Polymers for High Technology - American Chemical Society

Chapter 2 Primary Action of Ionizing Radiation on Condensed Systems 2

J. K.Thomas1and G. Beck

Downloaded by UNIV OF LEEDS on June 5, 2016 | http://pubs.acs.org Publication Date: August 26, 1987 | doi: 10.1021/bk-1987-0346.ch002

1Chemistry Department, University of Notre Dame, Notre Dame, IN 46556 2Hahn-Meitner Institut, Glienicker 100,1-Berlin-39,Federal Republic of Germany The initial effects of high energy radiation on condensed systems are discussed. Evidence of short lived intermediates, i.e. radical ions and excited states is illustrated by fast pico-second and nanosecond pulse radiolysis. A discusion of the nature of early events leading to excited states is discussed at length, and in particular comparisons are made to corresponding experiments at low photon energies, i.e. via laser flash photolysis. Excitation of molecules by radiation enters different regimes which depend on the energy of the quanta used. Excitation with low energy quanta, as in photochemistry, leads to discrete excited states as the quantum of energy is totally absorbed by the system; wavelengths down to ~ 2000 Â, i.e. energies of ~ 6.0 eV are typical in this work. High energy irradiation, or Radiation Chemistry utilises x- or γ-rays and electrons of high energy, typically 200 keV to 20 meV. Energy loss is primarily via ompton scatter to the electrons of the system, although the photoelectron effect becomes increasingly important at lower energies. In photochemistry low energy resonance processes excite the system or a part of the system; while in radiation chemistry a statistical loss of energy to the electrons of the system occurs, and the energy deposited in a section of the system depends on the electron fraction of that section (2_). It is usual in photochemistry to excite a solute directly, while in radiation chemistry the solvent is excited and energy or free radical chemistry is then transferred to the solute. In radiation chemistry, unlike photochemistry, the i n i t i a l high energy quantum is not completely lost on its first excitation, but, a fraction of the energy is lost to ionise an electron (secondary e") of the system. This process repeats as the electrons, both primary and secondary, continue to excite the medium causing ionization, until the last of secondary e~" fail to produce excitation. Thermalisation of the e" occurs to produce a trapped electron of the medium, this may be a solvated electron.

0097-6156/87/0346-0016$06.00/0 © 1987 American Chemical Society

Bowden and Turner; Polymers for High Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


2.

THOMAS A N D B E C K

Ionizing Radiation

on Condensed

Systems

17

D i r e c t e x c i t a t i o n t o e x c i t e d s t a t e s has never been o b s e r v e d i n r a d i a t i o n c h e m i s t r y a l t h o u g h i t i s p r e d i c t e d i n the so c a l l e d " o p t i c a l a p p r o x i m a t i o n " (2,3) · S p e c t r o s c o p i c evidence of d i r e c t e x c i t a t i o n b y v e r y l o w e n e r g y e l e c t r o n s i s f o r t h c o m i n g (_4) · R a d i a t i o n chemistry i s o f t e n c a l l e d the chemistry of i o n i s i n g r a d i a t i o n and the p o p u l a r c o n c e p t i s t h a t p r i m a r y energy l o s s i s t o p r o d u c e i o n i z a t i o n , t h e s u b s e q u e n t c h e m i s t r y t h e n d e p e n d i n g on the medium a n d i t s p e r t i n e n t c h e m i s t r y . I t i s d i f f i c u l t t o span the i n t e r v e n i n g energy gap between p h o t o - and r a d i a t i o n c h e m i s t r y , however, h i g h powered p u l s e d l a s e r s , u t i l i s i n g m u l t i p h o t o n a b s o r p t i o n b y t h e m e d i u m , d o much t o remedy t h i s s i t u a t i o n . F o r the most p a r t , the work d e s c r i b e d f a l l s i n t o two c a t e g o r i e s , d a t a w i t h s t e a d y s t a t e i r r a d i a t i o n i . e . light sources and Co-γ r a y s , and p u l s e d e x p e r i m e n t s as w i t h l a s e r s a n d p u l s e d e l e c t r o n a c c e l e r a t o r s s u c h a s V a n de G r a a f f s a n d L i n a c s . The i n t e r e s t s o f t h e m e e t i n g a r e i n p o l y m e r i s e d s y s t e m s , a n d h e n c e the m a j o r i t y of the paper w i l l d e a l w i t h hydrophobic systems. However, f o r c o m p l e t e n e s s a g e n e r a l d e s c r i p t i o n of r a d i a t i o n c h e m i s t r y i n p o l a r media i s a l s o i n c l u d e d . Radiolysis,

