113 



BURTON: May I say a word about heat which is not entirely semantics. 

 Consider a purely monolayer reaction. For occurrence of any reaction the ac- 

 tivated complex has to exist; the activated complex is a special configuration 

 with a special amount of energy located in certain degrees of freedom. Fre- 

 quently there will be one vibrational degree of freedom which becomes very im- 

 portant. This molecule is not characteristic of the whole system. It is an ex- 

 ceptional molecule, which exists with low probability in an ordinary temperature 

 situation. However, for a chemical reaction, it does not make any difference 

 from the point of view of what happens to this molecule, whether it happens to 

 obtain this energy by picking it up from the background (and then you look upon 

 it as an effect of heat) or it happens to get this particular arrangement of ener- 

 gy as a result of coming down from a higher level. The energy that is in it and 

 the distribution which is responsible for the chemical reaction is precisely the 

 same in either case, but the chances of ending up in this configuration may be 

 very much higher coming down from a higher excitation level than going up from 

 the ordinary temperature distribution. I think this remark is pertinent to what 

 Dr. Fano was saying. 



POLLARD: This is very tricky because the actual result of such reaction 

 depends not only on the energy of formation of the activated state but also the 

 entropy. 



BURTON: It is correct that the entropy of the final activated state is less 

 than that of the state from which it derived (by a transition). However, so is its 

 energy. The fact is that in the transition the free energy does actually decrease 

 so that there is no occasion for disturbance about the decrease in entropy in the 

 process. 



POLLARD: What you are saying is you have a different reaction kinetics 

 for higher excitation. That is what I feel may be true. 



KAMEN: In connection with the remarks about studying not only isolated 

 molecules but also intact systems, I should like to bring up two observations: 

 one fairly recent and one very recent, because they are typical and one can 

 probably find many instances of such observations. There is the well-known 

 effect of radiation on desoxyribose nucleic acid activity. It is a fact that if one 

 radiates any system, bacteria coli, say, or phage, the nucleic acid in the cyto- 

 plasm is usually not affected very much by the radiation as compared to the de- 

 soxyribose nucleic acid (DNA). There is no hard and fast rule for DNA distri- 

 butions. It is thought to be in the nucleus, but it turns up often in the cytoplasm. 

 However, in those cases where it is in the nucleus there is a profound effect on 

 the turnover on the desoxyribose nucleic acid. 



Recently Kellner (14) has done a rather interesting piece of work. What he 

 did was to use the phenomenon involving the light reversal of ultraviolet inac- 

 tivation. He wanted to know whether there was some process which is extreme- 

 ly sensitive as regards inactivation by radiation, which can be reactivated by 

 light. His contention was that if you have an effect which is reactivated by light 

 that is more of a bona fide radiation effect than some other effect which is per- 

 haps secondary. What he did was to look first at the growth behavior of the cell. 

 He found that the growth was not affected much and none of the oxidative enzymes 

 were affected much. Little that you could easily test was affected. Nothing 

 much happened, in other words, except to the division rate. What was observed 

 was a continued growth of the cell. The radiation effect did not begin until the 

 cell found itself in the position of having to divide. Then something happened. 

 This delay, of course, was caused by the fact that the division mechanism had 



