Wannier theory for Poand Destates of two electrons

Abstract
The M=0 components of the Po and De states of two continuum electrons are frequently produced by electron impact ionisation (or double photoionisation with polarised photons). Some experiments are able to measure the triple differential cross sections (TDCS) of such processes as functions of the two electron energies and spherical angles theta 1, phi 1, theta 2, phi 2 with respect to the incident beam direction (or polarisation). Here the authors use the Wannier theory and proper coordinates to derive theoretical expressions for these TDCS near threshold. As already shown by Peterkop (1983) different energy behaviours result from different nodal properties at the Wannier point. They show that the 1De state has a mixed character, i.e. it contains a first part with no angular node and a second part with a second-order angular node which, however, cannot be neglected. Consequently the resulting TDCS includes two different energy behaviours associated with two specific functions of angles. Finally they take advantage of these Po and De particular states to establish a link between some approaches using different methods and systems of coordinates which have been proposed so far within the frame of the Wannier theory.

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