Photo-Ionization of Light Atoms at Intermediate Energies

The photoionization cross sections are important parameters in the determination of the ionization structure of cosmic gas subjected to ultraviolet and x-ray radiation. We present a set of analytic fits to the Hartree-Dirac-Slater photoionization cross sections for the ground state shell of elements (He, Li, Be, N O). Comparison with experiment and theory demonstrates generally high accuracy of the fits up to energies of 200 eV.