Probing the nonlocal approximation to resonant collisions of electrons with diatomic molecules

Abstract

A numerically solvable two-dimensional model introduced by the authors [Phys. Rev. A 73, 032721 (2006)] is used to investigate the validity of the nonlocal approximation to the dynamics of resonant collisions of electrons with diatomic molecules. The nonlocal approximation to this model is derived in detail, all underlying assumptions are specified, and explicit expressions for the resonant and nonresonant (background) $T$ matrix for the studied processes are given. Different choices of the so-called discrete state, which fully determines the nonlocal approximation, are discussed, and it is shown that a physical choice of this state can in general give poorer results than other choices that minimize the nonadiabatic effects and/or the background terms of the $T$ matrix. Background contributions to the $T$ matrix, which are usually not considered in the resonant theory of electron-molecule collisions, can contribute significantly not only to elastic but also to vibrational excitation cross sections. Dissociative attachment cross sections, however, are found to be properly described in the nonlocal model with any choice of discrete state that minimizes the importance of nonadiabatic effects and goes to the proper limit at large internuclear separation.