Electron-impact single ionisation of W¹⁴⁺ ions: subconfiguration-average and level-to-level distorted wave calculations

Abstract

The cross section for electron-impact single ionisation of ions has been calculated by using two different approaches, i.e. the subconfiguration averaged distorted-wave (SCADW) method and the more involved level-to-level distorted-wave (LLDW) method. Both methods are found to yield very similar results except for the excitation-autoionisation (EA) channels that straddles the ionisation threshold. Accordingly, a hybrid theoretical cross section where the EA SCADW cross section is replaced by its LLDW counterpart is in good agreement with the experimental result from an electron-ion crossed-beams experiment. This is in contrast to pure SCADW calculations for and neighbouring charge states which exhibit significant deviations from the experimental near-threshold cross sections of Schury et al (2020 J. Phys. B: At. Mol. Opt. Phys. 53 015201).

Electron-impact ionization of Ar2+

“…Therefore, the theoretical value is lower than the NIST value by ∼1.6 eV (4%). Similar tendencies for the DFS ionization thresholds compared to the NIST data were obtained for other ions (Kwon & Savin 2012;Jonauskas et al 2015;Kynienė et al 2015;Jonauskas 2018;Konceviciūtė et al 2018;Jonauskas et al 2019;Jin et al 2020).…”

“…The input from the excitations to the shells with 25 < n 40 is lower than 1%. Studies of ionization for the tungsten ions revealed that the excitations to the high-nl shells play an important role in the EA process (Zhang & Kwon 2014;Jonauskas et al 2015;Kynienė et al 2015;Kynienė et al 2016;Jin et al 2020). On the other hand, all these ions have a ground configuration with an open 4 f subshell.…”

Electron-impact single ionisation of W q+ions: experiment and theory for 11 ≤ q ≤ 18

“…Comparisons with more elaborate LLDW calculations [42] suggest that the SCADW calculations underestimate the respective EA cross section by about 0.6×10 −18 cm 2 for energies close to the excitation threshold. Likewise, a Table 1.…”

Hybrid subconfiguration-average and level-to-level distorted-wave treatment of electron-impact single ionisation of W$^{15+}$ and W$^{16+}$

“…Our theoretical approach, which is based on SCADW and LLDW methods as implemented in the Flexible Atomic Code (FAC) [17], has already been described extensively in our previous publication on EISI of W 14+ [16].…”