Ab initio study of the O(1D) + CH4(X1A1) → OH(X2Π) + CH3(X2A2'') reaction: ground and excited potential energy surfaces

Abstract

The two potential energy surfaces (1 1A and 2 1A PESs) adiabatically correlating the reactants and products asymptotes of the title reaction were studied by means of the CASSCF and CASPT2 ab initio methods. The minimum energy path determined for the ground PES evolved through the barrierless insertion of the O(1D) atom into a C-H bond. The OH + CH3 products result from the dissociation of the CH3OH methanol intermediate formed. Reactivity on the excited 2 1A PES was found to proceed via an abstraction pathway. The energy barrier involved is low enough to expect the 2 1A PES to play a non-negligible role in the title reaction, even at the usual conditions attained in the experiments. The crossing between the 11A and 31A PESs was also investigated, the latter surface correlating with the excited OH(A 2Σ+) product.