The effect of nonadiabaticity on the C+ + HF reaction.

Abstract

The chemistry of fluorine in the interstellar medium is particularly simple, with only a few key species and important reactions. Of the latter, the rate of the reaction of C+ ions with HF is not well established but is one of the key reactions that sets the relative abundance of HF and the CF+ ion, the two fluorine-bearing species that have been observed in interstellar clouds. The C+ + HF → CF+ + H reaction proceeds through a deeply bound HCF+ well. In this work, statistical methods, namely, the statistical adiabatic channel method originally developed by Quack and Troe and the quantum statistical method of Manolopoulos and co-workers, are applied to compute the total cross section as a function of energy for this reaction. This reaction proceeds on the ground 12 A' potential energy surface (PES), and there are also two non-reactive PES's, 12 A″ and 22 A', correlating with the C+(2 P 1/2,3/2) + HF reactants. Two sets of scattering calculations were carried out, namely, a single-surface calculation on the 12 A' PES and the one in which all three PES's and the spin-orbit splitting of C+ are included in the description of the entrance channel. In the latter, reactivity of the spin-orbit excited 2 P 3/2 level can be computed, and not just assumed to be zero, as in the single-state adiabatic approximation.