general

concepts

I t i s now a g r e e d , t h a t f o r t h e m o s t p a r t , t h e r a d i o l y s i s o f p o l a r l i q u i d s s u c h as a l c o h o l , w a t e r , e t c . l e a d s t o the f o r m a t i o n of i o n s and s u b s e q u e n t l y r a d i c a l s r a t h e r than e x c i t e d s t a t e s . However, the p i c t u r e i s changed as the p o l a r i t y of t h e l i q u i d d e c r e a s e s , and i n the extreme case of arenes such as benzene o n l y e x c i t e d s t a t e s b o t h s i n g l e t and t r i p l e t a r e o b s e r v e d . In o t h e r l i q u i d s such as a l k a n e s , d i o x a n e , e t c . b o t h i o n s and e x c i t e d s t a t e s are o b s e r v e d , charge n e u t r a l i s a t i o n of the i o n s a l s o g i v i n g e x c i t e d s t a t e s . T a b l e I g i v e s d a t a f o r the y i e l d s of e x c i t e d s t a t e s and i o n s observed i n the r a d i o l y s i s of v a r i o u s l i q u i d systems. The y i e l d i s s t a t e d i n t e r m s o f t h e G v a l u e o r number o f m o l e c u l e s o f p r o d u c t p e r 100 e V o f e n e r g y a b s o r b e d b y t h e s y s t e m . An i m m e d i a t e generalization is possible: The r a d i o l y s i s o f n o n p o l a r l i q u i d s , a r e n e s , a l k a n e s , e t c . produces e x c i t e d s t a t e s and sometimes i o n s . I n c r e a s i n g the p o l a r i t y of the l i q u i d , e . g . , benzene to b e n z o n i t r i l e , b e n z y l a l c o h o l , p h e n o l , leads to a decrease i n the y i e l d of e x c i t e d s t a t e s w i t h a concomitant r i s e i n the observed y i e l d of i o n s . In v e r y p o l a r l i q u i d s such as water and a l c o h o l s only ions are observed. A t h e s i s t h a t a c c o m m o d a t e s t h e s e d a t a i s one w h e r e r a d i o l y s i s leads to s i g n i f i c a n t y i e l d s of i o n s the recombination of which leads to excited s t a t e s . E x c i t e d s t a t e s may a l s o b e p r o d u c e d v i a direct excitation. I t i s an a c c e p t e d f a c t t h a t the r e c o m b i n a t i o n o r n e u t r a l i z a t i o n of i o n s c a n l e a d t o b o t h e x c i t e d t r i p l e t and s i n g l e t s t a t e s , the process f a v o r i n g the f o r m a t i o n of t r i p l e t e x c i t e d s t a t e s (J5) · I n p o l a r media the o v e r a l l energy change of t h e i o n n e u t r a l i z a t i o n p r o c e s s may be t o o l o w t o g i v e e x c i t e d s t a t e s due t o t h e i n c r e a s e s o l v e n t s o l v a t i o n e n e r g y o f t h e i o n s i n these media. I n h y d r o x y l i e m e d i a i o n m o l e c u l e r e a c t i o n s may a l t e r the i o n s and e x c i t e d s t a t e s are a l s o e l i m i n a t e d . For example, i n water the f o l l o w i n g processes take p l a c e :


