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.
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.
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.
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