Multiple ionization of atoms and molecules in collisions with fast ions: Ion-atom collisions

A theoretical description of multiple ionization of atoms and molecules produced by an energetic ion impact is developed. It is based on the statistical energy-deposition model of Russek and Meli [Physica (Amsterdam) 46, 222 (1970)]. In this model the probability for the formation of a collision-induced final state with n electrons in the continuum is obtained, assuming that its value is proportional to the volume of phase space available at that ionization state for a certain value of statistically distributed deposited energy. The model is extended in two respects. First, the deposited energy for each trajectory is considered as a fluctuating quantity with a certain distribution and the ionization probability is calculated as a weighted average over the distribution. Second, the mean value and straggling of the deposited energy are calculated within the Lindhard-Scharff local plasma approximation [Mat. Fys. Medd. K. Dan. Vidensk. Selsk. 27, No. 15 (1953)]. Sample calculations for collisions of protons and F⁴⁺ ions with neon atoms at an energy of 1 Mev/amu are presented and compared with calculations within the independent-electron approximation and with experimental data.