Electron-impact triple ionization of ${\mathrm{Se}}^{2+}$

It is shown that triple ionization (TI) of the ${\mathrm{Se}}^{2+}$ ion is mainly formed in two ways: (i) Auger cascade following single ionization of the $3p$ shell and (ii) direct double ionization (DDI) with subsequent autoionization. A good agreement with recent experimental measurements is obtained when one of electrons in the DDI process acquires all the excess energy. The study also reveals negligible contribution of the direct TI by electron impact to the process. Single-ionization cross sections of the excitation-autoionization process show large dependence on the levels of the ground configuration. The obtained results demonstrate that the ions in the parent beam mainly reside in the highest level of the ground configuration.

Figure 1

Energy levels of the lowest configurations of the ${\mathrm{Se}}^{2+},{\mathrm{Se}}^{3+},{\mathrm{Se}}^{4+},{\mathrm{Se}}^{5+}$, and ${\mathrm{Se}}^{6+}$ ions. Ionization thresholds are presented by horizontal lines with the corresponding values.

Figure 2

Contributions of the CI and EA processes to SI of ${\mathrm{Se}}^{2+}$ for different energy levels of the ground configuration.

Figure 3

Electron-impact SI of ${\mathrm{Se}}^{2+}$ for the $4p^2{}^1{S}_0$ level. Short-dashed line (red): CI of $4p$ shell; long-dashed line (blue): CI of $4p$ and $4s$ shells; solid line (green): CI with EA; empty circles: experiment [13]. Calculated contributions of the CI and EA processes are represented by the differently shaded (colored) areas.

Figure 4

Contributions of various EA channels to the total EA cross sections for the ground $4p^2{}^3{P}_0$ level. The strongest EA channels are represented by the differently shaded (colored) areas.

Figure 5

Contributions of various EA channels to the total EA cross sections for the $4p^2{}^1{S}_0$ level. The strongest EA channels are represented by the differently shaded (colored) areas.

Figure 6

Electron-impact DI of ${\mathrm{Se}}^{2+}$. Dotted line (red): DDI cross sections when one of the electrons takes all excess energy; dashed line (blue): indirect DI cross sections; solid line (green): total DI cross sections; empty circles: experiment [13].

Figure 7

Contribution of various pathways to the electron-impact TI of ${\mathrm{Se}}^{2+}$. Superscript 1: TI cross sections when one of the electrons takes all excess energy in the DDI process; superscript 2: TI cross sections when scattered and ejected electrons share the excess energy equally in the DDI process; empty circles: experiment [13]. See explanations in the text for the DDI-AI, DDI(II)-AI, DDI(IEI)-AI, and DDI(EII)-AI processes.

Figure 8

Electron-impact SI of $3p$ shell of ${\mathrm{Se}}^{2+}$ for energy levels of the ground configuration.