Photoionization and electron-impact ionization of ${\mathrm{Kr}}^{5+}$

Absolute photoionization cross sections for ${\mathrm{Kr}}^{5+}$ were measured in the photon energy range $74–175\mathrm{eV}$ using synchrotron radiation. For comparison, a detailed energy scan of the electron-impact ionization cross section was made in the same energy range and normalized to previously published absolute measurements. The Flexible Atomic Code and Cowan atomic structure code were used to calculate energy levels, excitation energies, and oscillator strengths for $3d\to np$, $3\mathrm{d}\to nf$, and $4s\to np$ autoionizing transitions from the ground and metastable states. Within the experimental uncertainty, oscillator strengths determined from the photoionization measurements are in agreement with both calculations. Excitation-autoionization and resonant excitation-double-autoionization features are evident in the electron-impact ionization cross section.

Figure 1

Absolute photoionization cross section of ${\mathrm{Kr}}^{5+}$ measured with a photon energy resolution of $100\mathrm{meV}$, showing $4s\to np$ transitions. The vertical bars indicate the ionization thresholds for the ${}^{2}P^0{}_{3∕2}$ metastable state and the ${}^{2}P^0{}_{1∕2}$ ground state.

Figure 2

Corrected near-threshold photoionization cross-section measurement for ${\mathrm{Kr}}^{5+}$ (top panel) shows resonances due to $4s\to np$ excitation-autoionization. The vertical bars indicate the ionization thresholds for the ${}^{2}P^0{}_{3∕2}$ metastable state and the ${}^{2}P^0{}_{1∕2}$ ground state. The middle panel shows a measurement made at twice the photon energy, which was scaled to subtract second-order contributions from the raw measurement (bottom panel). Note the large difference in cross-section scales in these two energy ranges.

Figure 3

Absolute photoionization cross section for the $3d\to 4p$ transition in ${\mathrm{Kr}}^{5+}$ measured with an energy resolution of $50\mathrm{meV}$. The large open circles with error bars show absolute cross-section measurements made at the same energy resolution, with their estimated uncertainties.

Figure 4

Comparison of absolute cross-section measurements for photoionization of ${\mathrm{Kr}}^{5+}$ with the theoretical spectra, shifted by $+0.90\mathrm{eV}$ for Cowan code result and by $+1.67\mathrm{eV}$ for FAC code result.

Figure 5

Photoionization cross section in the energy range of $3d\to np$ $(n>4)$ and $3d\to nf$ $(n>3)$ transitions in ${\mathrm{Kr}}^{5+}$ measured with an energy resolution of $100\mathrm{meV}$. The large open circles with error bars represent the absolute cross-section measurements and their uncertainties.

Figure 6

Energy-scan measurement of the cross section for electron-impact ionization of ${\mathrm{Kr}}^{5+}$ (filled circles) normalized to the absolute measurement of Bannister et al. [10] (open circles). The experimental energy resolution is approximately $1\mathrm{eV}$. The solid curve is the Lotz formula prediction for the direct ionization cross section. The dot-dashed and dotted curves are direct and total ionization cross sections calculated by Gorczyca et al. [14], respectively.

Figure 7

Comparison of electron-impact ionization cross-section measurements for ${\mathrm{Kr}}^{5+}$ (a) with photoionization cross-section measurements (b) in the energy range $73.8\text{to}95.5\mathrm{eV}$. The photoionization cross section in the energy region from $74\text{to}87.2\mathrm{eV}$ has been multiplied by a factor of 20. In (a), the curve is the theoretical ionization cross-section calculation from Ref. 14.

Figure 8

Comparison of electron-impact ionization cross-section measurement for ${\mathrm{Kr}}^{5+}$ (a) with the photoionization cross section measurement, (b) in the energy range $95.5\text{to}173.3\mathrm{eV}$. In (a), the curve is the theoretical ionization cross section from Ref. 14.