POLYMERS FOR HIGH T E C H N O L O G Y

18

H_0

H 0

+ e

o

H 0 3

e

solution

+ OH~

+

S o l v a t i o n o f b o t h e~ a n d H o l e a d s t o a s i t u a t i o n where o n l y s o l v a t e d p r o t o n s H g O , h y d r a t e d e l e c t r o n s e~^ a n d h y d r o x y l r a d i c a l s OH a r e f o r m e d . The r e l a t i v e y i e l d o f i o n s v e r s u s e x c i t e d s t a t e s depends on the r e l a t i v e r a t e s of r e a c t i o n of t h e p r i m a r y i o n s w i t h the s o l v e n t and the r a t e s of i o n n e u t r a l i z a t i o n . The r a t e o f s p i n r e l a x a t i o n of the i o n s p r i o r to n e u t r a l i z a t i o n determines the r e l a t i v e y i e l d of t r i p l e t s versus s i n g l e t s (6)· The a b u n d a n c e o f e x c i t e d s t a t e s p r o d u c e d d i r e c t l y c a n b e c a l c u l a t e d v i a t h e o p t i c a l a p p r o x i m a t i o n (3_) · The o p t i c a l a p p r o x i m a t i o n s t a t e s t h a t the energy l o s t to a p a r t i c u l a r e l e c t r o n i c t r a n s i t i o n of a m o l e c u l e i s p r o p o r t i o n a l t o f/ε where f i s the o s c i l l a t o r s t r e n g t h f o r t h a t t r a n s i t i o n and ε i s the energy. F o r t h e E - ^ s t a t e o f b e n z e n e f ~ 1,0 a n d ε i s ~ 6 , 0 e V , the t o t a l o s c i l l a t o r s t r e n g t h f o r benzene b e i n g 4 2 . T h u s i f we t a k e a n a v e r a g e e n e r g y o f 14 e V f o r t h e e l e c t r o n i c t r a n s i t i o n s o f b e n z e n e t h e n ~ 5% o f t h e t o t a l e n e r g y l o s t i s t o t h e E ^ state. The y i e l d p e r 100 e V i s t h u s ~ 1 . 0 . +

2


+

u

u

Radiolysis

of

Alkanes

P u l s e r a d i o l y s i s ( 1 5 —•* 18) o f a l k a n e s o l u t i o n s o f a r e n e s g i v e s r i s e t o e x c i t e d s i n g l e t and t r i p l e t s t a t e s , and a n i o n s and c a t i o n s of the s o l u t e (19). The y i e l d s o f e x c i t e d s t a t e s i n a l k a n e s a r e g e n e r a l l y lower than those i n arene s o l v e n t s , w h i l e the reverse is o f t e n t r u e of the i o n y i e l d s . M o r e r e c e n t p s e c d a t a ( 2 0 ) show t h a t e x c i t e d s i n g l e t s t a t e s o f the a l k a n e a l s o t r a n s f e r s i n g l e t energy to the a r o m a t i c s o l u t e and t h a t t h e r a t e o f e n e r g y t r a n s f e r i s e x t r e m e l y r a p i d (k ~ 1 0 LM~ S" ). L a s e r p h o t o l y s i s o f b i p h e n y l ( φ ) i n b e n z e n e a n d C^H-j may be compared to the p u l s e r a d i o l y s i s of these systems t o i l l u s t r a t e the above e f f e c t s . F i g u r e I shows d a t a f o r s i n g l e p h o t o n l a s e r p h o t o l y s i s (λ = 2650 Â, e n e r g y 10 m j , p u l s e l e n g t h 20 n s e c ) , a n d 2 p h o t o n p h o t o l y s i s (λ = 3471 Â , e n e r g y 2 0 0 m j , p u l s e l e n g t h 20 n s e c ) of b i p h e n y l φ , i n C g H benzene. The f l u o r e s c e n c e d e c a y o f φ i s shown a t λ = 3300 Â a n d t h e r a t e o f a p p e a r a n c e o f t h e t r i p l e t φ a t 3 6 0 0 Â. No a p p a r e n t g r o w t h o f φ i s s e e n i n b e n z e n e i n t h e two p h o t o n l a s e r e x p e r i m e n t s . The l a s e r e x p e r i m e n t s a r e a n a l o g o u s t o t h e c o r r e s p o n d i n g r a d i o l y s i s s t u d i e s , as t h e two p h o t o n e n e r g y i s a b s o r b e d by benzene t o g i v e benzene e x c i t e d s t a t e s w h i c h t h e n t r a n s f e r energy to φ (21-22). The l a c k o f g r o w t h i s d u e t o a l m o s t p r e c i s e o v e r l a p of the e x c i t e d s i n g l e t φ and φ s p e c t r a as observed for naphthalene (22). I n t h e Φ2/ ^6 12 s i g n i f i c a n t growth of φ i s seen f o l l o w i n g t h e 2650 S l a s e r p u l s e . The r a t e o f g r o w t h o f φ h a s a 1 / 2 = 14.0 nsec which i s p r e c i s e l y the r a t e of decay of the fluorescence. Thus i n t e r s y s t e m c r o s s i n g , φ φ i s observed. The f

1 1

1

1

2

2

a

1 2

n

2

d

2

2

2

2

2

g

s

*

+

N

+ Ν

S 1

+

S

Τ (7)

N

S

+ Ν

+ +

fluorescence N

+

S

(8) C9.)

