Quantum statistical study of the C+ + OH → CO + H+/CO+ + H reaction: Reaction rate and product branching ratio at interstellar temperatures

Abstract

The C+ + OH reaction is an important process in the interstellar synthesis of the CO molecule and the CO+ ion. This reaction has two possible chemical outcomes, namely, formation of CO + H+ and CO+ + H products. Formation of CO + H+ occurs on the ground 11A′ potential energy surface (PES), while CO+ + H can be formed on the 13A′ and 21A′ PESs. The stationary points on these three PESs have been found in explicitly correlated internally contracted multireference configuration interaction (icMRCI-F12a+Q) calculations. The entrance channel on the 11A′ PES is barrierless, and the barriers on the 13A′ and 21A′ PESs are submerged so that the reaction to form both sets of products can occur at interstellar temperatures. The quantum statistical method of Manolopoulos and co-workers was employed with the three PESs in the reactant channel to compute the total reaction cross section and rate coefficient, as well as the product branching ratio, as a function of temperature. These PESs can be adiabatically accessed by the ground spin-orbit state, C+(2P1/2), and the rate coefficient for the reaction of this state was estimated by invoking the adiabatic approximation.