Low temperature quantum rate coefficient of the H + CH+ reaction

Abstract

In this paper we report the first theoretical study of the title reaction. A global, single-valued model of the ground-state potential energy surface has been obtained by fitting to an extensive set of high-level ab initio calculations. The surface is found to be attractive apart from linear geometries where energy barriers appear due to conical intersections. This model was then used to calculate the reactive reactant state selected cross sections for collision energies ranging from threshold up to 4000 cm⁻¹. These calculations were performed using our version of the Baer’s approach of the RIOSA-NIP method which is based on the use of a negative imaginary potential. We find that the reaction probability is extremely oscillatory as a function of kinetic energy as it is a case for insertion reactions with a low exoergicity. The resulting reaction rate coefficient is found to first increase slowly as a function of temperature up to a broad maximum around 20 K and then to decrease slowly when temperature keeps increasing.