Lyman line ratios in charge-exchange collisions of ${\mathrm{C}}^{6+}$ and ${\mathrm{O}}^{8+}$ ions with hydrogen and krypton atoms

Charge-exchange collisions of ${\mathrm{C}}^{6+}$ and ${\mathrm{O}}^{8+}$ ions with hydrogen and krypton atoms followed by radiative emissions are examined using the two-center basis generator method in the low- and intermediate-energy regimes. Capture cross sections are obtained within the independent-electron model and are used in a radiative cascade model to yield Lyman line-emission counts. The main focus of this analysis is on single-electron capture with the inclusion of autoionizing double capture in krypton collisions. Because hydrogen and krypton have the same first ionization potential, it is expected from the classical overbarrier model that the capture selectivity of these two atoms is the same, making krypton a good surrogate for hydrogen to study collision-induced radiative emissions in the laboratory. However, the present analysis shows that the subshell distributions with respect to the impact energy in krypton collisions can differ from hydrogen collisions and, hence, from predictions of the classical overbarrier model. Based on the comparison of present results with previous measurements, this difference in capture behavior of the two target atoms does not appear problematic for the Lyman line-emission results for ${\mathrm{C}}^{6+}$ collisions, but does appear to affect these results for ${\mathrm{O}}^{8+}$ collisions.

Figure 1

Capture cross sections plotted with respect to impact energy: (a) ${\mathrm{C}}^{6+}$-H collisions from present calculations and recommended SEC from Janev et al. [40], and (b) ${\mathrm{C}}^{6+}$-Kr collisions from present TC-BGM calculations.

Figure 2

$n$-state selective relative capture cross-section distributions at $E_{\text{P}}=1$, 8, and 25 keV/amu for (a) ${\mathrm{C}}^{6+}$-H collisions and (b) ${\mathrm{C}}^{6+}$-Kr collisions.

Figure 3

Lyman line-emission ratios of Ly-$\beta$/Ly-$\alpha$, Ly-$\gamma$/Ly-$\alpha$, Ly-$\delta$/Ly-$\alpha$, and Ly-$\epsilon$/Ly-$\alpha$. Calculated TC-BGM ratios from ${\mathrm{C}}^{6+}$-Kr (left column) and ${\mathrm{C}}^{6+}$-H (right column) collisions. Experimental ratios [17] in both columns correspond to ${\mathrm{C}}^{6+}$-Kr collisions only.

Figure 4

Capture cross sections with respect to impact energy: (a) ${\mathrm{O}}^{8+}$-H collisions from present calculations, HSCC results [43], and recommended SEC [40]; (b) ${\mathrm{O}}^{8+}$-Kr collisions from present TC-BGM calculations.

Figure 5

$n$-state selective relative capture cross-section distributions at $E_{\text{P}}=1$, 8, and 25 keV/amu for (a) ${\mathrm{O}}^{8+}$-H collisions and (b) ${\mathrm{O}}^{8+}$-Kr collisions.

Figure 6

Lyman line-emission ratios of Ly-$\beta$/Ly-$\alpha$, Ly-$\gamma$/Ly-$\alpha$, Ly-$\delta$/Ly-$\alpha$, and Ly-$\epsilon$/Ly-$\alpha$. Calculated TC-BGM ratios from ${\mathrm{O}}^{8+}$-Kr (left column) and ${\mathrm{O}}^{8+}$-H (right column) collisions. Experimental ratios [18] in both columns correspond to ${\mathrm{O}}^{8+}$-Kr collisions only.