Born cross sections for the ionization of He and Li+ by electron impact

First Born approximation cross sections are calculated for the ionization of the ground states of He and Li + by electron impact, in the energy range from threshold to 9 kev. An open-shell two-parameter wave function is used for the ground state of the target. A partial wave expansion is used for the ejected electron, the radial functions being continuum Hartree-Fock or Sloan polarized orbitals. The partial wave sums converge to within 0·1% of the total by l = 4. The calculations were carried out using both the length and velocity formulations of the Born approximation. The length results are approximately 9% higher than the velocity results for He and 6% higher for Li + . The cross sections obtained are in excellent agreement with experiment at energies in excess of twenty-five times threshold and approach the Bethe limit (within 3%) at energies in excess of fifty times threshold.