Electron impact double ionization of multiply charged iron ions

Abstract

Using the crossed-beams technique, cross sections for electron impact double ionization of Feq+ ions in charge states q = 1 - 6 (except 2) are measured in the energy range from the respective ionization thresholds up to 1 keV, partly up to 5 keV. The data for Fe4+, Fe5+ and Fe6+ show significant contributions from inner-shell processes. Using a high-resolution energy-scan technique, we study narrow resonances in the cross sections for Fe4+ and Fe5+. Besides contributions from excitation-autoionization processes, a remarkable number of structures arising from resonant-excitation triple-autoionization processes are observed. The results are compared with the scaling laws of Fisher et al and the semiempirical formula published by Shevelko and Tawara, respectively.