A l l t h e r a t e p a r a m e t e r s f o r t h e above p r o c e s s e s a r e known and t h e y i e l d o f N a s a f u n c t i o n o f n a p h t h a l e n e c o n c e n t r a t i o n c a n be c a l c u l a t e d (25). The y i e l d o f n a p h t h a l e n e t r i p l e t s , Y , i s g i v e n by T

T


POLYMERS FOR HIGH

Ο

TECHNOLOGY

Ο

4.0

3.0

*"o

2.0


1.0

2.0

1.0

log [cone.]-*

Figure 2a. y i e l d of s o l u t e t r i p l e t s versus c o n c e n t r a t i o n M . l i t e r ) i n p-xylene ( r a d i o l y s i s ) . Benzophenone (0); to o ^ r f , '* to c a l c u l a t e d d a t a . ί Δ )

p

P ^ «•>· b i l l e d p o i n t s correspond m these c a l c u l a t i o n s , φ taken as t

e

r

e

n

i s

,-1 χ i s taken as 0 5 f o r 1,1,'ΒΝ and k i s taken as 10,10 M" sec for benzophenone and p - t e r p h e n y l (Reproduced w i t h permission from Ref. 25. Copyright 1973 Academic P r e s s . ) 2

0

i 4.0

ι

ι

3.0

2.0

1

1

1.0

Ο

teg [ c o n e . ] - *

Figure 2b. Y i e l d of s o l u t e t r i p l e t s i n p-xylene. Naphthalene 30°C ( t ) ; napthalene 100° C ( Ο ); pyrene ( • ) ; c a l c u l a t e d for naphthalene ( » • · ) . Concentration u n i t s are M / l i t e r . In these c a l c u l a t i o n s φ, i s taken as 0.56, w h i l e φ i s 0.8 f o r naphthalene, and k i s taken as 3 χ 1 0 M" s e c " . (Reproduced with permission from Ref. 25. Copyright 1973 Academic P r e s s . ) χ

2

1 0

1

1


2.

THOMAS AND BECK

Y

T

=

Ionizing Radiation

*N 0 k;iSTÏâ T

(

)

+

*S

on Condensed

1

T

0 a k tN] (

+

7

) (

23

Systems

k [N] Y 9

+

)

w h e r e = 0 . 8 i s t h e q u a n t u m y i e l d f o r i n t e r s y s t e m c r o s s i n g f o r n a p h t h a l e n e s i n g l e t s , k^ a n d k a r e t h e r a t e c o n s t a n t s f o r r e a c t i o n s " E q u a t i o n 7 and 9 " , r e s p e c t i v e l y , [N] i s t h e n a p h t h a l e n e c o n c e n t r a t i o n and α and γ a r e the o v e r a l l r a t e c o n s t a n t s f o r decay of S and S , r e s p e c t i v e l y . The q u a n t u m y i e l d f o r i n t e r s y s t e m crossing i n toluene was t a k e n a s 0 . 7 (25). TQ the y i e l d o f , i s c a l c u l a t e d f r o m φ^ a n d t h e ^ y i e l d Y at 0.1 m o l d m " ^ n a p h t h a l e n e , a t w h i c h c o n c e n t r a t i o n a l l S * r e a c t s w i t h Ν t o g i v e N-j. The c a l c u l a t e d c u r v e i s s h o w n i n F i g u r e 3 . The agreement between c a l c u l a t i o n and e x p e r i m e n t i s good and s u p p o r t s the above mechanism. R a t e d a t a a r e i n t e r c h a n g e a b l e between two photon l a s e r p h o t o l y s i s and r a d i o l y s i s s u g g e s t i n g t h a t o n l y energy t r a n s f e r between e x c i t e d s o l v e n t and s o l u t e a r e i m p o r t a n t i n t h e above s t u d i e s . N

