Absolute cross section measurements for electron-impact single ionization of (q = 4 - 8) ions and for double ionization of and are reported. The animated crossed-beams method has been applied. The measurements cover the energy range from threshold to several keV. The and ion beams are found to contain an important population of ions formed in metastable states. For single ionization, results are in overall good agreement with direct ionization theoretical predictions, when available. Excitation - autoionization is observed in the ionization threshold region for and in the K - L transition energy region for and . Double ionization of and is found to be dominated by K-shell ionization followed by autoionization.

Absolute cross sections for electron impact ionization of multiply charged argon ions (Arq+) have been measured in an animated crossed electron–ion beam experiment. Results are reported for single ionization (SI) (q = 4–6, 8, 10 and 11) ions and for double ionization (DI) (q = 5–11). The measurements cover the energy range from threshold to about 6000 eV. The direct process is seen to dominate SI for q = 8, 10 and 11. For charge states 4–6, excitation–autoionization processes are seen to largely contribute to the ionization signal. In addition, metastable states are unambiguously identified for Ar5+ and Ar6 +. Ionization–autoionization (IA) from the L shell accounts predominantly for DI of Arq+ (q = 5, 6). For charge states 7–11 direct DI is found to decrease strongly with respect to IA from the K shell.