Homonuclear ion-atom collisions: Application to Li+−Li

Abstract

We present a theoretical framework for homonuclear, ground-state ion-atom collisions wherein the indistinguishability of direct elastic and resonant charge exchange (RCE) scattering channels is discussed. The discussion in terms of the total cross section(σtot) is motivated and derived. The standard cross-section expressions for direct elastic(˜σel) and RCE (˜σce) channels are obtained as high-energy approximations to σtot. We show that the total cross section resolves the inconsistency, at low energies, between the diffusion cross section (σD) and the high-energy approximation to the total cross section (˜σtot). The validity of the equivalence relation between the σD and 2טσce is also discussed. The differences which result in cross sections which are frequently used in the description of ion-atom collision is illustrated with specific calculations for an Li+−Li system. The use of σtot is advocated as a correct and consistent way to represent cross sections.