Photoionisation of Ca+ ions in the valence-energy region 20–56 eV: experiment and theory

Abstract

Relative cross sections for the valence shell photoionisation (PI) of ground level and 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 meV, covering the energy range 20–56 eV. Details of the PI spectrum were investigated at energy resolutions reaching the level of meV. The photon energy scale was calibrated with an uncertainty of ±5 meV. By comparison with previous absolute measurements the present experimental high-resolution data were normalized 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% ± 4%. Large-scale R-matrix calculations using the Dirac Coulomb approximation and employing 594 levels in the close-coupling expansion were performed for the and levels. The experimental data are compared with the results of these calculations and previous theoretical and experimental studies.