The ionization of hydrogen and of hydrogenic positive ions by electron impact

Abstract

Calculations of the ionization cross section of hydrogen and of hydrogenic positive ions are described in which the initial state is either the ground or the excited 2s state. The first procedures used are the Born (ii) and Born-exchange approximations. These results are compared with other theoretical calculations and with experimental data. It is seen that, for the case of ionization of hydrogen from its ground state, none of the theoretical results is in good agreement with the experimental data. A certain defect of the theory is then corrected by adopting a third procedure for this case in which an angle-dependent Coulomb potential is used in the description of the final state for the process. It is then found that, despite the sounder theoretical footing of this latter calculation, no improved agreement with experimental data is obtained. In the near threshold region, however, our third procedure yields a linear behaviour, whereas the first two approximations do not. This is in accord with theoretical predictions though there exists some uncertainty in the experimental situation.