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 interm ediate R-matrix (IERM) methods-are applied to this problem and the res ults are compared. It is found that the behaviour of the cross section in this energy region is closer to an E-2 threshold law than the E-3/ 2 dependence predicted by Temkin. Preliminary results for the full ele ctron-hydrogen-atom ionization problem for the S-1(e) partial wave hav e been obtained which indicate that these methods may also be used to study threshold ionization processes involving complex atoms and ions.