Valence-shell photoionization of Ag-like Xe$^{7+}$ ions : experiment and theory

TL;DR

This study combines high-resolution experiments and advanced theoretical calculations to analyze the photoionization of Xe$^{7+}$ ions, revealing detailed resonance features and the influence of metastable states.

Contribution

It provides the first detailed experimental and theoretical investigation of valence-shell photoionization of Xe$^{7+}$ ions, including resonance characterization and metastable state analysis.

Findings

Resonance at 122.139 eV with a peak cross-section of 1.2 Gb

Metastable ions constitute only a few percent of the beam

Good agreement between experimental and theoretical resonance widths

Abstract

We report on experimental and theoretical results for the photoionization of Ag-like xenon ions, Xe$^{7+}$, in the photon energy range 95 to 145~eV. The measurements were carried out at the Advanced Light Source at an energy resolution of $\Delta$E = 65 meV with additional measurements made at $\Delta$E = 28 meV and 39 meV. Small resonance features below the ground-state ionization threshold, at about 106 eV, are due to the presence of metastable Xe$^{7+} (4d^{10} 4f~^2{\rm F}^{\circ}_{5/2,7/2})$ ions in the ion beam. On the basis of the accompanying theoretical calculations using the Dirac Atomic R-matrix Codes (DARC), an admixture of only a few percent of metastable ions in the parent ion beam is inferred, with almost 100\% of the parent ions in the $(4d^{10}5s ~^2{\rm S_{1/2}})$ ground level. The cross-section is dominated by a very strong resonance associated with $4d \rightarrow 5f$ excitation and subsequent autoionization. This prominent feature in the measured spectrum is the $4d^95s5f ~^2{\rm P}^{\circ}$ resonance located at (122.139 $\pm$ 0.01)~eV. An absolute peak cross-section of 1.2 Gigabarns was measured at 38 meV energy resolution. The experimental natural width $\Gamma$ = 76 $\pm$ 3 meV of this resonance compares well with the theoretical estimate of 88 meV obtained from the DARC calculation with 249 target states. Given the complexity of the system, overall satisfactory agreement between theory and experiment is obtained for the photon energy region investigated.