Abstract
Two configuration-interaction-type wavefunctions each accounting for = 98% of the ground-state correlation energy in helium have been used to predict the differential (e, 2e) cross-section ratio leading to either the n = 2 or the n = 1 final ion states of helium. The findings are compared with known experimental data and two previous theoretical calculations. The predicted ratios using the various wavefunctions are in reasonable agreement with one another and with experiment up to q = 2.0 au. Thereafter, the dispersion for various wavefunctions increases significantly. Furthermore, the differential cross-section ratio for populating the He + (2p) to He + (2s) final ion states differ by an order of magnitude for correlated wavefunctions of equal quality in ground-state-energy terms. A reformation of the electron-impact cross-section theory beyond the plane-wave impulse approximation with the use of non-configuration-interaction-type correlated functions is required to assist the resolution of this problem.
Published Version
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