Valence-shell photoionization of chlorine-like Ar$^{+}$ ions

TL;DR

This study measures and analyzes the photoionization cross sections of Ar$^{+}$ ions, revealing complex resonance structures and interference effects, with results supported by theoretical calculations.

Contribution

It provides detailed experimental data and spectral assignments for Ar$^{+}$ photoionization, enhancing understanding of autoionizing resonances in chlorine-like ions.

Findings

Identification of multiple Rydberg series of autoionizing resonances

Observation of interference between indirect and direct photoionization

Theoretical calculations agree with experimental resonance energies

Abstract

Absolute cross-section measurements for valence-shell photoionization of Ar$^{+}$ ions are reported for photon energies ranging from 27.4 eV to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the $^2P^o_{3/2}$ ground state and the $^2P^o_{1/2}$ metastable state of Ar$^{+}$. Photoionization of this C$\ell$-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Observed resonance lineshapes indicate interference between indirect and direct photoionization channels. Resonance features are spectroscopically assigned and their energies and quantum defects are tabulated. The measurements are satisfactorily reproduced by theoretical calculations based on an intermediate coupling semi-relativistic Breit-Pauli approximation.