e n d i s s o c i a t e t o g i v e an H atom and an OH r a d i c a l w i t h s u f f i c i e n t energy t o escape t h e s o l v e n t cage. Thus t h e p r i m a r y species  i n the Samuel-Magee t h e o r y a r e H and OH r a d i c a l s formed  i n t h e immediate v i c i n i t y o f t h e s p u r .  -20-  An a l t e r n a t i v e model o f Lea^  and Gray^ s u g g e s t e d  that  the s e c o n d a r y e l e c t r o n would move about 150 A* from t h e p a r e n t p o s i t i v e i o n and t h u s beyond t h e e f f e c t o f i t s e l e c t r o s t a t i c field. ion  Under t h e s e c i r c u m s t a n c e s t h e e l e c t r o n and t h e p o s i t i v e  would r e a c t independently w i t h the s o l v e n t .  I t was p o s t -  u l a t e d t h a t t h e e l e c t r o n r e a c t s t o g i v e an H atom and OH", q  w h i l e t h e p o s i t i v e i o n produces an  OH r a d i c a l .  Platzman  e s s e n t i a l l y a g r e e d w i t h t h e Lea-Gray t h e o r y about t h e e l e c t r o n escaping  t h e Coulombic f i e l d o f H^O"^, however he p o i n t e d o u t  that the r e a c t i o n of thermal e l e c t r o n s w i t h water i s r e l a t i v e l y slow.  He c o n c l u d e d t h a t t h e e l e c t r o n might n o t undergo t h i s  r e a c t i o n b u t c o u l d s u r v i v e t o become s o l v a t e d .  The s o l v a t e d  e l e c t r o n w o u l d t h e n r e a c t i n a manner s i m i l a r t o t h e H atom. P l a t z m a n ' s p o s t u l a t e was l a t e r p r o v e n t o be c o r r e c t when i t was e x p e r i m e n t a l l y  d e t e r m i n e d t h a t an i o n i c  species with u n i t negative  charge was i n v o l v e d i n t h e r a d i o l y s i s  of water.'  reducing  T h i s s p e c i e s was s u b s e q u e n t l y i d e n t i f i e d as t h e  L0  h y d r a t e d e l e c t r o n by i t s i n t e n s e o p t i c a l a b s o r p t i o n  i n the r e d  w h i c h was s i m i l a r i n c h a r a c t e r i s t i c s t o t h e o p t i c a l  absorption  band o f c h e m i c a l l y produced s o l v a t e d e l e c t r o n s i n l i q u i d ammonia.^  Since  t h e s e " e a r l y " s t u d i e s , numerous r e p o r t s have  been made on t h e f o r m a t i o n of  liquids. The  of solvated electrons i n a v a r i e t y  5  e x a c t d e t a i l s o f t h e mechanism o f t h e s o l v a t i o n  process are s t i l l  s p e c u l a t i v e s i n c e no one has y e t been a b l e  t o , a c t u a l l y observe the formation  of solvated electrons  the f a c t t h a t time r e s o l u t i o n i n t o t h e 10  despite  second r e g i o n has  -21-  been a c h i e v e d .  The most g e n e r a l l y a c c e p t e d q u a l i t a t i v e p i c t u r e  o f the s o l v a t i o n p r o c e s s i n v o l v e s the t h e r m a l e l e c t r o n ( w i t h i n 10~1^ molecules.  seconds) e l e c t r o n i c a l l y p o l a r i z i n g the  initially  surrounding  This e l e c t r o n i c p o l a r i z a t i o n i s thought t o e f f e c t -  i v e l y "immobilize"  the e l e c t r o n w h i l e  the s l o w e r a t o m i c and  d i p o l a r p o l a r i z a t i o n s can o c c u r t o s o l v a t e i t . A s c h e m a t i c representation  o f t h e s e e v e n t s f o r w a t e r and a c o m p a r a t i v e l y  n o n - p o l a r l i q u i d , n-hexane, i s shown i n F i g u r e 4.  13  "TRAPPED" E L E C T RON  LOG  12  t (sec)  11  SOLVATED ELECTRON  F i g u r e 4. Q u a l i t a t i v e r e p r e s e n t a t i o n o f the p o t e n t i a l energy o f an e l e c t r o n as a f u n c t i o n o f t i m e a f t e r l o c a l i z a t i o n i n a l i q u i d , ( a f t e r F i g u r e 4, Freeman, r e f e r e n c e 12, page 23) Solvated greater  e l e c t r o n s a r e formed i n b o t h s y s t e m s , however the much p o t e n t i a l energy g a i n by the e l e c t r o n i n w a t e r due t o  d i p o l e o r i e n t a t i o n makes the h y d r a t e d e l e c t r o n a more " s t a b l e " species.  I n a d d i t i o n , because o f the d i e l e c t r i c  constant  d i f f e r e n c e s between n-hexane and w a t e r , the y i e l d o f e l e c t r o n s w h i c h escape geminate r e c o m b i n a t i o n w i l l be much l a r g e r f o r water. The and  e s s e n t i a l d i f f e r e n c e between the  the s o l v a t e d one i s s i m p l y  "trapped" e l e c t r o n  t h a t the d i e l e c t r i c has  i t s e q u i l i b r i u m p o i n t i n the case o f the s o l v a t e d  reached  electron,  -22-  whereas The  i t has n o t completely  solvated  while  the "trapped"  2.  the case  thermalized  In glassy  molecular quick  cooling.  of  pre-formed  an  effective  ion's  glassy  for  alcohols  methanol)  form  solvation  a  least much  of  exist  systems,  there  This  order  electrons  whereas  t h e medium  hand,  temperature  t h e randomness state  prevails.  of the  i s "frozen  i n " by  concentration  molecules  i s i n contrast Thus  efficiently  t h e same m a t e r i a l  wholly  i n the low  i s a large  very  by  the  forming  with to  the  parent  crystalline  f o r example, (G tr  =2.5  p  i n a polycrystalline  does n o t . ^ The  at  range  trap  which  a v a i l a b l e t o compete  attraction.  short  on the other  (i.e. dipole-oriented  p o s i t i v e hole)  where  case.  Systems  t o be s t a b i l i z e d  o f the l i q u i d  Consequently  Coulombic  systems  traps  amorphous  "traps"  systems,  are thought  orientations  equilibrium with  i n Frozen  of frozen  pre-formed  i n the "trapped"  i snot.  Trapping  electrons  partially  matrix.  i s i n thermal  state  Electron  In  or  electron  relaxed  trapping process  partial  greater  trapped  electron direct polar  process  discussed  trapping  the  spur  the  liquid).  although  efficiency.  are observed  the advantage  o f the fact  are stabilized  ( i . e . they Thus  don't  that  within travel  the s p a t i a l  Normally  relative  i n t h e same m a t e r i a l .  consequence media  above,  t o be s i m i l a r t o t h e  pre-orientation o f the dipoles  electrons  yield  i s thought  This  allows f o r higher  yields  to the solvated i s probably  the trapped  the immediate  a  electrons i n vicinity  as f a r i n t h e s o l i d  distribution  of  of  as i n  o f trapped  electrons  -23i s l i k e l y t o be v e r y d i f f e r e n t t o t h a t o f s o l v a t e d ones. 3.  P r o p e r t i e s of S t a b i l i z e d  Electrons  S t a b i l i z e d e l e c t r o n s formed by r a d i o l y s i s have p r o p e r t i e s v e r y s i m i l a r t o t h o s e o f s o l v a t e d e l e c t r o n s formed by solution  o f a l k a l i m e t a l s i n ammonia and  powerful reducing  amines.  dis-  They are  species, reacting often with d i f f u s i o n  t r o l l e d rate constants  i n solution,  and  very  con-  c o n s e q u e n t l y have  r e l a t i v e l y s h o r t l i f e t i m e s i n i r r a d i a t e d l i q u i d systems ( i . e . 10""^ seconds o r l e s s ) . Solvent-stabilized intense o p t i c a l absorption infrared  regions.  e l e c t r o n s a r e c h a r a c t e r i z e d by s p e c t r a i n the v i s i b l e o r near  T h i s i s t h e i r most i m p o r t a n t p r o p e r t y  f a r as d e t e c t i o n and k i n e t i c s t u d i e s are concerned. The a r e a l s o p a r a m a g n e t i c and (ESR)  broad  as species  t h e r e f o r e e l e c t r o n s p i n resonance  i s e x t e n s i v e l y used t o s t u d y the l o n g l i v e d t r a p p e d  e l e c t r o n s i n f r o z e n systems.  Recent advances i n ESR  techniques  have a l s o e n a b l e d the s h o r t l i v e d s o l v a t e d e l e c t r o n s produced by p u l s e r a d i o l y s i s o f l i q u i d s t o be S t a b i l i z e d e l e c t r o n s are now variety  studied.^ known t o e x i s t i n a whole  o f media from the n o n - p o l a r l i q u i f i e d n o b l e gases t o  h i g h l y p o l a r s o l v e n t s s u c h as w a t e r and contains  some o f the s p e c t r a l  alcohols.  data f o r electrons  Table 2 stabilized  i n a few of the more e x t e n s i v e l y s t u d i e d systems. 4.  Y i e l d s of S t a b i l i z e d  I t has  Electrons  been r e a s o n a b l y w e l l e s t a b l i s h e d t h a t the y i e l d  TABLE 2 SELECTED PROPERTIES OF STABILIZED ELECTRONS FORMED BY RADIOLYSIS ESR D a t a  O p t i c a l Data T(°K)  Medium 7N NaOH g l a s s  -  X max  (nm)  6 (M" cm~ ) 1  1  Yield G  q-factor  e"  77  580  19,000  2.0006  15  2.0 2.8 0.0003  Water  78.2  293 77  7 20 640  17,000 17,000  2.0002 2.0009  0.5 10.6  Heavy w a t e r  78. 5  293 77  700 630  20,200 20,200  2.0007  2.7  Methanol  32.6  293 77  630 526  17,000 11,000  2.0018  11.2  1.1 2.7  Isopropanol  18.6  293 77  820 615  13,000 15,300  2.0018  10  1.0 1.9  4.6  293 77  1250  16,800  2.0011  38.7  293 77  580 513  14,000  Methyl t e t r a hydrofuran Ethylene Glycol  -  4.5 10-15  0.0006° e  e  0.23 2.6 e  'e 2.6 1  2  e  F o o t n o t e s : a. D a t a from r e f e r e n c e s 4, 5d, and 5e. . b. S t a t i c d i e l e c t r i c c o n s t a n t a t room t e m p e r a t u r e . c. L i n e w i d t h between p o i n t s o f maximum s l o p e . solid, e. G l a s s y amorphous s o l i d .  d. P o l y c r y s t a l l i n e  -25of  solvated  constant  electrons  of  the  correlates with  liquid.  This  trated g r a p h i c a l l y i n Figure sources the is a  and  obtained  solvents, in fact  few an  or  a very  the  short  r e a s o n the because  geminate  the  that  could  ionic  be  one  "free ion yield",  G ^,  y i e l d s of  h o w e v e r , do physical order.  number o f  thermal  anion  and  electrons  in  formed  electron  solvent.  i s used  f  of  entity  Indeed,  thermal  the  several  some  reducing  a radical  with  illus-  from For  exist.  e i t h e r the  solvated  data  techniques. the  well  dielectric  For  i n Figure  this 5  i n essence i t  which  escape  recombination.  The  not  trapped  of  the  I n most g l a s s y and  electrons  i n frozen  seem t o c o r r e l a t e w e l l w i t h  property  high,  matrix,  other  s o l i d s the  i n the  result  of  the  may  operating  liquid  fact  that  i n the  material. one  particular  trapped  than the This  state  systems,  than i t s degree  o r more o f  glassy  any  y i e l d s of  i n many c a s e s h i g h e r  electrons  be  contains  i t i s more u n i v e r s a l l y a p p l i c a b l e  represents  are  proof  r e a c t i o n of  lived  term  5 which  static  correlation is  e l e c t r o n does n o t  species  ion-molecule  empirical  a v a r i e t y of  conclusive  a solvated  cases  by  by  the  yield  is likely the  of  electrons solvated  t o be  following  to lower  of  the  factors  the p r o b a b i l i t y  17  of  prompt g e m i n a t e r e c o m b i n a t i o n :  electrons  may  collision  i n the  (a)  "sub-ionization"  have a lower c r o s s - s e c t i o n solid  matrix  f o r energy l o s s  than i n the  liquid  because  f e w e r v i b r a t i o n a l and  rotational states  transferred,  t r a p depth r e s u l t i n g from e i t h e r  trapping the  by  (b)  the  suitably oriented  m a t r i x may  be  sufficient  dipoles to  or  per of  t o which energy can self  from imperfections  compete w i t h  the  be  Coulombic  in  •  1  •  1  •  1  -  • _  •  ^  O  -  -  o  o  S  0 o  /  0  •  •  —  i  • =Alcohols  and w a t e r s ; reference 5 e .  o = Nitrites, ketones, ethers, ami d e s , pyridine, dimethyl sulfoxide, propylene carbonate, hydrocarbons; X : Formamide ;  /  °  D = Ammonia;  D  o  1  20 Figure  to 0>  1 40  I  1  CL  5. Y i e l d o f r a d i o l y t i c a l l y g e n e r a t e d f r e e i o n s d i e l e c t r i c c o n s t a n t (D ) o f the l i q u i d . s  r e f e r e n c e 15. reference 16.  .  60  r e f e r e n c e 14.  t  .  80 (Gfi)  as a f u n c t i o n o f the  1  100 static  —  -27f o r c e o f the p o s i t i v e i o n , and  (c)  as the t r a p p e d charge con-  c e n t r a t i o n i n c r e a s e s w i t h dose, the presence o f competing tric fields  elec-  from s e v e r a l p o s i t i v e i o n s weakens the d i r e c t i o n a l  e f f e c t on the t r a p p e d e l e c t r o n .  Thus f o r example,  the y i e l d  o f t r a p p e d e l e c t r o n s i n g l a s s y methanol a t 77°K i s G  = e  tr  2.5  whereas the y i e l d o f s o l v a t e d e l e c t r o n s i n the same m a t e r i a l a t room temperature i s o n l y G _ s e  = 1.1  .  -28-  CHAPTER I I AN ATTEMPT AT NITROGEN FIXATION UTILIZING HYPRATED ELECTRONS A.  INTRODUCTION 1.  Background t o the Problem  Nitrogen  f i x a t i o n * has always been o f p a r t i c u l a r  interest  to s c i e n t i s t s because o f i t s importance t o the e v o l u t i o n o f l i f e on the e a r t h .  In c u r r e n t b i o l o g i c a l systems, n i t r o g e n i s  taken from the atmosphere and i n c o r p o r a t e d w i t h  the a i d o f  micro-organisms, v i a ammonia, i n t o o r g a n i c n i t r o g e n compounds under v e r y m i l d c o n d i t i o n s .  In c o n t r a s t t o t h i s ,  temperatures  of 300-600 °C and s e v e r a l hundred atmospheres p r e s s u r e o f n i t r o g e n a r e r e q u i r e d i n the i n d u s t r i a l Haber-Bosch process t o overcome the i n e r t n e s s o f the molecule and c o n v e r t  nitrogen to  ammonia.  evolution  Thus a c r u c i a l q u e s t i o n  to understanding  i s how n i t r o g e n was reduced i n p r e b i o l o g i c a l times when o n l y the b a s i c i n g r e d i e n t s ; n i t r o g e n , hydrogen, and methane e x i s t e d i n a r e l a t i v e l y mild  environment.  - A l t h o u g h the problem o f b i o l o g i c a l n i t r o g e n has  fixation  been, and c u r r e n t l y i s , one o f the major areas o f r e s e a r c h  i n b i o l o g y and b i o c h e m i s t r y ;  i t was o n l y r e c e n t l y t h a t the  c h e m i s t s ' i n t e r e s t i n non-enzymatic n i t r o g e n f i x a t i o n was r e k i n d l e d by A l l e n and S e n o f f ' s  d i s c o v e r y o f a t r a n s i t i o n metal  * f o o t n o t e 1. N i t r o g e n f i x a t i o n i s used here i n i t s broadest sense t o i n c l u d e any process which c o n v e r t s m o l e c u l a r n i t r o g e n to some other m o l e c u l e .  -2918 complex rapid the  of molecular  growth  nitrogen.  i n the f i e l d  additional  This  d i s c o v e r y and  subsequent 19 chemistry, with  o f n i t r o g e n complex  discovery that  t h e n i t r o g e n l i g a n d s c o u l d be  20 reduced  i n certain  oratory  i n the p o s s i b i l i t y  molecular  This in  agent  makes  chemical  a standard  i n this  lab-  fixation of  i s diminished aim o f t h i s  (1)  e occurs aq  a wide  by a s m a l l  investigation N  2  Literature  Non-enzymatic  complexes.  although  a  powerful  o f -2.7 V .  extremely  high  rate  o f compounds, 22  reactions proceed i n some  cases  t o determine  *• r a tNe H .  3  some  as n o n - r e d u c i b l e . with  virtually  the reaction 23  pre-exponential factor. was  sodium  nucleophile f o r simple  variety  regarded  a l l o f these  formed  strength to metallic  i ti s the ideal  + N~ • w i t h a n [o b s~ e ] rvable 2 i z J aq  o f ways  electrode potential  i n reducing  of activation,  species  t o be a n e x t r e m e l y  r e a c t i o n s a n d i t shows  almost  the  — (e ) , a p r i m a r y aq  i s known  had p r e v i o u s l y been  energy  variety  21  f o rr e a c t i o n s with  Furthermore,  rate  with  In addition,  constants  no  o f water,  transfer  which  of radiation  electron  i tcomparable  water.  electron  of  hydrated  the radiolysis  reducing  stimulated interest  nitrogen.  The in  systems,  (or N H 2  Thus  whether  reaction  o r NH 0H)  4  (1)  2  Survey  nitrogen fixation  i n addition  In addition  t o those  has been  involving  t o the Haber-Bosch  achieved  i n a  transition  process  for  the  24 catalytic  conversion o f N /H  oxidative  and/or  2  2  mixtures  t o ammonia,  reductive nitrogen fixation  g a s pi  has been  metal  -3025 (a) r a d i o l y s i s o f N /0 o r N /H gas m i x t u r e s , 2 2 2 2 26 (b) s o n o l y s i s of a i r , (c) gas d i s c h a r g e methods 27 , and (d)  a c c o m p l i s h e d by:  h e t e r o g e n e o u s r e a c t i o n of m o l e c u l a r and  n i t r o g e n w i t h some group I  I I m e t a l s to g i v e i o n i c n i t r i d e s w h i c h can be h y d r o l y s e d  g i v e ammonia  TO  .  The  e l e c t r o l y t i c reduction of molecular  to  nitrogen  i n an a p r o t i c s o l v e n t u s i n g an a l k a l i m e t a l o r the n a p t h a l e n e a n i o n r a d i c a l i n c o n j u n c t i o n w i t h a t r a n s i t i o n m e t a l i o n has 29 been r e p o r t e d nitrogen i n  and  the r a d i a t i o n c h e m i c a l  f i x a t i o n of  ^ - i r r a d i a t e d o r g a n i c compounds has been  molecular  claimed . 3 0  I n aqueous s o l u t i o n , the o x i d a t i o n o f n i t r o g e n by e x c i t e d s i n g l e t oxygen m o l e c u l e s was  reported^  and a p r o c e s s  for hetero-  geneous c a t a l y t i c f i x a t i o n o f n i t r o g e n o r a i r i n an aqueous s o l u t i o n u t i l i z i n g h i g h energy r a d i a t i o n has been  patented-'''.  I n a d d i t i o n t o the l i t e r a t u r e mentioned above,  and  p a r t i c u l a r l y r e l e v a n t t o the p r e s e n t s t u d y , are a number o f p u b l i c a t i o n s c o n c e r n e d w i t h the r a d i o l y s i s o f aqueous s o l u t i o n s 33 3 3 ci b o f n i t r o g e n and a i r . D m i t r i e v and P s h e z h e t s k i i ' reported t h a t the  ^ - r a d i o l y s i s o f n e u t r a l aqueous s o l u t i o n s c o n t a i n i n g  e i t h e r pure n i t r o g e n o r n i t r o g e n - o x y g e n  mixtures  produced  n i t r o g e n i n the form of n i t r i t e , n i t r a t e , and ammonia. y i e l d s o f these p r o d u c t s above the s o l u t i o n and  for  a pressure  80/20 m i x t u r e  o f one  3  pressure  the p r e s e n c e o f oxygen a p p a r e n t l y A v a l u e o f GdsTH^^O.! was  had quoted  atmosphere o f e i t h e r pure n i t r o g e n o r  o f n i t r o g e n and oxygen, w i t h t h i s r i s i n g  G ( N H ) ~ 0 . 7 a t 150  The  i n c r e a s e d w i t h i n c r e a s i n g gas  l i t t l e e f f e c t on the y i e l d s .  fixed  atmospheres.  An attempt was  an  to  made t o e x p l a i n  t h e s e r e s u l t s on the b a s i s o f r e a c t i o n s o f H, OH and  H0  2  -31r a d i c a l s w i t h n i t r o g e n ; however, on t h e b a s i s o f t h e now known r e a c t i o n r a t e c o n s t a n t s o f H (e~ ) and OH w i t h oxygen, i t i s aq v e r y d i f f i c u l t t o u n d e r s t a n d how n i t r o g e n a t 10~^ M (1 atm) w o u l d be a b l e t o e f f i c i e n t l y compete w i t h any oxygen o r i m p u r 33c i t i e s p r e s e n t and g i v e ammonia.  Hammar e t a l .  very c o n t r a r y r e s u l t s f o r nitrogen-hydrogen water u s i n g a r e a c t o r r a d i a t i o n source  N  3  2  mixtures  i nneutral  and t a k i n g c a r e t o  e l i m i n a t e t h e gas space above t h e l i q u i d . G 2 ( N H ) = 2.6 ± 1.3 f o r 7 5 % N  obtained  - 25% H  2  Their results of are at least  four  o r d e r s o f magnitude l o w e r t h a n those o f D m i t r i e v and P s h e z h e t s k i i s i n c e t h e G^2(NH3)  n o t a t i o n r e f e r s t o t h e y i e l d c a l c u l a t e d on  the b a s i s o f t h e e n e r g y a b s o r b e d d i r e c t l y by t h e d i s s o l v e d nitrogen.  A t one atmosphere l e s s t h a n 1/10,000 o f t h e e n e r g y  d e p o s i t e d i n t h e s o l u t i o n w o u l d be absorbed d i r e c t l y by t h e 33d dissolved nitrogen.  S a t o and S t e i n b e r g  w i t h t h e r e s u l t s o f Hammar e_t a_l. .  essentially  They s t u d i e d t h e * y ~ r a d i o l -  y s i s o f a i r i n aqueous s o l u t i o n and found t h a t G a t n e u t r a l pH, w i t h G and  a i r  designed  a i r  ( N H ) = 2.3 3  ( N H ^ ) v a r y i n g s i g n i f i c a n t l y w i t h pH  f l o w r a t e o f a i r through t h e i r 3. The C h e m i c a l System The  agreed  apparatus.  e x p e r i m e n t s r e p o r t e d i n t h i s d i s s e r t a t i o n were  t o s t u d y i n d e t a i l j u s t one a s p e c t o f t h e r a d i a t i o n  c h e m i s t r y o f aqueous n i t r o g e n ; namely t h e r e a c t i o n o f t h e hydrated  electron with dissolved nitrogen.  experimental  F o r t h i s reason the  c o n d i t i o n s were chosen t o o p t i m i z e t h e chances o f  o b s e r v i n g t h e r e a c t i o n s i n c e i t c e r t a i n l y w o u l d n o t be e x p e c t e d t o be v e r y  fast.  -32-  I n a l k a l i n e s o l u t i o n s c o n t a i n i n g hydrogen, t h e p r i m a r y r a d i o l y s i s s p e c i e s o t h e r t h a n e~ a r e c o n v e r t e d t o h y d r a t e d ag ( 2 ) , ( 3 ) , and ( 4 ) .  electrons v i a the s e r i e s o f reactions OH  +  H H  + 0  2  H —* H  +  2  H 0  (2) k = 4 x l 0  2  0 H ~ —> e ~ + H 0 + e~^—•  2  (3) k = 2xl0  2  q  OH  +  °2 very  +  e  1  1  7  M~ s"  1  1  (4) k = 1 . 2 x l 0  OH"  M^s"  1 0  4  Thus t h e  a q ~ * 2~~*" 2°2 0  M" s~  3  F u r t h e r m o r e t r a c e q u a n t i t i e s o f oxygen a r e a l s o q u i c k l y by r e a c t i o n (5).  7  2  H  2  k  5  eliminated  system produces a  H /OH~ ( 5 )  1  L^xlO  =  M" s"  1 0  1  1  "clean" source o f hydrated e l e c t r o n s w i t h a s u b s t a n t i a l  y i e l d G ( e ~ )*»»6 . A l t h o u g h t h e b i m o l e c u l a r  r e a c t i o n o f the  h y d r a t e d e l e c t r o n (6) has a h i g h r a t e c o n s t a n t , S  aq  +  e  aq-* 2 H  +  <> V 6  aq  2 0 H  5xl  r a t e s used, t h e s t e a d y s t a t e c o n c e n t r a t i o n  °  9  a t t h e l o w dose M  "  l s _ 1  o f hydrated  electrons  w i l l be s o low t h a t t h i s r e a c t i o n may be d i s r e g a r d e d . Nominally then, i n the  system c o n t a i n i n g  H /OH~ 2  n i t r o g e n , r e a c t i o n (1) w i l l be i n c o m p e t i t i o n  only  dissolved  with  [N ~ ] ^ - * - N H (or N H O H o r N ^ ) (1) 2 a q " ' L"2 J aq r e a c t i o n s o f t h e h y d r a t e d e l e c t r o n s w i t h i m p u r i t i e s o r hydrogen N  +  e  2  A  3  2  peroxide generated v i a the "molecular"  p r o c e s s (G  = 0.8) . 2  T Tn  H  2  0  2  A second advantage o f t h e p r e s e n c e o f m o l e c u l a r hydrogen was t o supply of N  2  the s t o i c h i o m e t r i c H necessary f o r the u l t i m a t e toNH3 .  reduction  I t seemed r e a s o n a b l e t o assume t h a t once t h e  b a r r i e r t o r e d u c t i o n had been overcome i n t h e f o r m a t i o n o f N  2  o r N H , then i t s eventual 2  l e a s t hydrazine reducing  conversion  t o ammonia ( o r a t  o r h y d r o x y l a m i n e ) would be i n e v i t a b l e i n the  environment.  Indeed b o t h N ~ and N H have been p r o -  posed as f e a s i b l e i n t e r m e d i a t e s  2  2  on the b a s i s o f t h e o r e t i c a l  -33-  electron  A this the  preliminary  laboratory  by  Walker  and  reaction  pressure cell to hold  several  performed  the  on  spectrophotometric  In  addition,  reaction  (1)  was  absorbed  the  ammonia  measured. in  which  B.  EXPERIMENTAL  N /H 2  by  2  of  this  isolation  stainless vessel  achieved.  the a  phase  to  above  the  nitrogen  the  was  Nessler  yields  from  produced  radiation  via dose  solution  was  also  t e c h n i q u e was  nitrogen  cell  reproducible.  the  radiolysis  the  analysis  determine  significant  a  variable  substantial  ammonia was  problem,  of  using  not  test  steel  Ammonia  were  in  to  dissolved  ^-radiolysis  mixture  of  attempt  pressurizing  impossible  gas  gas  By  performed  and  being developed  saturated  liquid  Reagents  All Solutions  chemicals used of various  sodium  prepurified nitrogen  the  a  a glass  results  a l l times  alleviate  possible.  and  at  i n an  Although  the  i f any,  produced  was  after  were  significant  be  virtually  much,  complete  a  J J  used  solution.  could  observed,  by  They  technique.  since  To  1.  M)  i t was  d a t a how  Edwards  atmospheres  the s o l u t i o n  ammonia w e r e  experiments  contained  aqueous  (~0.1  of  and  (1).  which  hundred  concentration  their  34  of  volume to  studies.  number  system  high  .  affinity  pH  hydroxide. grade.  were  were  m i x t u r e s was  made  Hydrogen  Further  analytical using  and  oxygen  a c h i e v e d by  grade  or  better.  "Analar" s u l f u r i c  nitrogen removal  were  from  incorporation  Matheson  the of  acid  hydrogena  "Deoxo"  -34p a l l a d i u m c a t a l y s t i n the gas t r a i n .  C o m p o s i t i o n s o f the gas  m i x t u r e s used were d e t e r m i n e d u s i n g a V a r i a n A e r o g r a p h A90-P-2 gas chromatograph w i t h a 20 f o o t 13X m o l e c u l a r s i e v e  column  and WX t h e r m a l c o n d u c t i v i t y d e t e c t o r s . Water was p u r i f i e d by t h r e e c o n s e c u t i v e  distillations;  the f i r s t from t a p w a t e r , t h e second from a c i d i f i e d d i c h r o m a t e , a f t e r w h i c h i t was  ^ - i r r a d i a t e d w i t h a 0.5 Mrad dose t o remove  trace organic impurities.  F i n a l l y i t was p l a c e d under c o n t i n -  uous c y c l i c r e f l u x d i s t i l l a t i o n from a l k a l i n e permanganate _7 u n t i l used.  The w a t e r was shown t o c o n t a i n l e s s t h a n 5 x 10  ammonium i o n s by the a n a l y s i s p r o c e d u r e t o be d i s c u s s e d  later  —6  and i t p r o b a b l y c o n t a i n e d much l e s s t h a n 10"  M reactive  organic i m p u r i t i e s . 2.  R a d i a t i o n Source 60  A  Co Gammacell 220 r a d i a t i o n s o u r c e was  used w h i c h had  an a c t i v i t y o f 6170 C u r i e s when l o a d e d i n June, 1967.  The  dose  r a t e was d e t e r m i n e d by the F r i c k e f e r r o u s s u l f a t e p r o c e d u r e w h i c h i s d i s c u s s e d i n d e t a i l i n Appendix 1. i n s i d e the high pressure min~l  The dose r a t e  c e l l was d e t e r m i n e d t o be 2500 r a d s  (1.6 x l O ^ eV g^min"- -) and the day t o day v a r i a t i o n i n 1  1  dose r a t e caused by decay o f the s o u r c e was  corrected f o r using  a computer program a l s o d i s c u s s e d i n Appendix 3. A p p a r a t u s and Techniques  1.  A s y r i n g e t e c h n i q u e by w h i c h the s o l u t i o n c o n t a i n i n g a h i g h c o n c e n t r a t i o n o f d i s s o l v e d n i t r o g e n c o u l d be  effectively  M  -35i s o l a t e d t o p r e v e n t gas phase r a d i o l y s i s was 50 ml a l l - g l a s s s y r i n g e s ( B e c t o n ,  D i c k i n s o n and Co.) were  m o d i f i e d by c u t t i n g o f f t h e f l a r e d ing  developed.  