Experiments in Electron-Impact Excitation and Ionization of Positive Ions.
Abstract
Absolute electron-impact excitation and ionization cross sections have been measured for several ion species. The excitation work reported in this thesis was performed for the transitions in rm Ar^{7+ }(3sto 3p) and rm O^ {5+}(2sto 2p) using the merged-beams electron-energy-loss technique recently developed in this laboratory. Experimentally measured cross sections were in good agreement with theoretical calculations for both ions over the near-threshold energy range studied. Strong backscattering, where more than 90 percent of the incident electrons are scattered by more than 90 degrees in the center-of-mass frame, was also deduced for both ions. This effect was unexpected and had not previously been observed for any ion. The observation of backscattering is supported by both quantum mechanical and semi-classical calculations. The ionization experiments were performed using crossed beams of ions and electrons and detecting the product, once-more-charged, ions. The ten ion species rm Cl^+, S^+, In^+, Xe^+, Se^+, Te^+, Si^+, Si^{2+}, Si^{6+}, and Si^ {7+} were studied. Cross sections were generally found to be in agreement with the semi-empirical formula of Lotz and the configuration-averaged-distorted -wave calculations of Pindzola. The largest discrepancies between the measured cross sections and the calculated cross sections were caused either by indirect processes contributing to the ionization cross section or the overstatement of the calculated contributions to the cross section from d-shell electrons. Evidence for significant contributions to the cross sections from indirect ionization processes was observed in Si^+ and Si^{2+ }..
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1993
- Bibcode:
- 1993PhDT.......229B
- Keywords:
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- Physics: Atomic