Electron impact ionization of argon ions (q = 4–11)

Absolute cross sections for electron impact ionization of multiply charged argon ions (Ar^q+) 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 Ar^{6 +}. Ionization–autoionization (IA) from the L shell accounts predominantly for DI of Ar^q+ (q = 5, 6). For charge states 7–11 direct DI is found to decrease strongly with respect to IA from the K shell.