end o f t h e b a r r e l and g r i n d -  t h e t a p e r e d g l a s s t i p t o f i t a m o d i f i e d B7 s o c k e t  flared  ( the  ends o f t h e B7 s o c k e t s were a l s o c u t o f f ) . The  plungers of the syringes  were a l s o c u t l e a v i n g a s e c t i o n about  1% i n c h e s l o n g t o f i t i n s i d e t h e m o d i f i e d s y r i n g e b a r r e l .  A  B14 s o c k e t was s e a l e d i n p l a c e " i n s i d e " t h e p l u n g e r s e c t i o n to  f a c i l i t a t e o p e r a t i o n o f t h e s y r i n g e by i n s e r t i n g a s e c t i o n  o f g l a s s t u b i n g w i t h a B14 cone on t h e end. m o d i f i e d B7 s o c k e t  In addition a  "cap" was ground t o f i t each s y r i n g e t i p i n  order to provide a l i q u i d t i g h t s e a l .  A photograph o f the  m o d i f i e d s y r i n g e and a t t a c h m e n t s appears i n F i g u r e 6. The m o d i f i e d s y r i n g e s were d e s i g n e d the s t a i n l e s s s t e e l h i g h p r e s s u r e a p p a r a t u s F i g u r e 7.  t o f i t snugly  inside  w h i c h i s shown i n  T h i s c e l l was m a n u f a c t u r e d from a s i n g l e p i e c e o f  #304 s t a i n l e s s s t e e l and i t s d i m e n s i o n s were 88 mm O.D. by 17 2 mm l o n g w i t h t h e bore f o r t h e s y r i n g e b e i n g 35 x 145 mm. The t o p , 25 mm t h i c k , was h e l d down by e i g h t 3/8 i n c h by 1% i n c h cap screws and t h e p r e s s u r e s e a l was made by a rubber "0" ring.  1/8 i n c h t h i c k c i r c u l a r r u b b e r pads were p l a c e d on t h e  i n s i d e o f the c e l l to protect the syringes during operation. H i g h p r e s s u r e n i t r o g e n was f e d i n t o t h e c e l l v i a 1/4 i n c h s t a i n l e s s s t e e l h i g h p r e s s u r e t u b i n g and v a l v e w h i c h were f i t t e d t o t h e s i d e o f t h e c e l l by a s t a n d a r d h i g h coupling.  A schematic  F i g u r e 8.  B e f o r e u s e , t h e apparatus  pressure  o f t h e p r e s s u r e system i s shown i n was p r e s s u r e t e s t e d t o  F i g u r e 6.  Photograph o f t h e m o d i f i e d  50 ml a l l - g l a s s s y r i n g e s and  attachments.  Figure 7 .  Photograph o f t h e s t a i n l e s s syringes.  s t e e l high pressure  c e l l used t o p r e s s u r i z e t h e  regulator (0-6000 psig ) 1/4"stainless steel high pressure tubing>ir  va I ve  I—X—I  valve | ^  vent  high pressure cell  Figure 8 .  6000 psig gas cylinder Schematic diagram o f t h e h i g h p r e s s u r e  system.  -3910,000 p s i g w h i c h was  more t h a n t w i c e the n o r m a l o p e r a t i n g  pressure. The mixture  s y r i n g e s were f i l l e d w i t h a n i t r o g e n - h y d r o g e n  and aqueous s o l u t i o n u s i n g the a p p a r a t u s  i n F i g u r e 9.  The  s y r i n g e was  illustrated  a t t a c h e d v i a t h e B7 s o c k e t  l u b r i c a t e d w i t h the s o l u t i o n .  sample c o u l d  t o the s y r i n g e and t h i s f o l l o w e d by the gas  aqueous s o l u t i o n .  and  By t i l t i n g t h e a p p a r a t u s i n  the a p p r o p r i a t e d i r e c t i o n s ; f i r s t the gas admitted  gas  be  saturated  Then a f t e r q u i c k l y removing the s y r i n g e from  the B7 s o c k e t , w h i l e f l u s h i n g a p o r t i o n o f t h e l i q u i d o u t , a B7 cap was  p l a c e d over t h e end.  p o s s i b l e to f i l l  the s y r i n g e s w i t h o u t any a p p r e c i a b l e atmos-  p h e r i c oxygen c o n t a m i n a t i o n . p r e s s u r i z e d , t h e gas was  U s i n g t h i s p r o c e d u r e i t was  When the s y r i n g e was  i n s i d e was  then  compressed and t h e  plunger  pushed down t o c o n t a c t the l i q u i d s u r f a c e s i n c e most of  t h e gas p r e s e n t d i s s o l v e d i n the s o l u t i o n a t t h e h i g h A s m a l l g l a s s p l a t e was  used as a m i x e r i n t h e s y r i n g e s and  s o l u t i o n s were made homogeneous by i n v e r t i n g t h e h i g h c e l l during  the  pressure  equilibration.  In a t y p i c a l experimental  s e r i e s , a l l of the g l a s s  a p p a r a t u s would f i r s t be s c r u p u l o u s l y c l e a n e d by soaking  pressure.  initially  i n permanganic a c i d (KMnO^ i n 95% E^SO^), f o l l o w e d  r i n s i n g with d i s t i l l e d water, soaking o f hydrogen p e r o x i d e  by  i n a n i t r i c acid solution  t o remove t r a c e s o f Mn0 , and 2  finally  r i n s i n g w e l l w i t h s i n g l y , d o u b l y and t r i p l y d i s t i l l e d w a t e r successively.  The  a p p a r a t u s was  o r g a n i c f r e e oven a t 100  then d r i e d i n a s p e c i a l  °C and t h e n a s s e m b l e d .  Corning  silicone  Figure 9 . w i t h gas  Diagram of the apparatus used t o f i l l and  l i q u i d samples, shown w i t h a s y r i n g e  the  syringes  attached.  -41g r e a s e was used on t h e s t o p c o c k s  w h i c h c o n t r o l l e d t h e gas f l o w ;  a l l o t h e r j o i n t s were l u b r i c a t e d w i t h t h e e x p e r i m e n t a l With the syringe disconnected  solution.  and a B7 p l u g s u b s t i t u t e d , t h e  s o l u t i o n was deoxygenated by b u b b l i n g h i g h p u r i t y hydrogen t h r o u g h t h e a p p a r a t u s f o r about one hour. stopcocks  Then, w i t h t h e  c l o s e d , t h e s o l u t i o n was " p r e - i r r a d i a t e d " f o r 30 5  m i n u t e s (~2 x 10  rads) under t h e hydrogen atmosphere.  p r e - i r r a d i a t i o n was i n t e n d e d  This  t o remove any t r a c e s o f r e d u c i b l e  o r g a n i c o r i n o r g a n i c contaminants i n the s o l u t i o n s .  Following  the p r e - i r r a d i a t i o n , a weighed s y r i n g e was a t t a c h e d t o t h e appa r a t u s and l u b r i c a t e d w i t h a b i t o f t h e s o l u t i o n . f l u s h i n g t h e e n t i r e system w i t h t h e ^2/^2  m  i  x t u r e  After f°  r  about  2-3 h o u r s , t h e s y r i n g e was f i l l e d w i t h ~ 3 0 m l o f gas and 20 m l o f l i q u i d , t h e n removed and capped u s i n g t h e p r o c e d u r e d e s c r i b e d above.  The s y r i n g e was t h e n weighed t o o b t a i n t h e  w e i g h t o f s o l u t i o n and p r e s s u r i z e d i n t h e h i g h p r e s s u r e u s i n g pure n i t r o g e n a t 3000 p s i g (200 a t m ) . A t t h i s  cell  pressure  v i r t u a l l y a l l o f t h e gas would d i s s o l v e i n t h e s o l u t i o n and t o ensure t h a t t h i s o c c u r e d ,  t h e p r e s s u r i z e d sample was l e f t t o  e q u i l i b r a t e f o r about one h o u r , d u r i n g w h i c h time i t was o c c a s i o n a l l y i n v e r t e d t o cause t h e m i x i n g p l a t e t o " s t i r " t h e solution.  The e q u i l i b r a t e d sample was t h e n i r r a d i a t e d i n t h e  Gammacell f o r v a r i o u s times r a n g i n g from 60 - 12,000 m i n u t e s . A f t e r t h e i r r a d i a t i o n , t h e c e l l was s l o w l y d e p r e s s u r i z e d  (fast  d e p r e s s u r i z a t i o n i n v a r i a b l y l e d t o a s h a t t e r e d s y r i n g e caused by t h e p l u n g e r becoming jammed) and t h e s y r i n g e was removed and  the s o l u t i o n analysed.  I t was noted t h a t when t h e s y r i n g e s  were removed (about 5 m i n u t e s a f t e r d e p r e s s u r i z a t i o n )  only  -42-  10 - 1 5  about was  ml  of  e v o l v i n g gas  allowing  gas  was  continuously.  sufficient  time,  its  original  value.  the  pressurization  stage  and  also  of  that  observed  most  the  These  gas  volume  leakage  gas  had  the  shaking  observations  no  the  By  above  of  solution  the  soon  syringe  that  syringe  dissolved  and  increased  indicated the  which  to during  occured  i n the  liquid  under  pressure.  using  4.  Analytical  The  irradiated  the  cedure  very  used  Procedures  solutions  sensitive  was  similar  were  analysed  "indophenol to  the  one  blue"  for  ammonia  method.  developed  by  The  Tetlow  proand  37 Wilson  and  data  given  are  complete  details  i n Appendix  and  hypochlorite i n very  630  nm  of .  ammonium  ammonia The  was  i o n s , however  discussed  the  i n the  of  technique  indophenol  related  sensitivity  the  Basically,  the  tration  to  2.  converting sodium  ammonia  of  the  the test  was  limited  the  calxbration  procedure dye  about  hydrogen working  involved  using  solution.  absorbance  i n t e r f e r e n c e of  Appendix  blue  alkaline to  the  and  of 5 x  phenol  The  concen-  the  dye  10  at  M  peroxide  as  sensitivity  to  —6 about  5 x  10  irradiated was  M  .  In  solution  analysed  was  i n the  NH^  standard  to  on  products  (such  as  Qualitative and  hydroxylamine  of  divided  normal  known q u a n t i t y o f check  analysis  any  manner  were  two  and  was  experiment,  p a r t s ; one  to  the  other  added  as  an  possible effects  of  other  hydrogen spot  typical  into  solution  +  a  of  the which  portion  a  "internal" radiolysis  peroxide).  checks  for  performed  the  using  presence  of  hydrazine  trinitro-benzene-sulfonic  -43C.  RESULTS The  p e r t i n e n t d a t a from the " s u c c e s s f u l " e x p e r i m e n t s  a r e l i s t e d i n T a b l e 3.  ( S e v e r a l e x p e r i m e n t s were  because of s h a t t e r e d s y r i n g e s . ) c u l a t e the y i e l d s of ammonia,  The  unsuccessful  two methods used t o  G (NHo) w  and G 2 N  (NH  )  cal-  , are based  3 on the dose absorbed by the water and d i r e c t l y by the J  molecules,  respectively.  Experiment A-4  was  nitrogen  done t o t i e i n 35  w i t h the p r e l i m i n a r y e x p e r i m e n t s o f Walker and Edwards t h i s e x p e r i m e n t the p l u n g e r was t h a t the s o l u t i o n was  removed from the s y r i n g e  i n c o n t a c t w i t h a l a r g e gas volume  gas phase r a d i o l y s i s c o u l d  were not p r e s e n t The  i n d i c a t i n g that these  and  and  hydroxyl-  "intermediates"  o v e r a l l r e s u l t s of t h e s e e x p e r i m e n t s may the y i e l d o f ammonia from an  s o l u t i o n of nitrogen at  D.  so  i n s i g n i f i c a n t y i e l d s a t the time o f a n a l y s i s .  i z e d as f o l l o w s :  y i e l d was  In  occur.  I n a l l cases the s p o t t e s t s f o r h y d r a z i n e amine were n e g a t i v e  .  0.1  M was  be summar-  isolated  G ( N H ) ~> 0.002 and W  3  this  i n d e p e n d e n t of the pH of the sample.  DISCUSSION The  f a c t t h a t the y i e l d o f ammonia based on the dose  absorbed by the water was the f a v o u r a b l e  G ( N H ) ~ 0.002 means t h a t W  3  c o n d i t i o n s f o r r e a c t i o n of h y d r a t e d  despite electrons  w i t h n i t r o g e n , i t does not o c c u r t o a s i g n i f i c a n t e x t e n t . v a l u e o f G 2 ( N H ) = 0.7 N  3  i s i n reasonable  f o r the n e u t r a l s o l u t i o n of  The  nitrogen  agreement w i t h t h a t measured by Hammar e t a l .  TABLE 3 SUMMARY OF NITROGEN FIXATION EXPERIMENTS  Exp  PH  D i s s o l v e d Gas ( M x l 0 ) a  N  M  G (NH,) W  ) 2  <5  0.0036 0.0036 0.060 1.9  $5 84  7.5 9.2 7.1  <0.001 <0.001 0.79  2.2 <0.001 <0.001  2.5 2.6 2.6  0.0052 0.0067 0.0052  <5 <5  7 7 7 7  8.0 9.2 8.0 9.6  <0.001 <0.001 1.2 0.72  2.4 <0.001 < 0.001 <0.001  23 24 26 280  0.051 0.062 0.056 0.64  $5 51  7 2  7.9 7.1  0.79 0.79  <0.001 < 0.001  25 25  0.056 0.050  $5 $5  7 7 7  C-l 2 3 4 D-l? 2  Footnotes:  G 2(NH N  6  1.6 1.5 23 1.5  B-l 2 3  b  (MxlO )  <0.001 <0.001 <0.001 < 0.001  1.8 8.9 8.9 13  e  2  -20  0.38 1.6 1.6 0.27  11 11 11 11  A-1 2 3 4  [H ]  Dose (eVxlO N Water  2  r )d  < 5  <5  f  « d 5  d  d d  <0.03 <0.03 $0,002 0.51 <0.02 <0.02 <0.02  <1.4 <1.4 $0.8 0.42 <10 <10 <10  $0,002 $0,002 $0,002 0.0016  «1.0 $1.0 $1.0 0.70  $ 0.002 $ 0.002  $1.0 $ 1.0  a. The c o n c e n t r a t i o n s o f d i s s o l v e d gases were c a l c u l a t e d from the s o l u b i l i t y d a t a - r e f . 39. b. G (NH ) i s the y i e l d o f ammonia based on the energy absorbed by the water, c. G 2(NH ) i s the y i e l d o f ammonia based on the energy absorbed d i r e c t l y by n i t r o g e n , d. Ammonia'concentrations g i v e n as an upper l i m i t because of the v e r y s m a l l absorbance (»**0.03) which c o u l d have been caused by p e r o x i d e . e. Plunger removed from the s y r i n g e , l a r g e gas volume above the s o l u t i o n . f. Severe hydrogen p e r o x i d e i n t e r f e r e n c e due t o presence o f oxygen, g. About 4 g o f s t a i n l e s s s t e e l c h i p s added t o the s o l u t i o n . W  3  3  ( G ( N H ) = 1.8 N 2  3  2.3)^"^.  - 0 . 9 ) ° and by Sato and S t e i n b e r g  (G  3 3  T h i s ammonia i s v e r y l i k e l y produced by the  a i r  (NH ) = 3  direct  a c t i o n o f the ^ - r a d i a t i o n on the d i s s o l v e d n i t r o g e n m o l e c u l e s to give  o r N^*  w h i c h t h e n r e a c t w i t h the s o l v e n t o r  s o l v e d hydrogen t o e v e n t u a l l y g i v e ammonia.  This  dis-  process  a p p a r e n t l y proceeds w i t h a s i m i l a r e f f i c i e n c y t o t h e gas r e a c t i o n s i n c e G^2(NH^) = 0.7  was  o b t a i n e d by Cheek  phase  and  Linnenbom f o r the gas phase r a d i o l y s i s o f nitrogen-hydrogen 25e N? , » mixtures. A f u r t h e r s i g n i f i c a n c e o f the G ^(NH^) v a l u e i s t h a t once the r e d u c t i o n p r o c e s s product  i s ammonia.  has  been i n i t i a t e d , the  T h i s agrees w i t h the r e s u l t s o f  q u a l i t a t i v e t e s t s f o r hydrazine  end  the  and h y d r o x y l a m i n e w h i c h i n d i c a t e d  t h a t these i n t e r m e d i a t e s were not formed i n a s i g n i f i c a n t amount.  (The  l i m i t o f d e t e c t i o n o f the t e s t was _3  for hydrazine  and about 10  corresponding  upper l i m i t s o f G ( N H ) ^ 0. 005  The  about 1 0 ~  5  M  M f o r hydroxylamine which gives W  2  4  f a c t t h a t some, i f not a l l ,  and G (NH OH) ^ 0. 5). w  2  o f the ammonia formed  i n t h e s e e x p e r i m e n t s a r i s e s from d i r e c t a c t i o n o f r a d i a t i o n on t h e d i s s o l v e d n i t r o g e n means t h a t an upper l i m i t o f G ( N H ) ^ 10" W  3  can be p l a c e d on the y i e l d o f ammonia produced t h r o u g h the r e a c t i o n of n i t r o g e n w i t h h y d r a t e d  electrons.  This allows a  c a l c u l a t i o n of an upper l i m i t f o r the r a t e c o n s t a n t o f r e a c t i o n (1).  Assuming the a l t e r n a t i v e f a t e o f the h y d r a t e d  i s r e a c t i o n w i t h u n s p e c i f i e d i m p u r i t y , X, a t t h e c o n t r o l l e d r a t e of 1 0 ^  M  \  diffusion  t h e n an e s t i m a t e o f the c o n -  c e n t r a t i o n of X w i l l a l l o w c a l c u l a t i o n o f k^. o f the w a t e r and  electrons  i t s deoxygenation probably  Purification  r e d u c e d the i m p u r i t y  -46level used  t o about  10~^ M .  i n the presence  Since  l a r g e r a d i a t i o n doses  of molecular  h y d r o g e n , most o f t h i s  i m p u r i t y w o u l d be e l i m i n a t e d w i t h i n t h e f i r s t the  irradiation.  the  "molecular"  fast  a s i t was b e i n g  state" fore  impurity  produced by  by e ~ ^ a l m o s t  produced and i t would r e a c h  c o n c e n t r a t i o n o f v e r y much l e s s  a very  steady  would be d e s t r o y e d  conservative estimate  —6  [xj , w o u l d be 10  treatment  to e  a  M .  There-  state reactive Applying the  : aq  rate  o f p r o d u c t i o n o f e~ = G(e~ ) • I * aq aq  rate of loss o f e " = k |X]„_ Te" | s s aq x L J I aqj where I is the radiation intensity, implies: s  [*a-q] s s =  G ( e  aq> [  k  x The  • x  rate  of production  s  1  ] ss  r a t e o f ammonia p r o d u c t i o n  i s g i v e n by:  o f NH  3  =  k^  ^N j 2  = G (NH ) W  3  Since  G(e~ ) = G _ 3 aq a  + G  R  £qJs s e a  • I  + G „ = 5.7 a t h i g h pH t h e n  e  U  n H  n i t r o g e n c o n c e n t r a t i o n o f 0.1 M i t f o l l o w s t h a t : k  x  = G (NH ) W  3  H  • I  [aq]ss S  =  G (NH ) W  3  • I  [N ] ' G(e^) ' I *x [*]s 2  as  "steady  10 ^ M .  o f the steady  r i  concentration,  state kinetic  than  initial  few minutes o f  In a d d i t i o n , hydrogen peroxide processes  were  f o ra  -47k.  <  1Q" -1 10 •  ^  3  Thus a c o n s e r v a t i v e for production  M-V  18  1  5.7 10 _6 10 • 10 ° upper l i m i t f o r the r e a c t i o n r a t e  of ammonia from h y d r a t e d e l e c t r o n s  constant  reacting  w i t h n i t r o g e n i s k ^ 18 M "*"s~^. T h i s i s one o f the s l o w e s t 1 r a t e constants estimated f o r hydrated e l e c t r o n s . (If reaction (1) gave h y d r o x y l a m i n e i n s t e a d o f ammonia, the upper l i m i t 3 the r a t e c o n s t a n t  would be about 5 x 10  -1 M  on  -1 s  , however  because o f the i n s e n s i t i v i t y of the t e s t t h i s c a l c u l a t i o n i s considerably The  l e s s c e r t a i n t h a n t h a t f o r ammonia.)  s i g n i f i c a n c e o f the e x p e r i m e n t a t pH 2 (D-2)  is  t h a t the hydrogen atom r e a c t i o n w i t h n i t r o g e n i s a l s o e x t r e m e l y slow.  A t pH 2, a l l o f the h y d r a t e d e l e c t r o n s would be  con-  v e r t e d t o H atoms v i a r e a c t i o n ( 7 ) . e~ acj  +  H*—*- H a<j  +  H,0 £  (7) k_  I  =  2xl0 M" s~ 1 0  1  1  T h i s r e s u l t i s not p a r t i c u l a r l y s u p r i s i n g s i n c e hydrogen atoms a r e much l e s s p o w e r f u l r e d u c i n g e l e c t r o n s and  agents t h a n h y d r a t e d  t h e i r r e a c t i o n r a t e s are g e n e r a l l y  slower.  Experiment D - l i n w h i c h the s o l u t i o n c o n t a i n e d s t e e l c h i p s i n d i c a t e d t h a t no c a t a l y t i c enhancement of  stainless the  r e a c t i o n c o u l d be a c h i e v e d by i t s p r e s e n c e . I n c o n c l u s i o n , t h e s e e x p e r i m e n t s have r e i t e r a t e d t h a t t h e n i t r o g e n m o l e c u l e i s e x t r e m e l y s t a b l e towards e i t h e r by h y d r a t e d e l e c t r o n s o r hydrogen atoms.  reduction, I t therefore  seems u n l i k e l y t h a t the f i x a t i o n of n i t r o g e n i n n a t u r e  (even  -48in  the  p r e - b i o t i c times)  action"  E.  of  high  energy  S U G G E S T I O N S FOR  Since molecular  the  hydrated  nitrogen,  molecular  the  introduction to the  an  nitrogen  ever  arise  through  "  indirect  radiation.  FURTHER  fix  of  could  STUDY  electron i s unable  interesting i n a bound  this  transition metal  study,  question form.  i t has  complexes  As  to  reduce  "free"  i s whether i t  can  was  in  discussed  been r e p o r t e d  apparently  can  be  that  some  reduced  20 in  organic  expected  solvents  that  reduction  of  the  to give  hydrated  coordinated  Unfortunately plexes the in  of  nitrogen  ammonia.  e l e c t r o n w o u l d be  the  with  to  initiate  unstable  known t r a n s i t i o n m e t a l i n aqueous s o l u t i o n .  o s m i u m c o m p o u n d s , h o w e v e r , was conjunction  able  be  nitrogen.  most of  are  Thus i t m i g h t  Professor  B.  t h o u g h t t o be  R.  James and  com-  One  stable  Dr.  E.  of and  Ochiai  II an  e x p e r i m e n t was  performed  be  reduced.  experiment proved  This  c o m p l e x was  fairly  and  some o f  the  OH~  ones. In  studies  of  light the  i f Os  (NH^) ^ 2 ^"2 N  t o be  r a p i d l y hydrolysed  of  the  reducing to  suitable nitrogen  hydrolysed  see  a  above remarks,  i n the  power of  examine  the  the  a  C  failure  area  ^ the  by  further  electron  towards  aqueous r a d i a t i o n  This  u  for  c o m p l e x e s when compounds w h i c h  have been s y n t h e s i z e d .  o  solution  replaced  suggestion  hydrated  c  since  alkaline  ammonia l i g a n d s were a p p a r e n t l y  n i t r o g e n w o u l d be of  to  of  chemistry are  research  not could  - 4 9 -  have coiranercial p o t e n t i a l  i f a suitable  where a t r a n s i t i o n m e t a l i o n would f i r s t  system were found c o o r d i n a t e the n i t r o g e n  and then a f t e r the i n i t i a t i o n o f r e d u c t i o n , complex another n i t r o g e n molecule.  A continuous c y c l i c p r o c e s s can be envisaged  wherein t h e t r a n s i t i o n m e t a l i o n a c t s e s s e n t i a l l y as a homogeneous c a t a l y s t , w i t h n i t r o g e n and hydrogen alkaline  f l o w i n g through an  s o l u t i o n under r a d i o l y s i s , and thus p r o d u c i n g  ammonia.  CHAPTER I I I ASPECTS OF THE RADIATION CHEMISTRY OF PROPYLENE CARBONATE  Propylene carbonate abbreviated  (4-methyl-2-dioxolone, which may be  as PC i n the f o l l o w i n g d i s c u s s i o n s )  p o l a r a p r o t i c s o l v e n t w i t h some e x t r a o r d i n a r y chemical p r o p e r t i e s .  I l l u s t r a t e d i n Figure  uV  i s a very  p h y s i c a l and  10, p r o p y l e n e  U  3  <V° /  \  M  o Figure  10.  One o f the s t e r e o i s o m e r s o f propylene carbonate.  carbonate i s a f i v e membered h e t e r o c y c l i c r i n g system which has  two s t e r e o i s o m e r s .  (a) a v e r y  Among i t s unusual f e a t u r e s ^ a r e : 0  l a r g e l i q u i d range from l e s s than -70 °C t o +240 ° c f °  (b) a moderately h i g h d i e l e c t r i c c o n s t a n t  o f 65 a t room temp-  e r a t u r e which i s v e r y temperature dependent, r i s i n g than 90 below -60 °C  , (c) a c o r r e s p o n d i n g v e r y —18  permanent d i p o l e moment o f 4.94 x 10 t h i s does not appear t o cause s t r o n g  to greater large  40d esu cm  although  intermolecular  association  i n the s o l v e n t as evidenced by a Kirkwood c o r r e l a t i o n f a c t o r o f near u n i t y and NMR .and IR d a t a 41 parency above 225 nm an  "organic"  carbonyl  40b, e ' , (d) u l t r a v i o l e t \  trans-  which i n d i c a t e s t h a t the ,0=0 i s not but r a t h e r t h a t the e l e c t r o n system i s  d e l o c a l i z e d as i n the CO^  i o n , and (e) c h e m i c a l  PC does not r e a c t w i t h s t r o n g  reducing  stability;  agents such as the  a  -5140g,41 a l k a l i metals  (or d i s s o l v e them), n o r i s i t e a s i l y 41 o x i d i z e d by s t r o n g o x i d a n t s such as permanganate. In a d d i t i o n , PC i s r e a d i l y p u r i f i e d by s i m p l e vacuum d i s t i l l a t i o n 42 and i t i s not t o x i c o r h y g r o s c o p i c . The major d i s a d v a n t a g e o f PC i s t h a t i t i s h y d r o l y s e d by a c i d s and b a s e s , 40a i t s n e u t r a l aqueous s o l u t i o n s a r e s t a b l e .  although  o  In  l i g h t o f t h e p a r t i c u l a r l y i n t e r e s t i n g and  aspects of propylene  unusual  c a r b o n a t e , the p r e s e n t i n v e s t i g a t i o n  was  i n i t i a t e d t o examine some o f the f a c e t s o f t h e r a d i a t i o n c h e m i s t r y o f PC.  I n p a r t i c u l a r , i t was  of i n t e r e s t to deter-  mine whether e l e c t r o n s c o u l d be s t a b i l i z e d i n the system, s i n c e t h i s l a b o r a t o r y has been p a r t i c u l a r l y i n v o l v e d w i t h 43a :ic s o l v a t e d e l e c t r o n s , both i n water and i n p o l a r a p r o t i c 15 s o l v e n t s o f h i g h d i e l e c t r i c c o n s t a n t , such as formamide 43b and d i m e t h y l s u l f o x i d e  .  A g e n e r a l i n v e s t i g a t i o n o f the  r a d i o l y s i s o f PC would a l s o p r o v i d e o r i g i n a l i n f o r m a t i o n about a c l a s s o f compounds whose r a d i a t i o n c h e m i s t r y i s e s s e n t i a l l y unexplored.  A thorough  s u r v e y o f the l i t e r a t u r e r e v e a l e d t h a t  a l t h o u g h t h e e l e c t r o c h e m i s t r y o f PC had been s t u d i e d t o a l i m i t e d e x t e n t , i t s r a d i a t i o n c h e m i s t r y has never been i n v e s t igated.*  Of the o t h e r c y c l i c o r g a n i c c a r b o n a t e s  (literally  dozens o f v a r i a t i o n s o f the b a s i c f i v e membered r i n g system c o u l d be s y n t h e s i z e d ) o n l y e t h y l e n e c a r b o n a t e  and i t s t e t r a 44  p h e n y l d e r i v a t i v e have been b r i e f l y examined. * f o o t n o t e 2. A f t e r t h i s s t u d y was begun, Hayon r e p o r t e d the f r e e i o n y i e l d f o r PC as o b t a i n e d by p u l s e r a d i o l y s i s o f i t s anthracene s o l u t i o n .  -52-  During the i n i t i a l stages o f t h i s i n v e s t i g a t i o n , i t was d i s c o v e r e d t h a t p r o p y l e n e c a r b o n a t e formed an e x c e l l e n t g l a s s y s o l i d when c o o l e d q u i c k l y i n l i q u i d n i t r o g e n .  Subsequent  ^ - i r r a d i a t i o n o f t h e s e g l a s s e s a t 77 °K and e x a m i n a t i o n by e l e c t r o n s p i n resonance spectra. proposed  r e v e a l e d some v e r y u n u s u a l  Because o f t h i s , t h e emphasis o f t h e i n i t i a l l y r a d i a t i o n c h e m i c a l i n v e s t i g a t i o n was s h i f t e d  t h e l i q u i d phase t o t h e g l a s s y s o l i d s t a t e . of  radical  t h e r e s u l t s presented here w i l l  from  Thus t h e m a j o r i t y  be concerned w i t h t h e  r a d i o l y s i s o f the low temperature g l a s s e s .  Although a s i g n i f -  i c a n t amount o f d a t a was o b t a i n e d from t h e l i q u i d phase e x p e r i m e n t s , t h i s s t u d y was n o t as e x t e n s i v e as was o r i g i n a l l y planned.  -53-  PART I - RADIOLYSIS OF PROPYLENE CARBONATE IN THE SOLID STATE A.  INTRODUCTION Studies  of the r a d i o l y s i s  o f f r o z e n p o l a r systems have  been m a i n l y concerned w i t h w a t e r , i t s s o l u t i o n s and t h e a l c o h o l s 4 , a l t h o u g h k e t o n e s and e s t e r s have been examined 45 and  comprehensive i n v e s t i g a t i o n s o f t h e v e r y p o l a r  acetonitrile  46 compounds have been p u b l i s h e d . The w e a k l y - p o l a r f r o z e n systems w h i c h have been t h e most e x t e n s i v e l y s t u d i e d a r e t h e g l a s s y e t h e r s , such as  47 methyl-tetrahydrofuran  I n v i r t u a l l y e v e r y compound w h i c h forms a g l a s s y  solid  (amorphous s t a t e i n w h i c h t h e random o r i e n t a t i o n o f t h e l i q u i d phase i s t h o u g h t t o be " f r o z e n i n " ) r a d i o l y t i c a l l y  generated 5  species  identified  These e n t i t i e s or v i s i b l e  as t r a p p e d e l e c t r o n s have been d i s c o v e r e d  a r e c h a r a c t e r i s e d by i n t e n s e ,  optical  absorption  near-infrared  s p e c t r a and s i n g l e narrow,  G a u s s i a n shaped, e l e c t r o n s p i n resonance l i n e s s p i n g - v a l u e o f 2.0023. power s a t u r a t e d .  .  