Theory of inelastic ion-atom scattering at low and intermediate energies

Abstract

We present ab initio calculations of inelastic energy loss and ionization phenomena associated with ${\mathrm{Ar}}^{+}$ -Ar collisions at small distances of closest approach and for laboratory collision energies ranging from several keV to several hundred keV. Outer-shell excitations are handled statistically; inner-shell excitations are calculated from the viewpoint of quasidiabatic molecular orbital promotion. Auger electron yield, average state of ionization, and average inelastic energy loss are calculated per collision as a function of distance of closest approach of the collision partners for several laboratory collision energies. Average charge-state probabilities per collision partner are calculated as a function of the average inelastic energy loss per atom. Our calculations agree with the available data. It is shown that the structure in the data is due to the underlying structure in the inner-shell independent-electron quasimolecular promotion probabilities. In particular, the fact that the dominant promotion mechanism involves rotational coupling means that all corresponding probabilities decrease dramatically for collisions involving laboratory scattering angles greater than 45\ifmmode^\circ\else\textdegree\fi{}. Thus, a sharp decrease in Auger electron yield, average ionization, and average inelastic energy loss is predicted for these supposedly more "violent" collisions.