DIFFUSION PROCESS OF THE BENZYL RADICAL CREATED BY PHOTODISSOCIATION PROBED BY THE TRANSIENT GRATING METHOD

Translational diffusion processes of the benzyl radical (BR) created b y the photodissociation from dibenzyl ketone (DBK) were studied by usi ng the transient grating (TG) method in organic solvents (hexane, cycl ohexane, ethanol, and 2-propanol). The values of the diffusion constan ts (D) of BR, DBK, and carbon monoxide (CO) and the rates for the self -termination reaction of BR in these solvents are accurately determine d from the TG signals. The ratios of D of BR to that of DBK are indepe ndent of the solvent, and they are close to 1.25, which is expected fr om the ratio of the molecular volume of BR to that of DBK. This result is contrary to those of radicals created by the photoinduced hydrogen abstraction reaction, which show anomalously slow diffusions. A possi ble origin of this difference is discussed by comparison of the spin d ensities, dipole moments, and polarizabilities of BR and the radicals produced by hydrogen abstraction.