near t h e f r e e  The ESR l i n e i s n o r m a l l y  quite  easily  T h i s s a t u r a t i o n does n o t cause t h e u s u a l  l i n e b r o a d e n i n g b u t r a t h e r i s an "inhomogeneous" t y p e o f s a t u r a t i o n where t h e l i n e shape does n o t change w h i l e i t s intensity  decreases uniformly.  Photobleaching of the trapped  e l e c t r o n s w i t h l i g h t i n the region corresponding t o t h e i r optical  absorption  spectrum a l s o o c c u r s .  The s p e c i e s  may  a l s o be e l i m i n a t e d by added s o l u t e s o f h i g h e l e c t r o n a f f i n i t y , i . e . e l e c t r o n s c a v e n g e r s , such as n a p t h a l e n e . s t a b l e f o r long periods  Though  normally  o f time i n v e r y p o l a r g l a s s e s a t 77 °K,  -54-  t r a p p e d e l e c t r o n s i n w e a k l y p o l a r systems (such as  methyl-  t e t r a h y d r o f u r a n ) a r e not s t a b l e and t h e y decay v i a p r o c e s s e s a t l e a s t p a r t i a l l y a t t r i b u t a b l e t o "geminate  recombination"  17  w i t h t h e i r parent p o s i t i v e ions Trapped r a d i c a l s produced by r a d i o l y s i s a r e however, n o t so e a s i l y i d e n t i f i e d .  S i n c e h i g h energy r a d i a t i o n i s not  v e r y d i s c r i m i n a t i n g i n i t s p r i m a r y e x c i t a t i o n , t h e r e i s seldom s p e c i f i c decomposition,  b u t r a t h e r numerous d i f f e r e n t  a r e g e n e r a l l y formed i n a s i n g l e system.  radicals  The c o m b i n a t i o n  p r o t o n h y p e r f i n e s p l i t t i n g o f the i n d i v i d u a l r a d i c a l  of  ESR  s p e c t r a and a n i s o t r o p y o f t h e s i g n a l s , t o g e t h e r w i t h the o v e r l a p p i n g o f the l i n e s u s u a l l y p r e v e n t s p o s i t i v e  identifi-  c a t i o n o f the s p e c i e s i n a l l b u t t h e v e r y s i m p l e s t s y s t e m s , such as w a t e r and m e t h a n o l . t h e o r y o f ESR  A b r i e f d i s c u s s i o n of the b a s i c  and i t s a p p l i c a t i o n s t o amorphous s o l i d s i s  g i v e n i n A p p e n d i x 3.  O p t i c a l absorption spectroscopy i s  a l s o of o n l y l i m i t e d value i n i d e n t i f y i n g organic r a d i c a l s s i n c e most a b s o r b i n t h e u l t r a v i o l e t and the s p e c t r a a r e a g a i n u s u a l l y b r o a d and o v e r l a p p i n g . scavenger  V a r i a b l e temperature  techniques, photobleaching  experiments,  studies,  and  ESR  r . f . power s a t u r a t i o n e f f e c t s sometimes h e l p t o u n r a v e l t h e c o m p l e x i t y o f i r r a d i a t e d o r g a n i c systems.  I n most cases  however, t h e r a d i c a l s p e c i e s d e f y p o s i t i v e  identification  u n l e s s t h e y can be g e n e r a t e d  i n an unambiguous manner, such  as OH r a d i c a l s by t h e p h o t o l y s i s o f Since propylene  carbonate  ^2 2' 0  i s a v e r y p o l a r compound and  because g l a s s y p o l a r systems a r e known t o t r a p e l e c t r o n s v e r y 4  5  e f f i c i e n t l y ' the p r e s e n t i n v e s t i g a t i o n was  begun.  I t s aim  -55was  t o d e t e r m i n e whether e l e c t r o n s c o u l d be s t a b i l i z e d i n  g l a s s y PC,  and  i f s o , t o s t u d y t h e i r p r o p e r t i e s b o t h by  and o p t i c a l t e c h n i q u e s .  Any  information obtained with  ESR regard  t o t h e r a d i c a l s p e c i e s produced would be c o n s i d e r e d an added b e n e f i t of the B.  investigation.  EXPERIMENTAL 1.  Reagents  Eastman Kodak p r a c t i c a l g r a d e p r o p y l e n e  carbonate  p u r i f i e d by f r a c t i o n a l d i s t i l l a t i o n under vacuum as i n A p p e n d i x 4.  The  p u r i f i e d s o l v e n t was  was  described  s t o r e d under d r y  h e l i u m i n a d i s p e n s i n g apparatus which i s a l s o discussed i n Appendix 4 along w i t h the p h y s i c a l analyses. A l l other chemicals  used were a n a l y t i c a l r e a g e n t grade  or equivalent. H e l i u m used f o r d e o x y g e n a t i o n was L i q u i d A i r and  i t was  s u p p l i e d by  Canadian  d r i e d by p a s s i n g t h r o u g h a l o n g copper  c o i l immersed i n l i q u i d n i t r o g e n . 2.  R a d i a t i o n Source 60  A The  Co Gammacell 220 was  source  a c t i v i t y was  6170  used f o r the  C u r i e s when l o a d e d i n June  An a p p r o x i m a t e dose r a t e o f 4000 rads min min"^") was  estimated  apparatus.  2 x 10  rads  to 1 x 10  6  (2.5 x  done f o r  T o t a l doses ranged from  (1 x 1 0  1 8  to 8 x 1 0  1 9  eV  1967.  10^eV  from f e r r o u s s u l f a t e d o s i m e t r y  other experimental 4  irradiations.  g' ). 1  -56-  3.  Sample P r e p a r a t i o n and I r r a d i a t i o n  E l e c t r o n s p i n resonance measurements were made on g l a s s y " b a l l s " o f PC, 2-3 mm i n d i a m e t e r , p r e p a r e d by d r o p p i n g t h e deoxygenated PC i n t o a dewar o f l i q u i d n i t r o g e n as d e s c r i b e d 48 by A l g e r  .  The samples p r e p a r e d i n t h i s way were n e a r l y  p e r f e c t spheres, completely c r a c k s , and m e c h a n i c a l l y  transparent,  sound.  f r e e from b u b b l e s and  Attempts t o prepare a g l a s s  i n s m a l l d i a m e t e r q u a r t z t u b i n g always gave a p o l y c r y s t a l l i n e sample. For t h e o p t i c a l s t u d i e s , t h e sample o f PC was s e a l e d i n a 1 cm square " s p e c t r o s i l " q u a r t z s p e c t r o p h o t o m e t e r  cell  a f t e r thorough d e g a s s i n g by m u l t i p l e freeze-pump-thaw c y c l e s . When immersed i n l i q u i d n i t r o g e n , t h e s e sample u s u a l l y became polycrystalline.  On o c c a s i o n , however, a r e a s o n a b l y  trans-  p a r e n t " g l a s s " was formed w i t h r e l a t i v e l y few c r a c k s and t h e s e samples were used.  I t was n o t e d t h a t t h e a d d i t i o n o f even  v e r y s m a l l q u a n t i t i e s o f water t o t h e PC d i d n o t improve t h e q u a l i t y of the g l a s s .  I n f a c t , a d d i t i o n o f o n l y 0.1% w a t e r  caused t h e samples t o become c l o u d y and v i r t u a l l y opaque. A l l g l a s s w a r e used i n h a n d l i n g  the propylene carbonate  samples, i . e . b e a k e r s , p i p e t t e s , s p e c t r o - c e l l s e t c . , was always s c r u p u l o u s l y c l e a n e d u s i n g t h e r o u t i n e permanganic a c i d -peroxide-distilled The  water  treatment.  sample b a l l s o f PC f o r t h e ESR s t u d i e s were i r r a d -  i a t e d i n a s m a l l p y r e x dewar c o n t a i n i n g l i q u i d n i t r o g e n .  In  some c a s e s , when k i n e t i c s t u d i e s and y i e l d measurements were made, t h e samples were p l a c e d i n a s m a l l b e a k e r l i n e d  with  -57aluminum f o i l t o p r e v e n t  p o s s i b l e b l e a c h i n g by the  blue  f l u o r e s c e n c e w h i c h p y r e x e m i t s under r a d i o l y s i s a t n i t r o g e n temperature.  liquid  S i m i l a r p r e c a u t i o n s were t a k e n  with  t h e samples f o r t h e o p t i c a l s t u d i e s . 4.  E l e c t r o n S p i n Resonance Measurements  A l l e l e c t r o n s p i n resonance s p e c t r a were measured u s i n g a V a r i a n A s s o c i a t e s E-3 9.3  GHz  spectrometer  (X-band) and w i t h 100 kHz  which operated  f i e l d modulation.  The  a t 77 °K were r e c o r d e d w i t h the samples c o n t a i n e d i n a dewar f i l l e d w i t h l i q u i d n i t r o g e n .  the custom-made q u a r t z dewar shown i n F i g u r e 11  used.  The  supported  spectra quartz  F o r measurements above  77 °K,  sample b a l l was  at  was  i n the c e n t e r o f t h i s  dewar on the end o f t h e t h i n e v a c u t e d q u a r t z tube w h i c h a l s o contained  the t h e r m o c o u p l e .  C o o l i n g was  achieved  using  nitrogen  f l o w i n g t h r o u g h a l o n g copper c o i l immersed i n a l a r g e dewar of l i q u i d nitrogen.  I n p r a c t i c e , the dewar was  t o t h e minimum p o s s i b l e t e m p e r a t u r e (85-90 °K) f l o w was  first  cooled  and the  gas  t h e n m o m e n t a r i l y i n t e r r u p t e d w h i l e a sample b a l l  q u i c k l y t r a n s f e r r e d from a l i q u i d n i t r o g e n b a t h and i n t o t h e t o p o f the dewar.  Continuous monitoring  was  dropped  o f the temp-  e r a t u r e w i t h a c h a r t r e c o r d e r i n d i c a t e d t h a t d u r i n g the t r a n s f e r process the gas  the samples p r o b a b l y warmed t o about 95 °K  f l o w was  restarted.  The  t e m p e r a t u r e was  before  varied simply  by a l t e r i n g t h e f l o w r a t e o f c o l d n i t r o g e n t h r o u g h the dewar. A g i v e n t e m p e r a t u r e c o u l d be m a i n t a i n e d  t o 1 2 °K by  this  method w h i c h p r o v e d t o be adequate f o r the purposes o f experiments reported  here.  the  -58-  •EVACUATED DEWAR  SAMPLE BALL THERMOCOUPLE  COLD NITROGEN  B 7 CONE / SOCKET JOINT  EVACUATED SAMPLE SUPPORT TUBE *  WAX SEAL THERMOCOUPLE LEADS  F i g u r e 11.  V a r i a b l e temperature ESR dewar  -59-  The m a g n e t i c f i e l d s t r e n g t h and f i e l d scan were c a l i b r a t e d w i t h a p r o t o n - p r o b e  linearity  gaussmeter and t h e m i c r o -  wave f r e q u e n c y was checked w i t h a H e w l e t t - P a c k a r d model 52 55A d i g i t a l frequency counter.  The microwave power l e v e l s were  not c a l i b r a t e d and t h e v a l u e s quoted  a r e those r e a d d i r e c t l y  from t h e power c o n t r o l d i a l o f t h e i n s t r u m e n t . S p e c t r o s c o p i c s p l i t t i n g f a c t o r s , g - v a l u e s , were d e t e r mined u s i n g a f i n e l y powdered sample o f DPPH ( d i p h e n y l p i c r y l h y d r a z y l ) s e a l e d i n a t h i n q u a r t z tube w h i c h was p l a c e d i n the dewar a l o n g w i t h t h e sample.  9DPPH  =  2.0036 was used and  the unknown g - v a l u e s were c a l c u l a t e d u s i n g t h e f o r m u l a g  = 2.0036  ( 1 - AH H  )  (viii)  (viii)  r  where AH i s t h e d i f f e r e n c e i n t h e m a g n e t i c f i e l d between t h e c e n t e r o f t h e unknown resonance  and t h a t o f t h e DPPH and H. r 48 i s t h e a b s o l u t e m a g n e t i c f i e l d o f t h e " r " resonance. Radiation yields  (G v a l u e s ) were e s t i m a t e d u s i n g i r r a d -  i a t e d methanol as a s t a n d a r d .  B o t h t h e PC sample and methanol  were p r e p a r e d under i d e n t i c a l c o n d i t i o n s ; i . e . t h e samples were made as c l o s e t o t h e same s i z e as p o s s i b l e and b o t h were i r r a d i a t e d s i m u l t a n e o u s l y i n t h e same dewar t o p r o v i d e i d e n t i c a l absorbed  doses (about 1.2 Mrad).  i n methanol were p h o t o - c o n v e r t e d  The t r a p p e d e l e c t r o n s  t o t h e CH^OH r a d i c a l t o a v o i d  the power s a t u r a t i o n problems o f t h i s s p e c i e s and G(CH^0H)= 6.7 was used f o r t h e t o t a l y i e l d o f C^OH  radicals . 4  The ESR  s p e c t r a o f b o t h PC and m e t h a n o l were r e c o r d e d f o r a s i n g l e b a l l i n i d e n t i c a l p o s i t i o n s i n t h e c a v i t y and under i d e n t i c a l spectrometer c o n d i t i o n s .  The a r e a s under t h e a b s o r p t i o n c u r v e s  -60were e s t i m a t e d by d o u b l e i n t e g r a t i o n ( s e e r e f . 63, page, 442 ) and t h e r e l a t i v e G v a l u e s were c a l c u l a t e d u s i n g t h e r a t i o o f the areas. due  These G v a l u e s were s u b j e c t t o c o n s i d e r a b l e e r r o r  t o the u n c e r t a i n t y i n the r e l a t i v e diameters of the  sample b a l l s , i n t h e i n t e g r a t i o n t e c h n i q u e  and i n G(CH^OH).  A l l t h e ESR s p e c t r a r e p r o d u c e d i n t h i s t h e s i s were recorded  d i r e c t l y onto t h e d r a w i n g p a p e r by t h e E-3 s p e c t r o -  meter u s i n g reduced g a i n and i n c r e a s e d f i e l d sweep. 5.  O p t i c a l A b s o r p t i o n Measurements  O p t i c a l a b s o r p t i o n s p e c t r a were r e c o r d e d model 14 s p e c t r o p h o t o m e t e r .  u s i n g a Cary  The sample c e l l was  a t 77 °K i n a. q u a r t z dewar w i t h o p t i c a l windows.  maintained Liquid  n i t r o g e n b u b b l i n g i n t h e dewar caused some " n o i s e " problems b u t by u s i n g a s l o w s c a n r a t e and maximum pen damping, a reasonable  s i g n a l - t o - n o i s e r a t i o was o b t a i n e d .  A sample o f  u n - i r r a d i a t e d PC i n a 1 cm c e l l a t room t e m p e r a t u r e was used i n t h e r e f e r e n c e compartment and t h e i n s t r u m e n t was ."balanced" u s i n g n e u t r a l d e n s i t y f i l t e r s i n t h e r e f e r e n c e beam.  This  was r e q u i r e d because t h e p a r t i a l c r y s t a l l i n i t y o f t h e sample caused a p p r e c i a b l e s c a t t e r i n g o f t h e sample beam. cardboard  Black  b a f f l e s were used t o b l o c k o u t most o f t h e s c a t t e r e d  light. F o r measurements i n t h e i n f r a r e d r e g i o n t h e sample was p r o t e c t e d from b l e a c h i n g by t h e v i s i b l e l i g h t o f t h e t u n g s t e n I R source  lamp by p l a c i n g a t h i c k U V - v i s i b l e c u t o f f f i l t e r  ( C o r n i n g # 2 - 6 1 ) between t h e s o u r c e  and t h e sample.  (When  -61the of the  C a r y 14 i s o p e r a t i n g i n t h e IR mode, t h e e n t i r e e m i s s i o n a t u n g s t e n lamp p a s s e s t h r o u g h t h e sample b e f o r e r e a c h i n g monochromator and d e t e c t o r . ) 6.  L i g h t Sources f o r P h o t o b l e a c h i n g E x p e r i m e n t s  An u n f i l t e r e d low p r e s s u r e mercury vapour lamp (Hanovia # 687A45) was g e n e r a l l y used f o r the u l t r a v i o l e t p h o t o l y s i s experiments.  T h i s lamp had a "Vycor" e n v e l o p e and  t r a n s m i t t e d o n l y w a v e l e n g t h s above 220 nm.  therefore  I n t h e ESR  e x p e r i m e n t s , t h e samples were e i t h e r b l e a c h e d d i r e c t l y i n t h e c a v i t y by s h i n i n g the l i g h t t h r o u g h t h e g r i l l o f the c a v i t y or  e l s e t h e dewar c o n t a i n i n g t h e sample b a l l s was p l a c e d  d i r e c t l y a g a i n s t t h e lamp e n v e l o p e and b o t h were s u r r o u n d e d w i t h aluminum f o i l . l i g h t i n t e n s i t y was  When p h o t o l y s e d i n t h e c a v i t y , t h e r a t h e r low b u t changes  i n the spectra  c o u l d be f o l l o w e d d i r e c t l y ; whereas i r r a d i a t i o n o u t s i d e t h e c a v i t y was  c o n s i d e r a b l y more i n t e n s e and caused r a p i d  changes.  An o r d i n a r y 100 w a t t t u n g s t e n lamp was used f o r the v i s i b l e p h o t o l y s i s e x p e r i m e n t s and t h e samples were u s u a l l y bleached d i r e c t l y i n the c a v i t y .  I s o l a t i o n o f v a r i o u s wave-  l e n g t h r e g i o n s was a c h i e v e d by u s i n g C o r n i n g g l a s s In  filters.  each case t h e s e were checked t o ensure t h a t an u n d e s i r ^ a b l e  UV o r IR "window" was n o t p r e s e n t .  C.  RESULTS AND 1.  The  (a)  DISCUSSION Trapped E l e c t r o n  E l e c t r o n s p i n resonance  observations  ^ - i r r a d i a t i o n of g l a s s y propylene  carbonate at  n i t r o g e n t e m p e r a t u r e w i t h a 1 Mrad dose i m p a r t e d p a l e g r e e n i s h c o l o u r t o the samples.  liquid  only a very  (This i s i n c o n t r a s t to  most o t h e r g l a s s y m a t e r i a l s w h i c h become i n t e n s e l y c o l o u r e d when i r r a d i a t e d a t low temperature.) The  ESR  d e r i v a t i v e s p e c t r u m o b t a i n e d u s i n g the  o p e r a b l e microwave power ( about 0.5  mW  ) immediately  t h e i r r a d i a t i o n i s shown i n F i g u r e 12. of nine p r i n c i p a l l i n e s spread and  centered  lowest following  This spectrum c o n s i s t s  over a r e g i o n some 130 G wide  a t the " f r e e - s p i n " g - v a l u e .  The most s t r i k i n g  f e a t u r e o f t h i s g r o u p i s the narrow c e n t r a l s i n g l e l i n e , l a b e l e d "A".  (The o t h e r e i g h t l i n e s i n F i g u r e 12 w i l l be examined i n  d e t a i l i n P a r t 2 of t h i s s e c t i o n which w i l l d e a l w i t h o t h e r t h a n e"^ above 0.5  mW  .)  As the microwave power l e v e l was  the i n t e n s i t y o f l i n e "A"  a t f i r s t u n t i l i t was 10 mW of the  increased  began t o s l o w l y d e c r e a s e  v i r t u a l l y completely  as i n d i c a t e d i n F i g u r e 13.  radicals  s a t u r a t e d a t about  This s a t u r a t i o n e f f e c t  "inhomogeneous" type where the l i n e w i d t h  was  remained  e s s e n t i a l l y c o n s t a n t w i t h o n l y the peak a m p l i t u d e  decreasing  uniformly.  A h i g h e r r e s o l u t i o n t r a c e of l i n e "A"  appears i n  F i g u r e 14.  The  l i n e was  d e t e r m i n e d t o be a t g = 2.0028 ± 0.0002  when measured r e l a t i v e t o DPPH ( t h i s v a l u e compares f a v o u r a b l y w i t h g = 2.0030 c a l c u l a t e d from the measured f i e l d frequency).  The  and  l i n e - w i d t h as measured between p o i n t s o f  F i g u r e 12.  ESR spectrum of ^ - i r r a d i a t e d  g l a s s y PC immediately f o l l o w i n g the i r r a d i a t i o n u s i n g  the lowest operable microwave power  (about 0.5 mW) . (Dose-'0.8 Mrad)  F i g u r e 13.  ESR spectrum o f t h e same sample as F i g u r e 12 o n l y a t about 10 mW microwave power.  F i g u r e 14.  H i g h r e s o l u t i o n ESR s c a n o f l i n e "A" o f F i g u r e 12. t r a p p e d e l e c t r o n s i n PC.  This l i n e i s a t t r i b u t e d to  -66-  maximum to  be  by  slope,  AH  _ = 4.5 ms  t h e method  ated the  technique Figure  0.1  of slopes  Analysis  o f the line-shape,  J  Gaussian  which  found both  both  analysis  On t h e b a s i s  g-value  similar  to line  o f the Gaussian saturation  t o those  ,  indicwith  normalization  and L o r e n t z i a n  and t h e power  are very  The  i s applied  the Gaussian  method  i s i n agreement  saturation characteristics.  15 w h e r e  o f which  .  and t h e n o r m a l i z a t i o n  nearly  of line-shape  "free-spin"  G  o n t h e d e r i v a t i v e , was  48  illustrated.  all  "peak-to-peak"  ±  i t t o be v e r y observed  are  i.e.  "A" i n  line-shapes  line-shape,  the  characteristics,  o f trapped  electrons i n  4 5 other  media  trapped  -  15  much  polar G)  atoms  single  narrower  line  assigned  to  i n PC as compared and i c e s where  and i c e s ,  by h y p e r f i n e  the trapping  be compared  of  by t h e absence  In the alcohols  t o be c a u s e d  surrounding  , "A", w a s  (e.g.alcohols  c a n be e x p l a i n e d  thought  line  i n PC.  glasses  i n PC.  should  , this  electrons The  other  '  sites.  =  ethers  10  hydrogen  broadening i s  i n t e r a c t i o n s o f t h e OH Therefore  to the glassy  AH  of hydroxylic line  to  i n this  where  ESR  protons  regard,  PC  line-widths  5 of  3  - 4 G are observed The  samples as  initial  was  yield  estimated  described  f o r trapped of trapped  using  glassy  i n the experimental  area  under  the absorption  area  under  t h e CH„OH  curve  triplet  2  electrons. electrons methanol  section. of line  gave  i n glassy  as t h e  standard  Comparison  "A" w i t h  G _ =0.3 t r indicated here  the  i 0.2  of the total  using  e  G(CH„0H)  = 6 . 7 „.  includes  t h e u n c e r t a i n t i e s i n GCCH^OH) , i n t h e r e l a t i v e  z  sizes  PC  (The e r r o r  and i n the i n t e g r a t i o n technique.)  f o r G^t r  This  e  only  yield i s  sample  F i g u r e 15.  H i g h r e s o l u t i o n ESR s c a n o f the t r a p p e d e l e c t r o n l i n e showing the n o r m a l i z a t i o n method of l i n e shape a n a l y s i s . •=  Gaussian,  x=  Lorentzian.  -68somewhat lower t h a n was  expected  on the b a s i s o f the  polarity  o f the s o l v e n t and t h e " v i s u a l q u a l i t y " o f the g l a s s .  For  example, i n most g l a s s y a l c o h o l s and i c e s  and  =2-3  even i n t h e r e l a t i v e l y n o n - p o l a r m e t h y l - t e t r a h y d r o f u r a n g l a s s G _ = 2 . 6 , . I n a d d i t i o n , the room temperature l i q u i d phase tr r a d i o l y s i s r e s u l t s t o be d i s c u s s e d l a t e r i n t h i s t h e s i s and 14 e  t h o s e o f Hayon  i n d i c a t e t h a t the y i e l d of s o l v a t e d e l e c t r o n s  (or f r e e i o n s ) i s G ~ 2 ,  which would p r e d i c t a y i e l d of  e l e c t r o n s g r e a t e r t h a n 2 f o r the low temperature  trapped  glass, since  i n most o t h e r systems G _ > G (e.g. i n methanol G - = 2.7 •®tr etr as compared w i t h G _ = 1.1). A probable e x p l a n a t i o n of t h i s e e  s  d i s c r e p a n c y i s t h a t a t the microwave power l e v e l used a subs t a n t i a l degree o f s a t u r a t i o n was o c c u r r i n g t o g i v e a m i s l e a d i n g result.  I n any e v e n t , y i e l d measurements by ESR a r e s u b j e c t  t o so many u n c e r t a i n t i e s t h a t t h e i r a b s o l u t e v a l u e s a r e not particularly reliable.  The r e l a t i v e v a l u e s o b t a i n e d a r e ,  however, s i g n i f i c a n t and i n t h i s case t h e v a l u e o f G _ •** e  0.3  t r  means t h a t e l e c t r o n s a r e t r a p p e d r e a s o n a b l y e f f i c i e n t l y i n the g l a s s y PC.  D e t e r m i n a t i o n o f the e x a c t degree o f t r a p p i n g  e f f i c i e n c y w i l l r e q u i r e a much more a c c u r a t e G v a l u e o b t a i n e d by some method o t h e r t h a n ESR.  A spectrophotometric  technique  whereby t h e e l e c t r o n s a r e c o n v e r t e d t o a s t r o n g l y a b s o r b i n g s p e c i e s w i t h a known m o l a r a b s o r p t i v i t y , such as the  napthalene  a n i o n , t o g e t h e r w i t h a b s o l u t e d o s i m e t r y , would g i v e a "good" A t t e m p t s t o scavenge the t r a p p e d e l e c t r o n s i n g l a s s y G value. PC w i t h s i l v e r n i t r a t e , carbon monoxide and c a r b o n d i o x i d e were u n s u c c e s s f u l .  T h i s was  l i k e l y due  to their  limited  s o l u b i l i t y i n PC, w h i c h was  l e s s t h a n 10  _2  M ; whereas much  l a r g e r s o l u t e c o n c e n t r a t i o n s a r e n o r m a l l y r e q u i r e d t o scavenge electrons i n glassy solids.  A d d i t i o n o f w a t e r and aqueous  s o l u t i o n s o f hydrogen p e r o x i d e o r formaldehyde gave c l o u d y p o l y c r y s t a l l i n e samples w h i c h were not s t u d i e d . i o d i n e a t 0.02 ESR  However,  M d i d c o m p l e t e l y remove the t r a p p e d e l e c t r o n  l i n e as w e l l as m o d i f y the r a d i c a l s p e c t r u m somewhat as  shown i n F i g u r e 16.  T h i s i s i n a c c o r d w i t h t h e known e f f i c i e n c y  o f i o d i n e as an e l e c t r o n s c a v e n g e r ,  w h i c h f o r example r e a c t s 10 -1 -1 22 w i t h the h y d r a t e d e l e c t r o n a t k = 5 x 10 M s . Iodine has a l s o been r e p o r t e d t o be a t r a p p e d e l e c t r o n s c a v e n g e r i n 49 glassy ethanol. The absence o f ESR s i g n a l s f o r the e x p e c t e d 50 product I ion p r o b a b l y can be e x p l a i n e d on t h e b a s i s o f 2 2  d i s s o c i a t i o n of I  2  t o form I  and I * , w i t h the I r a d i c a l  u n d e r g o i n g s e c o n d a r y r e a c t i o n s w h i c h r e s u l t i n the m o d i f i c a t i o n o f the ESR N a p t h a l e n e , a t 0.1  then  observed  s p e c t r u m o f the o t h e r r a d i c a l s .  M , a l s o removed the t r a p p e d e l e c t r o n ESR  s i g n a l , r e p l a c i n g i t w i t h an i n c o m p l e t e l y r e s o l v e d m u l t i - l i n e s i g n a l as shown i n F i g u r e 17. was  T h i s new  most p r o b a b l y the n a p t h a l e n e  paramagnetic species  a n i o n , an assignment w h i c h i s  supported  by the o b s e r v a t i o n t h a t t h e s e samples were g r e e n i n 48 c o l o u r w h i c h i s c h a r a c t e r i s t i c o f the n a p t h a l e n e a n i o n N a p t h a l e n e has been used as an e l e c t r o n s c a v e n g e r i n the g l a s s y 49 51 alcohols  '  a l t h o u g h t h e s p e c i e s formed was  the p r o t o n a t e d The  b e l i e v e d t o be  a n i o n i n these systems.  o b s e r v a t i o n t h a t t h e t r a p p e d e l e c t r o n s were not  s t a b l e i n t h e i r r a d i a t e d PC g l a s s e s a t 77 °K was most p u z z l i n g d i s c o v e r y o f t h i s s t u d y .  The  perhaps the  f a i r l y rapid  F i g u r e 17.  ESR spectrum of  ^ - i r r a d i a t e d g l a s s y PC a t 77 °K c o n t a i n i n g 0.1 M n a p t h a l e n e .  -72-  spontaneous decay o f t h e ESR l i n e was f i r s t n o t i c e d i n a sample t h a t had s t o o d i n t h e d a r k f o r s e v e r a l h o u r s f o l l o w i n g the i r r a d i a t i o n .  The i n t e n s i t y o f l i n e "A" r e l a t i v e t o t h e  r a d i c a l s p e c t r u m was found t o be g r e a t l y reduced.  This n a t u r a l  d e c a y d i d n o t appear t o produce any new p a r a m a g n e t i c s p e c i e s n o r was t h e r e any n o t i c e a b l e change i n t h e i n t e n s i t y o f t h e other r a d i c a l spectra.  ( I t w o u l d however be d i f f i c u l t t o  d e t e c t an o v e r a l l change i n t h e broad r a d i c a l s p e c t r u m s i n c e t h e change i n a r e a w o u l d o n l y be about 10%.) experiments,  t h e n a t u r a l decay o f e ^  r  I n subsequent  was f o l l o w e d d i r e c t l y  by ESR f o r s e v e r a l h o u r s a f t e r t h e i r r a d i a t i o n .  These s t u d i e s  r e v e a l e d t h e decay c h a r a c t e r i s t i c s i l l u s t r a t e d i n F i g u r e 18, where d a t a o b t a i n e d f o r t h r e e d i f f e r e n t t o t a l doses i s g i v e n . The p e a k - t o - p e a k h e i g h t o f t h e ESR d e r i v a t i v e s i g n a l i s p l o t t e d S i n c e t h e peak w i d t h , A H  as a f u n c t i o n o f t i m e .  , d i d not ms  change s u b s t a n t i a l l y was m o n i t o r e d ,  d u r i n g t h e i n t e r v a l o v e r w h i c h t h e decay  t h e d e r i v a t i v e peak h e i g h t i s p r o p o r t i o n a l t o  t h e t o t a l number o f s p i n s p r e s e n t . s l o w , smooth d e c r e a s e  in  i n t e r v a l o f 350 m i n u t e s .  (In a c t u a l f a c t , a very  o f about 8% o c c u r e d o v e r an T h i s was n o t c o n s i d e r e d t o be s i g n i f -  i c a n t however, s i n c e when a c o r r e c t i o n was made f o r t h i s decrease  i t d i d not a l t e r the r e s u l t s of the k i n e t i c  Because d a t a f o r t h e v e r y e a r l y s t a g e s o f t h e decay  analyses.) (first  10 m i n u t e s ) c o u l d n o t be e x p e r i m e n t a l l y o b t a i n e d , t h e c u r v e s p l o t t e d i n F i g u r e 18 were n o r m a l i z e d u s i n g an e x t r a p o l a t e d " z e r o t i m e " peak h e i g h t .  T h i s was o b t a i n e d from t h e second  o r d e r k i n e t i c p l o t s by e x t r a p o l a t i o n o f t h e i n i t i a l r e g i o n (see F i g u r e 2 0 ) .  linear  TIME (minutes) F i g u r e 18.  I s o t h e r m a l spontaneous decay o f trapped e l e c t r o n s i n ^ - i r r a d i a t e d g l a s s y P C 77 °K as f o l l o w e d b y ESR. (Data are a r b i t r a r i l y n o r m a l i z e d a t "0" time.)  -74-  F i g u r e 19 shows the f i r s t o r d e r k i n e t i c a n a l y s e s o f d e c a y d a t a i n which t h e l o g a r i t h m p l o t t e d versus time.  o f the peak h e i g h t s a r e  A l l t h r e e s e t s o f d a t a g i v e smooth c u r v e s  w h i c h i n d i c a t e s t h a t t h e decay mechanism does not f o l l o w s i m p l e f i r s t order k i n e t i c s .  F i r s t o r d e r decay would be  expected  i f t h e e l e c t r o n s were s i m p l y r e a c t i n g w i t h one o f the s o l v e n t molecules  constituting their  traps.  Second o r d e r a n a l y s i s o f the d a t a i s g i v e n i n F i g u r e 20 where t h e i n v e r s e o f t h e n o r m a l i z e d peak h e i g h t s are p l o t t e d versus time. initial  These graphs a l l have two l i n e a r r e g i o n s ; an  " f a s t e r " decay whose d u r a t i o n depends on the l e n g t h o f  t h e i r r a d i a t i o n , f o l l o w e d by a " s l o w e r " decay which i s f o l l o w e d for  a t l e a s t one  "half-life".  D a t a not shown i n t h e s e F i g u r e s  was  o b t a i n e d a t 500 and 1500 m i n u t e s a f t e r a 300 minute i r r a d -  i a t i o n and t h e s e p o i n t s f i t t h e e x t r a p o l a t e d second  order p l o t  i n F i g u r e 20 w i t h i n t h e e x p e r i m e n t a l e r r o r i n v o l v e d i n removing t h e dewar from the ESR c a v i t y . d e c a y p r o c e s s was T h i s apparent  T h i s i n d i c a t e d t h a t the " s l o w e r "  f o l l o w e d f o r a t l e a s t two  "half-lives".  second o r d e r decay i s not c o n s i s t e n t w i t h a  homogeneous r e a c t i o n o f t h e e l e c t r o n s w i t h p o s i t i v e i o n s ( t h e s e s p e c i e s would be p r e s e n t i n e q u a l c o n c e n t r a t i o n ) because t h e s l o p e s o f t h e second o r d e r k i n e t i c p l o t s a r e a p p a r e n t l y d i f f e r e n t , i m p l y i n g a dose-dependent r a t e c o n s t a n t .  The  difference  i n t h e s l o p e s i s p a r t i a l l y due t o the n o r m a l i z a t i o n f a c t o r s u s e d , a l t h o u g h the u n - n o r m a l i z e d slopes.  d a t a a l s o gave d i f f e r e n t  I t s h o u l d be noted however, t h a t t h e d a t a were o b t a i n e d  u s i n g d i f f e r e n t s p e c t r o m e t e r c o n d i t i o n s ( g a i n and sample s i z e ) and thus a b s o l u t e s p i n c o n c e n t r a t i o n s c o u l d not be measured.  • = 300 min i r r a d i a t i o n X= 30 min i r r a d i a t i o n A = 5 min i r r a d i a t i o n  100  F i g u r e 19.  200 TIME (minutes)  300  F i r s t order k i n e t i c analyses o f the trapped e l e c t r o n decay d a t a from F i g u r e 18.  TIME (minutes) F i g u r e 20.  Second order k i n e t i c analyses o f the trapped e l e c t r o n decay d a t a from F i g u r e 18  -77I t i s t h e r e f o r e p o s s i b l e that the d i f f e r e n c e s i n slope of the l i n e s i n F i g u r e 20 may be a consequence o f t h e e x p e r i m e n t a l methods used.  I n any e v e n t , i f t h e r e a c t i o n p r o c e s s i n v o l v e d  a homogeneous d i s t r i b u t i o n o f e l e c t r o n s , t h e n t h e i n i t i a l t r a n s i e n t d e v i a t i o n w o u l d have t o be a t t r i b u t e d t o a non-homog e n e i t y o f t h e system d u r i n g t h e e a r l y s t a g e s irradiation.  f o l l o w i n g the  On t h i s b a s i s , t h e l o w e s t dose e x p e r i m e n t  should  have t a k e n t h e l o n g e s t t i m e t o become homogeneous because t h e s p u r s e p a r a t i o n d i s t a n c e would be g r e a t e s t .  In addition,  F i g u r e 18 shows t h a t t h e o v e r a l l decay i s f a s t e s t f o r t h e l o w e s t dose, b u t t h i s may a r i s e from t h e f a c t t h a t a much l a r g e r p r o p o r t i o n of the species observed a f t e r the long i a t i o n a r e " l o n g - l i v e d " ones.  irrad-  I t i s also d i f f i c u l t t o envisage  e i t h e r species being s u f f i c i e n t l y mobile to d i f f u s e r a p i d l y t h r o u g h t h e h i g h l y p o l a r l o w t e m p e r a t u r e m a t r i x and become homogeneously d i s t r i b u t e d . T h e i r i n i t i a l d i s t r i b u t i o n would c e r t a i n l y n o t be homogeneous.  S i m p l e homogeneous second  order  d e c a y would t h e r e f o r e seem t o be r u l e d o u t u n l e s s some v e r y u n u s u a l p r o c e s s f o r c h a r g e m i g r a t i o n e x i s t s i n t h i s system. A t h i r d p o s s i b i l i t y f o r t h e spontaneous decay mechanism i s that the electrons are "pre-destined" icular positive ion.  to react with a part-  I n t h i s case t h e k i n e t i c s may n o t f o l l o w  any s i m p l e r e a c t i o n o r d e r b u t r a t h e r t h e decay would depend on t h e s e p a r a t i o n - d i s t a n c e cations.  d i s t r i b u t i o n s o f t h e e l e c t r o n s and  T h i s t y p e o f decay i s t h o u g h t t o o c c u r i n 3-methyl 17  pentane and m e t h y l - t e t r a h y d r o f u r a n decay r a t e s o f t h e t r a p p e d  glasses.  The i n i t i a l  e l e c t r o n s i n t h e s e systems were  found t o be d i r e c t l y p r o p o r t i o n a l t o dose and by n o r m a l i z a t i o n  -78of for  t h e d a t a t h e decay c u r v e s were found t o be s u p e r i m p o s a b l e a t l e a s t the f i r s t  a b l e v a r i a t i o n i n dose.  50% o f the decay and o v e r a c o n s i d e r I n t h e s e systems t h e decay o f each  e l e c t r o n i s a p p a r e n t l y by a p r o c e s s w h i c h i s i n d e p e n d e n t o f the  t o t a l number o f p o s i t i v e charges i n t h e m a t r i x .  not  e a s y t o see i f t h i s i s t h e case f o r e ~  r  It is  i n PC g l a s s e s  because t h e i r r a d i a t i o n t i m e s and t h e decay " h a l f - l i v e s " a r e comparable. The e l e c t r o n decay k i n e t i c s i n PC as shown by F i g u r e 18 most p r o b a b l y r e p r e s e n t t h e s p e c i e s r e a c t i n g w i t h p o s i t i v e i o n s v i a a t o t a l l y non-homogeneous p r o c e s s . the  The r e s u l t s o f  5 m i n u t e i r r a d i a t i o n e x p e r i m e n t i n d i c a t e t h a t 50% o f t h e  e l e c t r o n s p r o d u c e d a r e l o s t w i t h i n 15 m i n u t e s a f t e r t h e end of  the i r r a d i a t i o n .  Therefore a large f r a c t i o n of those p r o -  duced d u r i n g t h e e a r l y s t a g e s o f t h e 30 and 300 m i n u t e i a t i o n s have decayed b e f o r e t h e i r r a d i a t i o n was  irrad-  finished.  The i n i t i a l t r a n s i e n t f e a t u r e s i n d i c a t e d i n t h e second o r d e r plots  ( F i g u r e 20) a r e t h e r e f o r e due t o decay o f t h e " s h o r t -  l i v e d " s p e c i e s formed d u r i n g t h e l a s t few m i n u t e s o f t h e irradiation. to  These s p e c i e s may be t h o s e t r a p p e d c l o s e enough  t h e i r parent p o s i t i v e i o n that they are already  effectively  " c a p t u r e d " and t h u s have no c h o i c e b u t t o r e a c t .  The r e m a i n d e r  of  distant  the e l e c t r o n s are those which are s u f f i c i e n t l y  f r o m a p o s i t i v e i o n t h a t t h e t r a p energy i s comparable t o o r g r e a t e r t h a n t h e Coulombic f o r c e s and t h e r e f o r e t h e y have a r e l a t i v e l y l o n g l i f e t i m e governed p r i m a r i l y by d i f f u s i o n . I n t e r p r e t a t i o n o f the k i n e t i c s o f t h i s system w i l l be a complex m a t h e m a t i c a l problem.  A general t h e o r e t i c a l treatment of  -79-  b i m o l e c u l a r r e a c t i o n s i n s o l i d and l i q u i d systems where d i f -  52  f u s i o n i s t h e r a t e c o n t r o l l i n g f a c t o r has been made by Waite . S o l u t i o n s o f t h e problem a r e however e a s i l y o b t a i n e d  only i f  the d i s t r i b u t i o n o f t h e r e a c t i n g s p e c i e s i s assumed t o be random and i f no long-range f o r c e s a r e i n v o l v e d .  These assump-  t i o n s would n o t be expected t o be v a l i d i n t h e case o f i o n i c r a d i c a l s produced i n i r r a d i a t e d low temperature s o l i d s  since  Coulombic i n t e r a c t i o n s may be i n v o l v e d i n a d d i t i o n t o a nonrandom d i s t r i b u t i o n .  A l t h o u g h W a i t e ' s g e n e r a l t r e a t m e n t has  p r o v i s i o n s f o r e x t e n s i o n t o i n c l u d e non-random d i s t r i b u t i o n s and  i n t e r - i o n i c f o r c e s , s o l u t i o n s a r e e x t r e m e l y complex and  not e a s i l y a p p l i e d t o t h e e x p e r i m e n t a l  data.  In addition,  because t h e i n i t i a l d i s t r i b u t i o n o f t h e s p e c i e s i s most o f t e n unknown, t h i s would r e q u i r e a s u c c e s s i v e a p p r o x i m a t i o n to f i t the theory to the experimental  data using  method  various  assumed d i s t r i b u t i o n s . One i m p o r t a n t the y i e l d o f t r a p p e d  i m p l i c a t i o n o f t h e decay s t u d i e s i s t h a t electrons estimated  methanol i s o b v i o u s l y low.  by c o m p a r i s o n w i t h  Since the experiment i n v o l v e d a  l o n g i r r a d i a t i o n time (300 m i n u t e s ) i n o r d e r t o o b t a i n a reasonable  s i g n a l l e v e l , the e l e c t r o n s measured were c l e a r l y  o n l y t h e " l o n g - l i v e d " ones.  Most o f t h e s h o r t - l i v e d s p e c i e s  would have a l r e a d y decayed d u r i n g t h e i r r a d i a t i o n .  Thus t h e  value of G _ = 0.3 i s u n d o u b t e d l y low (perhaps by as much tr 0 e  as a f a c t o r o f 10) .  I t must t h e r e f o r e r e f l e c t o n l y a lower  l i m i t f o r the primary y i e l d of trapped propylene carbonate.  electrons i n glassy  -80As would be e x p e c t e d ,  t h e t r a p p e d e l e c t r o n s were  t h e r m a l l y u n s t a b l e above l i q u i d n i t r o g e n t e m p e r a t u r e . a sample was  warmed above 90 °K,  almost immediately.  line  disappeared  A b r o a d s i g n a l showing u n r e s o l v e d  f i n e s t r u c t u r e r e p l a c e d the e ~ was  the ESR  When  s i g n a l but t h i s new  r  species  b e l i e v e d t o o r i g i n a t e from t h e decay o f one o f the  r a d i c a l s p e c i e s and not from t h e e l e c t r o n . on warming was  The  hyper-  other  electron's f a t e  most l i k e l y the same as i t s f a t e a t  liquid  n i t r o g e n t e m p e r a t u r e , o n l y the r e a c t i o n irate i n c r e a s i n g w i t h temperature. Photobleaching  experiments using a tungsten  lamp and  v a r i o u s o p t i c a l f i l t e r s were p e r f o r m e d on a sample i n the  ESR  cavity.  was  The most s i g n i f i c a n t r e s u l t o f t h e s e e x p e r i m e n t s  t h a t t h e n a t u r a l decay o f the t r a p p e d by l i g h t w i t h X>500 nm b u t i t was by l i g h t i n t h e 300  e l e c t r o n s was  not a f f e c t e d  substantially accelerated  - 500 nm r e g i o n .  the next s e c t i o n , t h i s r e s u l t supports  As w i l l be d i s c u s s e d i n the assignment o f  an a b s o r p t i o n band i n t h e v i o l e t r e g i o n t o t h e t r a p p e d e l e c t r o n s . I t i s a l s o i n agreement w i t h t h e v i s u a l o b s e r v a t i o n o f o n l y a p a l e g r e e n c o l o u r i n d i c a t i n g t h a t t h e r e a r e no broad a b s o r p t i o n bands i n the v i s i b l e o r near i n f r a r e d r e g i o n s . t h e n a t u r a l decay a t 77 °K, new  p h o t o l y s i s d i d not produce  p a r a m a g n e t i c s p e c i e s as shown by the  s p e c t r u m i n F i g u r e 21.  The  As i n  "photobleached"  s i g n a l s remaining  near t h e  o f t h i s s p e c t r u m ( i n a d d i t i o n t o a s m a l l amount o f  trapped  r  line.  center  trapped  e l e c t r o n s r e m a i n i n g ) were most l i k e l y t h e r e i n i t i a l l y , o b s c u r e d by t h e more i n t e n s e e ^  any  only  A g a i n t h e f a t e of  e l e c t r o n s on p h o t o l y s i s i s p r o b a b l y the same as  the  the  Figure  21.  ESR spectrum o f ^ - i r r a d i a t e d g l a s s y PC a f t e r v i s i b l e p h o t o l y s i s t o remove most of the trapped e l e c t r o n s .  -82n a t u r a l decay, i . e . r e a c t i o n w i t h a p o s i t i v e i o n , t h e p r o c e s s m e r e l y b e i n g a c c e l e r a t e d by t h e energy i n p u t o f t h e l i g h t , probably v i a a p h o t o i o n i z a t i o n process. •(b)  O p t i c a l a b s o r p t i o n spectrum  As mentioned a t t h e b e g i n n i n g  of the previous s e c t i o n ,  i r r a d i a t e d g l a s s y PC b a l l s became p a l e g r e e n i n c o l o u r .  This  e f f e c t was more e a s i l y seen f o r t h e samples i n t h e 1 cm s p e c t r o p h o t o m e t e r c e l l s , w h i c h were a d a r k g r e e n f o l l o w i n g i r r a d i a t i o n w i t h a 1 Mrad dose. The  o p t i c a l a b s o r p t i o n spectrum recorded  a f t e r the i r r a d i a t i o n i s represented  by c u r v e  immediately  1 o f F i g u r e 22.  There was a s t r o n g a b s o r p t i o n band i n t h e UV w i t h a maximum below 280 nm. products  T h i s was p r o b a b l y due t o r a d i c a l s o r r a d i o l y s i s  h a v i n g an o r g a n i c c a r b o n y l group s i n c e PC does n o t  a b s o r b above 22 5 nm.  The more i n t e r e s t i n g p a r t s o f t h i s  s p e c t r u m a r e t h e s h o u l d e r on t h e UV band i n t h e 300 - 500 nm r e g i o n and t h e complex band showing " v i b r a t i o n a l " s t r u c t u r e between 500 and 7 50 nm .  As w i l l be d i s c u s s e d i n a l a t e r  s e c t i o n t h e 500 - 7 50 nm a b s o r p t i o n can be a t t r i b u t e d t o a s m a l l i n i t i a l y i e l d o f CO^ absorb i n t h i s r e g i o n .  and HCO r a d i c a l s b o t h o f w h i c h  A s e a r c h o f t h e near i n f r a r e d  region  r e v e a l e d no a b s o r p t i o n beyond 7 50 nm o u t t o 1300 nm f o r a sample i r r a d i a t e d w i t h , a 1 Mrad dose. When t h e i r r a d i a t e d PC was s t o r e d i n t h e d a r k a t 77 °K f o r 24 h o u r s , t h e s h o u l d e r o f t h e UV band was g r e a t l y r e d u c e d i n i n t e n s i t y as i n d i c a t e d by c u r v e 2 o f F i g u r e 22 and t h e  Figure  22.  O p t i c a l a b s o r p t i o n s p e c t r a of ^ - i r r a d i a t e d PC a t 77 °K (sample p a r t i a l l y c r y s t a l l i n e ) i n a 1 cm c e l l . Curve 1 was o b t a i n e d i m m e d i a t e l y a f t e r the i r r a d i a t i o n , c u r v e 2 was o b t a i n e d 24 hours l a t e r . (Dose ~ 1.3 Mrad)  -84sample appeared p a l e b l u e  i n c o l o u r due t o t h e r e m a i n i n g  absorption i n the red region. the t r a p p e d  S i n c e t h e n a t u r a l decay o f  e l e c t r o n s was a c c e l e r a t e d by p h o t o l y s i s w i t h  l i g h t and s i n c e about 9 0 % o f t h e t r a p p e d decayed n a t u r a l l y i n t h e 24 hour p r e i o d ESR  blue  e l e c t r o n s would have (as i m p l i e d from t h e  s t u d i e s ) , a l o g i c a l assignment o f t h e s h o u l d e r  o f t h e UV  band i s t o e ~ . r  The  s p e c t r u m c o n s t r u c t e d by s u b t r a c t i n g c u r v e 2 from  c u r v e 1 o f F i g u r e 22 i s a broad band w i t h a X  ^  370 nm  max (3.4 eV) as shown i n F i g u r e 23.  The w i d t h o f t h i s band a t  h a l f maximum, W , i s a p p r o x i m a t e l y  0.9 eV, w h i c h i s o f t h e same  o r d e r o f magnitude as t h a t o f t r a p p e d The  l a c k o f any asymmetry on t h e h i g h energy s i d e o f t h e  a b s o r p t i o n band, w h i c h i s n o r m a l l y and  e l e c t r o n s i n o t h e r media.  c h a r a c t e r i s t i c o f trapped  s o l v a t e d e l e c t r o n s p e c t r a , i s p r o b a b l y due t o t h e method  used t o c o n s t r u c t t h e spectrum.  I n t h e 300 - 350 nm r e g i o n  d i f f e r e n c e s between two l a r g e absorbances > 1 were i n v o l v e d and  therefore there i s a considerable u n c e r t a i n t y i n the net  absorbance due t o e ~ . r  I t i s a l s o p o s s i b l e , i f not probable,  t h a t t h e n a t u r a l decay o f t h e t r a p p e d  e l e c t r o n s does n o t i n v o l v  a U n i f o r m l o s s o f e l e c t r o n s from t h e d i f f e r e n t d e p t h t r a p s , i . e . t h e e l e c t r o n s i n t h e l o w e s t energy t r a p s may be l o s t ferentially.  Since the a b s o r p t i o n s p e c t r a o f trapped  are b e l i e v e d t o r e p r e s e n t  pre-  electrons  a population d i s t r i b u t i o n of the  d i f f e r e n t t r a p d e p t h s , t h e above method f o r c o n s t r u c t i n g t h e s p e c t r u m would t h e n g i v e a f a l s e p i c t u r e o f t h e a b s o r p t i o n band shape and i t s  X . max  Obviously  F i g u r e 23 may n o t r e p r e -  s e n t t h e t r u e a b s o r p t i o n band, however i t does g i v e a  F i g u r e 23.  A b s o r p t i o n spectrum a t t r i b u t e d t o t r a p p e d e l e c t r o n s i n PC a t 77 °K as by s u b t r a c t i o n of curve 2 from curve 1 o f F i g u r e 22.  constructed  -86q u a l i t a t i v e p i c t u r e o f the  spectrum.  The assignment o f t h i s band t o t r a p p e d e l e c t r o n s i s 5d c o n s i s t e n t w i t h the h i g h d i e l e c t r i c c o n s t a n t o f PC.  Ekstrom  p r e s e n t e d some " u n p u b l i s h e d " d a t a f o r t r a p p e d e l e c t r o n s i n a formamide + 15% water g l a s s a t 77 °K where an a b s o r p t i o n w i t h X *" 400 nm-was a p p a r e n t l y o b s e r v e d . (Pure formamide has max a d i e l e c t r i c c o n s t a n t o f 109 and t h e presence o f 15%  water  would p r o b a b l y reduce t h e e f f e c t i v e d i e l e c t r i c c o n s t a n t siderably.)  con-  I n a d d i t i o n i f the c o r r e l a t i o n between t h e room  temperature d i e l e c t r i c c o n s t a n t and t h e a b s o r p t i o n maxima f o r o 5d e l e c t r o n s t r a p p e d i n v a r i o u s g l a s s y media a t 77 K i s extended, U  t h e n a AX  i n the r e g i o n o f 400 nm may  be e x p e c t e d f o r  t r a p p e d e l e c t r o n s i n PC w i t h i t s d i e l e c t r i c c o n s t a n t o f 65. F u r t h e r e v i d e n c e s u p p o r t i n g the above assignment i s an approximate  c a l c u l a t i o n o f the m o l a r a b s o r p t i v i t y ,  f o r t h e a b s o r p t i o n band. i n PC i s G tr  =  e  0-3  media where  €  m  Assuming t h a t t h e y i e l d o f e l e c t r o n s 6  ( i . e . t h a t measured by ESR), t h e n  c a l c u l a t e d t o be 9 x 1 0 lower t h a n t h e  €  a  x  3  M~lcm ^. -  observed  €• _„ ranges from max  i max  s  This i s only s l i g h t l y  f o r trapped e l e c t r o n s i n other 8 x 10  3  to 2 x 10  4  M cm . - 1  - 1  3  The y i e l d measured by ESR d i s c u s s e d above.  i s undoubtedly  not a c c u r a t e as  I n a d d i t i o n the samples used f o r t h e  s t u d i e s were not "good" g l a s s e s but r a t h e r p a r t i a l l y  optical  cryst-  a l l i n e and thus t h e t r a p p e d e l e c t r o n y i e l d i n t h e s e samples c o u l d have been c o n s i d e r a b l y lower t h a n t h a t f o r t h e g l a s s e s used i n t h e ESR measurements. C o n s e q u e n t l y a more m e a n i n g f u l quantity to calculate i s G - x € . and t h i s has a v a l u e tr max e  of about  3 x 10  (c)  M  cm  (electrons/100 eV).  Summary  I n summary, t h e above d a t a p r e s e n t s  a s t r o n g case f o r  the e x i s t e n c e o f trapped e l e c t r o n s i n g l a s s y propylene carbonate.  T h e i r p r o p e r t i e s , as l i s t e d i n T a b l e 4, a r e i n  a c c o r d w i t h t h e p r o p e r t i e s o f t r a p p e d e l e c t r o n s i n o t h e r media (see T a b l e 2 and r e f e r e n c e s  4,5), with the exception  mysterious i n s t a b i l i t y of the species. particularly d i f f i c u l t to rationalize a s s i g n m e n t o f t h e a b s o r p t i o n band w i t h species.  o f the  This i n s t a b i l i t y i s on t h e b a s i s o f the  X  max  = 370 nm t o t h e  I f t h i s a s s i g n m e n t i s c o r r e c t , i t means t h a t t h e  a v e r a g e t r a p d e p t h f o r t h e e l e c t r o n s i s about 3.5 eV.  This  i n d i c a t e s t h a t t h e e l e c t r o n i s v e r y s t r o n g l y bound i n i t s t r a p as would be e x p e c t e d from t h e v e r y l a r g e d i p o l e moment o f -18 PC (4.9 x 10  esu cm).  Consequently t o t r y t o e x p l a i n the  n a t u r a l decay on t h e b a s i s o f " t h e r m a l d i f f u s i o n " o f t h e e l e c t r o n s from t r a p t o t r a p i s n o t p o s s i b l e . the h i g h d i e l e c t r i c c o n s t a n t  In addition,  o f t h e medium s h o u l d weaken t h e  i n t e r i o n i c f o r c e s between t h e c a t i o n s and t h e e l e c t r o n s  unless  the e l e c t r o n s a r e t r a p p e d i m m e d i a t e l y a d j a c e n t t o a p o s i t i v e ion.  -88-  TABLE 4  CHARACTERISTICS OF ELECTRONS TRAPPED IN PROPYLENE CARBONATE GLASSES AT 77 °K ESR g-factor  AH  2.0028 ± 0.0002 4.5 ± 0.1 G  ms line-shape.  Gaussian  OPTICAL  X  ~ 3 7 0 nm (3.4 eV)  max  W,  ^ 0 . 9 * eV  h YIELD G _ tr  >0.3 e l e c t r o n s / 1 0 0 eV  e  STABILITY Not s t a b l e a t 77 °K; spontaneous decay v i a a non-homogeneous p r o c e s s b e l i e v e d t o be r e a c t i o n w i t h p o s i t i v e ions.  Approximate f i r s t  "half-life"  f o r 1 Mrad dose  i s about 4 h o u r s ; w i t h t h e a p p a r e n t " h a l f - l i f e " d e c r e a s i n g w i t h dose a t a g i v e n dose r a t e  (0.3 Mrad/hr)  -89-  2. (a) The  Trapped R a d i c a l s i n I r r a d i a t e d  PC  R a d i c a l s formed d u r i n g r a d i o l y s i s a t 77 radicals  K  formed d u r i n g the i n i t i a l r a d i o l y s i s  of  g l a s s y PC a t 77 °K gave an ESR  spectrum w h i c h c o n s i s t e d of  e i g h t p r i n c i p a l l i n e s centered  a t e s s e n t i a l l y the f r e e - s p i n  g - v a l u e and s p r e a d F i g u r e 12.  No  over a r e g i o n some 130 G wide as shown i n  i n d i c a t i o n of any s i g n a l s w i t h a s p l i t t i n g  500 G a t t r i b u t a b l e  t o H atoms was  shown i n F i g u r e 12, l a b e l e d "C", as the microwave i n t e n s i t y was F i g u r e 13. was  found. was  One  lines  i n c r e a s e d as i n d i c a t e d i n  T h i s b r o a d d o u b l e t , w i t h a s p l i t t i n g o f 58 - 3  i t decayed r a p i d l y "B",  p a i r o f the  e a s i l y power s a t u r a t e d  t h e r m a l l y u n s t a b l e above about 90 °K and  lines,  of  "D",  to completely  "E",  a t about 110  G, °K  r e v e a l the u n d e r l y i n g s i x  as i l l u s t r a t e d i n F i g u r e 24.  A  new  paramagnetic species w i t h incompletely r e s o l v e d s m a l l hyperfine s p l i t t i n g  "grew" i n a t the c e n t e r o f the s p e c t r u m as  b r o a d d o u b l e t decayed. doublet  "C"  The  r a d i c a l r e s p o n s i b l e f o r the broad  c o u l d not be c o n c l u s i v e l y i d e n t i f i e d a l t h o u g h  s p e c u l a t i v e guess would be the r a d i c a l :  CH3 \  w h i c h might be e x p e c t e d t o g i v e a v e r y broad ESR a large proton hyperfine The  the  a  H  H  doublet  with  splitting.  o t h e r s i x l i n e s were j u s t as e l u s i v e i n t h e i r i d e n t -  i f i c a t i o n as d o u b l e t  "C".  However, w i t h the a i d of p h o t o -  b l e a c h i n g , i s o t h e r m a l decay and s c a v e n g e r e x p e r i m e n t s ,  i t was  p o s s i b l e t o show t h a t the s i x l i n e s were r e a l l y t h r e e s e t s of  D  F i g u r e 24.  ESR spectrum o f ^ - i r r a d i a t e d g l a s s y PC a t <*110 t r a p p e d e l e c t r o n s and o t h e r r a d i c a l s .  °K a f t e r t h e r m a l  decay of  the  -91d o u b l e t s w i t h h y p e r f i n e s p l i t t i n g o f 42 i 2, 8 3 - 3 , 124 - 4 G r e s p e c t i v e l y . g = 2.0023 ± 0.0003.  and  A l l t h r e e d o u b l e t s were c e n t e r e d a t  When a sample was  110 °K t o remove the b r o a d d o u b l e t "C" r e s o l u t i o n o f l i n e s "B" and "D")  f i r s t warmed t o about (which o b s c u r e d t h e  and t h e n p h o t o l y s e d w i t h the  u n f i l t e r e d mercury lamp, t h e m i d d l e d o u b l e t "D" was  observed  to decrease i n i n t e n s i t y f a i r l y r a p i d l y w i t h a concomitant p r o d u c t i o n o f a new i n t e n s e l i n e , spectrum.  "F", a t t h e c e n t e r o f the  L i n e "F" appeared superimposed on t h e e x i s t i n g  t r a l multicomponent  signal.  cen-  T h i s i s i l l u s t r a t e d i n F i g u r e 25  where i t i s c l e a r t h a t d o u b l e t "D" has d e c r e a s e d m a r k e d l y i n i n t e n s i t y a f t e r o n l y a few m i n u t e s o f UV i r r a d i a t i o n . "E" was a l s o s l i g h t l y r e d u c e d i n i n t e n s i t y f o l l o w i n g  Doublet photo-  l y s i s but the r e l a t i v e l y s m a l l e r decrease suggested t h a t t h i s was  a separate r a d i c a l .  I n a d d i t i o n , i f a f i l t e r was used t o  e l i m i n a t e t h e UV l i g h t below 240 nm,  d o u b l e t "E" was not s i g -  n i f i c a n t l y a f f e c t e d by p h o t o l y s i s but d o u b l e t "D" s t i l l although a t a reduced r a t e .  D o u b l e t "B" d i d n o t seem t o be  i n f l u e n c e d a t a l l by t h e u l t r a v i o l e t l i g h t . to support the i n d i v i d u a l i t y  Further evidence  o f d o u b l e t "B" was o b t a i n e d by  a l l o w i n g a sample t o s t a n d i n the d a r k f o r s e v e r a l hours a t l i q u i d n i t r o g e n t e m p e r a t u r e .  