28 



field is strong enough to bring the electron back (as Dr. Magee claims). I 

 might point out that one must beware of identifying "Coulomb's law" with a 

 simple, static l/r^ force between the positive ion and electron. Actually, all 

 of the polarization charges participate; moreover, the problem is a complex 

 dynamical one. 



ALLEN: I don't quite follow your statement about the dielectric constant. 

 Relaxation time may be of the order of 10-13, but the electron may pass 

 through many molecules in that time. The time it takes to go through one mol- 

 ecule will be pretty much shorter. 



PLATZMAN: Most of the polarization comes from greater distances. 



ONSAGER: The charge is in the medium, moving in the direction of the 

 electron. The electron is moving so the effect of the motion of the charge in 

 the medium is a sort of compromise between the position where the electron is 

 and the position where the electron was. The result is that there is on the 

 average a drag felt on the electron. There is a time lag in the adjustment of 

 the molecules here. 



PLATZMAN: Thus far, we have found the total time for the energy to be 

 dissipated. The total path length is much harder to calculate. That is, to say 

 the actual total path length is easy to calculate, but the path is tortuous. Here 

 all we can do is assume perfectly random scattering at every encounter with a 

 water molecule. One finds the following figures, which are highly tentative: 

 The actual distance measured along the track is of the order of 10" 5 cm. and, 

 therefore, the separation of the final and initial points is the geometrical mean 

 of this and the molecular diameter, or about 50 ]±, I am inclined to think that 

 this is a minimum estimate. In any event one can at best expect that it is cor- 

 rect only to order of magnitude. 



MAGEE: The path is measured from the positive ion? 



PLATZMAN: Yes. 



ALLEN: That is the root mean squared distance? 



PLATZMAN: Yes. 



ONSAGER: There may be some subtle effects which would tend to hold 

 the electron a little closer to the origin. 



PLATZMAN: Yes. For instance, the charge of the positive ion would 

 tend to do so. 



BURTON: So the electron would not be randomly scattered. It scatters 

 inward all the time, so that one would sny your estimate of the positive ion - 

 electron separation is definitely too great. 



PLATZMAN: No. I don't think that the field of the positive ion will have 

 much influence on the electron until, perhaps, it is slowed down to near ther- 

 mal energy. The internal field of a water molecule is, after all, very great. 



MAGEE: What is the infrared value of the dielectric constant? 



PLATZMAN: About five. 



