Photoionization and electron-impact ionization of ${\mathrm{Xe}}^{3+}$

Photoionization and electron-impact ionization of ${\mathrm{Xe}}^{3+}$ ions in the region of $4d$ inner-shell excitation-autoionization have been studied using interacting-beam spectroscopic techniques. Absolute cross sections for photoionization of ${\mathrm{Xe}}^{3+}$ have been obtained and the electron-impact spectrum has been normalized to previously published absolute data. The ${\mathrm{Xe}}^{3+}$ spectra show large contributions from $4d\to nf$ excitation-autoionization processes compared to the lower charge states of Xe due to the significant collapse of the $nf$ wave functions into the ion core as the initial charge state of the ion is increased. In addition, a tentative value for the ionization potential of ${\mathrm{Xe}}^{3+}$ of $42.2\pm 0.2\mathrm{eV}$ was obtained.

Figure 1

Relative photoion yield of ${\mathrm{Xe}}^{4+}$ in the near-threshold region in photoionization of ${\mathrm{Xe}}^{3+}$. Contamination from second-order lines for the $4d\to 4f$ transition band (centered near 87.0 eV in first order) has been subtracted (see text). The vertical dashed line at 42.39 eV marks a prominent level shift in the spectrum. The dashed line at 37.97 eV would be the onset of ionization of the ${}^{2}P_{3∕2}$ metastable state if 42.39 eV were the ground-state ionization potential. A small feature at an energy of 37.8 eV leads to the conclusion that the ground-state ionization potential is likely actually near 42.2 eV. Inset: spectrum prior to subtraction of higher-order contamination. The upper curve shows the original spectrum and the lower curve shows the second-order feature that was subtracted to obtain the final spectrum.

Figure 2

Single-photoionization cross sections for the $4d\to 5p$ transitions in ${\mathrm{Xe}}^{3+}$ measured with an energy resolution of 20 meV. The open diamonds with error bars show the uncertainty in the absolute cross section measurements. The statistical (counting) uncertainty is as low as 0.9%.

Figure 3

Single-photoionization cross sections for the $4d\to nf$ transitions in ${\mathrm{Xe}}^{3+}$ measured with an energy resolution of 51 meV. The diamonds with associated error bars show individual absolute cross-section measurements that were used to normalize the spectrum. The statistical (counting) uncertainty is as low as 1.1%.

Figure 4

Double-photoionization cross sections for the $4d\to nf,ϵf$ transitions in ${\mathrm{Xe}}^{3+}$. The data below 104 eV show discrete structure due to $4d\to nf$ excitation-autoionization. The data above 104 eV show the discrete $4d\to ϵf$ transitions that form the “giant” resonance. The diamonds with associated error bars show individual absolute cross-section measurements that were used to normalize the spectrum. Typical statistical (counting) uncertainties are approximately 7%.

Figure 5

Electron-impact single-ionization cross sections for the $4d\to nf,ϵf$ transitions in ${\mathrm{Xe}}^{3+}$ measured with an energy resolution of 0.75 eV.