hundred  D u r i n g t h i s time the  r e l a t i v e i n t e n s i t y o f d o u b l e t "B" was s u b s t a n t i a l l y as shown i n F i g u r e 26.  decayed  reduced  I n a d d i t i o n , F i g u r e 16 i n d i c a t e d  that  i o d i n e scavenged t h i s r a d i c a l as w e l l as t h e e l e c t r o n s ,  since  d o u b l e t "B" i s c o n s p i c u o u s l y absent from t h i s spectrum.  This  s c a v e n g i n g c o u l d have o c c u r e d by a s e c o n d a r y p r o c e s s i n v o l v i n g t h e I atoms formed from  decomposition.  Alternatively, i t  F i g u r e 25.  ESR spectrum of ^ - i r r a d i a t e d g l a s s y PC a t ~110 o f the r a d i c a l r e s p o n s i b l e f o r d o u b l e t "D".  °K a f t e r p a r t i a l UV  photolysis  F i g u r e 26.  ESR spectrum o f ^ - i r r a d i a t e d g l a s s y PC a t 77 °K a f t e r s t a n d i n g f o r 200 h o u r s i n t h e dark.  -94may  have i n v o l v e d a d i r e c t r e a c t i o n w i t h t h e i o d i n e m o l e c u l e  since  i s known t o be a good r a d i c a l scavenger  e l e c t r o n scavenger.  A l l of the r a d i c a l s  formed by t h e r a d i o l -  y s i s decayed v e r y r a p i d l y i f t h e temperature o was  r a i s e d above 150  a t about 110 °K  as w e l l as  o f t h e sample  K, a l t h o u g h they were r e l a t i v e l y s t a b l e  ( e x c e p t f o r t h e d o u b l e t "C" r a d i c a l )  i n d e f i n i t e l y s t a b l e a t 77 °K  and were  (except f o r t h e d o u b l e t  "B"  radical). Thus t h e r a d i o l y s i s o f g l a s s y PC a t 77 °K appears t o g i v e r i s e t o f o u r major r a d i c a l s p e c i e s .  These a r e a l l c h a r -  a c t e r i s e d by v e r y l a r g e d o u b l e t h y p e r f i n e s p l i t t i n g  which  c l e a r l y must r e s u l t from c o u p l i n g o f t h e u n p a i r e d e l e c t r o n w i t h Ctprotons. t h e comparison  The t o t a l r a d i c a l y i e l d as e s t i m a t e d  from  w i t h i r r a d i a t e d methanol was  = 4 - 2 .  None o f t h e s e p r i m a r y s p e c i e s can be  conclusively  i d e n t i f i e d because o f t h e i r u n u s u a l ESR  spectra, s p e c i f i c a l l y  t h e v e r y l a r g e p r o t o n h y p e r f i n e s p l i t t i n g and t h e  isotropic  appearance o f the l i n e s w h i c h would not be e x p e c t e d from v e r y simple r a d i c a l s  such as HCO,  HC0 , OH, 2  etc.  A very speculative  a s s i g n m e n t o f the r a d i c a l formed on UV p h o t o l y s i s o f t h e r a d i c a l "D"  i s t o the C0 ~ 2  a narrow ESR  radical ion.  CO~ i s known t o g i v e  l i n e v e r y near the f r e e - s p i n g (g = av  and l i n e "F" i s e s s e n t i a l l y i n t h i s p o s i t i o n .  2.001)  to g i v e H  +  and C0~) . 2  ( i . e . t h i s may  4  I f this assign-  ment i s c o r r e c t , t h e n a p o s s i b l e c a n d i d a t e f o r t h e r a d i c a l would be the HCO2 r a d i c a l  5  "D"  be p h o t o d i s s o c i a t e d  T h i s s p e c u l a t i o n i s s u p p o r t e d t o some  e x t e n t by t h e l i q u i d phase r a d i o l y s i s r e s u l t s  t o be d i s c u s s e d  i n a l a t e r s e c t i o n , where a l a r g e y i e l d o f " m o l e c u l a r "  C0  2  -95was  found.  s u c h as HCO  CO^ might be e x p e c t e d t o o r i g i n a t e from a r a d i c a l o r t o produce HCXX, by s c a v e n g i n g r e a c t i o n s . 54  However Nazhat e_t a l .  have r e p o r t e d o b s e r v i n g t h e r a d i c a l  HCO2 i n i r r a d i a t e d f r o z e n sodium f o r m a t e s o l u t i o n s .  They  a t t r i b u t e d a s i n g l e l i n e t o i t a t g = 2.0121 i n d i c a t i n g  that  t h e u n p a i r e d e l e c t r o n i s l o c a l i z e d on the oxygen atoms. I n summary, t h e most u n u s u a l f e a t u r e o f t h e r a d i c a l s p e c i e s formed by t h e p r i m a r y a c t i o n o f r a d i a t i o n on g l a s s y PC i s t h e a p p a r e n t absence o f "normal" r a d i c a l s w i t h s m a l l CL,/?  p r o t o n c o u p l i n g such as i s o b s e r v e d i n most o t h e r i r r a d -  i a t e d o r g a n i c systems.  F o r example, one m i g h t have e x p e c t e d  H atom a b s t r a c t i o n t o o c c u r i n t h i s system t o g i v e r a d i c a l s such a s :  ^  c  Q  „  o p  0  ti  H  \r  Y  o  0  o  b u t t h i s a p p a r e n t l y does n o t o c c u r w i t h a s i g n i f i c a n t a t l e a s t not d u r i n g the primary r a d i o l y s i s .  yield,  (Radicals of  t h i s t y p e c o u l d a c c o u n t f o r t h e m u l t i l i n e spectrum i n t h e c e n t e r o f F i g u r e 24 caused by t h e r m a l r e a c t i o n o f some o f the primary r a d i c a l s w i t h the s o l v e n t . )  Instead of t h i s type  of r a d i c a l ; at l e a s t four d i f f e r e n t s p e c i e s , a l l a p p a r e n t l y w i t h o n l y Cl p r o t o n s , were formed.  I t i s hoped t h a t  further  s t u d i e s o f PC, i n c l u d i n g i t s d e u t e r a t e d forms, w i l l h e l p t o r e v e a l t h e i d e n t i t y o f t h e p a r a m a g n e t i c s p e c i e s g e n e r a t e d by the r a d i o l y s i s .  -96-  (b)  R a d i c a l s formed by UV p h o t o l y s i s o f the PC g l a s s e s a t 77  irradiated  °K  U l t r a v i o l e t p h o t o l y s i s o f the  ^ - i r r a d i a t e d glasses  l i q u i d n i t r o g e n t e m p e r a t u r e produced r a d i c a l s w h i c h c o u l d positively identified.  F i g u r e 27 shows the ESR  at be  spectrum of  an i r r a d i a t e d PC sample a f t e r a v e r y s h o r t exposure t o t h e f u l l i n t e n s i t y o f the mercury lamp. very dramatic  The  samples underwent a  c o l o u r change and became a deep b l u e .  As shown  i n F i g u r e 27, a new  i n t e n s e asymmetric l i n e , l a b e l e d  appeared d o w n - f i e l d  from t h e f r e e - s p i n g - v a l u e and a v a l u e  of g  ^  2.015  was  r e l a t i v e t o DPPH.  "G",  measured from the c e n t e r o f t h i s l i n e By f o l l o w i n g the changes i n the ESR  spectrum  u s i n g low i n t e n s i t y UV i l l u m i n a t i o n o f the sample d i r e c t l y i n t h e ESR  c a v i t y , i t was  b l u e c o l o u r a t i o n was  due  concluded  t h a t at l e a s t p a r t of  t o t h e new  paramagnetic species  a s s o c i a t e d w i t h l i n e "G".  In a d d i t i o n , t h i s r a d i c a l  was  a p p a r e n t l y g e n e r a t e d by the p h o t o l y s i s o f the s p e c i e s s i b l e f o r the b r o a d d o u b l e t was  supported  "C" o f F i g u r e 12.  This  l i n e "G"  i n the 500  The  nor  c o u l d be produced by UV p h o t o l y s i s o f  t h e samples a t 110 °K a f t e r the b r o a d d o u b l e t had thermally.  respon-  observation  by the f a c t t h a t n e i t h e r the b l u e c o l o u r  the narrow ESR  the  b l u e c o l o u r was  due  decayed  to a very large increase  - 7 50 nm a b s o r p t i o n band t h a t was  shown i n F i g u r e  22.  UV p h o t o l y s i s o f the samples used f o r the o p t i c a l s t u d i e s produced t h e same b l u e c o l o u r and t h e i n t e n s i t y o f the - 7 50 nm band was  g r e a t l y increased.  500  F i g u r e 28 shows t h i s  band i n more d e t a i l , p a r t i c u l a r l y what appears t o be  vibrational  F i g u r e 27.  ESR spectrum of ^ - i r r a d i a t e d g l a s s y PC Samples were dark b l u e i n c o l o u r .  a t 77  °K  a f t e r b r i e f UV  photolysis.  i  550  F i g u r e 28.  1  1  600 650 W A V E L E N G T H (nm)  r  700  A b s o r p t i o n spectrum i n the 500 - 750 nm r e g i o n f o r " ^ - i r r a d i a t e d PC a f t e r b r i e f UV p h o t o l y s i s .  Spectrum a t t r i b u t e d t o a c o m b i n a t i o n o f the HC0  and CO^" bands.  -99-  fine structure.  On t h e b a s i s o f t h e b l u e c o l o u r and t h e s i n g l e  ESR l i n e a t g ~ 2 . 0 1 5 , t h i s new r a d i c a l can be a s s i g n e d CO^  r a d i c a l anion.  CO~  t o the  has been o b s e r v e d s p e c t r o s c o p i c a l l y  i n aqueous s o l u t i o n where a broad asymmetric a b s o r p t i o n w i t h X.max*' 600 nm was d e t e c t e d on f l a s h p h o t o l y s i s and p u l s e r a d 55 56 i o l y s i s o f aqueous c a r b o n a t e s o l u t i o n s . Ershov e t a l . r e p o r t e d e s s e n t i a l l y t h e same o p t i c a l s p e c t r u m f o r CO" i n f r o z e n aqueous c a r b o n a t e g l a s s e s i r r a d i a t e d a t 77 °K .  They  a l s o a t t r i b u t e d an asymmetric ESR l i n e a t g_„ = 2.011 t o t h e species.  I t i s t h e r e f o r e e v i d e n t t h a t what appears t o be  v i b r a t i o n a l f i n e s t r u c t u r e on t h e 500 - 7 50 nm band i s r e a l l y a b s o r p t i o n bands due t o a n o t h e r s p e c i e s superimposed on t h e b r o a d s t r u c t u r e l e s s band o f CO^ . -  The o n l y l i k e l y s p e c i e s w h i c h c o u l d g i v e a m u l t i p l e l i n e v i b r o n i c s p e c t r u m i n t h i s system i s HCO.  HCO i s known  t o show a t l e a s t s e v e n narrow a b s o r p t i o n bands i n t h e r e g i o n between 500 and 7 50 nm when t r a p p e d o 57 a t 20  K .  Although  i n a c a r b o n monoxide m a t r i x  t h e p o s i t i o n s o f t h e bands o b s e r v e d  i n PC a t 77 °K ( ~ 6 9 0 , ~ 6 5 0 , *- 630, ^ 6 1 0 , ~ 5 9 0 ,  and ^57 5 nm)  do n o t agree p r e c i s e l y w i t h t h o s e o b s e r v e d i n t h e CO m a t r i x a t 20 °K (670, 635, 605, 579, 555, 533, and 510 nm) t h e d i f f e r e n c e s a r e p r o b a b l y caused by t h e o v e r l a p p i n g o f t h e C 0 ~ s p e c t r u m and r a t h e r p o o r r e s o l u t i o n .  The p r e s e n c e o f HCO 58  d e f i n i t e l y e s t a b l i s h e d by i t s ESR s p e c t r u m  was  which i s the  asymmetric d o u b l e t , l a b e l e d "H", i n F i g u r e 27.  (A l a r g e  i s o t r o p i c h y p e r f i n e s p l i t t i n g f a c t o r o f 137 G i s r e s p o n s i b l e f o r the doublet; while g  = 2.0041, g j^Ji.  f  yy  = 2.0027 and g„=  together w i t h the a n i s o t r o p i c part of the hyperfine  ZZ  1.9960  tensor,  -100B  xx  = -4.2  G, B  yy  = -0.8  G, B  Y  2  r i s e t o t h e complex l i n e s h a p e .  = 5.8 5 8 b  G  )  and B  a t low l i g h t i n t e n s i t y , d o u b l e t  = 5 G  give  (  These s i g n a l s a r e i n  e s s e n t i a l l y the same p o s i t i o n as d o u b l e t are apparently d i f f e r e n t r a d i c a l s .  2 2  "E" but t h e s e  species  On f o l l o w i n g t h e p h o t o l y s i s  "E" was  observed to  first  d e c r e a s e i n i n t e n s i t y and t h e n s l o w l y change shape and i n i n t e n s i t y as t h e new  s p e c i e s "grew" i n .  i c a t i o n was  made by c o m p a r i s o n w i t h HCO 4, 59 l y s i s of i r r a d i a t e d methanol.  increase  Positive identif-  g e n e r a t e d by UV  A l s o e v i d e n t i n F i g u r e 27 a r e s i g n a l s due  photo-  to other  p a r a m a g n e t i c s p e c i e s w h i c h i n c r e a s e d i n i n t e n s i t y as t h e p h o t o l y s i s was  prolonged.  UV  A f t e r about 20 m i n u t e s o f i n t e n s e  p h o t o l y s i s , t h e samples became n e a r l y c o l o u r l e s s w i t h complete l o s s of the COj s i g n a l a t g "2.015. a l s o bleached the C0  3  The HCO  radical  was  t o some degree by the u l t r a v i o l e t l i g h t .  and HCO  s i g n a l s c o u l d a l s o be b l e a c h e d  f r o m a h e l i u m neon l a s e r . ) t h e i n t e n s e UV  The  ESR  by r e d  spectrum recorded  (Both light after  i l l u m i n a t i o n i s shown i n F i g u r e 29 where i t  i s c l e a r t h a t s e v e r a l new  paramagnetic species are  Remaining p o r t i o n s o f r a d i c a l s "B" and appropriately.  "D"  present.  are i n d i c a t e d  I n a d d i t i o n t o t h e s e and an u n i d e n t i f i e d s i g n a l  " I " , f o u r narrow l i n e s a r e e v i d e n t as marked by t h e a r r o w s . A t f i r s t i t was sample was  t h o u g h t t h a t t h e y were u n r e l a t e d but when t h e  UV i r r a d i a t e d f o r a f u r t h e r 30 m i n u t e s , a l l f o u r  s i g n a l s i n c r e a s e d e q u a l l y as shown i n F i g u r e 30 i n d i c a t i n g t h e y were i n d e e d was  related.  S i n c e t h e s p l i t t i n g o f the  that  quartet  21 - 2 G and s i n c e t h e y were c e n t e r e d a t e s s e n t i a l l y  the  f r e e - s p i n g - v a l u e w i t h an i n t e n s i t y r a t i o o f 1:3:3:1, t h i s  o  Figure  30.  ESR  y - i r r a d i a t e d glassy  spectrum o f  Photolysis.  A  r  r  o  £  s  i  n  d  i  c  a  t  e  ^  J£  P  C  a t 77 °ir ll ^" 7  , -ter  n  .  50 m.nutes o f i n t e n s e  uv  -103species  i s undoubtedly the methyl r a d i c a l .  ment i s c o n f i r m e d b y t h e r e l a t i v e  instability  as d e t e c t e d b y t h e s l o w d e c r e a s e i n s i g n a l sample s t o o d f o r s e v e r a l hours {A h a l f - l i f e  The d e c a y p r o d u c e d  t h e broad asymmetric  as i n d i c a t e d  following  This  i n Figure  signal 31.  intensity  an i n c r e a s e  qualitative  i n the i n t e n s i t y  " I " a t the center o f the spectrum  This  species  i s probably a  °K produced  radicals  of irradiated  identified  as C 0  3  , HCO  radicals.  PC g l a s s e s a t and C H  the l a t t e r being u n s t a b l e i n the matrix a t l i q u i d temperature.  radical  splitting,  b y H atom a b s t r a c t i o n by t h e r e a c t i v e m e t h y l  I n summary, UV p h o t o l y s i s 77  as t h e  the photolysis.  w i t h o n l y ^ p r o t o n s and t h u s v e r y s m a l l h y p e r f i n e formed  assign-  of the r a d i c a l  o f a b o u t 2 h o u r s was e s t i m a t e d f r o m a  decay study.) of  4,59  3  ;  nitrogen  -105-  PART I I - RADIOLYSIS OF PROPYLENE CARBONATE IN THE A.  LIQUID PHASE  INTRODUCTION This s e c t i o n requires l i t t l e i n t r o d u c t i o n i n a d d i t i o n  t o t h a t g i v e n i n C h a p t e r I and a t the b e g i n n i n g  i n the g e n e r a l  of the c u r r e n t  remarks made  Chapter.  P r o p y l e n e c a r b o n a t e as a " s a t u r a t e d " o r g a n i c would be e x p e c t e d t o be r e l a t i v e l y u n r e a c t i v e w i t h  compound thermal  e l e c t r o n s g e n e r a t e d by r a d i o l y s i s . I t s i n e r t n e s s towards 40g,41 r e a c t i o n w i t h the a l k a l i metals prediction. should  The  tends t o s u p p o r t t h i s  high d i e l e c t r i c constant  o f t h e medium  a l l o w a l a r g e f r a c t i o n o f the t h e r m a l e l e c t r o n s  escape geminate r e c o m b i n a t i o n . —18 moment o f PC provide  (4.9 x 10  The  esu cm)  (65) to  l a r g e permanent d i p o l e  would be s u f f i c i e n t  to  ample s o l v a t i o n e n e r g y i f the t h e r m a l e l e c t r o n s  v i v e l o n g enough t o become s o l v a t e d . known p h y s i c a l and  sur-  Thus on the b a s i s of i t s  c h e m i c a l p r o p e r t i e s , one m i g h t p r e d i c t t h a t  s o l v a t e d e l e c t r o n s would be g e n e r a t e d i n a r e l a t i v e l y l a r g e 14 y i e l d i n t h i s system. Indeed, Hayon recently published a d e t e r m i n a t i o n o f t h i s y i e l d by an i n d i r e c t method w h i c h gave G _ = 2.25. However, by h i s t e c h n i q u e o f m e a s u r i n g the s e  y i e l d of anthracene anions generated i n the pulse  irradiated  l i q u i d , i t i s not p o s s i b l e t o say c o n c l u s i v e l y whether the reducing  s p e c i e s measured was  a solvated electron.  solvent anion could conceivably  a l s o undergo a f a s t  A reactive charge  t r a n s f e r r e a c t i o n w i t h a n t h r a c e n e t o g i v e the a n t h r a c e n e  anion.  -106-  S u p p o r t f o r t h i s a l t e r n a t e mechanism was obtained  by a c o l l e a g u e  recently  i n t h i s l a b o r a t o r y f o r the  radiolysis  43b  of dimethyl  sulfoxide  , where the r e d u c i n g  species  does  a p p e a r t o be a s o l v e n t a n i o n formed i n a y i e l d e q u a l t o t h a t e x p e c t e d f o r s o l v a t e d e l e c t r o n s and measured as s u c h by Hayon^f Experience i n t h i s l a b o r a t o r y w i t h another high  dielectric  15  s o l v e n t , formamide  , also indicated that solvent  c o u l d w e l l be the r e a c t i v e r e d u c i n g  anions  s p e c i e s , a l t h o u g h compet-  i t i o n k i n e t i c studies for reduction reactions with s c a v e n g e r s s u c h as N 0, 2  H , and Ag  electron  gave r a t e c o n s t a n t  ratios  v e r y s i m i l a r t o t h o s e known f o r s o l v a t e d e l e c t r o n s i n w a t e r . I t can be i n f e r r e d from t h e above d i s c u s s i o n  that  s c a v e n g e r s t u d i e s i n i r r a d i a t e d systems can produce v a l u a b l e i n f o r m a t i o n about the f r e e i o n y i e l d i n a s o l v e n t . t h e y c a n n o t always be r e l i e d upon t o i d e n t i f y t h e unambiguously.  O n l y by d i r e c t o b s e r v a t i o n  However, species  , u s i n g ESR  o p t i c a l techniques i n conjunction with pulse  or  radiolysis  (or f l a s h p h o t o l y s i s ) , can s o l v a t e d e l e c t r o n s be  positively  i d e n t i f i e d i n a medium. W i t h the above t h o u g h t s i n mind, the b a s i c o b j e c t i v e o f t h e c u r r e n t s t u d y was  t o i n v e s t i g a t e the r a d i o l y s i s  of  l i q u i d p r o p y l e n e c a r b o n a t e , b o t h pure and w i t h added s o l u t e s . By d e t e r m i n i n g and  observing  y i e l d s and i t was  the r a d i o l y t i c a l l y g e n e r a t e d p r o d u c t y i e l d s the e f f e c t s o f the added s c a v e n g e r s on  the y i e l d s of p r o d u c t s from s c a v e n g e r r e a c t i o n s ,  hoped t h a t the y i e l d o f r e d u c i n g  deduced.  these  species  could  be  -107B.  EXPERIMENTAL 1.  Reagents  Eastman Kodak p r a c t i c a l g r a d e p r o p y l e n e ' c a r b o n a t e (PC) was p u r i f i e d by f i r s t d r y i n g o v e r L i n d e 4A m o l e c u l a r s i e v e s and t h e n d o u b l e vacuum f r a c t i o n a t i o n as d e s c r i b e d i n Appendix 4. The d r y p u r i f i e d s o l v e n t was s t o r e d under d r y h e l i u m i n a g l a s s d i s p e n s i n g a p p a r a t u s w h i c h i s a l s o d i s c u s s e d i n Appendix 4, a l o n g w i t h t h e p h y s i c a l a n a l y s e s o f t h e s o l v e n t . N i t r o u s o x i d e , used as an e l e c t r o n s c a v e n g e r , was o b t a i n e d from Matheson and p u r i f i e d by " t r a p - t o - t r a p "  dist-  i l l a t i o n i n a h i g h vacuum system, where i t was s u b s e q u e n t l y stored i n a f i v e l i t r e flask u n t i l  required.  A l l o t h e r c h e m i c a l s used as s c a v e n g e r s were a n a l y t i c a l r e a g e n t g r a d e o r e q u i v a l e n t and were used as r e c e i v e d .  Water  was p u r i f i e d as d e s c r i b e d i n C h a p t e r I I . H e l i u m used f o r d e o x y g e n a t i o n o f the samples and f o r chromatography was s u p p l i e d by C a n a d i a n L i q u i d A i r .  I t was  d r i e d by p a s s i n g t h r o u g h a l o n g copper c o i l immersed  in a  l i q u i d nitrogen bath. 2.  R a d i a t i o n Source  The  Co Gammacell 220 was used f o r t h e i r r a d i a t i o n s .  F e r r o u s s u l f a t e d o s i m e t r y done i n the sample c e l l used i n the c u r r e n t s t u d y , as d e t a i l e d i n Appendix 1, i n d i c a t e d t h a t the dose r a t e f o r t h e f e r r o u s s u l f a t e s o l u t i o n was 4500 r a d s min""^ (2.84 x 1 0  1 7  eV g "  1  m i n ) on August 1, 1970. - 1  Corrections f o r  -108the  " e l e c t r o n d e n s i t y " d i f f e r e n c e b e t w e e n PC  solution  and  f o r the  w e r e made as  3.  described  Apparatus  (a)  i n Appendix  and  Sample c e l l  The used  n a t u r a l decay of  pyrex glass  in this  study  the  and  the  source  dosimeter  activity  1.  Techniques  and  sample  sample  preparation  cell  were s i m i l a r  and  to  experimental  those  techniques  originally  used  by  60 Head was  .  The  sample c e l l  inserted into  using  a pipette with  through cell.  the The  B7  stainless  stopcock  the  external  socket  springs. and  The  sample  the  vacuum  the  four-way  v i a S13  stopcock.  direction,  the  or  exposed  to  at  the  bubbles  the  volatile  By  vacuum  line  through  on the  cell  or  radiolysis  with  two  was  also  liquid  an  Figure  the  32.  because analysis  e i t h e r to  GC  the  other  stopcock  the  could loop.  into  the  two  arms  e i t h e r be The a  GC.  to of  i n a suitable isolated  fritted fine  f o r deoxygenation  products  with  aluminum  were r e q u i r e d  sample s e c t i o n provided the  the  chromatography system or  turning  the  opening  sparingly  psig during  joints  i n the  with  connected  gas  sample  the  greased  photograph of  30  was  the  ball  -  sample  sample s e c t i o n of  i n place  20  PC  socket  together  springs  PC  bottom of  gas  of  B7  A  four-way stopcock  the  sample c e l l  32.  t i p which would f i t  was  held  shown i n the  "loop"  line  and  held  r e t a i n e r and  the  joint  The  pressurized to  procedure.)  above  vacuum g r e a s e  r e t a i n e r as  was  drawn out,  tubing  Apiezon N  stopcock cell  fine,  cone and  steel  greased with  apparatus v i a the  a  capillary  Apiezon N high  (The  this  i s shown i n F i g u r e  or  disk  stream  of  flushing  Figure  32.  Photograph liquid  o f the sample  phase  radiolysis  cell of  PC.  used  f o r the  -110Th e sample c e l l and a s s o r t e d a u x i l i a r y g l a s s w a r e ( i . e . b e a k e r s , p i p e t t e s , e t c . ) were r o u t i n e l y c l e a n e d a f t e r each e x p e r i m e n t ( o r s e r i e s ) u s i n g a s t a n d a r d p r o c e d u r e .  The  sample c e l l was f i r s t d e g r e a s e d u s i n g hexane and t h e n was t h o r o u g h l y f l u s h e d w i t h hexane and t h e n d i s t i l l e d w a t e r , u s i n g a w a t e r a s p i r a t o r t o suck t h e s o l v e n t s t h r o u g h t h e c e l l . F o l l o w i n g t h i s i n i t i a l w a s h i n g , t h e c e l l was e i t h e r a n n e a l e d i n t h e g l a s s b l o w e r s ' oven o r baked i n a 300 °C l a b oven t o remove t h e brown c o l o u r a t i o n produced by t h e r a d i a t i o n i n t h e glass.  A f t e r a n n e a l i n g , t h e c e l l and o t h e r g l a s s w a r e were  soaked f o r a t l e a s t 12 h o u r s i n permanganic with d i s t i l l e d  w a t e r and soaked f o r s e v e r a l h o u r s i n a c o n -  c e n t r a t e d hydrogen p e r o x i d e - n i t r i c t r a c e s o f Mn02.  water.  a c i d s o l u t i o n t o remove  F o l l o w i n g t h i s , t h e a p p a r a t u s was t h o r o u g h l y  rinsed, f i r s t with singly d i s t i l l e d distilled  a c i d , then r i n s e d  w a t e r and t h e n w i t h  triply  F i n a l l y t h e g l a s s w a r e was d r i e d i n a " c l e a n "  oven a t 250 °C f o r s e v e r a l h o u r s b e f o r e u s e . In  a t y p i c a l e x p e r i m e n t a l s e r i e s , t h e pre-weighed  clean  c e l l was f i l l e d w i t h a sample o f p u r i f i e d PC w h i c h had been d i s p e n s e d from t h e g l a s s s t o r a g e f l a s k i n t o a s m a l l b e a k e r . The same f i l l i n g p i p e t t e was used f o r a l l e x p e r i m e n t s and i t d e l i v e r e d 17.9 m l o f t h e s o l v e n t i n t o t h e c e l l . of the  The w e i g h t  each PC sample was however d e t e r m i n e d a c c u r a t e l y by w e i g h i n g c e l l on a beam b a l a n c e t o t h e n e a r e s t 1/100*-* o f a gram. 1  T h i s sample w e i g h t was t h e n used i n subsequent dose  calculations.  F o l l o w i n g w e i g h i n g and g r e a s i n g o f t h e c e l l , t h e PC sample was deoxygenated by f l u s h i n g w i t h d r y h e l i u m f o r about 30 m i n u t e s , a f t e r w h i c h t h e c e l l s t o p c o c k was t u r n e d about 45° and t h e  -Illsample was t h e r e b y s e a l e d i n t h e c e l l under a h e l i u m atmosphere.  (The s t o p c o c k was o n l y t u r n e d 45° so t h a t t h e sample  would r e m a i n above t h e f r i t t e d g l a s s d i s k .  I f i t was t u r n e d  90°, t h e sample tended t o f l o w t h r o u g h t h e d i s k and f i l l opposite s i d e of the c e l l .  The l a t t e r was n o t d e s i r e a b l e  s i n c e t h e d o s i m e t r y had been done w i t h t h e f e r r o u s s o l u t i o n above t h e d i s k . )  the  sulfate  A f t e r deoxygenation, the c e l l  was  e i t h e r i r r a d i a t e d o r e l s e a t t a c h e d t o t h e vacuum system f o r a d d i t i o n o f n i t r o u s o x i d e t o t h e sample p r i o r t o i r r a d i a t i o n . S o l i d and l i q u i d s c a v e n g e r s were always added d i r e c t l y t o the PC i n a s m a l l b e a k e r b e f o r e t h e sample was p u t i n t h e c e l l . I n a l l c a s e s , i r r a d i a t i o n s were p e r f o r m e d w i t h t h e sample c e l l m a i n t a i n e d a t 25 °C i n a c i r c u l a t i n g a l c o h o l b a t h w h i c h f i t i n s i d e the Gammacell c a v i t y . (b)  Gaseous p r o d u c t a n a l y s i s  F o l l o w i n g i r r a d i a t i o n t h e sample c e l l was a t t a c h e d t o the of  e x t e r n a l l o o p o f t h e gas chromatograph.  In the m a j o r i t y  the experiments, a s p e c i a l l y m o d i f i e d V a r i a n Aerograph  A-90-P2 GC was used f o r a n a l y s i s o f t h e gaseous products  ( N , CH^, 2  CO and C 0 ) . 2  radiolysis  D e t a i l s o f t h i s system a r e  g i v e n i n Appendix 5 a l o n g w i t h o p e r a t i n g and c a l i b r a t i o n d a t a . B r i e f l y , t h e chromatograph was equipped w i t h d u a l columns connected i n s e r i e s w i t h the d e t e c t o r s .  The c a r r i e r g a s ,  a f t e r f l u s h i n g t h r o u g h t h e sample c e l l , passed t h r o u g h a 2 f o o t by 1/8 purpose was  i n c h Porapak Q "pre-column" vapour t r a p whose  t o p r e v e n t PC vapour from e n t e r i n g t h e GC  system.  ( T h i s pre-column was b a c k - f l u s h e d a f t e r each e x p e r i m e n t t o  -112remove t h e PC vapour.)  The c a r r i e r gas t h e n f l o w e d  through  a 1 f o o t b y 1/4 i n c h copper c o i l immersed i n a l i q u i d b a t h where t h e c o n d e n s i b l e trapped out.  Following  8 f o o t by 1/8 the  gases, i . e . C 0  nitrogen  and N^O, were  2  t h i s , t h e h e l i u m p a s s e d t h r o u g h an  i n c h Porapak Q column a t 0  C before  reaching  "sample" s i d e o f t h e t h e r m a l c o n d u c t i v i t y d e t e c t o r s  WX f i l a m e n t s .  