Close-coupling calculations for inelastic processes in intermediate energy ion-atom collisions

Abstract

A modified two-centre atomic orbital expansion is proposed for close-coupling calculations of inelastic electronic processes in ion-atom collisions at intermediate energy, and electron transfer cross sections are calculated for H++H and He+H+ collisions. For close collisions, the inclusion of united-atom orbitals in the expansion is shown to be essential for reproducing experimental data as well as earlier calculations based on multi-state molecular orbital or other pseudostate expansions. The convergence of two-state atomic orbital expansion calculations for KK charge transfer is assessed for various asymmetries of the collision system. It is argued that the present expansion is convenient and fast converging over a broad range of collision energies, particularly for close collisions. In another application, K-shell excitation in Ne++O collisions is modelled. At low collision velocities, no deviations from the predictions of 2p pi -2p sigma molecular orbital studies are found even with extended basis sets.