Photoionisation of Ca$^{+}$ ions in the valence-energy region 20$\sim$eV~--~56$\sim$eV : experiment and theory

TL;DR

This study combines high-resolution experimental measurements and advanced theoretical calculations to analyze the photoionisation cross sections of Ca$^{+}$ ions in the 20-56 eV energy range, providing detailed insights into their valence-energy ionisation processes.

Contribution

It presents the first high-resolution measurements of Ca$^{+}$ photoionisation cross sections and compares them with large-scale Dirac R-matrix calculations, improving understanding of ionisation dynamics.

Findings

Experimental cross sections calibrated with high precision.

Metastable fraction in the ion beam determined to be 18±4%.

Good agreement between experiment and theory.

Abstract

Relative cross sections for the valence shell photoionisation (PI) of $\rm ^2S$ ground level and $\rm ^2D$ metastable Ca$^{+}$ ions were measured with high energy resolution by using the ion-photon merged-beams technique at the Advanced Light Source. Overview measurements were performed with a full width at half maximum bandpass of $\Delta E =17$~meV, covering the energy range 20~eV -- 56~eV. Details of the PI spectrum were investigated at energy resolutions reaching the level of $\Delta E=3.3$~meV. The photon energy scale was calibrated with an uncertainty of $\pm5$~meV. By comparison with previous absolute measurements %by Kjeldsen et al in the energy range 28~eV -- 30.5~eV and by Lyon et al in the energy range 28~eV -- 43~eV the present experimental high-resolution data were normalised to an absolute cross-section scale and the fraction of metastable Ca$^{+}$ ions that were present in the parent ion beam was determined to be 18$\pm$4\%. Large-scale R-matrix calculations using the Dirac Coulomb approximation and employing 594 levels in the close-coupling expansion were performed for the Ca$^{+}(3s^23p^64s~^2\textrm{S}_{1/2})$ and Ca$^{+}(3s^2 3p^6 3d~^2\textrm{D}_{3/2,5/2})$ levels. The experimental data are compared with the results of these calculations and previous theoretical and experimental studies.