Ab-initio-based model for the charge transfer mechanisms in Ar + + H 2O collisions

Abstract

The mechanism of the charge-transfer reaction between water molecules and argon ions is analysed using a two-dimensional model with the reaction and HOH bending coordinates, which maintains the C 2v symmetry of the reaction system. Potential energy surfaces and nonadiabatic coupling matrix elements are computed using ab initio Möller-Plesset perturbation theory with multiple partitioning of the full Hamiltonian. Both ab initio calculations and semiclassical simulations of the vibrational distributions of the product H 2O +(Ã) ion indicate two possible charge-transfer mechanisms. The first involves a nonadiabatic transition induced by radial coupling, whereas the second is governed by the curve crossing along the bending coordinate. The coexistence of two mechanisms agrees qualitatively with that inferred from the experimental measurements.