Acetone, liquid phase photolysis

QUANTUM YIELDS OF CASEOUS PRODUCTS OF THE PHOTOLYSIS OF ACETONE IN THE LIQUID PHASE AND IN SOLUTION AT 2537 A AND 25 °C... 

The results of the investigations carried out with mixtures of acetone and ace-tone- /6 in the presence of inhibitors clearly indicate the free radical character of the photolysis in the liquid phase , in inert solvents as well as in aqueous media . The available evidence supporting the formation of primary products other than CH3CO and CH3 is not convincing. Although some radicals, which could possibly be formed in the primary process, were detected by the paramagnetic resonance spectra, these studies were made under extreme conditions. Essentially, all the experimental observations on photolysis in the condensed phase can be interpreted by the mechanism derived for the reaction in the gas phase. 

The fact that the quantum yields determined in the condensed phase are lower than those obtained in the vapour phase may be due to (i) efficient deactivation of the excited acetone molecules, or ( ) recombination of the CH3CO and CH3 radicals in the solvent cage . A decision between these alternatives might be made by studying the solvent effect. Namely, the lowest quantum yields are expected to occur in the photolysis of liquid acetone or in the photolysis in aqueous solution if efficient deactivation or if the cage effect, respectively, were responsible for the low quantum yields in condensed phase. On the basis of the results presented in Table 18, as well as on those of Pieck and Steacie made with mixtures of liquid acetone and acetone-rfg, the quenching hypothesis seems to be more likely. However, probably both effects play some role. 

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