Ionization of atoms by electron impact

Abstract

In Chapter I of this thesis a short review of the quanta! theory of ionizing collisions is presented, with particular regard to recent theoretical developments. A brief discussion is given of quantal and classical approximations and their predictions compared with experimental data, and a brief outline of some useful empirical formulae. The impulse approximation is derived in Chapter II and the evaluation of cross sections for the processes H (Is) + e →H(^+) + 2e and H (Is) + H(^+)→2H(^+) + e is described in detail. The results obtained for the above processes are presented . and are compared with the results obtained by other authors. In Chapter III the evaluation of cross sections for the processes He + e→He(^+) + 2e and Li(^+) + e→Li(^2+) + 2e in which both He and Li+ are initially in their ground states is described in detail. An open shell two-parameter wave function has been used for the ground state of the target. The cross sections obtained using both the length and velocity formulations of the Born approximation are in excellent agreement with experiment at energies higher than 25 times threshold and approach the Bethe limit (within 3%) at energies higher than 50 times threshold. The evaluation of cross sections with Hylleraas type correlated wave functions for the ground state of the target forms the subject of Chapter IV. Cross sections are calculated in the length formulation of the Born approximation, for the processes studied in Chapter III and the results obtained are presented and are compared with the length and velocity formulation results obtained in the latter Chapter.