Multichannel photoionization spectroscopy of Ar: Total cross section and threshold photoelectrons

Argon photoionization is studied using the R-matrix technique. Total photoionization cross sections, as well as partial cross sections for emission of a 3s electron, are obtained and compared with experimental results in the photon energy range between 30 and 38 eV. As a by-product of the photoionization calculations, threshold cross sections have been estimated for Ar⁺ states up to 38 eV above the Ar ground state, and are compared with experiment. These comparisons show that the present approach can describe Ar autoionizing states reasonably well, even up to 38-eV photon energy. However, some modifications of previously used techniques have proven to be important in order to stabilize the calculation in this difficult energy range.