Ionization and charge transfer in He2+-rare-gas collisions. II.

Abstract

New measurements of absolute cross sections for multiple ionization of helium, neon, argon, and krypton by 50--500-keV/amu ${\mathrm{He}}^{2+}$ impact are presented. By measuring projectile-ion--target-ion coincidences, these cross sections are obtained for the direct ionization as well as the single- and double-electron-capture channels. The present data are combined with previous measurements by the author that covered the energy range between 5 and 67 keV/amu in order to provide a broader description of ${\mathrm{He}}^{2+}$ impact ionization of atomic targets. The earlier measurements were found to require reevaluation in order to correct ion detection efficiencies used in that study. An analysis of the direct-multiple-ionization cross sections demonstrates that a simple impact-parameter, independent-electron model can be used to describe these cross sections over a broad range of low to intermediate impact energies. In particular, this analysis, when applied to fully stripped ion (1\ensuremath{\le}Z\ensuremath{\le}8) impact on helium, yields a single universal curve in the velocity range investigated here.