Theoretical threshold cross section of electron-impact ionization of the hydrogen atom

Single differential and total cross sections of the electron-impact ionization of the hydrogen atom are calculated numerically in the two-potential distorted-wave approximation for excess energies from 0 to 1 eV. Partial-wave contributions to the cross sections are also investigated. The near-threshold cross section is parametrized by the power γ and the proportionality constant a0 for models with various asymptotic charges, and the dependence of a0 on the asymptotic charge is studied. The validity range of the threshold power law is also discussed. (Author)