(γ, 2e) in He - a practical parametrization of the triple differential cross section

Abstract

Several model functions capable of representing the symmetrized transition amplitudes within the parametrization formalism of Huetz et al for the photodouble ionization of helium are proposed. The model is based on the well documented features of the gerade transition amplitude in the cases of symmetric energy sharing and/or small excess energies. Those are extended towards the higher excess energies and for an arbitrary energy sharing, where both the gerade and the ungerade components of the transition matrix contribute, with a minimum of modifications. Excellent agreement between a sample of experimental and theoretical triple differential cross sections (TDCS) extending up to 40 eV on one side and the parametric form on the other is obtained by using just three adjustable parameters which could be reliably extracted from most experiments. This creates the possibility for a complete dynamical parametrization of the TDCS in the low to intermediate excess energy range.