A measurement of the cross section for electron impact ionization of Ar²⁺, Kr²⁺and Xe²⁺

Abstract

The crossed electron-ion beams technique was used to measure absolute cross sections for single ionization of Ar2+, Kr2+ and Xe2+ ions at electron energies ranging from threshold to 2000 eV. The total error in the cross sections at a 90% confidence level is estimated to be +or-4.8, +or-4.9 and +or-7% or less for Ar2+, Kr2+ and Xe2+ respectively, at energies more than a few electron volts above threshold. In contrast to some previous measurements, the metastable contents of the ion beams were small even in the case of Xe2+. All measured cross section curves show significant contributions from excitation-autoionization and possibly direct ionization of inner-shell electrons. There is evidence for resonance-excitation-double-autoionization in the case of Xe2+. Comparisons are made with other available experimental and theoretical data.

Electron-impact ionization of Ar2+

“…Furthermore, the cross-sections below the ionization threshold demonstrated the presence of metastable states. The later measurements by Man et al (1993) showed excellent agreement with data from Diserens et al (1988); the same apparatus was used in both experiments (Man et al 1993;Diserens et al 1988). The measure-ments of Mueller et al (1985) provided greater values for the cross-sections compared to the results of Younger (1981) and Man et al (1993) at the higher energies.…”

“…The later measurements by Man et al (1993) showed excellent agreement with data from Diserens et al (1988); the same apparatus was used in both experiments (Man et al 1993;Diserens et al 1988). The measure-ments of Mueller et al (1985) provided greater values for the cross-sections compared to the results of Younger (1981) and Man et al (1993) at the higher energies. The difference was attributed to the presence of the metastable fraction in the former case.…”

“…The difference was attributed to the presence of the metastable fraction in the former case. A comparison of the experimental data obtained by Man et al (1993) to the semi-empirical formulae of Lotz (1967) and Burgess & Chidichimo (1983) and parametrized distorted wave (DW) formula (Younger 1981) was provided. The Lotz formulae with one and three parameters were used in their study (Man et al 1993).…”

“…A comparison of the experimental data obtained by Man et al (1993) to the semi-empirical formulae of Lotz (1967) and Burgess & Chidichimo (1983) and parametrized distorted wave (DW) formula (Younger 1981) was provided. The Lotz formulae with one and three parameters were used in their study (Man et al 1993). All peaks in theoretical curves shift to the highenergy side compared to the peak from the measurements.…”

X-ray emission from thin plasmas

“…For Ar iii, we followed the discussion in Diserens et al (1988) and did not include the data of Müller et al (1980), Mueller et al (1985), and Danjo et al (1984),whose data are larger at high energies than the presently adopted data of Diserens et al (1988) and Man et al (1993). As explained by Diserens, the increased cross-sections may indicate the presence of metastable ions in the beam.…”