Quasi-molecular binding corrections to the two-state atomic expansion method for electron capture at low energies

Abstract

The two-centre, two-state atomic expansion method previously developed for calculating electron capture cross sections for ion-atom collisions at intermediate energies is generalised to the lower energy region. By replacing the asymptotic energy defect term between initial and final states of the atomic expansion theory by the difference of the corresponding quasi-molecular energies, the effect of transient molecule formation during the collision is partially accounted for. The increased quasi-molecular binding at small internuclear separation has the effect of reducing electron capture cross sections at lower incident energies; the cross sections thus calculated show improved agreement with experimental data.