Long-range configuration interaction of ionic and covalent states

Abstract

A simple approximation based on asymptotic wavefunctions is used to calculate the splitting ΔV(R c) between the pair of adiabatic potential energy curves that arise from pseudo-crossing of ionic and covalent states of a diatomic molecule at a large internuclear distance R c. In this approximation, ΔV(R c) is an exponentially decreasing function of R c and otherwise depends only on the ionization potential of the donor atom and the electron affinity and atomic radius of the acceptor atom. Results obtained for the H*(2s, 2p) + H(1s)→H+ + H- interaction are found to agree well with the ΔV(R c) derived from spectroscopic data for the B 1Σu + excited state of H2 and a variational calculation of Kolos and Wolniewicz. Results for the alkali hydride interactions, M + H→M+ + H-, agree well with estimates of ΔV(R c) derived from spectroscopic data for the A 1Σ+ excited states and a variational calculation of Brown and Shull. Results for the alkali halides agree well with photo-dissociation spectra and with collisional ionization cross sections. The method is also applied in a preliminary way to estimate the entrance-channel interaction involved in the ‘electron-jump’ model for reactions of alkali atoms with halogen molecules.