Electron-impact double ionization of rare-gas ions

Cross sections for the removal of two electrons from rare-gas ions by single collisions with incident electrons have been both measured using crossed beams of ions and electrons, and calculated using Hartree-Fock distorted-wave theory. For initial ions Ar4+, Kr4+, and Xe4+ the measured peak cross sections are 1.4 x 10-18, 6.5 x 10-18, and 9.0 x 10-18 cm2, respectively. These measurements confirm and extend the measurements of Mueller and Frodl and of Achenbach et al. Calculations were performed for the charge-state-4+ ions and for Xe+, Xe2+, and Xe3+. Comparison of experiment and theory indicates that the double ionization of rare-gas ions is dominated by the indirect mechanism of inner-shell single ionization followed by autoionization. The distorted-wave calculations for the 4d ionization cross section of Xe/sup q/+ (q = 1 to 4) ions are strongly influenced by term dependence in the ejected-electron continuum, and by ground-state correlations