19 



I am certain that Dr. Pollard does not mean to give the impression that this 

 process is a new conception. In case anyone is confused, my opinion is that it 

 is neither new nor questionable. As a matter of fact, instead of saying that the 

 charge moves, one could rephrase the argument and state that there is no justi- 

 fication for saying that the charge is localized in any one atom of the molecule 

 -- until, of course, the charge is found in a region where part of the energy of 

 the system may be converted into vibrational energy, i.e. , heat. As Mazia has 

 just said, once dissipation starts it cannot be reversed. 



Less is known about the mode of migration of energy inside a molecule 

 than about the related (but by no means identical) phenomena involving migration 

 of excitation energy. The latter have been studied extensively in a variety of 

 systems. For example, Weissman (13) has investigated the migration from a 

 carbonyl group at one end of a molecule to a rare earth atom at the other, under 

 a variety of conditions. Bucher and Kaspers (14) have shown that, in the carbon 

 monoxide-myoglobin complex, light absorbed in the protein component can dis- 

 sociate the CO from a prosthetic group. Franck and Livfngston (9) have ana- 

 lyzed these and other cases and have concluded that the mechanism of energy 

 migration is most likely of the "sensitized fluorescence" type, in all cases. 



One wishes that some information were available on the extent to which 

 Pollard's "ionization migration" can occur. A point to bear in mind is that the 

 distance through which sensitized fluorescence can occur is determined essenti- 

 ally by the wavelength of light, which is much greater, of course, than the 

 wavelength of the migrating "electron. " The most stable position, if it could be 

 reached, is at a site that one might crudely identify with the atom of lowest ioni- 

 zation potential. This statement must be interpreted loosely, but the fact that 

 it is not strictly correct does not mean that it is completely wrong or may not 

 be of great help in qualitative reasoning. 



CURTIS: You say the lowest ionization potential? 



PLATZMAN: Yes, for that is where the greatest amount of energy 

 would be available for heat. 



CURTIS: To put this into more visual terms, this charge sort of goes 

 back and forth and up the side chains? 



PLATZMAN: To some extent. 



CURTIS: Hunting around until it kind of samples all the different 

 atoms, and then finally picks out the one that has the lowest ionization potential 

 and nestles there. 



PLATZMAN: Except that it goes so fast you cannot say it is at any 

 particular place at any particular time. 



POLLARD: It has a higher probability of nestling there. 



PLATZMAN: In radiation chemistry this argument is not uncommon. 

 For instance, Kamen's objection that ionization ought to cause dissociation at 

 once is met by the observations that in certain molecules this does not occur, at 

 least with a high yield. For example, in benzene the probability of dissociation 

 is comparatively small. 



KAMEN: When don't you get if 



