Valence and L-shell photoionization of Cl-like Argon using R-matrix techniques

Abstract: Photoionization cross sections are obtained using the relativistic Dirac Atomic R-matrix Codes (DARC) for all valence and L-shell energy ranges between 27-270eV. A total of 557 levels arising from the dominant configurations 3s$^2$3p$^4$, 3s3p$^5$, 3p$^6$, 3s$^2$3p$^3$[3d, 4s, 4p], 3p$^5$3d, 3s$^2$3p$^2$3d$^2$, 3s3p$^4$3d, 3s3p$^3$3d$^2$ and 2s$^2$2p$^5$3s$^2$3p$^5$ have been included in the target wavefunction representation of the Ar III ion, including up to 4p in the orbital basis. We also performed a smaller Breit-Pauli (BP) calculation containing the lowest 124 levels. Direct comparisons are made with previous theoretical and experimental work for both valence shell and L-shell photoionization. Excellent agreement was found for transitions involving the $^2$P$^{\rm o}$ initial state to all allowed final states for both calculations across a range of photon energies. A number of resonant states have been identified to help analyze and explain the nature of the spectra at photon energies between 250 and 270eV.