A reinvestigation of the near-ultraviolet photodissociation dynamics of the methyl radical

Abstract

The translational energy spectrum of H Rydberg atoms resulting from the photolysis of the methyl radical (CH 3) at 216.3 nm has been recorded. The use of pulsed supersonic jet flash pyrolysis of azomethane (CH 3N 2CH 3) as a clean source of methyl radicals has allowed a clear analysis of the data, eliminating possible interference from other molecular species. The measured time-of-flight of the resulting H atoms indicate that the partner CH 2 fragments resulting from predissociation of CH 3 (B̃) radicals are formed in their low-lying ã 1A 1 excited state, as predicted by theory. An earlier contradictory report of this dissociation process, using methanethiol (CH 3SH) as a photolytic precursor to generate methyl radicals, has been reinterpreted in terms of secondary dissociation of ground-state thomethoxy radicals (CH 3S) yielding electronically excited thioformaldehyde CH 2S(Ã 1A 2)+H( 2S).