Quantal near-threshold ionization of He by electron impact

A more accurate variant of the semiclassical quantum-mechanical treatment o f Crothers (1986 J. Phys. B: At. Mol. Phys. 19 463-83) has been used to rei nvestigate the ionization cross sections of He by electron impact at an exc ess energy of 2 eV above the threshold. All partial wave contributions for singlets and triplets are accounted for up to L = 6. It is found that withi n the coplanar geometry, both the symmetric and asymmetric triple different ial cross sections, peaking at and near the Wannier ridge, are greatly impr oved when compared to the measurements (Rosel et al 1992 Phys. Rev. A 46 25 39-52). However, far away from the Wannier ridge the triple differential cr oss sections tend to show qualitative differences from the measurements of Rosel et al.