Near-threshold electron impact ionization of atomic hydrogen

Electron impact ionization of atomic hydrogen within the simplified S-wave model problem of Temkin and Poet is studied in the energy region between the ionization threshold and 5 eV excess energy. Three of the currently most accurate close-coupling approaches - the convergent close-coupling (CCC), the R-matrix with pseudo-states (RMPS) and the intermediate R-matrix (IERM) methods - are applied to this problem and the results are compared. It is found that the behaviour of the cross section in this energy region is closer to an E2 threshold law than the E3/2 dependence predicted by Temkin. Preliminary results for the full electron-hydrogen-atom ionization problem for the 1Se partial wave have been obtained which indicate that these methods may also be used to study threshold ionization processes involving complex atoms and ions. (author)