Imaging the elusive C–C bond dissociation channel of photoexcited ethyl radical

Abstract

The C–C bond dissociation channel of the ethyl (CH–CH) radical is investigated at 197.4, 199.98 and 201 nm by velocity map imaging and resonance enhanced multiphoton ionisation (REMPI) detection of the produced CH fragments. On the light of high-level ab initio calculations performed in this work, up to four dissociation pathways are identified leading, respectively, to ground state CH radicals in correlation with CH fragments in the first four electronic states. The major pathway is associated with threshold dissociation over an exit barrier located at the point of a conical intersection between the initially populated 3 state and a dissociative valence state. As discussed in the text, the concomitance of both features opens the narrow window in which C–C bond dissociation occurs for ethyl and, presumably, for other similar alkyl radicals.