Electron-impact ionization of neon ions (q=4-8)

Absolute cross section measurements for electron-impact single ionization of Ne-q+ (q = 4-8) ions and for double ionization of Ne5+ and Ne6+ are reported. The animated crossed-beams method has been applied. The measurements cover the energy range from threshold to several keV. The Ne4+ and Ne6+ 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 Ne4+ and in the K-L transition energy region for Ne6+ and Ne7+. Double ionization of Ne5+ and Ne6+ is found to be dominated by K-shell ionization followed by autoionization

Electron-impact single ionization of krypton ions (q=12-18)

Absolute cross sections for electron-impact single ionization of krypton ions Krq+ (q = 12-18) have been measured. The animated crossed-beam method has been applied. The measurements cover the energy range from threshold to about 5.5 keV. The presence of ions formed in metastable states is observed for Kr18+, Kr16+ and Kr14+. Inner-shell excitation from the 2s, 2p, 3s and 3p subshells followed by autoionization is seen to play a dominant role for this reaction over the whole energy range. The importance of these excitation-autoionization processes explains the large underestimation of cross sections from the available theoretical and semi-empirical estimations which include direct processes only

Electron impact double ionization of krypton ions (q=14-17)

Absolute cross sections for electron impact double ionization of krypton ions Krq+ (q = 14-17) have been measured from threshold to 5 keV. The animated crossed beam method has been employed. Direct double ionization is seen to reduce strongly along the isonuclear sequence. Ionization-autoionization from the inner L-shell is seen to be the dominant process. It is roughly approximated by the semi-empirical Lotz formula assuming total autoionization of the ionic intermediate states. Resonant capture and excitation processes implying the L-shell are also obtained for charge states 14-16

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

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

Electron impact single and double ionization of Niq+ ions (q=10, 11, 13 and 15)

Absolute cross sections for electron impact single and double ionization of Niq+ ions (q = 10, 11, 13 and 15) have been measured for energies from threshold to about 5 keV, Experimental results for Ni11+, Ni13+ and Ni15+ are in good agreement with the calculations of Pindzola et al, obtained in the average configuration distorted-wave approximation for the 3s(2)3p(n)(n = 5, 3 and 1) ground configurations, respectively. The Ni10+ results show a significant ionization signal below the ground state [Ne]3s(2)3p(6) threshold due to ions formed in the metastable configuration [Ne]3s(2)3p(5)3d in the parent ion beam. The theoretical calculations including direct ionization and excitation-autoionization from both the ground and the excited configurations underestimated the cross section. The difference is probably due solely to the 3s --> nl excitations. In this isonuclear sequence, the whole results shows that ions with an odd number of electrons behave differently from ions with an even number. Our measurements show clearly that double ionization is dominated by L-shell ionization followed by autoionization