1

T


T

Origin

of

Excited States

i n the

Radiolysis

of

Aromatic

Liquids

Scavenging S t u d i e s . The s o l v e n t e x c i t e d s t a t e s p r o d u c e d by r a d i o l y s i s o f a r o m a t i c l i q u i d s c o u l d be p r o d u c e d d i r e c t l y , o r formed, v i a charge n e u t r a l i s a t i o n of s o l v e n t i o n s . The l o w o s c i l l a t o r s t r e n g t h s of the f i r s t and second e x c i t e d s t a t e s of benzene, t o l u e n e and p - x y l e n e p r e c l u d e d i r e c t e x c i t a t i o n i n t o these states. However, the t h i r d e x c i t e d s t a t e c o u l d be e x c i t e d w i t h a y i e l d as h i g h as u n i t y . E l e c t r o n scavengers such as c h l o r o b e n z e n e (24), C C 1 and C H C 1 (21,26) reduce the i n i t i a l y i e l d of s i n g l e t s t a t e s i n the r a d i o l y s i s of aromatic l i q u i d s . T h i s s u g g e s t s t h a t a t l e a s t some of the p r e c u r s o r s a r i s e from an i n i t i a l e v e n t of i o n combination. In the case of chlorobenzene, i t i s a l s o noted t h a t t h i s scavenger does not reduce the y i e l d of e x c i t e d s t a t e s formed i n t h e two p h o t o n l a s e r p h o t o l y s i s o f p - x y l e n e , s u g g e s t i n g t h a t t h e t h i r d e x c i t e d state of p-xylene i s unreactive w i t h t h i s scavenger. Some r e d u c t i o n i n e x c i t e d s t a t e y i e l d b y C H C l g a n d CH^OH i s o b s e r v e d i n t h e two p h o t o n p h o t o l y s i s o f t o l u e n e s u g g e s t i n g t h a t these scavengers r e a c t w i t h h i g h e r e x c i t e d s t a t e s as w e l l as w i t h electrons. Theory i n d i c a t e s t h a t the y i e l d of e x c i t e d s t a t e s I, i n t h e p r e s e n c e o f a n e l e c t r o n s c a v e n g e r (Q) i s r e l a t e d t o t h e i n i t i a l y i e l d I , v i a a r e l a t i o n s h i p of the form 4

3

Q

α

lo/

z

[Q]

n

where η i s 0 . 5 (27) o r ( 0 . 7 ) (28) w h i c h r e f l e c t s on t h e k i n e t i c s o f gemination i n decay. Indeed, t h i s i s found for chlorobenzene scavenging of the p r e c u r s o r s of e x c i t e d s t a t e s of p - x y l e n e , (24) and i n s i m i l a r s t u d i e s w i t h C H C I 3 i n t o l u e n e t o be d i s c u s s e d shortly. However, i n o t h e r systems c a s e s , e . g . b e n z y l c h l o r i d e i n s i e t h y l a n i l i n e (29) a s i m p l e S t e r n V o l m e r dependence o f Ιο

/ τ

α

[Q]



24

i s found, for quenching of s o l v e n t emission i n d i c a t i n g t h a t the e x c i t e d s t a t e p r e c u r s o r decays e x p o n e n t i a l l y , w i t h time, u n l i k e the k i n e t i c s of geminate i o n r e c o m b i n a t i o n . T y p i c a l data are given i n F i g u r e 4, f o r C H C l ^ s c a v e n g i n g of t o l u e n e f l u o r e s c e n c e i n r a d i o l y s i s a n d i n two p h o t o n l a s e r p h o t o l y s i s , λ = 343 nm. Stern V o l m e r k i n e t i c s a r e o b e y e d i n t h e c a s e o f two p h o t o n p h o t o l y s i s , and i o n - n e u t r a l i s a t i o n k i n e t i c s i n the r a d i o l y s i s s t u d i e s . However, S t e r n Volmer k i n e t i c s are obeyed f o r r a d i o l y s i s s t u d i e s of scavenging of toluene fluorescence w i t h benzyl c h l o r i d e . The e l e c t r o n s c a v e n g e r s C H C 1 and c h l o r o b e n z e n e reduce the fluorescence y i e l d s o f a r e n e s i n a manner t h a t s u g g e s t s : a) t h a t i n r a d i o l y s i s t h e i n i t i a l l o s s o f e n e r g y l e a d s t o i o n i z a t i o n f o l l o w e d by n e u t r a l i s a t i o n l e a d i n g t o e x c i t e d s t a t e s , the s c a v e n g i n g of e x c i t e d s t a t e s v a r y i n g w i t h [Scavenger] ; and b ) t h a t i n t h e two p h o t o n l a s e r p h o t o l y s i s C H C l ^ , b u t n o t chlorobenzene, r e a c t s w i t h the t h i r d e x c i t e d s t a t e , the scavenging v a r y i n g as [ S c a v e n g e r ] η =1. Benzyl c h l o r i d e always d i s p l a y s Stern Volmer k i n e t i c s , even though i t i s an e l e c t r o n s c a v e n g e r . These d a t a are d i f f i c u l t to f i t i n w i t h the c o n v e n t i o n a l p i c t u r e i l l u s t r a t e d but other quenchers. If, u n l i k e other quenchers benzylchloride reacts e f f i c i e n t l y , both with high excited states a n d w i t h e l e c t r o n s , t h e n t h e d a t a may be e x p l a i n e d . I t remains f o r further studies to f u l l y elucidate t h i s point. 2

