66 



ent to eliminate the possibility of a columnar effect. 



FANO: It depends on how effective the scavenger is. 



ALLEN: There are scavengers which work from 10~" molar up to 10" 1 

 molar. For all this range of concentration the same yield is obtained. 



FANO: If there are scavengers which suppress any large columnar ef- 

 fect, then this must be taken at face value, that you must start with r of 

 the order of 10 A. Otherwise you cannot get yield like that 0.2 or 0.3. 



ALLEN: One of the lines of evidence on the size of these regions con- 

 cerns the fraction of radicals which escape; another is this business of 

 concentration of scavengers, which gives the same result regardless of con- 

 centration over a wide range; and the third is the variation of the molecu- 

 lar yields with ionization density of the radiation. They all appear to lead 

 to something like 10 A. 



KAMEN: I think for some of us that it is important to make a point 

 about the difference between Dr. Magee's theory and the older ideas, be- 

 cause everybody has been entertaining the notion that you make the ion-pair 

 first and then you make the radicals from the dissociated ions. Now what 

 Dr. Magee is saying is that you have no ionizations, and, therefore, there 

 is no meaning to assigning an energy value, like 30 ev, for the work re- 

 quired to produce an ion-pair in liquid water. 



BURTON: Excited molecules, no matter where or how originated, can 

 be considered from the point of view of whether they contain enough energy 

 to give radical pairs. The theoretical minimum that is required to give 

 you a radical pair in the case of water is about 4. 5 ev. Thus the theoreti- 

 cal maximum jG_ for decomposition is 23, but it is evident that some ex- 

 cited molecules have far in excess of the energy required to give a radical 

 pair, and some of them, for example those in low-lying triplet excited 

 states, may not have enough energy to give a radical pair. All you can 

 speak of is an average effect in a particular locale. In other words, if you 

 can get n radical pairs there are enough sufficiently excited molecules there 

 to give you n radical pairs. Where they originate is beside the point right 

 now. 



ZIRKLE: But you can get radical formation from excitations which are 

 essentially primary energy transfers. 



BURTON: If you really want to get complicated about this, then there 

 is another thing that we have to consider, and that is that in these clusters 

 there are also large numbers of excited molecules produced at a low excited 

 state with a very high probability that such excited molecules may react with 

 each other and produce reactions which are not radical reactions at all. 



MAGEE: I have thought occasionally there is evidence that some of 

 these excited molecules may be reactive. For example, there have been 

 reported radical pair yields of up to 1 3 in certain cases. That is, I am 

 talking about some of Dainton's results (15). He reports the highest value 

 I have ever seen in water. 



HOCHANADEL: That value of 13 radical pairs per 100 ev was based 

 upon peroxide decomposition studies. 



