Modelling of three-body effects in a double continuum

Theoretical calculations of double ionisation by electron or photon impact require a final state wavefunction which takes account both of the Coulomb repulsion between the pair of free electrons and of their interaction with the residual ionic core. It is desirable that this should be separable so as to facilitate the introduction of electron-pair correlations in the initial state wavefunction for the collision system. We propose a method for calculating coupled classical trajectories for the free electrons and deducing from these potentials from which their quantum mechanical wavefunctions may be obtained. Test calculations are reported for electron impact single ionisation of hydrogen