Distribution of excitation between the reaction products

In the study of chemiluminescence in elementary transfer reactions the behavior of the new-bond molecule has been emphasized over the past decade. This is understandable. The initial successful experiments showed new-bond excitation. Also, the work was conditioned by the observation of a highly non-thermal emission from OH in the upper atmosphere59 and the demonstration60 that a likely cause was the reaction H+03 -+ OH +Oj. Indeed, early work aimed at a test of the possibility that the principal excitation channel was via the highest accessible level. This hypothesis has not been proven. The available facts contradict it. Many levels of the new-bond molecule are populated by reaction. Ample evidence for this is provided by the reactions listed in Table 1. 

Unfortunately, most of these experiments do not define the energy distribution between the products. In many cases it was possible to examine only one of the products. The problem has been to devise experiments in which it is possible to observe the spectra of both products simultaneously, preferably with the same technique. The present state of our knowledge is that there is ample evidence for excitation of the new-bond molecule up to levels corresponding to the energy released by reaction, and there are data, fewer in number but no less certain, showing some excitation in the old-bond product. These are considered below. 

Ozone was flash photolyzed in the presence of 180 enriched water and added argon (03 H20 Ar =1 1 8). Vibrationally excited OH was observed56. 

The results show 16OH(t = 2,1,0) and 18OH(u =1,0) with the ratio 18OH(t = l)/16OH(t = 1) 0.01. This ratio is larger than can be attributed to 180 atoms formed in the photolysis due to the natural abundance (0.002) of lsO, but still is very low compared to the 16OH excitation. Rotational excitation was not observed. 

When a mixture of chlorine and NOC1 (in N2) was flash photolyzed through a Pyrex filter (to suppress NOC1 photolysis) appreciable NOC1 decomposition occurred57. The nitric oxide was observed in absorption but with virtually no excitation. The reaction is 

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