Classical and semiclassical calculations of electron transfer cross sections in keV-energy ion-molecule collisions

We apply a many-body classical model and a semiclassical coupled-channel approach to study the electronic processes occurring in the course of fast collisions between atomic and molecular species. The methods are applied in a comparative study of electron transfer in He²⁺∕Ar²⁺−H₂⁺ collisions at keV u⁻¹ impact energies. The classical calculations are in agreement with recent experimental data [ et al. J. Phys. B 34 L321 (2001)] for projectile velocities larger than the initial electron velocity. The semiclassical model is based on the sudden approximation where the electronic wave function is expressed by linear combinations of traveling atomic capture states and target molecular states obtained at fixed nuclei. The related charge transfer cross sections are slightly underestimated (overestimated) for He²⁺ (Ar²⁺) when considering H₂⁺ in its initial vibrational ground state. These cross sections do, however, depend strongly on the internuclear distance of the hydrogen molecular ion: when involving an initial vibrational excitation of the target, the averaged cross sections obtained from the semiclassical approach become in fair agreement with experiments.