Momentum transfer between ions and neutrals in molecular gas

Abstract

We have performed quantum mechanical calculations of the cross-section for momentum transfer in collisions between para-H2 molecules and HCO+ ions. At low temperatures, the computed values of the rate coefficient are close to the Langevin value. As the mean collision velocity increases, so does the rate coefficient, which is approximately four times the (constant) Langevin value when the relative velocity reaches 10 km s−1. Our results imply that the strength of the ion–neutral coupling has been underestimated in studies of C-type shock waves propagating in molecular gas.