Some Aspects of the Photochemistry of Benzene

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Abstract
Three methods of measuring absolute gas‐phase‐emission yields from benzene are described. Two of the three proved to have large possible errors due to scattered light. One was used to give a value of Q2537=0.18 at a pressure of 10 torr at 25°C. This is in agreement with one value in the literature and slightly lower than the other although all three agree within the limits of error prescribed by the various authors. There is no significant variation with pressure but there is a marked wavelength effect. Below 2500 Å the emission decreases rapidly and it is essentially zero at 2400 Å and below in agreement with the findings of Poole. Variation at wavelengths longer than 2537 Å may exist but seems to be small. By implication the emission yield of biacetyl vapor as determined by Almy and Gillette is probably accurate within the errors specified by those authors. By use of these data it is shown that there is now excellent agreement on the extent of cross‐over of excited‐singlet benzene molecules to the triplet state by at least two methods. Some process competes with emission and crossover from the singlet state and the extent of this process increases with frequency. Benzene and oxygen react photochemically with a small yield to give an unstable peroxide.

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