80 



BURTON: Would you mind stating which bond it is that breaks? 



LINSCHITZ: The bond between the carbon and nitrogen. Hydrazine is 

 formed. This is some work of Terenin et al (3) about 1939. 



KASHA: May I make one point about heating. It is possible that local heat- 

 ing does not always accompany these processes. For example, what about in- 

 frared (IR) emission? 



LINSCHITZ: This is a very slow process. What would you estimate to be 

 the time for IR emission? 



KASHA: I do not have any oscillator strength data for a single IR vibration- 

 al band. However, if quenching collisions are successively decreased in rate, 

 as for example, at low temperature, certainly IR emission of vibrational energy 

 may become important. 



MAZIA: Does internal conversion imply the absence of chemical change in 

 the usual sense? 



LINSCHITZ: This is competition for the chemical change. That is, the very 

 rapid loss of energy as heat here will tend to compete with free radical forma- 

 tion. 



BURTON: May I ask another question. Do you remember the quantum yield 

 for the photolysis of aniline? 



LINSCHITZ: No quantum yield is given in the article by Terenin. In con- 

 sequence of this kind of radiationless transition from one level to a lower one, 

 we might expect to find a shift in the energy from the region in which the excita- 

 tion originally takes place to the bond which is ultimately ruptured. For exam- 

 ple, one of the few pieces of photochemistry on fairly complex molecules that 

 seems to be well established is the case of certain ketones, in which excitation 

 of electrons that are undoubtedly in the carbonyl group leads to bond rupture in 

 the less strong adjacent C-C bonds. Thus in acetone, we have: 



CH.CCH, > CH 3 C-+ CH V 



o o 



However, we would not expect this vibrational energy to move very far through 

 the molecule before being degraded in liquid systems. 



With regard to even more complex molecules, I might mention some photo- 

 chemical studies on stearic acid anilid monolayers on water, which are relevant 

 here (4). Excitation in the aromatic ring leads to hydrolysis of the relatively 

 weak amide link with quantum yield of about 0. 2. So that in general although one 

 might say that the tendency here is to lose vibration in a general process of de- 

 gradation, this vibrational loss is very closely coupled to adjacent bonds, as we 

 might expect in some cases. 



KAMEN: This is a gas reaction? 



LINSCHITZ: This is in a monolayer. 



KAMEN: Are there any data on the effect of X rays? 



LINSCHITZ: I don't think so. I have never seen any paper on it. 



