PHOTOLYSIS OF DIBENZYLKETONES IN SUPERCRITICAL ETHANE AND CARBON-DIOXIDE

The Norrish Type I photofragmentation of two dibenzylic ketones (1,3-diphenyl-2-propanone and 1-(4-methylphenyl)-3-phenyl-2-propanone) in supercritical ethane and carbon dioxide proceeds without evidence for cage recombination of the photogenerated radical pair. A statistical mixture of the bibenzyls formed by random coupling of benzyl and p-xylyl radicals was observed and the first order rate constant for the depletion of the reactant was independent of pressure. These results indicate that solvent cage effects are not operative in these low viscosity supercritical fluids even in the near critical region where solute-solvent clustering is presumably maximal.