with  The permanent gases ( N , CO and CH^) were n o t 2  s e p a r a t e d by t h i s column and a l l e l u t e d a t t h e same t i m e t o g i v e a s i n g l e peak on t h e r e c o r d e r .  The gas t h e n  flowed  i n t o a 20 f o o t by 1/4 i n c h 13X m o l e c u l a r s i e v e column a t 100  °C where t h e N^, CO and CH^ were s e p a r a t e d b e f o r e  the  "reference"  continuously  side of the detectors.  entering  The sample c e l l was  f l u s h e d by t h e c a r r i e r gas u n t i l a f t e r t h e e l u t i o n  o f methane (about 15 m i n u t e s from i n i t i a l exposure a t 60 ml/min f l o w r a t e ) ; a t t h i s p o i n t , t h e sample l o o p was bypassed t o prevent overloading  o f t h e pre-column vapour t r a p .  About f i v e  m i n u t e s a f t e r t h e sample l o o p was c l o s e d CO e l u t e d and was measured.  S u b s e q u e n t l y , CO^ was d e t e r m i n e d by warming t h e t r a p  and v a p o u r i z i n g  t h e gas condensed t h e r e .  column a t 0 °C h e l d t h e C 0 allowed  the "pressure  2  The 8 f o o t Porapak Q  back f o r s e v e r a l m i n u t e s and thus  peak", caused by warming t h e t r a p , t o  pass t h r o u g h t h e d e t e c t o r s .  I f n i t r o u s o x i d e was p r e s e n t  b o t h CO^ and N 0 e l u t e d n e a r l y s i m u l t a n e o u s l y 2  v e n t e d measurement o f C 0  2  and t h i s  pre-  i n the presence o f N 0. 2  I t was found t h a t w i t h a 60 ml/min f l o w r a t e , t a i l i n g o f t h e N » CH^ and CO peaks was n o t s e r i o u s . 2  Since C0  2  t r a p p e d o u t , i t gave a v e r y narrow peak w i t h no t a i l i n g .  was In  a d d i t i o n , "double f l u s h " e x p e r i m e n t s on t h e same i r r a d i a t e d  -113sample showed t h a t d u r i n g t h e 15 minute exposure t o t h e c a r r i e r g a s , g r e a t e r t h a n 9 9 % o f t h e permanent gases were removed from t h e c e l l and about 9 8 % o f t h e CC^ was  removed.  A t y p i c a l chromatogram and s e n s i t i v i t y d a t a a r e a l s o p r e s e n t e d i n A p p e n d i x 5.  The s e n s i t i v i t y was d e t e r m i n e d by  i n j e c t i n g known amounts o f t h e v a r i o u s gases w i t h an sample l o o p o f c a l i b r a t e d volume. by manual t r i a n g u l a t i o n . was  "in-line"  Peak a r e a s were measured  The l i n e a r i t y o f d e t e c t o r r e s p o n s e  checked by i n j e c t i n g known q u a n t i t i e s o f t h e gases w i t h  a second sample l o o p f i l l e d on a vacuum l i n e t o v a r i o u s p r e s s ures.  The d a y - t o - d a y v a r i a t i o n i n s e n s i t i v i t y was m o n i t o r e d  by i n j e c t i n g a n i t r o g e n " s t a n d a r d " w i t h t h e " i n - l i n e " l o o p b e f o r e each e x p e r i m e n t .  sample  Since the v a r i a t i o n i n these  n i t r o g e n s t a n d a r d peak a r e a s was always l e s s t h a n - 5% o f t h e mean, no c o r r e c t i o n s were made t o the e x p e r i m e n t a l d a t a .  The  5% d e v i a t i o n c o u l d be a c c o u n t e d f o r on t h e b a s i s o f changes i n a t m o s p h e r i c p r e s s u r e and t e m p e r a t u r e as w e l l as u n c e r t a i n t y i n t r o d u c e d by t h e manual i n t e g r a t i o n t e c h n i q u e . Because t h e hydrogen r e s p o n s e o f t h e A-90-P2 system w i t h h e l i u m as t h e c a r r i e r gas was  i n s u f f i c i e n t t o d e t e c t the  q u a n t i t i e s o f hydrogen formed d u r i n g t h e r a d i o l y s i s , p r o d u c t was measured  u s i n g a V a r i a n A e r o g r a p h 1720 GC w i t h  a r g o n as t h e c a r r i e r gas.  T h i s chromatograph was  w i t h 13X m o l e c u l a r s i e v e columns and WX detectors.  this  equipped  thermal c o n d u c t i v i t y  The same e x t e r n a l sample l o o p system was  the e s s e n t i a l operating d i f f e r e n c e s being a d i f f e r e n t r a t e and column t e m p e r a t u r e .  Only H  2  used, flow  (and N_ f o r a n i t r o u s  -114o x i d e s e r i e s ) was  measured because o f the e x c e s s i v e l y  r e t e n t i o n times f o r CH„  4  (c)  and  long  CO.  Vacuum t e c h n i q u e s and d e t e r m i n a t i o n s o l u b i l i t y of n i t r o u s  of  the  oxide  Deoxygenated PC samples were vacuum degassed by  attach-  ing  t h e c e l l t o the vacuum system i l l u s t r a t e d i n F i g u r e  The  S13  33.  b a l l j o i n t s o f the c e l l were c o n n e c t e d t o the two  sockets,  each o f w h i c h was  a small stopcock,  and  S13  i s o l a t e d from the vacuum l i n e  S^.  A t h i r d s t o p c o c k , S^,  by  further  s e p a r a t e d the e x t e r n a l c o n n e c t i o n s from t h e main vacuum manifold.  I n i t i a l l y , w i t h t h e four-way s t o p c o c k o f the  cell  turned  so as t o i s o l a t e t h e sample from the vacuum, s t o p c o c k s  S^,  and  S  2  were opened and  the l i n e up t o and  "bore" o f t h e four-way s t o p c o c k was  i n c l u d i n g the  pumped t o a good vacuum  —6  (10  mm  o f Hg)  u s i n g a t h r e e s t a g e mercury d i f f u s i o n pump  backed by a r o t a r y o i l pump. t h e four-way s t o p c o c k was  Then w i t h t h e s t o p c o c k S  s l o w l y r o t a t e d 90°  u n t i l the  i n s i d e the c e l l s t a r t e d t o "bubble" out v i a S^. the procedure r e q u i r e d c o n s i d e r a b l e  care.  closed,  2  gas  This part  I f the c e l l  was  opened t o o q u i c k l y , the sample would b u b b l e e x c e s s i v e l y s p l a s h i n t o the vacuum l i n e .  Once most o f t h e h e l i u m  pumped out o f the c e l l v i a S^, the t r a c e s o f gas were removed.  The  was  of  and  was  c a u t i o u s l y opened  and  r e m a i n i n g on t h a t s i d e o f t h e s i n t e r e d d i s k c e l l and  sample were f i n a l l y pumped down  t o a good vacuum, a f t e r w h i c h , S , S  and  S  were c l o s e d . 3  N i t r o u s o x i d e , w h i c h had i n t r a p T^  p r e v i o u s l y been t r a p p e d  out  ( u s i n g a l i q u i d n i t r o g e n bath) and w e l l degassed,  Figure 3 3 .  Schematic diagram o f the vacuum system used to add n i t r o u s o x i d e t o the PC i n the "bubbler" c e l l .  samples  -116-  was  t h e n v a p o u r i z e d i n t o t h e e v a c u a t e d l i n e t h a t was i s o l a t e d  from t h e vacuum pumps by s t o p c o c k S^.  The i n i t i a l N 0 p r e s s 2  u r e was r e a d on t h e mercury manometer and from t h e known volume o f t h e l i n e between  and S^, t h e i n i t i a l amount o f  N^O was c a l c u l a t e d u s i n g t h e i d e a l gas l a w ; PV =nRT. S  was opened, f o l l o w e d by S  w h i c h was s l o w l y opened t o a l l o w  t h e N 0 t o b u b b l e t h r o u g h t h e PC sample. 2  at t h i s stage.  Then  S  1  remained  closed  A g a i n i t was n e c e s s a r y t o u s e g r e a t c a r e i n  o p e n i n g S , o t h e r w i s e t h e sample would s p l a s h i n t o t h e l i n e . 2  The  was a l l o w e d t o b u b b l e s l o w l y t h r o u g h t h e sample u n t i l  e q u i l i b r i u m was r e a c h e d  (about 30 m i n u t e s ) .  Then  was  opened, t h e four-way s t o p c o c k c l o s e d by t u r n i n g 4 5 ° and t h e f i n a l p r e s s u r e was r e a d from t h e manometer.  From t h e c a l -  i b r a t e d t o t a l volume o f t h e system, t h e f i n a l amount o f gaseous N 0 was c a l c u l a t e d . 2  (A s u i t a b l e c o r r e c t i o n was made f o r t h e  manometer volume change.)  The d i f f e r e n c e between t h e i n i t i a l  a n d f i n a l amounts o f gaseous n i t r o u s o x i d e gave t h e q u a n t i t y w h i c h had d i s s o l v e d i n t h e PC sample. o f PC t h e c o n c e n t r a t i o n o f ^ O  U s i n g t h e known volume  was c a l c u l a t e d .  The v a r i a t i o n  of n i t r o u s oxide c o n c e n t r a t i o n w i t h e q u i l i b r a t e d p r e s s u r e i s p l o t t e d i n F i g u r e 3 4 . From t h e s l o p e o f t h e l i n e  through  t h e s e d a t a , t h e s o l u b i l i t y o f N O i n PC a t room t e m p e r a t u r e —4  (20-25  C) was e s t i m a t e d t o be 1.5 x 10  1  M mm  .  The s l i g h t  s c a t t e r i n t h e d a t a most p r o b a b l y i s a r e s u l t o f t e m p e r a t u r e v a r i a t i o n s from e x p e r i m e n t t o e x p e r i m e n t .  The "non-zero"  i n t e r c e p t i s b e l i e v e d t o be due t o t h e p r e s e n c e o f t h e s i n t e r e d d i s k i n the apparatus.  F i g u r e 34.  C o n c e n t r a t i o n o f d i s s o l v e d n i t r o u s o x i d e i n PC a t room t e m p e r a t u r e (20 - 25 as a f u n c t i o n o f the n i t r o u s o x i d e p r e s s u r e i n t h e " b u b b l e r " c e l l .  -118-  C.  RESULTS 1.  Pure PC - Gaseous R a d i o l y s i s P r o d u c t s  The f o u r gaseous p r o d u c t s formed w i t h y i e l d i n PC i r r a d i a t e d a t 25 °C were H^, CH^, T h e i r y i e l d was  1 9  CO and  C0 . 2  found t o be independent o f dose up t o a t l e a s t  0.3 Mrad (1.9 x 1 0 (8.6 x 1 0  significant  eV g" )  1 9  eV g" )  1  f o r CH^,  1  for H  and a t l e a s t 1.4  2  CO and C 0 .  (Yields f o r larger  2  doses t h a n t h e s e were n o t measured.)  Mrad  Some o f t h e s e d a t a a r e  p l o t t e d i n F i g u r e 35, where from the s l o p e s o f the l i n e s the G v a l u e s were c a l c u l a t e d t o be: G(H )  = 0.75 i  2  0.05  G(CH )= 0.20  ±  0.02  G(CO)  ±  0.1  ±  0.2  4  =1.2  G ( C 0 ) = 3.3 2  No oxygen was produced by t h e r a d i o l y s i s and non-gaseous p r o d u c t s were not measured. 2.  Scavenger  Experiments  S e v e r a l s e r i e s o f e x p e r i m e n t s were performed w i t h n i t r o u s o x i d e p r e s e n t as a s c a v e n g e r .  The y i e l d o f n i t r o g e n  produced by s c a v e n g i n g r e a c t i o n s a t a f i x e d n i t r o u s o x i d e c o n c e n t r a t i o n was i n F i g u r e 36.  found t o be dependent  on dose as  illustrated  F o r a n i t r o u s o x i d e c o n c e n t r a t i o n o f 0.05  t h e i n i t i a l G(N ) 2  = 1.8 d e c r e a s e d t o G(N ) 2  = 0.9  a f t e r the 19  sample had a b s o r b e d a t o t a l o f about 0.8 Mrads (5 x 10 T h i s d e c r e a s e i n G(N ) 2  M,  eV g  was b e l i e v e d t o be caused by a  n o n - v o l a t i l e p r o d u c t b u i l d i n g up i n t h e system and  competing  -1 ).  - 1 1 9 -  Figure  35.  Y i e l d s o f gaseous r a d i o l y s i s p r o d u c t s from PC *y - i r r a d i a t e d a t 25 °C, as a f u n c t i o n o f dose.  I  NJ O I  F i g u r e 36.  N i t r o g e n y i e l d as a f u n c t i o n o f accumulated sample dose f o r a c o n s t a n t oxide concentration  (0.05 M).  nitrous  -121w i t h n i t r o u s o x i d e f o r the r e d u c i n g s p e c i e s .  This  conclusion  i s based on the o b s e r v a t i o n t h a t the n i t r o g e n y i e l d measured f o r a s m a l l dose g i v e n t o a sample p r e v i o u s l y i r r a d i a t e d w i t h a l a r g e dose, but f l u s h e d t o remove the v o l a t i l e was  much s m a l l e r t h a n t h a t o b t a i n e d  a f r e s h sample.  products,  f o r a s m a l l dose g i v e n t o  Because o f t h i s dependence o f G(N  ) on dose,  a l l o t h e r e x p e r i m e n t s i n v o l v i n g n i t r o u s o x i d e were done on a new  sample u s i n g the s m a l l e s t p r a c t i c a l dose o f about 18 —1  0.08  Mrad (5 x 10  G(N )  c o u l d be  2  eV g  ) f o r which a reasonably  accurate  determined.  N i t r o u s o x i d e d i d not a f f e c t the hydrogen o r c a r b o n monoxide y i e l d s o r s i g n i f i c a n t l y lower the methane y i e l d . t h e low doses used i n most e x p e r i m e n t s , d e t e r m i n a t i o n was  a c c u r a t e methane  not p o s s i b l e because o f i t s low y i e l d  " t a i l i n g " ' of the n i t r o g e n peak.  At  and  However, the y i e l d c a l c u l a t e d  f o r l a r g e dose e x p e r i m e n t s w i t h N 0  were i n agreement w i t h  2  G(CH ) o b t a i n e d f o r pure PC and the y i e l d s measured a t 4  doses were never l e s s t h a n G(CH^) = 0.1  .  low  Carbon d i o x i d e  c o u l d not be measured w i t h n i t r o u s o x i d e p r e s e n t because of the i n t e r f e r e n c e mentioned i n the e x p e r i m e n t a l The  y i e l d of n i t r o g e n , G ( N ) , f o r c o n s t a n t dose e x p e r 2  i m e n t s , p l o t t e d as a f u n c t i o n o f n i t r o u s o x i d e i s shown i n F i g u r e 37. 0.01  section.  G  ( 2^ N  concentration  i n c r e a s e d r a p i d l y between 0  and  M n i t r o u s o x i d e and t h e n i n c r e a s e d more s l o w l y , e v e n t u a l l y  r e a c h i n g a near p l a t e a u v a l u e o f G(N ) 2  = 2.0  above 0.07  M .  (The maximum e x p e r i m e n t a l l y o b t a i n a b l e n i t r o u s o x i d e c o n c e n t r a t i o n was  0.1  M, w h i c h c o r r e s p o n d e d t o 7 50 mm  pressure.)  »122-  -123S e v e r a l e x p e r i m e n t s were performed w i t h second s c a v engers p r e s e n t i n a d d i t i o n t o n i t r o u s o x i d e .  These d a t a a r e  l i s t e d i n T a b l e 5, a l o n g w i t h d a t a f o r t h e e f f e c t s o f t h e second s c a v e n g e r s a l o n e .  Iodine, a very e f f i c i e n t  electron  and r a d i c a l s c a v e n g e r , d i d n o t a f f e c t the c a r b o n monoxide o r carbon d i o x i d e y i e l d s .  I t d i d , however, reduce t h e methane  y i e l d by a f a c t o r o f a t l e a s t 10.  I n t h e p r e s e n c e o f 0.077 M  n i t r o u s o x i d e , i o d i n e a t 0.001 M competed e f f e c t i v e l y f o r t h e p r e c u r s o r o f n i t r o g e n and r e d u c e d G(N ) 2  As t h e i o d i n e c o n c e n t r a t i o n was i t o n l y d e c r e a s e d G(N ) 2  by a f a c t o r o f 2.  i n c r e a s e d 70 f o l d t o 0.068 M  by a f u r t h e r f a c t o r o f 2, c o n t r a r y t o  t h a t e x p e c t e d on t h e b a s i s o f s i m p l e c o m p e t i t i o n k i n e t i c s . Water a t 0.22  M d i d not a f f e c t the n i t r o g e n y i e l d or t h a t of  any o f t h e o t h e r gaseous p r o d u c t s . did  n o t a f f e c t G(N ) 2  Methanol a t 0.18  o r G(CH ) and G(CO). 4  M also  S e v e r a l experiments  were performed w i t h s u l f u r i c a c i d a l t h o u g h i t was known t o cause h y d r o l y s i s o f t h e p r o p y l e n e c a r b o n a t e ; p r o d u c i n g CO,,, 40a p r o p y l e n e o x i d e and p r o p i o n a l d h y d e A t 0.33  M H  +  among o t h e r p r o d u c t s .  t h e n i t r o g e n y i e l d was r e d u c e d by more t h a n a  f a c t o r o f 2 w i t h n i t r o u s o x i d e a t 0.07 5 M.  I t d i d n o t appear  t o s i g n i f i c a n t l y a f f e c t t h e hydrogen y i e l d a l t h o u g h i f 0.2 m e t h a n o l was added, t h e hydrogen y i e l d d i d i n c r e a s e t o G(H ) 2  D.  = 0.95  M  slightly  .  DISCUSSION S i n c e t h e hydrogen, c a r b o n monoxide and c a r b o n d i o x i d e  y i e l d s were n o t a f f e c t e d by t h e p r e s e n c e o f the e l e c t r o n and  TABLE 5 SUMMARY OF SECOND SCAVENGER EXPERIMENTAL RESULTS S  Second Scavenqer  2  (M)  N 0 (M)  G(H )  G(N )  Nil  0.75  Nil  0.094  0.76  2.0  2  Nil  Nil  Nil Nil  Nil Nil  Iodine  0.053  Nil  0.0010  0.077  Water II  Methanol H  +  »  (H,SOj 2  b  0.0046  0.077  0.012  0.077  0.022  0.077  0.068  0.077  •  a a a a a a  G(CH ) 4  0.20  a  G(CO)  3.3  a  2.0  0.15  1.1  a a  Nil  0.02  1.1  3.4  1.1  0.03  1.1  0.86  0.01  1.1  0.75  0.01  1.2  0.65  0.03  1.1  0.55  0.02  1.1  a a a a a  0.17  1.2  3.5  a  a a  Nil  0.77  Nil  0.077  0.77  1.9  0.18  0.051  a  1.7  0.14  1.2  0.60  0.14  1.1  0.075  0 . 2 9  c  Nil Nil  a 0.78 0.95  G(CO  1.2  0.22  0.29  n  a  2  0.22  0.33  4  Footnotes:  0.077  2  Nil Nil  a  a a  a a  a a a  a. Not d e t e r m i n e d , b. A c i d caused s l o w h y d r o l y s i s o f t h e PC p r o d u c i n g C 0 among o t h e r p r o d u c t s . T h i s may have i n f l u e n c e d t h e r e s u l t s , c. 0 . 2 M methanol added i n a d d i t i o n t o t h e a c i d . 2  -125r a d i c a l s c a v e n g e r s , n i t r o u s o x i d e and i o d i n e a t g r e a t e r t h a n 10  M, t h e s e p r o d u c t s a r e most l i k e l y formed v i a m o l e c u l a r  processes.  A p r o b a b l e mechanism f o r the f o r m a t i o n o f CO  C 0 2 i s t h r o u g h "spontaneous"  and  d i s s o c i a t i o n of e l e c t r o n i c a l l y  e x c i t e d p r o p y l e n e c a r b o n a t e m o l e c u l e s , a l t h o u g h r a p i d decompo s i t i o n o f p o s i t i v e i o n s c o u l d a l s o produce t h e s e p r o d u c t s . Indeed, t h e mass spectrum o f PC  (see Appendix  4)  indicates  t h e PC p o s i t i v e i o n i s v e r y u n s t a b l e i n t h e gas phase and i t does appear t o l o s e CO and CO2 v e r y r e a d i l y . hydrogen,  The  molecular  on t h e o t h e r hand, i s b e l i e v e d t o r e s u l t from  fast  H atom a b s t r a c t i o n r e a c t i o n s . The p r e c u r s o r o f methane was _3 i o d i n e , even a t 10  r e a d i l y scaveng/ed  by  M, w h i c h i n d i c a t e s t h e methane a r i s e s  from r e l a t i v e l y l o n g - l i v e d m e t h y l r a d i c a l s formed i n t h e r a d i o l y t i c decomposition processes of propylene  carbonate.  The f a c t t h a t n i t r o u s o x i d e d i d n o t s i g n i f i c a n t l y lower G(CH^) as compared w i t h i o d i n e , most p r o b a b l y r e f l e c t s t h e much slower r e a c t i o n rate constants f o r r a d i c a l r e a c t i o n s of  N 0 2  5  as compared w i t h i o d i n e .  I o d i n e , f o r example, r e a c t s 4 x 10 22 t i m e s f a s t e r w i t h H atoms i n aqueous s o l u t i o n . The s i g n i f i c a n c e o f t h e w a t e r e x p e r i m e n t s i s t o i n d i c a t e  t h a t e i t h e r w a t e r does not scavenge t h e p r e c u r s o r s o f the m o l e c u l a r p r o d u c t s , H , CO, 2  CO  and C H , ^ 4  or the precursor of  n i t r o g e n , o r e l s e t h e PC samples a l r e a d y c o n t a i n e d s u f f i c i e n t water so t h a t t h e a d d i t i o n a l amount added i n t h e s e would not have any i n c r e a s e d e f f e c t .  experiments  Water would be  expected  t o a c t as an e f f i c i e n t p o s i t i v e i o n s c a v e n g e r , a c c e p t i n g a p r o t o n t o form  H_0 . +  -126I n a d d i t i o n t o t h e independence o f t h e hydrogen y i e l d on t h e p r e s e n c e o f n i t r o u s o x i d e , t h e f a i l u r e o f m e t h a n o l a t 0.2 M t o a f f e c t t h e n i t r o g e n y i e l d f o r a n i t r o u s o x i d e c o n c e n t r a t i o n o f 0.05 M, a l s o r u l e s o u t t h e p o s s i b i l i t y o f H atoms b e i n g t h e r e d u c i n g s p e c i e s .  M e t h a n o l i s known t o be  a good h y d r o g e n atom s c a v e n g e r i n aqueous s o l u t i o n s , w i t h t h e r a t i o o f t h e r a t e c o n s t a n t s f o r H atom r e a c t i o n s w i t h m e t h a n o l 22 and n i t r o u s o x i d e b e i n g 20. Thus t h e major r e d u c i n g s p e c i e s i n i r r a d i a t e d PC would appear t o be a n e g a t i v e i o n , e i t h e r a s o l v a t e d e l e c t r o n o r a molecular anion.  T h i s s p e c i e s , X~, w h i c h i s r e a d i l y scavenged  by n i t r o u s o x i d e t o g i v e n i t r o g e n , a p p a r e n t l y has a y i e l d o f G ( X " ) v 2 as i n d i c a t e d b y t h e " p l a t e a u " v a l u e o f G ( N ) .  I f the  2  a l t e r n a t i v e f a t e o f s p e c i e s X~ i s assumed t o be r e a c t i o n w i t h u n s p e c i f i e d i m p u r i t y o r s o l v e n t "S", t h e n a n a l y s i s o f t h e n i t r o g e n y i e l d dependence on n i t r o u s o x i d e c o n c e n t r a t i o n may be made on t h e b a s i s o f s i m p l e c o m p e t i t i o n k i n e t i c s .  The two  r e a c t i o n s o c c u r i n g a r e (8) and ( 9 ) . X~  +  S —  X"  + N 0 _ N2£L> N  k  s  » products  k  2  Steady s t a t e treatment  2  (8)  + products  (9)  o f t h i s r e a c t i o n mechanism f o r s p e c i e s  X~ g i v e s t h e k i n e t i c e x p r e s s i o n ( i x ) . k  G(N )  G(X-)  2  K  [s]  s  N 0 2  Thus a p l o t o f  1/G(N ) 2  w i t h slope equal t o k  s  versus  (ix)  [ 2°3 N  1/ [N o3 s h o u l d be a s t r a i g h t  L"s] / k j j ^ g  2  G  ( ~) x  a n <  3 the i n t e r c e p t  line  -127e g u a l t o 1/G(X~) i f t h e s i m p l e c o m p e t i t i o n h o l d s .  Such a  p l o t f o r t h e d a t a o f F i g u r e 37 i s g i v e n i n F i g u r e 38. r e l a t i v e l y good l i n e a r i t y o f t h e e x p e r i m e n t a l d a t a  The  supports  the s i m p l e c o m p e t i t i o n mechanism and t h e i n t e r c e p t o f 0.45 i m p l i e s t h a t G(X ) = 2 . 2  , a v a l u e i n good agreement w i t h t h e  v a l u e o f G(N2) = 2.0 a t 0.1 M n i t r o u s o x i d e .  Another  impli-  c a t i o n o f t h e s i m p l e c o m p e t i t i o n mechanism i s t h a t a p p a r e n t l y o n l y one r e d u c i n g s p e c i e s i s r e a c t i n g w i t h n i t r o u s o x i d e t o give nitrogen. The a s s i g n m e n t o f t h e r e d u c i n g s p e c i e s t o a n e g a t i v e i o n and t h e measured y i e l d o f X~ a r e i n good agreement w i t h 14 the work r e c e n t l y p u b l i s h e d by Hayon i o n y i e l d i n propylene  carbonate.  on t h e f r e e n e g a t i v e  He d e t e r m i n e d G(X~) = 2.25  by m e a s u r i n g t h e y i e l d o f a n t h r a c e n e a n i o n s  formed on p u l s e  r a d i o l y s i s of the l i q u i d . The c o m p e t i t i o n e x p e r i m e n t s between n i t r o u s o x i d e and i o d i n e f o r s p e c i e s X~ gave some i n t e r e s t i n g r e s u l t s .  At the  f i x e d n i t r o u s o x i d e c o n c e n t r a t i o n o f 0.077 M, w h i c h was s u f f i c i e n t t o scavenge a t l e a s t 9 0 % o f t h e X~, i o d i n e a t o n l y -3 10  M r e d u c e d t h e n i t r o g e n y i e l d by a l m o s t a f a c t o r o f two.  However, as t h e i o d i n e c o n c e n t r a t i o n was i n c r e a s e d t o 0.068 M, the n i t r o g e n y i e l d d i d n o t d e c r e a s e as r a p i d l y as would be expected  on t h e b a s i s o f a s i m p l e c o m p e t i t i o n mechanism.  Indeed i f t h e s i m p l e c o m p e t i t i o n k i n e t i c e x p r e s s i o n  (ix) given  above i s m o d i f i e d so t h a t t h e a l t e r n a t e f a t e o f s p e c i e s X~ i s r e a c t i o n w i t h I , then the e x p r e s s i o n  (x) s h o u l d h o l d .  -128-  -129-  k  G(N )  G(X")  2  K  l2  P ]  N 0  [N 0]  2  A p l o t of 1 / G ( N ) 2  with slope equal cept equal  .  then be  2  ^N 0  to the r a t i o ^ j ^ /  to 1/G(X~)  2  L"N O] should  /  versus  ( ~)  G  x  2  (x)  2  a n c  linear  * *~he i n t e r -  T h i s graph f o r the d a t a i n Table  i s shown i n F i g u r e 39.  The  f a c t t h a t i t i s f a r from  5  linear  means t h a t a secondary r e a c t i o n must be o c c u r i n g between the product  o f the i o d i n e scavenging r e a c t i o n and  to g i v e n i t r o g e n . s i n c e the product probably The  of the r e a c t i o n of X~ w i t h  + N 0  * N  X  + I  »• I  -  2  2  +  I"  + N 0  » N  I  + S  • products  + products  C  N  2  °3  a n <  prevail:  (10) (11) (12)  the a l t e r n a t e f a t e of the  U n f o r t u n a t e l y k i n e t i c a n a l y s i s of r e a c t i o n s  checked a g a i n s t the e x p e r i m e n t a l  data.  (12)  on  2  3 t h e r e f o r e the mechanism cannot be  iodine  (9) -  f o r the dependence o f G ( N )  g i v e s a complex e x p r e s s i o n  to  (9)  + products  2  where r e a c t i o n (12) r e p r e s e n t s  2  2  the n i t r o u s oxide  + products  2  I  2  I ~.  the f o l l o w i n g r e a c t i o n scheme might  X"  £ l 3 and  iodine i s  an i o d i n e atom formed v i a the i n t e r m e d i a t e  g i v e n i t r o g e n and  oxide  T h i s r e s u l t i s not p a r t i c u l a r l y s u p r i s i n g  i o d i n e atom c o u l d then r e a c t w i t h  atoms.  nitrous  the  easily  However, the  data  shown i n F i g u r e 39 do i n d i c a t e t h a t i o d i n e r e a c t s much more r a p i d l y with evident very  low  s p e c i e s X~  from the i n i t i a l  than does n i t r o u s oxide.  s l o p e of the curve of about 40.  iodine concentrations,  anism should  the simple  competition  h o l d a t l e a s t a p p r o x i m a t e l y , and  then mean t h a t k j ^ / ^ J J O ^ 2  This i s  S  A  PP  r  o  x  i  m  a  t  e  ly  At  mech-  the s l o p e would  equal  to 80.  This  -130-  F i g u r e 39.  P l o t o f 1/G(N ) v e r s u s 2  p J / ^ O ]  f o r [T^O] = 0.077 M.  -131i s o n l y a f a c t o r o f 9 g r e a t e r t h a n t h a t measured f o r h y d r a t e d e l e c t r o n s i n water where k /  k  r e a c t i o n (10)  u o  =  *  9  2  l 2  Assuming t h a t  o c c u r s a t a r a t e s i m i l a r t o the r a t e o f r e a c t i o n  o f h y d r a t e d e l e c t r o n s w i t h i o d i n e i n w a t e r (k  = <3  a  10 5 x 10  —1 —1  ) t h i s would i m p l y t h a t s p e c i e s X  w i t h n i t r o u s oxide w i t h a r a t e constant M n i t r o u s o x i d e was  t o be a p p r o x i m a t e l y 10  reacts  o f about 5 x 10  M~  s~" .  r e q u i r e d t o scavenge h a l f o f ,  t h e s p e c i e s , the n a t u r a l l i f e t i m e o f X  The  2  22  Ms  S i n c e 0.02  I  +  seconds (100  f a c t t h a t a c i d a t 0.3  can t h e n be  estimated  nsec).  M H"*" was  a b l e t o reduce  the  n i t r o g e n y i e l d s i g n i f i c a n t l y i s supplementary evidence f o r the a n i o n i c c h a r a c t e r p r o d u c t o f the H  +  o f the r e d u c i n g  species  i n PC.  The  s c a v e n g i n g r e a c t i o n w i t h s p e c i e s X~ does  not  appear t o be m o l e c u l a r hydrogen as i n d i c a t e d by the l a c k o f an i n c r e a s e i n the hydrogen y i e l d .  However, i t i s  conceivable  t h a t hydrogen atoms (formed by r e a c t i o n o f H+ w i t h a s o l v a t e d e l e c t r o n ) m i g h t r e a c t w i t h the  ^C=0  system o f PC  preferentially  to g i v e a n o n - v o l a t i l e product r a t h e r than a b s t r a c t i n g a h y d r o g e n atom t o form m o l e c u l a r hydrogen.  T h i s argument i s  p a r t i a l l y s u p p o r t e d by the e x p e r i m e n t i n w h i c h methanol added and  a s l i g h t i n c r e a s e i n the hydrogen y i e l d was  was  observed.  (Methanol i s known t o be a good H atom s c a v e n g e r i n aqueous s y s t e m s , p r o d u c i n g hydrogen i n the s c a v e n g i n g r e a c t i o n . ) t h e o t h e r hand, i f a m o l e c u l a r a n i o n i s the r e d u c i n g i n PC t h e n an i n c r e a s e i n the H^ y i e l d would not be on a d d i t i o n o f a c i d .  