Studies of the Cage Effect of Solvents. V. The Photolysis of Azoethane in n-Heptane

Abstract

Abstract The effect of a solvent cage on the photolysis of azoethane in n-heptane was investigated at 366 mμ, in the temperature range from −75 to 99°C. Among the gaseous products, nitrogen served as a measure of the azoethane decomposed. The other gaseous products were n-butane, ethane and ethylene; these three hydrocarbons accounted for ninety per cent of the decomposition at 0°C. The quantum yield of nitrogen was found to decrease with a lowering of the temperature. The value obtained at 0°C was 0.021. In the presence of a sufficient amount of styrene, which was used as a scavenger for ethyl radicals, the yields of the gaseous hydrocarbons were more or less reduced to constant values; from these the ratio of rate constants for the combination and disproportionation of the geminate ethyl radicals formed by the photolysis in a solvent cage was determined to be kcomb⁄kdisp=11.5exp(−371⁄RT). The fraction of ethyl radicals that reacted in these ways in the solvent cage, before escaping it, was dependent on the temperature; it decreased from 0.838 at −75°C to 0.467 at 99°C. In the absence of styrene, the reactions for ethyl radicals that escaped the original solvent cages were inferred to be hydrogen abstraction, addition, combination and disproportionation.