Measurement of the proportion of radiationless decay processes in the photolysis of pentan-2-one

Abstract

Measurements have been made of the rate of production of acetone and the rate of consumption of the parent ketone in the photolysis, at 313 nm, of pentan-2-one mixed with various amounts of cyclohexene in benzene solution.

The results show that the type II reaction of pentan-2-one to form acetone can be partially quenched, as has been noted before, but that the quenching process is accompanied by an increase in the consumption of the ketone. The apparent quenching of the reaction is due to an alternative chemical reaction of the triplet state which reacts with the olefin. The efficiency of the chemical reaction is equivalent to that of energy transfer processes. Comparison of the rates at various concentrations allows the proportion of radiationless decay from triplet pentanone to be estimated, and, from the measured quantum yield, the ratios of all the processes for both singlet and triplet states have been deduced for a simple reaction scheme.