A measurement of the cross section for electron impact ionization of Ar2+, Kr2+and Xe2+

The crossed electron-ion beams technique was used to measure absolute cross sections for single ionization of Ar 2+ , Kr 2+ and Xe 2+ ions at electron energies ranging from threshold to 2000 eV. The total error in the cross sections at a 90% confidence level is estimated to be +or-4.8, +or-4.9 and +or-7% or less for Ar 2+ , Kr 2+ and Xe 2+ respectively, at energies more than a few electron volts above threshold. In contrast to some previous measurements, the metastable contents of the ion beams were small even in the case of Xe 2+ . All measured cross section curves show significant contributions from excitation-autoionization and possibly direct ionization of inner-shell electrons. There is evidence for resonance-excitation-double-autoionization in the case of Xe 2+ . Comparisons are made with other available experimental and theoretical data.