A theoretical prediction of vibrational enhancement for dissociative charge transfer in the HeH2+ system

Abstract

A model has been developed to treat dissociative charge exchange occurring on excited‐state surfaces in the weak adiabatic limit. This process is analogous to collisionally induced predissociation with the added feature that electronic as well as translational energy is used to effect the dissociation. The consequences of weak adiabaticity and the location of the avoided crossing seam are to require the consideration of tunnelling through a barrier in the dissociation curve. An appealing feature of the model is the reduction of a three‐dimensional trajectory problem to one dimension by neglect of coupling of translation to vibration and rotation. Configuration interaction ground‐ and excited‐state calculations have been performed in the vicinity of the curve crossing seam for He⁺+H₂→He+H⁺+H. Use of the parameters derived from these ab initio results in the dynamics model yields cross section and rate coefficient values in qualitative agreement with experimental measurements. Vibrational excitation from the v=0 to v=1 states in H₂ leads to an increase in cross section of approximately two orders of magnitude due to enhancement of the tunnelling.