LASER FLASH-PHOTOLYSIS INVESTIGATIONS OF DIFFUSION-CONTROLLED REACTIONS IN SUPERCRITICAL FLUIDS

Laser flash photolysis has been used to investigate the triplet-triple t annihilation (TTA) process of benzophenone (Ph2C=O) and the self-ter mination reaction of benzyl radical (PhCH2) in supercritical CO2 and e thane. Kinetic measurements were performed at various pressures above the critical pressure along two isotherms, one close to the critical t emperature of the solutions (35-degrees-C) and one further removed (50 -degrees-C). The second-order rate constants obtained indicate that ea ch reaction occurs at the diffusion limit when spin statistical factor s are considered. No evidence of enhanced cage effects due to supercri tical solvent clustering about diffusive encounter pairs or enhanced s olute/solute interactions were observed in these experiments. Addition ally, the photocleavage of dibenzyl ketone and the rate constants for decarbonylation of phenylacetyl radical (PhCH2CO) have been examined u nder the above conditions and do not show any anomalous behavior or ca ge effects.