Electron-impact double ionization of rare-gas ions

Abstract

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 ${\mathrm{Ar}}^{4+}$, ${\mathrm{Kr}}^{4+}$, and ${\mathrm{Xe}}^{4+}$ the measured peak cross sections are 1.4 × ${10}^{-18\mathrm{}}$, 6.5 × ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$, respectively. These measurements confirm and extend the measurements of Müller and Frodl and of Achenbach et al. Calculations were performed for the charge-state-4 + ions and for ${\mathrm{Xe}}^{+}$, ${\mathrm{Xe}}^{2+}$, and ${\mathrm{Xe}}^{3+}$. 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 ${\mathrm{Xe}}^{q+} (q=1\mathrm{} \mathrm{to} 4)$ ions are strongly influenced by term dependence in the ejected-electron continuum, and by ground-state correlations.