X-ray emission produced in charge-exchange collisions between highly charged ions and argon: Role of the multiple electron capture

In this work we use the classical trajectory Monte Carlo method within an eight-electron scheme to theoretically study photonic spectra that follow charge-exchange processes between highly charged ions of charge states 10+, 17+, 18+, and 36+ with neutral argon. The energy range considered is 18 eV/amu to 4 keV/amu, covering typical electron beam ion traps and solar wind energies. The role played by multiple electron capture processes for the different collision systems under consideration is explicitly analyzed and its contribution separated as arising from radiative decay and autoionizing multiple capture. For the present collision systems we find that multiple electron capture is responsible for 50%–60% of the resulting x-ray spectra. The present results are of direct relevance to the astrophysical program.

Figure 1

CTMC line emission cross sections for 4 keV/amu $\mathrm{N}{\mathrm{e}}^{10+}+\mathrm{Ar}$ collisions. Present results are compared to the NIST experimental data of Tawara et al. [22]. The partial contributions of true single capture SEC, autoioinizing multiple electron capture, and radiative decay channels are explicitly shown.

Figure 2

Same as Fig. 1 but for $\mathrm{A}{\mathrm{r}}^{18+}+\mathrm{Ar}$ collisions.

Figure 3

Same as Fig. 1 but for $\mathrm{K}{\mathrm{r}}^{36+}+\mathrm{Ar}$.

Figure 4

CTMC line emission cross sections for 218 eV/amu $\mathrm{A}{\mathrm{r}}^{18+}+\mathrm{Ar}$ collisions. Present results are compared to the Berlin-EBIT experimental data of Allen et al. [21]. The partial contributions of the SEC, autoionizing multiple electron capture, and radiative decay channels are explicitly shown.

Figure 5

Same as Fig. 4 but for 18 eV/amu $\mathrm{A}{\mathrm{r}}^{18+}+\mathrm{Ar}$.

Figure 6

Hardness ratio as a function of impact energy for $\mathrm{A}{\mathrm{r}}^{18+}+\mathrm{Ar}$ collisions. Previous results obtained with a CTMC code that included three electrons [16] are shown for comparison.

Figure 7

CTMC line emission cross sections for the $1snp\to 1s^2$ transitions following 7 keV/amu $\mathrm{A}{\mathrm{r}}^{17+}+\mathrm{Ar}$ charge-exchange collisions. The experimental data are those of Trassinelli et al. [27].