Overview of the inner-subshell excitations n0l0 → nl included in the present calculations
Table 2. Overview of the inner-subshell excitations n0l0 → nl included in the present calculations. All subshells with quantum numbers nl, where n ≤ nmax and l ≤ lmax, providing at least one vacancy to which the n0l0 electron can be excited were considered. The orbital quantum numbers l0, lmax = 0, 1, 2, ... are expressed by their spectroscopic symbols s, p, d,..., respectively. For ions in the ground-state configuration, m is the number of electrons in the 4d subshell. It is equal to 10 for Sn4 + and 1 for Sn13 +. As far as long-lived excited ions are concerned, we only had to consider 4d-subshell-excited configurations for the charge states up to q = 12. In the configurations of interest, the 4d subshell is initially populated with m − 1 electrons and the excited electron is initially in subshell n1l1. The subshells n1l1 taken into account in the present analysis are listed in table 1. For the case of Sn13 +, the only excited configuration of relevance to the present measurements is the 4p54d2 configuration.
Electron-impact single-ionization cross sections of Snq + ions in charge states q = 4–13 with 4d[10 − (q − 4)] outer-shell configurations have been studied in the energy range from the corresponding thresholds up to 1000 eV. Absolute cross sections and fine-step energy-scan data have been measured employing the crossed-beams technique. Contributions of different ionization mechanisms have been analysed by comparing the experimental data with calculations employing the configuration-averaged distorted wave approximation. Ionization plasma rate coefficients inferred from the experimental data are also presented.