THE THEORY OF FAST-ION ATOM COLLISIONS

This chapter describes the theory of fast ion-atom collisions that are based upon high-energy, Born-type expansions, or their distorted-wave generalization. The chapter focuses on Born theories of processes involving only one active electron. The collisions of multi-electron species exhibit all of the features of the one electron prototype, but also include new types of motion arising from the electron–electron interaction. Effects because of this electron–electron interaction are even dominant in some ranges of ion charge, collision velocity, or secondary-electron energy. Collisions involving only one or two active electrons have been considered to isolate the separate effects of electron–nucleus and electron–electron interactions as clearly as possible. For one-electron collisions, the first Born approximation has been analyzed in terms of the qualitative features of differential excitation and ionization cross sections that it predicts. For ionization, the first Born approximation, either in direct or capture form, is fundamentally inadequate. The influence of higher-order processes, in particular double-binary collisions of the Thomas type, is emphasized in the chapter. © 1991 Academic Press Inc.