Nonperturbative effects in inner-shell ionization

A theoretical investigation of ion-induced inner-shell ionization is described, in which some physical effects that are nonperturbative in nature are included within the formalism of perturbation theory. In particular, the effects of the dynamical response of the outer electrons under the influence of the incident projectile are considered. Special emphasis is given to the use of nonorthogonal basis states in perturbation theory. Calculations for the proton- and ³He ion-induced total cross sections for K-shell ionization in titanium and copper are performed and compared with experimental data. Significant discrepancies between the theoretical results and the measured values are found to exist. Possible improvements to the theory are discussed.