DISTORTED-WAVE EFFECTS AT LOW MOMENTUM IN BINARY (E, 2E) CROSS-SECTIONS FOR D-ORBITAL IONIZATION

Unexpected and previously unexplained behaviour showing appreciable in tensity at low momenta in previously published binary (e, 2e) cross se ctions for ionization from nd atomic orbitals including Xe 4d, Zn 3d a nd Cd 4d is investigated. Similar effects have also been observed rece ntly in binary (e, 2e) studies of metal hexacarbonyls for the least ti ghtly bound molecular orbitals which are dominated by metal nd charact er. 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 ef fects at low momenta appear to be due to a high-l effect and the even- parity nature of nd atomic orbitals.