Electron ionisation cross sections of excited atoms and ions

A general approach for calculating cross sections for electron impact ionisation of atoms and ions with a single valence electron in either the ground or an excited state is presented. The differential energy exchange cross sections are based on the semiclassical treatments of Burgess (1963) and Vriens (1966). The model takes into account direct as well as electron exchange collisions, and also includes interference effects. The motion of an atomic electron in the nl state is represented by the semiclassical energy distribution function. The criterion of validity of the method is given, from this it follows that the theory is applicable to the calculation of the electron impact ionisation cross sections for H I, He II, Li III, C IV, N V, O VI, Ne VIII and Ne X. The present results are compared both with experimental data and with other theoretical calculations.