2017MNRAS.464.1990M

Absolute photoionization cross-sections for the Cl⁺ ion in its ground and the metastable states, 3s²3p^{4 3}P_2,1,0 and 3s²3p^{4 1}D₂,¹S₀, were measured recently at the Advanced Light Source at Lawrence Berkeley National Laboratory using the merged beams photon-ion technique at a photon energy resolution of 15 meV in the energy range 19-28 eV. These measurements are compared with large-scale Dirac-Coulomb R-matrix calculations in the same energy range. Photoionization of this sulphur-like chlorine ion is characterized by multiple Rydberg series of auto-ionizing resonances superimposed on a direct photoionization continuum. A wealth of resonance features observed in the experimental spectra is spectroscopically assigned, and their resonance parameters are tabulated and compared with the recent measurements. Metastable fractions in the parent ion beam are determined from this study. Theoretical resonance energies and quantum defects of the prominent Rydberg series 3s²3p³nd, identified in the spectra as 3p - nd transitions, are compared with the available measurements made on this element. Weaker Rydberg series 3s²3p³ns, identified as 3p - ns transitions and window resonances 3s3p⁴(⁴P)np features, due to 3s - np transitions, are also found in the spectra.