Electron impact multiple ionisation of multiply charged krypton ions

Abstract

Absolute cross sections for double ionisation of Krq+ ions (q=1,. . ., 4) and for triple ionisation of Krq+ ions (q=1, 2) in single collisions with incident electrons have been measured by using a dynamic crossed-beams technique. Electron energies ranged from below threshold up to 1000 eV for Kr2+ and up to 700 eV for the other charge states. With increasing q the cross sections for double ionisation are determined by an increasing relative contribution of single ionisation of the 3d subshell and subsequent autoionisation. The authors' data for double ionisation of Kt4+ are in good agreement with measurements of Pindzola et al. (1984). For electron energies about 300 eV triple ionisation appears to be dominated by ionisation-double-autoionisation contributions from the 3p and 3s subshells. Between threshold and about 200 eV, however, the observed cross sections sigma q,q+3 seem to be due to direct multiple-electron processes.