Valence-shell photoionization of the C$\ell$ like Ar$^+$ ion

The properties of Argon ions are of importance in atmospheric and astrophysical plasmas where abundances are required in the modeling of B-type stars in the Orion nebula, and the interstellar medium. Absolute cross-section measurements made at the Advanced Light Source in Berkeley California, for M-shell photoionization of Ar$^+$ are reported on for discrete photon energies ranging from 27.4 eV to 60.0 eV. The high-resolution spectroscopic absolute photoionization cross-section measurements indicate the target ion beam is a statistical admixture of the $^2$P$^o_{3/2}$ ground state and the $^2$P$^o_{1/2}$ metastable state of Ar$^+$. At all of the photon energies considered, the experimental photoionization cross sections are in excellent agreement with the predictions made from theoretical calculations performed using a parallel version of the R-matrix codes in intermediate coupling within the semi-relativistic Breit-Pauli approximation. Further details and a comprehensive set of results will be presented at the meeting.