Electron-impact double ionization of tungsten atoms and ions at low ionization stages
The double ionization of neutral tungsten atoms and W2+, W4+, and W6+ ions by electron impact is investigated. The calculations are performed taking into account the Auger decay of single ionization states with inner vacancies in the 4d, 4f, 5s, 5p, and 5d shells as well as the direct double ionization using sudden perturbation model. The direct single ionization cross-section is obtained in relativistic distorted wave or binary-encounter-dipole approximations; the contribution from the indirect ionization by excitation-autoionization process is included too. It is shown that both processes – Auger decay of inner vacancy states and direct double ionization – play an important role in the double ionization process. The calculated cross-sections are compared with the experimental data.
Keywords: tungsten, electron-impact double ionization, Auger transitions, sudden perturbation
PACS: 34.50.Fa, 52.20.Fs, 31.15.A-