Exchange effects in ionization of hydrogenic ions by electron impact

Abstract

The symmetric electron-exchange binary-encounter theory of Burgess and Vriens (1968, 1969) is extended to include an accurate account of the interference contributions. The direct, exchange, interference and interference-bound terms are all derived from the Mott scattering formula for identical electrons with isotropic spin orientations. Accurate values of the interferences contributions are presented and compared with simple analytic approximations. The present model is exact for the interaction of an intense mono-energetic electron beam with a low density isotropic gas of free mono-energetic electrons. The theory is applied to the process of ionization of highly ionized and excited hydrogenic ions by electron impact. The present model should be most reliable when the nuclear charge Ze and the initial principal quantum number n are both large. The model may be extended to non-hydrogenic target ions.