A shape function for single-photon multiple ionization cross sections

Recently, a universal shape function for cross sections of ionization by charged particle impact has been established. Here, we show how an analogous shape function for multiple ionization by photons can be constructed along the same lines. It is argued that this shape function provides an excellent parametrization of photoionization cross sections in cases where all electrons are ionized. In more complicated situations, the parametrization can still be useful, although its applicability may be limited.