Far-Ultraviolet Photolysis of Acetone

Abstract

A survey of the trends in acetone decomposition in the range from the near-ultraviolet photolysis to gamma radiolysis has been made using a xenon discharge (1470 and 1295 Å) and a krypton discharge (1236 and 1165 Å) for room temperature photolysis. The variation of the ratios to CO of products as a function of acetone pressure and wavelength has been noted. Analysis of the mixed products from mixtures of acetone and acetone-d6 presents evidence for methyl radicals in the production of ethane, of hot methyl radicals in the production of methane and of hydrogen atoms in the production of hydrogen. Deviation from the H2—D2 equilibrium indicates molecular hydrogen elimination. The conclusions are confirmed by scavenger studies using propylene, iodine, and oxygen, as well as by the effects of added xenon and neon. The results are consistent with the existence of two excited states of acetone, the higher state eliminating either H or H2; the lower state, methyl. The far-ultraviolet photolysis appears to be closer in over-all behavior to the gamma radiolysis than to the near-ultraviolet photolysis and the trend of the decomposition may be explained by the increase in energy of the radiation.