Relativistic calculations of photoionization cross-section of Mg-like Ca IX

Abstract

Relativistic calculations of the photoionization cross-sections are carried out for the ground state 1s²2p⁶3s² (¹S₀) and first three excited states 1s²2p⁶3s3p (³\({\text{P}}_{{0,1,2}}^{{\text{o}}}\)) of Mg-like Ca IX ion using the Breit–Pauli R-matrix (BPRM) approach. Configuration interaction method (CIV3) is used to construct the target wavefunctions. A total of lowest lying 21 fine structure levels corresponding to 2p⁶nl (3 ≤ n ≤ 5) configurations are considered for the expansion of target wavefunctions. Reported target state eigen energies of the 21 fine structure levels of core ion Ca X agree with the available data. To assess the accuracy of our BPRM results, we have also performed similar calculations using the fully relativistic Dirac atomic R-matrix code (DARC) for the ground state of Mg-like Ca IX ion. Further, relativistic distorted wave (DW) method is also used for the comparison purpose, and a good agreement has been found with the R-matrix results. The quantum number (n), resonance width (Γ) and resonance energies (E_r) of the 3dnp (³P₁, ¹P₁, ³D₁, ¹D₂), 3dnf (³P₁, ¹P₁) and 4snp (³P₂, ³P₀, ³P₁, ¹P₁) series have also been predicted using Quigley and Berrington (QB) method. We believe that the present results will be helpful for modeling and diagnostics of laboratory and astrophysical plasmas.