I n any  Carbon d i o x i d e and  species expected  e v e n t , s i n c e a c i d i s known t o  cause h y d r o l y s i s o f PC t h e s e r e s u l t s are not reliable.  On  particularly  p r o p i o n a l d e h y d e a r e among the  -132h y d r o l y s i s p r o d u c t s40a and b o t h a r e good H atom and e l e c t r o n scavengers.  I t was m a i n l y because o f t h i s h y d r o l y s i s  problem  t h a t a s y s t e m a t i c e x a m i n a t i o n o f t h e c o m p e t i t i o n between H  +  and N.O was n o t made. On t h e b a s i s o f t h e r e s u l t s d i s c u s s e d above, i t appears  that  ^-radiolysis  o f l i q u i d p r o p y l e n e c a r b o n a t e produces t h e  p r i m a r y m o l e c u l a r p r o d u c t s ; hydrogen, carbon d i o x i d e w i t h y i e l d s : and G,Q C  = 3.3 * 0.2,  G  c a r b o n monoxide and  = 0.75 - 0.05, G  = 1.2 ± 0.1,  and methane v i a a s e c o n d a r y  process  i n v o l v i n g m e t h y l r a d i c a l s w i t h a y i e l d G(CH^) = 0.20 ± 0.02 . I n a d d i t i o n , an i o n i c r e d u c i n g s p e c i e s i s formed w i t h a y i e l d G  = 2.0 i 0.2 .  T h i s s p e c i e s i s most l i k e l y a s o l v a t e d  e l e c t r o n a l t h o u g h because o f t h e l i m i t e d  amount o f d a t a a v a i l -  a b l e , a m o l e c u l a r a n i o n cannot be r u l e d o u t .  The b e s t  arguements i n f a v o u r o f t h e s o l v a t e d e l e c t r o n h y p o t h e s i s a r e : (a) t h e l a c k o f r e a c t i v i t y t h a t e l e c t r o n attachment  o f PC w i t h a l k a l i m e t a l s s u g g e s t i n g  t o PC i s n o t f a v o u r e d , and (b) t h e  l a r g e permanent d i p o l e moment o f PC would s u p p l y ample s o l v a t i o n energy t o a l l o w s t a b i l i z a t i o n o f the thermal e l e c t r o n s i f t h e y s u r v i v e d l o n g enough t o a l l o w d i p o l e r e l a x a t i o n .  The  measured y i e l d o f t h e r e d u c i n g s p e c i e s i s i n good agreement 14 w i t h t h a t found by Hayon  and w i t h t h a t e x p e c t e d on t h e b a s i s  o f t h e e m p i r i c a l r e l a t i o n s h i p between t h e y i e l d o f f r e e i o n s and t h e s t a t i c d i e l e c t r i c c o n s t a n t o f t h e l i q u i d i n Chapter I ) .  (see F i g u r e 5  -133-  PART I I I - GENERAL CONCLUSION AND SUGGESTIONS FOR FURTHER STUDY OF THE RADIATION CHEMISTRY OF PROPYLENE CARBONATE  The  p r e l i m i n a r y i n v e s t i g a t i o n s reported here f o r the  e f f e c t s o f r a d i a t i o n on t h e v e r y p o l a r p r o p y l e n e c a r b o n a t e s y s t e m have p r o v i d e d  some i n t e r e s t i n g r e s u l t s .  Trapped e l e c -  t r o n s were i d e n t i f i e d i n t h e l o w t e m p e r a t u r e g l a s s and i t i s very l i k e l y that the i o n i c reducing l i q u i d phase were a l s o s t a b i l i z e d  species  formed i n t h e  electrons.  From t h e p h y s i c a l p r o p e r t i e s shown by t h e t r a p p e d e l e c t r o n i t i s p o s s i b l e t o make a p r e d i c t i o n about t h e o p t i c a l a b s o r p t i o n maximum o f a s o l v a t e d s p e c i e s  i n t h e l i q u i d phase.  I n most systems where b o t h t r a p p e d and s o l v a t e d have been o b s e r v e d s p e c t r o s c o p i c a l l y , X  m  a  x  electrons  consistently  shows a b l u e s h i f t o f between 50 and 200 nm on g o i n g from t h e s o l v a t e d t o t h e t r a p p e d s p e c i e s a t 77 °K. of the assigned ^"max" ^ ®  n m  '  Thus on t h e b a s i s  a b s o r p t i o n band f o r t r a p p e d e l e c t r o n s i n PC, t  n  e  s  °l  v a t e <  ^ e l e c t r o n would be e x p e c t e d t o  absorb p r e f e r e n t i a l l y i n the v i s i b l e r e g i o n w i t h a X the r e g i o n o f 400 - 600 nm .  in max This p r e d i c t i o n i s contrary t o  t h a t e x p e c t e d from t h e proposed c o r r e l a t i o n between t h e i o d i d e i o n " c h a r g e - t r a n s f e r - t o - s o l v e n t " a b s o r p t i o n maximum and t h e \ 61 A max o f s o l v a t e d e l e c t r o n s p e c t r a . This c o r r e l a t i o n places  X  max  f o r s o l v a t e d e l e c t r o n s i n PC a t about 1200 nm,  a v a l u e d i f f i c u l t t o a c c e p t on t h e b a s i s o f t h e p o l a r i t y o f PC.  I f t h e s o l v a t e d e l e c t r o n a b s o r p t i o n does r e p r e s e n t  d i s t r i b u t i o n p r o f i l e o f the d i f f e r e n t t r a p depths, then  a  -134e l e c t r o n s i n PC s h o u l d be bound i n r e l a t i v e l y deep t r a p s  due  t o i t s l a r g e d i p o l e moment and thus s h o u l d a b s o r b somewhere i n t h e v i s i b l e r e g i o n and n o t i n the i n f r a r e d .  Hence an  experiment of p a r t i c u l a r importance to i d e n t i f y i n g  the  r e d u c i n g s p e c i e s i n PC i s an i n v e s t i g a t i o n o f i t s p u l s e r a d i o l y s i s t o d e t e r m i n e i f any t r a n s i e n t o p t i c a l a b s o r p t i o n w h i c h can be a t t r i b u t e d t o  e~.  I n l i g h t o f the above remarks, some t r i a l were p e r f o r m e d on t h e p u l s e r a d i o l y s i s apparatus a c o l l e a g u e , Dr. G.A.  Kenney-Wallace^ .  experiments designed  l i g h t from a h e l i u m - n e o n l a s e r t o m o n i t o r  a b s o r p t i o n a t 633  i n a sample p u l s e i r r a d i a t e d w i t h a 3 nsec p u l s e o f 0.5 e l e c t r o n s from a F e b e t r o n a c c e l e r a t o r .  A  MeV  d e t e c t e d a t 633 nm  for liquid The  PC  species  c o u l d c o n c e i v a b l y have been the s o l v a t e d e l e c t r o n ,  however, CO~  and HCO  r a d i c a l s a r e b o t h known t o a b s o r b i n t h i s  r e g i o n and t h e s e s p e c i e s c o u l d n o t be e x c l u d e d as the o f the t r a n s i e n t a b s o r p t i o n on the b a s i s o f t h e d a t a The  nm  significant,  and a c i d i n c r e a s e d the r a t e o f decay m a r k e d l y . observed  by  T h i s system used the  2  s h o r t - l i v e d a b s o r p t i o n was  occurs  source obtained.  a u t h o r hopes t o p u r s u e t h e s e l e a d s a t The Ohio S t a t e  U n i v e r s i t y where p u l s e r a d i o l y s i s equipment i s a v a i l a b l e t o d e t e r m i n e c o m p l e t e v i s i b l e and i n f r a r e d a b s o r p t i o n s p e c t r a . An i n t e r e s t i n g o p p o r t u n i t y a l s o e x i s t s w i t h carbonate  propylene  t o i n v e s t i g a t e t h e e f f e c t s o f changes i n d i e l e c t r i c  c o n s t a n t on the y i e l d  (and s p e c t r a ) o f s o l v a t e d e l e c t r o n s .  S i n c e PC shows s u c h a l a r g e change i n d i e l e c t r i c  constant  o v e r a c o m p a r a t i v e l y s m a l l t e m p e r a t u r e range (90 a t - 60  °C  -135t o 60 a t +30 ° C ) , t h i s e f f e c t may be o b s e r v a b l e i n v a r i a b l e temperature s t u d i e s .  Some e f f e c t s a r e c e r t a i n l y e v i d e n t i n o  t h e s t e a d y s t a t e r a d i o l y s i s where t r i a l e x p e r i m e n t s a t -40  C  showed t h a t t h e y i e l d s o f gaseous p r o d u c t s d e c r e a s e d subs t a n t i a l l y w i t h G(CH ) = 0.10 - 0.02, = 0.9 - 0.1 and G„ = 2.6 ± 0.3 as compared w i t h G(CH.) = 0.20 i 0.02, 4  co  G  c 0  *  2  = 1.2 t 0.1 and  GQ Q  = 3.3  2  1  0.3 a t 25 °C .  In addition,  t h e n i t r o g e n y i e l d f o r a sample c o n t a i n i n g 0.08 M n i t r o u s o x i d e d e c r e a s e d t o G ( N ) = 1.6 as compared w i t h G ( N ) = 2.0 2  a t 25 °C .  2  Some o f t h e s e changes may o f c o u r s e be due t o  v i s c o s i t y e f f e c t s since the v i s c o s i t y increases s u b s t a n t i a l l y on c o o l i n g .  However, one would have e x p e c t e d t h e d i e l e c t r i c  c o n s t a n t i n c r e a s e t o cause an i n c r e a s e i n G ( N ) and t h e o b s e r 2  ved d e c r e a s e must have r e s u l t e d from a c o m b i n a t i o n o f d i f f e r e n t temperature  effects.  F u r t h e r s t u d i e s o f t h e r a d i a t i o n c h e m i s t r y o f PC i n the s o l i d s t a t e are c l e a r l y warranted t o u n r a v e l the mystery o f t h e abnormal spontaneous  decay o f e ^  r  .  Optical kinetic  s t u d i e s o f t h e i r r a d i a t e d g l a s s y m a t e r i a l and c o r r e l a t i o n o f t h e s e d a t a w i t h t h e ESR measurements would be h e l p f u l ,  part-  i c u l a r l y i n c o n f i r m i n g t h e assignment o f t h e v i o l e t a b s o r p t i o n band t o e  .  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Kevan, Eds., I n t e r s c i e n c e , New Y o r k , N.Y., 1968.  48.  R. S. A l g e r , " E l e c t r o n P a r a m a g n e t i c Resonance - Techniques and A p p l i c a t i o n s " , I n t e r s c i e n c e , New Y o r k , N.Y., 1969.  -14049.  C. Chachaty and E. Hayon, N a t u r e , 200, 59, 1963.  50.  E. Boesman and D. Schoemaker, J . Chem. Phys., 37.' 671, 1962.  51.  F. S. D a i n t o n , J . P. Keene, T. J . Kemp, G. A. Salmon and J . T e p l y , P r o c . Chem. S o c , 265, 1964.  52.  (a) T. R. W a i t e , P h y s i c a l Review, 107, 4 6 3 , 1957.  t  (b)  T. R. W a i t e , J . Chem. Phys., 28, 103, 1958.  (c)  T. R. W a i t e , J . Chem. Phys., 32, 2 1 , 1960.  53.  P. W. A t k i n s and M. C. R. Symons, "The S t r u c t u r e o f I n o r g a n i c R a d i c a l s " , E l s e v i e r , Amsterdam, 1967.  54.  R. A. Nazhat, N. B. N a z h a t , P. N. Moorthy and J . J . W e i s s , J . Phys. Chem., 74, 1901, 1970.  55.  (a) G. E. Adams, J . W. Boag and B. D. M i c h a e l , P r o c . Chem. S o c , 4 1 1 , 1964. (b)  D. Behar, G. C z a p s k i and I . Duchovny, J . Phys. Chem., 74, 2206, 1970.  56.  B. G. E r s h o v , 0. F. Khodzhaev and A. K. P i k a e v , H i g h Energy C h e m i s t r y , 2^, 29, 1968. (A t r a n s l a t i o n o f K h i m i y a V y s o k i k h E n e r g i i , _2* 35, 1968.)  57.  G. E. Ewing, W. E. Thompson and G. C. P i m e n t e l , J . Chem. P h y s . , 32, 927, 1960.  58.  (a) J . A. B r i v a t i , N. Keen and M. C. R. Symons, J . Chem. Soc., 237, 1962. (b)  F. J . A d r i a n , E. L. Cochran and W. A. Bowers, J . Chem. Phys., 36., 1661, 1962.  59.  P. J . S u l l i v a n and W. S. K o s k i , J . Am. Chem. S o c , 85, 384, 1963.  60.  D. A. Head, PhD T h e s i s , 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 , 1969.  61.  M. J . Blandamer, R. C a t t e r a l l , L. S h i e l d s and M. C. R. Symons, J . Chem. S o c , 4357, 1964.  62.  G. A. Kenney, PhD T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, 1970.  63.  P. B. Ayscough, " E l e c t r o n S p i n Resonance Methuen and Co. L t d . , London, 1967.  i n Chemistry",  -141APPENDIX 1 FERROUS SULFATE DOSIMETRY A.  THEORY F r i c k e f e r r o u s s u l f a t e d o s i m e t r y was used t o d e t e r m i n e 60  the dose r a t e d e l i v e r e d by t h e  Co Gammacell.  dosimeter u t i l i z e s the o x i d a t i o n of ferrous  The F r i c k e  iron to ferric  i r o n i n a c i d i c , oxygenated aqueous s o l u t i o n t o measure t h e dose a b s o r b e d .  I n 0.8N a c i d s o l u t i o n c o n t a i n i n g  oxygen, t h e two r a d i o l y t i c a l l y  atmospheric  generated primary reducing  s p e c i e s , e~g and H atoms, a r e c o n v e r t e d t o o x i d i z i n g by r e a c t i o n s e~ aq H  (A-1) and + +  H+ aq °  species  (A-2).  H  +  (A-1) k =  H o O  2 x l 0  1  0  M~ s1  1  * *"  2  H  0  2  (  The H O 2 r a d i c a l s formed v i a r e a c t i o n  A _ 2  )  k  =  l  x  l  °  1  0  M'-'-s"  1  ( A - 2 ) and t h e p r i m a r y  OH r a d i c a l s and m o l e c u l a r h y d r o g e n p e r o x i d e t h e n o x i d i z e t h e ferrous  i r o n to f e r r i c v i a reactions X  H+ H  + 0 + H H 0  H  +  +  +  2  o 2  OH  + + FF ee  + 2 + 2  +2  + Fe  2 2 W  +2  o  _  „  Fe  accurately 15.5  .  + 3  + 3  +J 3  +  H 0 2  leads  2  0  (A-3) (A-4) (A-5)  t o the oxidation of  and each p r i m a r y OH r a d i c a l o x i d i z e s one F e  *y~rays t h e t o t a l y i e l d  Co  (A-4) and (A-5).  •»- H F, e0+ 3, ++ OH F+ eH  Thus each p r i m a r y r e d u c i n g s p e c i e s t h r e e Fe  (A-3),  using  o f Fe  ,-5  + Z  .  For  has been d e t e r m i n e d  c a l o r i m e t r y as t h e s t a n d a r d , and G(Fe  ) =  3  The f e r r o u s s u l f a t e d o s i m e t e r i s v e r y s e n s i t i v e t o traces of organic  impurities.  Oxidation  of the organic  material  -142-  by OH r a d i c a l s and subsequent r e a c t i o n o f t h e o r g a n i c  radical  w i t h oxygen v i a r e a c t i o n s (A-6) and (A-7) produces an o r g a n i c OH  +  RH  • R«  R*  +  0  * R0 -  peroxide.  2  +  H 0  (A-6)  2  (A-7)  2  The o r g a n i c p e r o x i d e t h e n r e a c t s w i t h t h e Fe  +Z  in  +3 .  an analagous way t o HO^ t o produce t h r e e Fe instead o f the n o r m a l one f o r each OH r a d i c a l . Thus i n t h e p r e s e n c e o f +3  o r g a n i c s u b s t a n c e s G(Fe  ) > 15.5 . To s u p p r e s s r e a c t i o n (A-6)  c h l o r i d e i o n i s n o r m a l l y added t o t h e d o s i m e t e r s o l u t i o n . OH r a d i c a l s r e a c t v e r y e f f i c i e n t l y w i t h c h l o r i d e i o n s v i a reaction OH  (A-8). +  Cl"  • OH"  +  C l - (A-8) k = 4 x l 0 +2  The r e s u l t i n g c h l o r i n e atom o x i d i z e s o n l y one Fe  9  M~ s~ 1  1  v i a reaction  (A-9) B.  Cl* + PROCEDURE  Fe  + 2  *• F e  + 3  +  Cl"  (A-9)  A s t o c k s o l u t i o n o f f e r r o u s s u l f a t e was made by d i s s o l v i n g 0.4 g o f a n a l y t i c a l grade f e r r o u s ammonium s u l f a t e , 0.065 g o f a n a l y t i c a l g r a d e sodium c h l o r i d e and 22.0 m l o f a n a l y t i c a l grade s u l f u r i c a c i d i n t r i p l y d i s t i l l e d water t o a t o t a l volume o f 1.00 l i t r e .  A l l a p p a r a t u s and c e l l s used  i n t h e d o s i m e t r y work were s c r u p u l o u s l y c l e a n e d u s i n g t h e permanganic a c i d - hydrogen p e r o x i d e - d i s t i l l e d w a t e r r o u t i n e . The f e r r o u s s u l f a t e s o l u t i o n was i r r a d i a t e d i n t h e sample c e l l s u s i n g t h e a p p r o p r i a t e volumes and p o s i t i o n s i n the Gammacell c a v i t y .  The i r r a d i a t i o n s were a u t o m a t i c a l l y  -143t i m e d w i t h t h e b u i l t - i n t i m e r on t h e Gammacell.  The times  ranged from 0.1 second t o 10 m i n u t e s w i t h t h e c o r r e s p o n d i n g doses o f about 1000 t o 50,000 r a d s . were a v o i d e d  Longer i r r a d i a t i o n times  because above 50,000 rads oxygen d e p l e t i o n i n  the s o l u t i o n causes G ( F e ) t o d e c r e a s e . + 3  A f t e r i r r a d i a t i o n , t h e f e r r i c i o n c o n c e n t r a t i o n was d e t e r m i n e d s p e c t r o p h o t o m e t r i c a l l y by measuring t h e absorbance a t 304 nm u s i n g e i t h e r 1 o r 5 cm c e l l s and a C a r y 14 s p e c t r o photometer.  The i r r a d i a t e d samples were measured w i t h an  unirradiated  " b l a n k " i n t h e r e f e r e n c e beam o f t h e s p e c t r o m e t e r .  The  a b s o r b e d dose was t h e n c a l c u l a t e d u s i n g t h e e q u a t i o n : Dose  =  0.965 x 1 0 x ( A ° t ) 9  €  304  P  1  3  3  G  <  Fe+3  r  a  d  s  >  304 where A  i s t h e n e t absorbance o f t h e i r r a d i a t e d sample  n e t  a t 304 nm,  €  i s t h e m o l a r a b s o r p t i v i t y o f Fe.  1 i s t h e o p t i c a l p a t h l e n g t h and ferrous sulfate solution  pis  the density of the  (1.024 ± 0.001 between 15 and 25 ° C ) .  G ( F e ) = 15.5 was used i n a l l c a l c u l a t i o n s .  €  + 3  t o be 2174 M^cm""! i n one s e r i e s o f e x p e r i m e n t s , other series  a t 304 nm,  ( r a d i o l y s i s o f l i q u i d PC)  ^-^04  w  a  s  w  a  s  taken  while i n the measured  experimentally. C.  RESULTS 1.  N i t r o g e n F i x a t i o n Experiments  The  dose r a t e f o r t h e s y r i n g e s i n s i d e t h e s t a i n l e s s  s t e e l high pressure  c e l l was d e t e r m i n e d u s i n g t h e above p r o -  c e d u r e w i t h 15 ml o f t h e f e r r o u s s u l f a t e s o l u t i o n i n t h e s y r i n g e .  -144On December 3, 1969 t h e dose r a t e was found t o be 2500 rads m i n " ,o 304 assuming € = 2174 and G(Fe ) = 15.5 . A__o. was d e t e r 304 netmined as a f u n c t i o n o f time by i r r a d i a t i n g samples f o r v a r i o u s 304 t i m e i n t e r v a l s and t h e s l o p e o f t h e p l o t o f  versus  t i m e was u s e d i n t h e dose r a t e c a l c u l a t i o n .  The i n t e r c e p t  o f t h i s l i n e was p o s i t i v e r a t h e r t h a n z e r o because t h e samples r e c e i v e d a dose e q u i v a l e n t lowering field. was  t o about 1/10 minute d u r i n g t h e  and r a i s i n g o f t h e Gammacell c a v i t y i n t o t h e r a d i a t i o n (The m i c r o - s w i t c h  which a c t i v a t e d t h e automatic  timer  n o t engaged u n t i l t h e Gammacell drawer was f u l l y lowered.)  T h i s s m a l l c o r r e c t i o n f a c t o r was t a k e n i n t o a c c o u n t i n subs e q u e n t dose c a l c u l a t i o n s . experimental checking  Since the dosimetry f o r t h i s  s e t u p was done a t ambient t e m p e r a t u r e and w i t h o u t  the value  more t h a n * 5%.  of ^ ^ 0 4 '  W  a  S  P °k kly r  a  n  o  t  accurate t o  T h i s u n c e r t a i n t y was however t o l e r a b l e s i n c e  p r e c i s e G v a l u e d e t e r m i n a t i o n s were n o t i n v o l v e d . 2. R a d i o l y s i s o f L i q u i d PC The  determination  o f t h e dose r a t e f o r t h i s  experimental  s e t u p was done more p r e c i s e l y t o m i n i m i z e t h e u n c e r t a i n t y . The  r a d i o l y s i s c e l l containing  17.9 m l o f t h e f e r r o u s s u l f a t e  s o l u t i o n was t h e r m o s t a t e d a t 25 * 0.1 °C d u r i n g t h e i r r a d i a t i o n s and  a b s o r b a n c e measurements f o r F e  temperature.  + 3  were a l s o made a t t h i s  The l a t t e r was r e q u i r e d s i n c e t h e v a l u e o f € 3 0 4  +3 for  Fe  has a l a r g e t e m p e r a t u r e c o e f f i c i e n t and u n c e r t a i n t y  i n the temperature can introduce dose c a l c u l a t i o n s .  s i g n i f i c a n t e r r o r i n t o the  I n a d d i t i o n the value o f € 3 0 4  w  a  s  exper-  i m e n t a l l y d e t e r m i n e d u s i n g t h e same s p e c t r o m e t e r and c e l l s . S o l u t i o n s o f known Fe  c o n c e n t r a t i o n were made from f r e s h  -145a n a l y t i c a l g r a d e ( > 9 9 % pure) f e r r i c ammonium s u l f a t e . data obtained of the l i n e  The  a r e p l o t t e d i n F i g u r e A l - 1 and from t h e s l o p e €  304  was d e t e r m i n e d t o be 2184 i 8 a t 25 °C .  T h i s i n i n good agreement w i t h t h e v a l u e o f 2194 c a l c u l a t e d from data g i v e n i n r e f e r e n c e The  dosimetry  3 f o r 25 °C.  r e s u l t s f o r i r r a d i a t i o n s o f t h e sample  c e l l are plotted i n Figure Al-2.  From t h e s l o p e o f t h e l i n e ,  t h e e x p e r i m e n t a l l y d e t e r m i n e d v a l u e o f ^^04 = 15.5,  a  n  d  t a  ^i g n  G(Fe )  t h e dose r a t e was c a l c u l a t e d t o be 4545 r a d s m i n "  1  f o r t h e f e r r o u s s u l f a t e s o l u t i o n on August 1, 1970. The i n t e r c e p t was found t o be e q u i v a l e n t t o 725 r a d s o r about 10 seconds i r r a d i a t i o n 3.  time.  Dose C o r r e c t i o n P r o c e d u r e s - Computer Program  C o r r e c t i o n s f o r " e l e c t r o n d e n s i t y " d i f f e r e n c e s between t h e f e r r o u s s u l f a t e s o l u t i o n and t h e e x p e r i m e n t a l  l i q u i d were  i n c o r p o r a t e d i n a computer program w h i c h a u t o m a t i c a l l y c o r r e c t e d f o r the n a t u r a l decay o f t h e source a c t i v i t y .  T h i s program  * was  d e v i s e d by a c o l l e a g u e and w i l l be p u b l i s h e d  elsewhere.  I t c o r r e c t e d f o r t h e e l e c t r o n d e n s i t y d i f f e r e n c e by t a k i n g t h e a v e r a g e Z/A v a l u e f o r t h e f e r r o u s s u l f a t e s o l u t i o n (0.5533), w a t e r (0.5551) and p r o p y l e n e c a r b o n a t e (0.5289) and m u l t i p l y i n g the dose c a l c u l a t e d f o r t h e f e r r o u s s u l f a t e s o l u t i o n by t h e r a t i o o f t h e Z/A v a l u e s o f t h e e x p e r i m e n t a l ferrous s u l f a t e s o l u t i o n . a c t i v e decay o f t h e ^ C o *footnote  3.  w  l i q u i d and t h e  Correction f o r the n a t u r a l r a d i o a  s  made from t h e known h a l f - l i f e  G„ J . F l y n n , t h i s l a b o r a t o r y , communicated.  -146-  -147-  100  Figure A l - 2 .  200 300 IRRADIATION  400 500 TIME (sec)  600  F e r r o u s s u l f a t e dosimetry r e s u l t s f o r the "bubbler" c e l l used i n the l i q u i d phase r a d i o l y s i s o f PC.  u s i n g t h e formula: Dose  corr  =  Dose  orig  •  e  - days x 0.693 1924.9  where "days" i s the e l a p s e d time i n days from the date o f the 60 o r i g i n a l d o s i m e t r y , 1924.9 i s the h a l f - l i f e o f and 0.693 i s a c o n s t a n t e q u a l t o l n 2 .  Co i n days  -149-  APPENDIX 2 INDOPHENOL BLUE AMMONIA ANALYSIS A.  THEORY The method used t o produce t h e i n d o p h e n o l b l u e  dye  i n v o l v e s r e a c t i o n o f ammonia w i t h sodium h y p o c h l o r i t e and p h e n o l i n a v e r y a l k a l i n e s o l u t i o n as d e s c r i b e d b y T e t l o w 37  and W i l s o n . The r e a c t i o n mechanism i s b e l i e v e d t o i n v o l v e t h e f o l l o w i n g s e r i e s o f r e a c t i o n s (A-10), ( A - l l ) and NH  +  3  NH C1 2  OCl" + ^3"0"  • NH C1 2  +  2  0 C 1  £ J - 0 ' + Cl-N=<^>0  +  (A-12).  OH" ( f a s t )  ~ " ~ * CI-N=<^)rO + 2 C l " (A-ll) + 2 OH" (slow)  -  "°- C^ 0 <  N=  =0  +  C  1  ~  i•n d*o p hve n o lT b l u e ' The  (A-10)  i n d o p h e n o l b l u e dye has a b r o a d asymmetric  (A-12) (fast)  optical  a b s o r p t i o n band w i t h a maximum a t 630 nm as i l l u s t r a t e d i n Figure B.  A2-1.  EXPERIMENTAL PROCEDURE 1.  Reagents  A s t o c k s o l u t i o n o f sodium h y p o c h l o r i t e w i t h a v a i l a b l e c h l o r i n e was  p r e p a r e d from F i s h e r  NaOCl s o l u t i o n and d o u b l y d i s t i l l e d w a t e r . c h l o r i n e i n the u n d i l u t e d reagent  reagent The  ( 4 - 6 %) was  1.00% grade  available determined  600 F i g u r e A2-1.  A b s o r p t i o n spectrum  650 W A V E L E N G T H (nm)  700  o f the indophenol b l u e dye i n a l k a l i n e aqueous  solution.  -151p r e c i s e l y by r e a c t i o n w i t h i o d i d e and t i t r a t i o n o f t h e f r e e i o d i n e w i t h s t a n d a r d i z e d sodium t h i o s u l f a t e i n a c i d  solution  36 using a starch indicator. The sodium t h i o s u l f a t e s o l u t i o n was s t a n d a r d i z e d u s i n g s o l i d p o t a s s i u m i o d a t e as t h e p r i m a r y 36 s t a n d a r d as d e s c r i b e d i n V o g e l .  The 1.00% (weight/volume)  a v a i l a b l e c h l o r i n e s t o c k s o l u t i o n was s t o r e d i n a darkened volumetric f l a s k i n a r e f r i g e r a t o r u n t i l immediately before use.  I t was s t a b l e under t h e s e c o n d i t i o n s f o r a t l e a s t 4  months. S t o c k s o l u t i o n s o f sodium phenate were made f r e s h b e f o r e each r u n by d i s s o l v i n g 62.5 i 0.1 g o f r e a g e n t g r a d e p h e n o l i n 135 m l o f 5N sodium h y d r o x i d e s o l u t i o n and t h e n d i l u t i n g t h i s w i t h d o u b l y d i s t i l l e d w a t e r t o a t o t a l volume o f 500 m l . T h i s s o l u t i o n was a l s o p r o t e c t e d from l i g h t and was s t a b l e o n l y f o r about 6 h o u r s . Acetone used as a " c a t a l y s t " i n t h e p r o c e d u r e was Fisher  spectrograde. Doubly d i s t i l l e d water was used t o make up a l l s o l u t i o n s .  The f i r s t d i s t i l l a t i o n was from t a p water and t h e second from a c i d i f i e d dichromate s o l u t i o n . S t a n d a r d ammonia s o l u t i o n s were p r e p a r e d from r e a g e n t grade ammonium s u l f a t e . 2.  A n a l y s i s Procedure  A l l g l a s s a p p a r a t u s used i n t h e p r o c e d u r e ( i . e .  flasks,  p i p e t t e s , b u r e t t e s e t c . ) were i n i t i a l l y c l e a n e d w i t h t h e  -152normal permanganic a c i d - hydrogen p e r o x i d e - d i s t i l l e d routine.  water  S u b s e q u e n t l y t h e a p p a r a t u s was washed w e l l w i t h  d o u b l y d i s t i l l e d water a f t e r each use and a l l o w e d t o a i r d r y . The v o l u m e t r i c f l a s k s were s t o r e d f i l l e d w i t h d o u b l y  distilled  water. The r e a g e n t s o l u t i o n s were d e l i v e r e d i n t o 50 ml volumetric flasks using fast flow burettes. standard  ( o r unknown sample) was  The ammonia  f i r s t added t o t h e f l a s k  and d i l u t e d a p p r o p r i a t e l y so t h a t t h e t o t a l sample volume was  25 m l .  I f t h e unknown s o l u t i o n was  b a s i c , i t was  f i r s t n e u t r a l i z e d u s i n g s t a n d a r d I^SO^  To t h e 25 ml o f sample 0.30  ± 0.05 ml o f a c e t o n e was  and t h e s o l u t i o n mixed w e l l . phenate of  strongly a c i d i c or  s o l u t i o n was  o r NaOH. added  Then 10.0 i 0.2 ml o f t h e  sodium  added, i m m e d i a t e l y f o l l o w e d by 5.0 ± 0 . 2  the standard h y p o c h l o r i t e s o l u t i o n .  The sample was  mixed and d i l u t e d " t o t h e mark" w i t h d o u b l y d i s t i l l e d The v o l u m e t r i c f l a s k was  t h e n s t o p p e r e d , shaken  quickly water.  vigorously  and p l a c e d i n a darkened c o n s t a n t t e m p e r a t u r e b a t h a t 25 * °C f o r 6 0 - 5 developed.  ml  0.5  m i n u t e s d u r i n g w h i c h t i m e t h e i n d o p h e n o l dye The absorbance was  t h e n measured ( w i t h i n - 5 minutes  o f 60 minutes developement time) i n a 5 cm c e l l v e r s u s d i s t i l l e d w a t e r a t 630 nm u s i n g a C a r y 14 r e c o r d i n g s p e c t r o m e t e r . The absorbance v a l u e s o b t a i n e d above were c o r r e c t e d f o r t h e absorbance t h e absorbance  o f t h e r e a g e n t s o l u t i o n s by d e t e r m i n i n g  o f a "reagent b l a n k " .  T e t l o w and W i l s o n found  t h a t i f t h e r e a g e n t s were mixed t o g e t h e r f i r s t and a l l o w e d t o s t a n d f o r s e v e r a l minutes b e f o r e a d d i n g an ammonia s o l u t i o n ,  -153-  t h e n no i n d o p h e n o l b l u e was d e v e l o p e d e x c e p t f o r t h a t p r o duced by any t r a c e s o f ammonia i n t h e r e a g e n t s .  