Direct excitation of states of high l by electron impact

One consequence of the Wannier theory of correlations between electrons is that states of high orbital angular momentum can be populated efficiently by electron impact on the ground (or a low-lying excited) state of an atom, provided the incident energy is close to the ionisation threshold of the atom. This feature was first pointed out by Fano (1974), who gave a qualitative estimate that l values up to O(n 1 2/) would be populated. A recent note by Drukarev (1982), based on an assumption of the nature of the wavefunction involved, provides a quantitative distribution which peaks at l max approximately=( 1 / 2 n) 1 2/. An alternative argument, which follows from the description of angular correlation between the electrons in O 4 group symmetry is presented and supported by numerical evidence. The peak of the distribution lies at l max approximately= 1 / 2 n 1 2/.