Ejected-energy differential cross sections for the near-threshold electron-impact ionization of hydrogen

We have calculated, independently, the S-1 singly differential cross section for the electron-impact ionization of hydrogen at an incident energy of 4.0 eV above threshold using two different methods: time-dependent close coupling and exterior complex scaling, The absolute value of the S-1 cross section for equal energy sharing is critical in assessing recent theoretical and experimental results for coplanar triply differential cross sections at low energies. Convergence of the cross section is studied as a function of the number of coupled channels. We find that at this energy the singly differential cross section is relatively flat over the entire ejected-energy range as predicted by semiclassical calculations.