Production and decay of sulfur excited species in an electron-cyclotron-resonance ion-source plasma

The most important processes for the creation of ${\text{S}}^{12+}$ to ${\text{S}}^{14+}$ ions excited states from the ground configurations of ${\text{S}}^{9+}$ to ${\text{S}}^{14+}$ ions in an electron cyclotron resonance ion source, leading to the emission of $K$ x-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double-$KL$ and triple-$KLL$ ionizations, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multiconfiguration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical $K\alpha$ x-ray spectrum is obtained, which is compared to recent experimental data.

Figure 1

Theoretical spectra for $K$ excitation and single $K$ ionization processes obtained with intrashell (- - -) and outer-shell correlations $\left(\text{−}\cdot \text{−}\right)$ plotted against experimental data $(●)$. The peak 1 refers to the M1 $1s2s{{}^{3}S}_1\to 1s^2$ line, the peaks 2 and 3 have contributions from the $1s2s2p{{}^{2}P}_{1/2,3/2}\to 1s^{2}2s$, and the $1s2p{{}^{3}P}_1\to 1s^2$ lines, and the peak 4 refers to the $1s2s2p^2{{}^{3}S}_1\to 1s^{2}2s2p{{}^{3}P}_{0,1,2}$ lines.

Figure 2

(Color online) Excitation, ionization, and decay processes considered in this work: $K$ excitation (- - -), single-$K$ ionization $\left(–\cdot –\right)$, double-$KL$ ionization $\left(–\cdot \cdot –\right)$, triple-$KLL$ ionization $\left(–\cdots –\right)$, radiative decay (—), and radiationless decay $(\cdots )$.

Figure 3

Theoretical spectra obtained with single-ionization $\left(\text{−}\cdot \text{−}\right)$ and multiple-ionization (—) processes plotted against experimental data $(●)$ in log scale (a) and linear scale (b). For the legend of the peaks, see caption in Fig. 1.