PHOTOIONIZATION OF DIARYLMETHYL RADICALS IN ACETONITRILE AND ALCOHOL WATER - LASER FLASH PRODUCTION OF DIARYLCARBENIUM IONS

Diarylmethyl radicals Ar2CH. were produced by 248-nm laser photolysis (20 ns) of diphenylmethane, diphenylmethanol, and diarylmethyl halides in acetonitrile and water:alcohol mixtures. A few microseconds after their generation, the radicals were subjected to a laser pulse (20 ns) of 308-nm light. As products of the photolysis of the radicals, the electronically excited radicals, Ar2CH.* (D] state), and the corresponding cations, Ar2CH+, were identified. The electronically excited radicals decay with emission of light (almost-equal-to 550 nm in the case of Ph2CH.*) to their ground state (D0), whereas the cations react with solvent or (other) nucleophiles. The formation of cation from AT2CH. requires two photons (is biphotonic) and proceeds by photoionization of Ar2CH.*. The photoejected electrons were directly observed in aqueous alcohol. In acetonitrile, the yield of photoionization of Ar2CH. (as measured greater-than-or-equal-to 20 ns after the 308-nm pulse) can be increased by the electron scavenger n-butyl chloride, which does not react with Ar2CH.*. In contrast, CCl4, which does react with Ar2CH.*, does not lead to an increase in cation yield.