Resonant and non-resonant modes of transfer and excitation processes in ion-atom collisions

Abstract

The simultaneous transfer and excitation (TE) process in ion-atom collisions has received a considerable interest over the past decade. The situation where a doubly excited (autoionising) state is formed on the projectile invokes, at least, a two-electron process at the lowest order of perturbation. In this case, two modes have been identified: the resonant mode (RTE), where the excitation of the projectile is mainly due to the dielectronic interaction between the projectile electron and the target electron which is captured, and the non-resonant mode (NTE), where projectile excitation comes from the interaction with the rest of the target. The advancement of theoretical investigations of RTE and NTE modes is examined. A process connected to the NTE mode is briefly reviewed: the uncorrelated transfer and excitation (UTE), where projectile excitation is made by a third target electron which is not captured. A noticeable part of the present paper is devoted to investigations of possible interferences between RTE and NTE modes. Despite the limited number of these studies, destructive interferences have been identified in a few cases.