3


1 1

Pulsed

Studies

F i g u r e 5 shows t h e g r o w t h o f f l u o r e s c e n c e from b i p h e n y l ( φ ) in t o l u e n e i r r a d i a t e d by f i n e s t r u c t u r e p u l s e s of 30-ps d u r a t i o n . The o b s e r v e d f l u o r e s c e n c e i s p r o d u c e d by e n e r g y t r a n s f e r from the excited solvent state T to b i p h e n y l . 2

s

+ Τ

+ φ

fluorescence The s o l i d l i n e i s c a l c u l a t e d u t i l i s i n g t h e r e s p o n s e o f t h e e l e c t r o n i c systems ( a c c e l a t o r p u l s e l e n g t h and r i s e time of the detection electronics). H a l f l i v e s o f 26 a n d 34 p s e c w e r e m e a s u r e d f o r the r a t e of energy t r a n s f e r from e x c i t e d t o l u e n e t o 1 and 0.5 M biphenyl. The r a t e c o n s t a n t f o r e n e r g y t r a n s f e r was t h e n m e a s u r e d as 5.3 χ 1 0 M~ s " a g r e e i n g w e l l w i t h t h a t measured by photochemical techniques (30)· The r i s e t i m e o f t o l u e n e f l u o r e s c e n c e e m i s s i o n was w i t h i n t h a t o f t h e s y s t e m , i . e . , f a s t e r t h e n 15 p s e c , w h i c h g i v e s a n u p p e r l i m i t e s t i m a t i o n f o r the time of i o n recombination i n t o l u e n e . Figure 5 also contains s i m i l a r studies i n d i e t h y l a n i l i n e D.E. and, shows t h a t h e r e t h e r i s e t i m e o f D . E . f l u o r e s c e n c e i s 2 4 . 4 p s e c and slower than that i n toluene. I t was a l s o n o t e d t h a t b e n z y l c h l o r i d e reduced the i n i t i a l y i e l d of D . E . f l u o r e s c e n c e , the k i n e t i c s being Stern Volmer. D e c r e a s i n g t e m p e r a t u r e has a marked e f f e c t on energy t r a n s f e r p r o c e s s e s i n r a d i o l y s e d s y s t e m s , as n o t e d e a r l i e r i n s o l i d p o l y m e r 1 0

1

1



Ionizing Radiation

on Condensed τ

KT*

HT

3

Systems

r

σ

2

Κ)"

1


[naphthalene]

Figure 3. Y i e l d of naphthalene t r i p l e t (N ) i n the laser photolysis of naphthalene i n toluene; as a function of naphthalene concentration [N] i n moles/L; · . • represents calculated y i e l d as_a function of naphthalene concentration, at [N] = 1.2 mol dm 3 with various concentrations of n i t r o methane. Concentrations i n moles/L. T

Θ.6,

Θ. 11 0

•

2

,

.

— 4

(CHC^r

•

• 6

7

Figure 4. Stern Volmer p l o t s and i o n quenching p l o t s of scavenging precursors of fluorescence i n the r a d i o l y s i s and two photon l a s e r p h o t o l y s i s of aromatic l i q u i d s , (a) CHCl^ quenching of toluene fluorescence, F, two photon l a s e r e x c i t a t i o n . Continued on next page.



0.5,

8.3

0.2


0.0l 0

.

, 2

,

, 4

b

a.ftl

0

.

.

.

4

8

.

.

12

(CHCU)

(Benzyl Chloride) Figure 4.—Continued, (b) S i m i l a r t o (a) b u t i o n i s i n g r a d i a t i o n used as e x c i t a t i o n ( r a d i o l y s i s ) . (c) B e n z y l c h l o r i d e quenching of toluene fluorescence (radiolysis).



Ionizing Radiation

on Condensed

Systems

- 1 0 τ :-2.574Ε-11 R2: 0.938

ι

1/2

-

? f

>


Polymers for High Technology - American Chemical Society

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