Calculations of photoionization and radiative recombination in warm dense plasmas by average-atom method

Peculiarities of photoionization and radiative recombination of ions in warm dense plasmas are studied with the average-atom model using the Dirac-Slater electron wave functions. Relativistic calculations of the photoionization and radiative recombination cross sections as well as the quadrupole photoelectron angular distribution parameters were performed for various shells of the oxygen, argon, iron, and germanium ions occurring in astrophysical and laboratory plasmas. When the results are compared with calculations for relevant free ions, it is apparent that taking into account the plasmas temperature and density in the average-atom approach affect the behavior and magnitude of the photoionization and radiative recombination cross sections as well as of angular parameters at photoelectron energies up to  ∼ 1000 eV. In particular, the cross sections and angular parameters obtained with the average-atom model are demonstrated to oscillate distinctly at photoelectron energies  ≲ 100 eV. The occurrence of the oscillations is shown to be associated with a behavior of the continuum function normalization factor in the average-atom potential.