Photoionization Cross Sections of He and H 2

Abstract

We combine accurate measurements at low energies and theoretical calculations at high energies to construct sets of photoionization cross sections of He and H2 that should be reliable at all energies. We control the accuracy of the recommended cross section data by ensuring that they satisfy a range of oscillator strength sum rules. We provide accurate analytic formulae for the photoionization cross sections that have the proper asymptotic form. At high frequencies the cross sections for H2 are 2.8 times those for H.