Distorted-wave effects at low momentum in binary (e, 2e) cross sections for d-orbital ionization

Unexpected and previously unexplained behaviour showing appreciable intensity at low momenta in previously published binary (e, 2e) cross sections for ionization from nd atomic orbitals including Xe 4d, Zn 3d and Cd 4d is investigated. Similar effects have also been observed recently in binary (e, 2e) studies of metal hexacarbonyls for the least tightly bound molecular orbitals which are dominated by metal nd character. The finite cross sections at low momenta (i.e. non-nodal behaviour) are not predicted by plane-wave calculations for atomic targets, but can be accounted for using distorted-wave theory. These distortion effects at low momenta appear to be due to a high-l effect and the even-parity nature of nd atomic orbitals.