This reagent  b l a n k procedure a l s o allowed f o r the d e t e r m i n a t i o n of the ammonia c o n c e n t r a t i o n i n t h e "pure" d o u b l y and t r i p l y water C.  distilled  samples.  RESULTS The c o r r e c t e d absorbance  a t 630 nm was found t o be  l i n e a r w i t h ammonia c o n c e n t r a t i o n up t o a t l e a s t 1 0 ~ M NH^ 4  as shown i n F i g u r e A2-2 where t h e r e s u l t s c a l i b r a t i o n run are plotted. are  of a t y p i c a l  The c o n c e n t r a t i o n s quoted h e r e  the o r i g i n a l undiluted concentration of  o f sample b e f o r e a d d i n g t h e r e a g e n t s . effective  c o n c e n t r a t i o n o f NH^  +  i n t h e 25 m l  (This i s t w i c e the  i n t h e f i n a l 50 m l o f s o l u t i o n . )  From t h e s l o p e o f t h e c a l i b r a t i o n l i n e t h e r e s p o n s e was c a l c u l a t e d  +  factor  t o be: —5  Response = 0.156 absorbance u n i t s / 10 f o r a 5 cm p a t h l e n g t h c e l l .  + M NH^  S i n c e t h e minimum p r a c t i c a l  a b s o r b a n c e w h i c h c o u l d be measured was 0.005 u n i t s , t h e _7 a b s o l u t e s e n s i t i v i t y o f t h e t e c h n i q u e was about 5 x 10 M The pure w a t e r samples always gave i d e n t i c a l absorbance readings t o those o f the reagent blank s o l u t i o n s -7 t h a t t h e w a t e r c o n t a i n e d l e s s t h a n 5 x 10  indicating +  M NH^ .  S i n c e t h e s e n s i t i v i t y o f t h e method depended on t h e age o f t h e phenate r e a g e n t and t h e p a r t i c u l a r b a t c h o f 37 a c e t o n e used uently.  , t h e c a l i b r a t i o n c u r v e s were r e c h e c k e d  freq-  Each t i m e an unknown sample was a n a l y s e d , an i n t e r n a l  Figure  A2-2.  T y p i c a l c a l i b r a t i o n graph f o r the indophenol b l u e ammonia a n a l y s i s  procedure.  -155s t a n d a r d as w e l l as a normal s t a n d a r d were r u n t o be s u r e t h a t t h e p r o c e d u r e and r e a g e n t s were a l r i g h t . I t was found on a n a l y s i s o f i r r a d i a t e d s o l u t i o n s w h i c h c o n t a i n e d oxygen d u r i n g t h e i r r a d i a t i o n , t h a t hydrogen p e r o x i d e formed d u r i n g t h e r a d i o l y s i s i n t e r f e r e d q u i t e m a r k e d l y w i t h the a n a l y s i s .  I n f a c t a n a l y s i s o f a sample c o n t a i n i n g o n l y  -4 6 x 10  M hydrogen p e r o x i d e gave an orange c o l o u r e d  w h i c h had an absorbance o f 0.8 a t 630 nm i n a 5 cm  solution  cell.  T h i s absorbance was due t o t h e t a i l o f an i n t e n s e UV  band.  O x i d a t i o n o f t h e phenate r e a g e n t t o g i v e a q u i n o n e was t h o u g h t t o be r e s p o n s i b l e f o r t h i s UV a b s o r p t i o n .  Because o f t h i s  i n t e r f e r e n c e , the working s e n s i t i v i t y of the a n a l y s i s p r o c e d u r e was about 5 x 10"^ M NH^  +  when a d e f i n i t e peak c o u l d  be o b s e r v e d a t 630 nm i n d i c a t i n g t h e absorbance was due t o i n d o p h e n o l b l u e and n o t caused by hydrogen p e r o x i d e i n t e r ference.  r  -156APPENDIX 3 ELECTRON SPIN RESONANCE* A.  BASIC THEORY By v i r t u e o f i t s i n t r i n s i c a n g u l a r momentum and i t s  c h a r g e , an e l e c t r o n has a m a g n e t i c moment a s s o c i a t e d w i t h i t . I n t h e p r e s e n c e o f an e x t e r n a l l y a p p l i e d m a g n e t i c f i e l d , H, t h e a l i g n m e n t o f t h e e l e c t r o n ' s m a g n e t i c moment has a p r e f e r r e d d i r e c t i o n , i . e . p a r a l l e l t o the external f i e l d .  From quantum  mechanics i t i s known t h a t t h e e l e c t r o n has a s p i n quantum number o f % w h i c h means t h a t i t s s p i n a n g u l a r momentum c a n have o n l y two o r i e n t a t i o n s w i t h r e s p e c t  t o a given axis.  t h e m a g n e t i c moment a s s o c i a t e d w i t h t h e e l e c t r o n ' s  spin  a n g u l a r momentum may e i t h e r be a l i g n e d w i t h t h e e x t e r n a l or against  it.  Thus  field  Since the p a r a l l e l configuration i s preferred,  an e n e r g y d i f f e r e n c e e x i s t s between t h e two s p i n o r i e n t a t i o n s . T r a n s i t i o n s i n w h i c h t h e e l e c t r o n changes i t s s p i n o r i e n t a t i o n may be i n d u c e d by s u p p l y i n g magnetic energy. energy r e q u i r e d  the appropriate  amount o f e l e c t r o -  T h i s i s b a s i c a l l y what ESR measures; t h e t o reverse  t h e s p i n o f an u n p a i r e d e l e c t r o n .  N o r m a l l y i n ESR a c o n s t a n t e n e r g y s o u r c e i n t h e form o f microwave r a d i a t i o n i s used and t h e e x t e r n a l m a g n e t i c f i e l d i s v a r i e d u n t i l the unpaired e l e c t r o n "resonates".  When t h e  d i f f e r e n c e i n energy between t h e two s p i n s t a t e s e q u a l s t h e e n e r g y o f t h e microwave r a d i a t i o n , t h e r e i s an exchange o f *footnote  4.  P r e p a r e d from r e f e r e n c e s  4 8 , 53 and 63.  -157-  e n e r g y between t h e two energy systems w h i c h i s e f f e c t i v e l y a "resonance" process.  T h i s resonance c o n d i t i o n i s n o r m a l l y  written as: h V = g/?H where h V  (A3.1)  i s t h e microwave  energy, H i s t h e e x t e r n a l  and /3is t h e Bohr magneton, splitting  field  g i s called the spectroscopic  f a c t o r and i t i s t h e parameter w h i c h d e s c r i b e s t h e  p o s i t i o n o f t h e resonance a b s o r p t i o n .  The v a l u e o f g f o r  an e l e c t r o n w i t h o n l y s p i n a n g u l a r momentum, i . e . t h e " f r e e - s p i n " g - f a c t o r , i s 2.0023 .  (The d e v i a t i o n from t h e  i n t e g r a l number i s due t o r e l a t i v i s t i c For  velocity  corrections.)  t h e X-band s p e c t r o m e t e r used i n t h i s r e s e a r c h , t h e m i c r o -  wave f r e q u e n c y was about 9.3 GHz f o r w h i c h t h e f i e l d  corres-  p o n d i n g t o t h e resonance o f a f r e e e l e c t r o n i s about 3300 G . I n most r a d i c a l s u n p a i r e d e l e c t r o n s have o r b i t a l a n g u l a r momentum i n a d d i t i o n t o s p i n a n g u l a r momentum.  The  e f f e c t o f t h e o r b i t a l a n g u l a r momentum i s t o s h i f t t h e g - v a l u e of  t h e r e s o n a n c e from t h e f r e e - s p i n v a l u e .  The degree o f  s p i n - o r b i t c o u p l i n g d e t e r m i n e s t h e magnitude o f t h e s h i f t . For  most o r g a n i c r a d i c a l s t h e d e v i a t i o n s a r e s m a l l and may be  t h o u g h t t o a r i s e t h r o u g h an a d d i t i o n a l s m a l l p e r t u r b i n g m a g n e t i c f i e l d caused by a v e r y s l i g h t o r b i t a l m o t i o n . modifies the effective f i e l d  This  that the unpaired e l e c t r o n  e x p e r i e n c e s by v e c t o r i a l l y a d d i n g t o t h e e x t e r n a l l y a p p l i e d f i e l d and t h u s causes p o s i t i v e o r n e g a t i v e g - f a c t o r s h i f t s . T h e r e f o r e e q u a t i o n (A3.1) may be r e w r i t t e n a s : h^= where H  g j2 ( H  e  + H.)  (A3.2)  and H- a r e t h e e x t e r n a l and i n t e r n a l f i e l d s  respectively.  -158-  From e q u a t i o n  (A3.2) i t i s e v i d e n t t h a t t h e g - f a c t o r depends  b o t h on t h e magnitude o f t h e e x t e r n a l f i e l d and i t s o r i e n t a t i o n w i t h r e s p e c t t o the l o c a l i n t e r n a l f i e l d s .  This anisotropy  of the g - f a c t o r i s the reason t h a t i t i s c u s t o m a r i l y  expressed  as a t e n s o r w i t h p r i n c i p a l v a l u e s : g„ . g„ c c xx yy  ; where  3  t h e axes a r e g e n e r a l l y chosen t o c o r r e s p o n d  and g zz  t o the symetry  axes o f t h e r a d i c a l . H y p e r f i n e s p l i t t i n g o f t h e e l e c t r o n ' s resonance  line  i n t o m u l t i p l e t s i s the r e s u l t of i n t e r a c t i o n s of the e l e c t r o n w i t h t h e m a g n e t i c moments a s s o c i a t e d w i t h t h o s e n u c l e i nuclear spin.  having  Since the o r i e n t a t i o n of nuclear s p i n i s  q u a n t i z e d , t h e n u c l e a r f i e l d s do n o t cause a d i s p l a c e m e n t  of  t h e r e s o n a n c e b u t r a t h e r s p l i t i t i n t o a number o f components corresponding  t o the d i f f e r e n t o r i e n t a t i o n s of the nuclear  moment w i t h r e s p e c t t o t h e e x t e r n a l f i e l d .  In the simplest  c a s e o f t h e i n t e r a c t i o n o f an u n p a i r e d e l e c t r o n w i t h a n u c l e u s w i t h s p i n % (e.g. a proton)  t h e r e a r e two o r i e n t a t i o n s o f  t h e n u c l e a r m a g n e t i c moment, one opposing to  the e x t e r n a l f i e l d .  a f i e l d of H - § H  The u n p a i r e d e l e c t r o n t h e n  adding  experiences  where § H i s t h e f i e l d due t o t h e n u c l e u s .  Thus two l i n e s are o b s e r v e d  e q u a l l y spaced about t h e p o s i t i o n  where t h e resonance would have o c c u r e d fine interaction.  and t h e o t h e r  i f t h e r e were no h y p e r -  I n general f o r a nucleus o f s p i n I , the  s p e c t r u m w i l l c o n s i s t o f 21+1 l i n e s o f e q u a l i n t e n s i t y .  A much  more complex s i t u a t i o n e x i s t s when t h e u n p a i r e d e l e c t r o n i n t e r a c t s w i t h more t h a n one m a g n e t i c n u c l e u s , when t h e y a r e n o t e q u i v a l e n t .  particularly  -159S i n c e h y p e r f i n e s p l i t t i n g r e s u l t s from t h e i n t e r a c t i o n o f two d i p o l e s , ation.  t h i s e f f e c t depends on t h e i r m u t u a l o r i e n t -  Thus f o r e l e c t r o n s  i n o r b i t a l s which are not s p h e r i c a l l y  s y m m e t r i c , e.g. p - o r b i t a l s , t h e h y p e r f i n e i n t e r a c t i o n i s anisotropic  and t h i s g i v e s r i s e t o a h y p e r f i n e t e n s o r , A,  where t h e p r i n c i p a l v a l u e s a r e u s u a l l y c a l c u l a t e d same a x i s s y s t e m used f o r t h e g - t e n s o r , i . e . A  f o r the  , A  Because o f t h e s p h e r i c a l symmetry o f e l e c t r o n s  and A jf jf  XX  . zz  i n s-orbitals,  a l l t h e d i p o l a r i n t e r a c t i o n w i t h t h e n u c l e u s average t o z e r o . However, s i n c e  s - o r b i t a l s have a non-zero w a v e f u n c t i o n a t t h e  n u c l e u s , t h i s p e r m i t s a h y p e r f i n e i n t e r a c t i o n w h i c h i s known as t h e F e r m i c o n t a c t i n t e r a c t i o n and i t i s i s o t r o p i c . C o n s e q u e n t l y i f an e l e c t r o n  i s i n a s p - h y b r i d o r b i t a l on an  a t o m i c n u c l e u s t h e r e w i l l be b o t h an i s o t r o p i c term w i t h an anisotropic B.  component superimposed on i t .  APPLICATION OF ESR TO AMORPHOUS SYSTEMS F o r r a d i c a l s formed i n amorphous o r p o l y c r y s t a l l i n e  m a t r i c e s t h e r e i s a complete randomization of the r a d i c a l orientations  w i t h respect t o the e x t e r n a l magnetic  a l t h o u g h i n t h e p o l y c r y s t a l l i n e system e n v i r o n m e n t on t h e m i c r o s c o p i c s c a l e .  t h e r e i s an o r d e r e d I n these systems, the  ESR s p e c t r u m o b t a i n e d i s an e n v e l o p e c o n t a i n i n g for a l l possible  orientations  field;  of the r a d i c a l .  a l l the features The t y p e o f  l i n e shape t h a t one o b s e r v e s w i l l depend on t h e magnitudes o f the  anisotropics  o f t h e g - f a c t o r and h y p e r f i n e  I t w i l l a l s o depend on c o n t r i b u t i o n s interactions.  interactions.  t o l i n e w i d t h from  F i g u r e A3-1 shows some o f t h e t h e o r e t i c a l  dipolar  -160-  (a)  (b)  jj yspectrum in the absence of  yA  r  A  • •V '/ T  911  9l  f  splitting  1r  A||  (C)  Figure  A3-1.  T h e o r e t i c a l ESR d e r i v a t i v e l i n e s h a p e s f o r amorphous s a m p l e s when t h e r a d i c a l i s c h a r a c t e r i z e d b y : (a) a n a x i a l l y s y m m e t r i c g - t e n s o r a n d n o h y p e r f i n e s t r u c t u r e , (b) a n a s y m m e t r i c g-tensor and no h y p e r f i n e s t r u c t u r e , a n d (c) a x i a l l y s y m m e t r i c g - a n d A - t e n s o r s w i t h t h e same s y m m e t r y axes and a l a r g e h y p e r f i n e s p l i t t i n g o f a s p i n % nucleus. ( a f t e r F i g u r e s 9.3, 9.4, 9.7 i n A y s c o u g h , reference 63, p a g e s 324, 325, a n d 327)  -161l i n e shapes f o r t h e t h e more s i m p l e c a s e s : (a) an a x i a l l y symmetric g - t e n s o r ( i . e . g = g = g | | and g = g j L w i t h g^ / xx  and no h y p e r f i n e s t r u c t u r e ,  yy  z2  g) ±  (b) an asymmetric g - t e n s o r and no  h y p e r f i n e s t r u c t u r e , a n d (c) a x i a l l y symmetric g - and A - t e n s o r s w i t h t h e same symmetry axes and w i t h t h e h y p e r f i n e s p l i t t i n g o f a s p i n % n u c l e u s b e i n g much l a r g e r t h a n t h e q u a n t i t y y$H(gj|-g^ ) .  A n a l y s i s o f t h e l i n e shapes f o r t o t a l l y  asymmetric  g- and A - t e n s o r s w i t h more t h a n one i n t e r a c t i n g n u c l e u s i s not e a s i l y accomplished. When t h e magnitude o f t h e d i p o l a r b r o a d e n i n g o f t h e ' l i n e s i s g r e a t e r t h a n t h e a n i s o t r o p i c s o f t h e g - and A - t e n s o r s then the l i n e broadening r e s u l t s i n l o s s of the i n d i v i d u a l f e a t u r e s c o r r e s p o n d i n g t o g^ , g^  e t c . and t h e f o r m a t i o n o f 63  a l i n e o f a p p r o x i m a t e l y a G a u s s i a n shape. t h e peak-to-peak  In this  case,  s e p a r a t i o n corresponds f a i r l y c l o s e l y t o the  i s o t r o p i c component o f t h e h y p e r f i n e s p l i t t i n g .  This i s the  s i t u a t i o n most o f t e n e n c o u n t e r e d f o r o r g a n i c r a d i c a l s t r a p p e d i n low temperature m a t r i c e s . o g e n e r a l l y 10 -15 G a t 77  The o b s e r v e d l i n e w i d t h s a r e  K, a l t h o u g h t u m b l i n g o r p a r t i a l  r o t a t i o n o f t h e r a d i c a l s c a n reduce t h e l i n e w i d t h s t o some e x t e n t by t i m e a v e r a g i n g t h e d i p o l a r  interactions.  -162APPENDIX 4 PURIFICATION AND Propylene  ANALYSIS OF PROPYLENE CARBONATE  c a r b o n a t e was  p u r i f i e d using the f o l l o w i n g  procedure: 7 l i t r e s o f Eastman Kodak p r a c t i c a l grade c a r b o n a t e was sieves.  propylene  d r i e d f o r s e v e r a l weeks o v e r L i n d e 4A  (The m o l e c u l a r  molecular  s i e v e s were p r e v i o u s l y d r i e d by  h e a t i n g t o 300 °C under a dynamic vacuum o v e r n i g h t . ) d r i e d s o l v e n t was  vacuum f r a c t i o n a t e d i n two  3.5  The  litre  portions  u s i n g a c l e a n , d r y , s t i l l w i t h a 5 l i t r e s t i l l - p o t and 4 f o o t by 1 i n c h column packed w i t h 3/16 The d i s t i l l a t i o n s  r a t e o f about 0.4 3.5  l i t r e s per hour.  l i t r e batches,  about 1.8  inch glass helices.  were c a r r i e d out a t l e s s t h a n 1 mm • o  w i t h a column head t e m p e r a t u r e o f 86  about 0.7  1  1  C and a  l i t r e s o f t h e m i d d l e f r a c t i o n was The  two  l i t r e f i r s t d i s t i l l a t i o n f r a c t i o n was  r e j e c t i n g 0.8  two  r e j e c t e d and  collected, leaving  1.8  l i t r e middle cuts  were combined and d r i e d o v e r n i g h t w i t h m o l e c u l a r 3.6  pressure  distillation  From each o f t h e  l i t r e f o r e - r u n was  a b o u t 1 l i t r e i n the s t i l l - p o t .  a  then  sieves.  The  redistilled,  l i t r e s o f t h e f o r e - r u n and c o l l e c t i n g about  l i t r e s of the middle f r a c t i o n i n a thoroughly  cleaned 2  1.9  litre  round bottom f l a s k . T h i s d o u b l y d i s t i l l e d PC was  immediately  and f l u s h e d f o r s e v e r a l h o u r s w i t h d r y h e l i u m  deoxygenated (dried v i a a  l i q u i d n i t r o g e n t r a p ) and t h e n s e a l e d i n the 2 l i t r e  storage  -163flask.  A s i n t e r e d g l a s s b u b b l e r - d i s p e n s e r u n i t as shown i n  F i g u r e A4-1 was used i n t h e 2 l i t r e f l a s k t o f l u s h and d i s p e n s e t h e PC.  T h i s s i n g l e sample o f p u r i f i e d PC was t h e n used f o r  a l l experiments  reported i n t h i s thesis.  The r e q u i r e d q u a n t i t y  was d i s p e n s e d by a p p l y i n g h e l i u m p r e s s u r e above t h e l i q u i d . The f l a s k was t h e n w e l l f l u s h e d w i t h d r y h e l i u m v i a t h e s i n t e r e d g l a s s b u b b l e r and s e a l e d under t h e h e l i u m atmosphere w i t h the t e f l o n stopcocks. The d i s t i l l a t i o n and d r y i n g p r o c e d u r e most p r o b a b l y r e d u c e d t h e w a t e r c o n t e n t t o l e s s t h a n 1 ppm  (6 x 10  M)  s i n c e i t was more e l a b o r a t e t h a n t h a t used by J a s i n s k i and 42a Kirkland  who found t h a t d o u b l e vacuum f r a c t i o n a t i o n  t h e w a t e r c o n t e n t t o l e s s t h a n 2 ppm.  lowered  In a d d i t i o n , the  c o n t i n u e d f l u s h i n g p r o c e d u r e w i t h d r y h e l i u m h e l p e d t o remove 42a t r a c e s o f l o w b o i l i n g o r g a n i c i m p u r i t i e s as w e l l as w a t e r . The p h y s i c a l a n a l y s e s made on t h e p u r i f i e d PC i n c l u d e d a mass s p e c t r u m , u l t r a v i o l e t spectrum, n u c l e a r m a g n e t i c resonance A4-2, of  s p e c t r u m and i n f r a r e d spectrum as shown i n F i g u r e s  A4-3, A4-4 and A4-5 r e s p e c t i v e l y .  t h e PC was found t o be n  2 0  l i t e r a t u r e values of 1.4214  4 0 b  The r e f r a c t i v e i n d e x  = 1.4213 as compared w i t h t h e and 1 . 4 2 1 2  4 0 d  .  -164-  F i g u r e A4-1.  S t o r a g e - d i s p e n s i n g f l a s k used t o keep t h e p u r i f i e d PC under a h e l i u m atmosphere.  { P C - C O 3 - C H 3 ) * : (CH =CH)*  90  2  80 UJ U  z  <  a  70  z z>  60  <  50  DO  UJ > .— 40  cn l  H20*  UJ 30| CO*  °  O , (CH3-C^)  (PC-C0 H)* 2  4  201  10 (PC-CH3)*  CO,  u 10  20  30  40  PC* 1.  50  60  70  80  90  100  m/e F i g u r e A4-2.  Mass spectrum o f d o u b l y d i s t i l l e d p r o p y l e n e c a r b o n a t e (PC)  220  240  260  280  WAVELENGTH  F i g u r e A4-3.  300  320  340  (nm)  U l t r a v i o l e t a b s o r p t i o n s p e c t r a o f Eastman Kodak p r a c t i c a l g r a d e PC and i t s s i n g l y and d o u b l y d i s t i l l e d f r a c t i o n s .  y  CH*  x.3  O  4.0  c  II C  /  C^  b  30  PPM(S) F i g u r e A4-4.  60 MHz  nuclear  2.0  1.0  magnetic resonance spectrum o f d o u b l y d i s t i l l e d  PC.  WAVENUMBER (cm ) -1  3000 I I  11  I I I  I  I  2000 I  I  I  I  I  I I l  1500 I l  I I  I  l  I  I  |  I  I  I  |  L _ _ J  J  1  1—  1  1  L_  4  5  6  7  8  9  |  1000  I.... 1  900 . . I .  I  800 . .  I . I . . . .  700  1  . . . . t.  I  J  I  •  i  10  11  12  13  14  WAVELENGTH ( nmx10" = microns) 3  F i g u r e A4-5.  I....  I n f r a r e d a b s o r p t i o n spectrum o f doubly d i s t i l l e d PC.  -169APPENDIX 5 GAS CHROMATOGRAPHIC ANALYSIS SYSTEM A V a r i a n A e r o g r a p h A-90-P2 gas chromatograph was s p e c i a l l y m o d i f i e d t o measure t h e gaseous p r o d u c t  yields  from t h e r a d i o l y s i s o f l i q u i d PC.  designed  to separate  The system was  and measure q u a n t i t a t i v e l y n i t r o g e n , methane,  c a r b o n monoxide and c a r b o n d i o x i d e . d e t e c t e d by t h i s t e c h n i q u e  Hydrogen c o u l d a l s o be  b u t w i t h v e r y poor s e n s i t i v i t y .  F i g u r e A5-1 i s a s c h e m a t i c drawing o f t h e a n a l y s i s system.  An 8 f o o t by 1/8 i n c h Porapak Q column m a i n t a i n e d a t  0 °C o u t s i d e t h e chromatograph was c o n n e c t e d between t h e i n p u t o f t h e sample s i d e o f t h e d e t e c t o r and t h e i n j e c t i o n system v i a 1/8 i n c h copper t u b i n g .  The e x i t o f t h e sample s i d e o f  the d e t e c t o r was c o n n e c t e d , t h r o u g h a f l o w r e v e r s i n g v a l v e , t o a 20 f o o t by % i n c h 13X m o l e c u l a r o maintained  a t 100  s i e v e column t h a t was  C i n t h e chromatograph oven.  E f f l u e n t from  t h i s column t h e n passed t h r o u g h t h e r e f e r e n c e s i d e o f t h e d e t e c t o r b l o c k and was v e n t e d i n t o t h e atmosphere.  The t h e r m a l  c o n d u c t i v i t y d e t e c t o r s used WX f i l a m e n t s o p e r a t i n g a t 180 ma and  140 - 150 °C .  The o u t p u t o f t h e d e t e c t o r b r i d g e was  c o n n e c t e d v i a a p o l a r i t y r e v e r s i n g s w i t c h t o a Leeds and N o r t h r u p - Speedomax W  1 mV f a s t reponse c h a r t r e c o r d e r .  (The p o l a r i t y r e v e r s i n g s w i t c h a l l o w e d s i g n a l s from t h e r e f e r e n c e d e t e c t o r t o be d i s p l a y e d i n t h e normal " p o s i t i v e " manner.)  8' Porapak Q column at 0 t  EXTERNAL SAMPLE LOOP gas standards  to  recorder polarity reversing switch  Porapak Q 'pre-column _ ^ connectors for sample cell  standards loop  y sample loop valve flow reversing valve flow  •Q-  u  liquid regulator fl n i t rogen rl flow ° meter vapour septum I I me outlet for trap vdeoxygenat ing i samples x  I  F i g u r e A5-1.  20' 13X molecular sieve column at 100%  Schematic diagram o f the m o d i f i e d V a r i a n Aerograph gas chromatography  system.  -171-  P r o i r t o e n t e r i n g the 8 f o o t Porapak Q column, the c a r r i e r gas  p a s s e d t h r o u g h a 1 f o o t s e c t i o n o f % i n c h copper  t u b i n g , mounted e x t e r n a l l y , w h i c h c o u l d be c o o l e d n i t r o g e n t e m p e r a t u r e t o t r a p out C 0 had  a h e a t e r s e c t i o n on the 1/8  2  and N 0. 2  to  The  trap also  i n c h t u b i n g i n p u t and  c o n n e c t i o n s t o p r e v e n t b l o c k a g e o f t h i s narrow bore caused by c o n d u c t i o n c o o l i n g and CO  2  and  liquid  output tubing  subsequent c o n d e n s a t i o n o f  N 0. 2  The  e x t e r n a l sample l o o p system was  connected i n t o  i n j e c t o r p o r t i o n of the chromatograph v i a a s t a i n l e s s bypass v a l v e and  1/8  i n c h copper t u b i n g .  steel  I t consisted of  s o c k e t c o n n e c t i o n s f o r the sample c e l l , a 2 f o o t by 1/8 Porapak Q "pre-column" v a p o u r t r a p and a g l a s s s t a n d a r d s gas  the  S13  inch  "in-line"  sample l o o p of c a l i b r a t e d volume.  H e l i u m , u s e d as t h e c a r r i e r gas,was f e d a t 65 p s i g  into  the chromatograph v i a a l i q u i d n i t r o g e n t r a p w h i c h removed w a t e r v a p o u r and r a t e was  t r a c e s of o r g a n i c c o n t a m i n a n t s .  60 ml/min.  W i t h the columns a t 0 and  Normal f l o w  100  °C,  nitrogen  e l u t e d i n about 10 m i n u t e s , methane i n about 15 m i n u t e s c a r b o n monoxide i n about 20 m i n u t e s . sequently  Carbon d i o x i d e was  and sub-  measured by warming the e x t e r n a l t r a p q u i c k l y t o  room t e m p e r a t u r e .  I t e l u t e d from the Porapak Q column about  4 m i n u t e s l a t e r t o be d e t e c t e d d e t e c t o r as a s h a r p peak.  by the sample s i d e o f  I t was  then "trapped"  the  i n the m o l e c -  u l a r s i e v e column.  N i t r o u s o x i d e had v i r t u a l l y t h e same  r e t e n t i o n t i m e as C 0  2  i n i t s presence.  The  s i e v e column a l l o w e d  and  thus p r e v e n t e d measurement o f  C0  2  f l o w r e v e r s i n g v a l v e on the m o l e c u l a r the C 0  n  and N 0 o  t o be  "back-flushed"  from i t .  -172A t y p i c a l chromatogram i s shown i n F i g u r e A5-2.  A  n i t r o g e n s t a n d a r d was r o u t i n e l y i n j e c t e d from t h e " i n - l i n e " sample l o o p b e f o r e each sample t o m o n i t o r any changes i n detector s e n s i t i v i t y .  Peak a r e a s were measured by manual  triangulation. The l i n e a r i t y o f t h e d e t e c t o r r e s p o n s e and a b s o l u t e s e n s i t i v i t y was d e t e r m i n e d by i n j e c t i n g known q u a n t i t i e s o f the  sample g a s e s u s i n g a second sample l o o p o f c a l i b r a t e d  volume w h i c h was I t was  f i l l e d on a vacuum l i n e t o known p r e s s u r e .  c o n n e c t e d t o the e x t e r n a l sample l o o p system v i a t h e  S13 s o c k e t s used f o r t h e r a d i o l y s i s c e l l .  The graphs o f  d e t e c t o r r e s p o n s e (peak area) v e r s u s sample s i z e ( m o l e c u l e s ) were a l l l i n e a r o v e r a range o f a t l e a s t 100 from t h e l i m i t o f d e t e c t i o n as shown i n F i g u r e A5-3.  The r e s p o n s e f a c t o r s as  d e t e r m i n e d from the s l o p e s o f t h e s e p l o t s were c a l c u l a t e d t o be: =  3.2 ± 0.1  X  io  CH =  3.6 + 0.1  X  10  CO =  3.1 + 0.1  X  io  co =  2.7 + 0.1  X  10  X  io  N  2  4  2  (H,  ~ 220  molecules  1 4  1 4  1 4  1 4  mm  •i  M  II  •I  n  II  II  1 4  S i n c e t h e minimum a r e a w h i c h c o u l d be measured r e a s o n a b l y 2 2 a c c u r a t e l y was about 100 mm f o r C0 and about 500 mm for 2  the  o t h e r g a s e s , t h e d e t e c t i o n l i m i t s were t h u s a p p r o x i m a t e l y : 19 (H^ N  2  ~  x  10  /~ 1.6 x  10  1 7  "  (0.3  "  "  )  10  1 7  "  (0.3  "  "  )  CH. ^  1  1.8 x  molecules  (20 m i c r o - m o l e s ) )  DETECTOR RESPONSE  -ZL1-  F i g u r e A5-3.  D e t e c t o r response t o N , CH , 4  CO and CO  f o r the GC system shown i n F i g u r e  A5-1.  -17 5CO ~ 1.6 x  10  17  C0 ~0.28 x 1 0  1 7  2  molecules "  (0.3 micro-moles) (0.04  "  "  )  The v a r i a t i o n o f d e t e c t o r s e n s i t i v i t y from day t o day as monitored by the n i t r o g e n standards was found t o be l e s s than - 5% from the mean.  S i n c e the m a j o r i t y o f t h i s  c o u l d be accounted f o r on the b a s i s o f u n c e r t a i n t i e s  deviation introduced  by the manual i n t e g r a t i o n technique and by atmospheric p r e s s u r e and temperature changes, no c o r r e c t i o n s were a p p l i e d t o the e x p e r i m e n t a l d a t a f o r t h i s apparent s e n s i t i v i t y  variation.  

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