Coupling of discrete and continuum electronic states in atom-atom collisions: A coupled-channels investigation of Penning ionization inHe*(1s2s, S3)+ Ar

Transitions among discrete and continuum electronic states of diatomics, induced by atom-atom collisions and leading to ionization, are described by rigorously making the continuous electron energies $\epsilon$ discrete. An expansion in functions of $\epsilon$ leads to a set of coupled-channel scattering equations which may be solved to obtain differential and integral cross sections per unit of electron energies. This procedure is applied to Penning ionization in ${\mathrm{He}}^{*}(1s2s, {}_{}{}^3{}_{}{}^{}S)$ + Ar collisions by choosing a suitable expansion basis and numerically integrating a selected set of coupled equations. Results confirm the Franck-Condon nature of electron emission used in previous theoretical analyses. They were obtained with a parametrized exponential coupling potential between the states of HeAr* and He${\mathrm{Ar}}^{+}$+$e^{-}$. The calculations include total integral cross sections per unit electron energies and the contribution of individual partial waves at a given final energy. These cross sections show prominent features that may be related to the potential of the product heavy particles.