38 



BURTON: On your picture would you expect any difference between the ef- 

 fects of alpha particles and slow electrons? 



PLATZMAN: Yes. 



ONSAGER: It occurs to me that it might be possible that dissociative cap- 

 ture goes a little faster in some way, because these two steps of making a hole 

 for the electron and then attachment of the electron might be telescoped. 



PLATZMAN: Yes. 



ONSAGER: That the electron might attach directly, so that one hydrogen 

 atom does not have to make a hole. After all, what makes the hydration is 

 simply that the charge is here which gives rise to the orientation of dipole mo- 

 ments. 



PLATZMAN: But you cannot telescope it too much. The dissociation re- 

 quires approximately one vibrational period, and, therefore, about two electron 

 volts of energy must be acquired during the 10" ^^ second. 



MAGEE: I don't think there is a cross section known for dissociative cap- 

 ture in the gas that is greater than maybe lO" 1 ^ cm 2. They just aren't any big- 

 ger than that and most of them are even smaller. 



ALLEN: What about Bradbury's experiments (14) on water vapor? 



MAGEE: He didn't measure anything greater than that. 



ALLEN: That is because his instruments gave out. It went up too high for 

 him to measure. 



ONSAGER: Now let's translate that cross section into time. In the liquid, 

 a cross section of 10" ^ cm 2 corresponds, for a thermal electron, to a time of 

 lO" 1 ^ second. 



PLATZMAN: If the electron is hydrated, its thermal velocity would be 

 somewhat smaller. 



ONSAGER: Well, I guess with this effect we cannot expect much to happen 

 then until the electron has been pinned down to one neighborhood. So it should 

 be of the same order as the dielectric relaxation time after the electron has 

 started orienting the molecules around it, or in moving about has found a place 

 in which a water molecule happened to be pointing the right way. It wouldn't, 

 I think, find many places. That is a question of potential fluctuations in water. 

 It might actually be that the electron starts out by finding a place where, thanks 

 to the accidental orientation of the water molecule, the potential is a little high, 

 where the potential might be 0. 3 or 0. 4 of a volt plus, and then the electron 

 lands there and stays in the neighborhood, and the water molecules around grad- 

 ually fall into place and the potential drops. We might have to visualize the 

 process that way. 



PLATZMAN: Essentially, I believe that it is proper to say that the modes 

 of energy loss of the swiftly-moving electrons are essentially correct as I have 

 given them. The other questions to which the answers are uncertain are: the 

 time required for the capture of the electrons by the dipoles; secondly, the time 

 required for dissociation after it is captured; and, third, consideration of the 

 many things that I have neglected, namely, the electrostatic field, time varia- 



