Ab initio studies on the radiationless deexcitation mechanism of ketene and its rearrangement to oxiranylidene

Abstract

Multiconfiguration self-consistent-field (MCSCF) and multireference configuration interaction (MRCI) calculations have been performed to investigate a possible surface crossing between the ground state and first excited 1A″ state of ketene, and to determine a rearrangement path between ketene and its isomer oxiranylidene. The crossing of the excited 1A″ surface with the ground 1A′ surface is near the excited state equilibrium geometry, providing a firm basis for a fast internal conversion mechanism for electronically excited ketene. The transition state for the ketene to oxiranylidene rearrangement is found to lie 81 kcal/mol above the 1A1 state of ketene and 5 kcal/mol below the CH2(1A1) + CO(1Σ+) dissociation limit. Mechanisms emerging from the present study for radiationless deexcitation, and for isotope scrambling in the photolysis of doped ketene, are presented and discussed. © 1988 American Institute of Physics.