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Coulomb phase interferences for small-angle inelastic scattering from ions

The author investigates the expected behaviour of the small-angle differential cross section for inelastic e--atom and e--ion collisions. The presence of the Coulomb phaseshift in the expression for the scattering amplitude for e --ion collisions leads to destructive interference between the individual partial-wave components at small angles. As a result, forward-angle differential cross sections for ions will be much smaller than for atoms. One consequence of this is that the limiting value of generalised oscillator strength for a dipole transition at zero momentum transfer is not the optical oscillator strength. Calculations for the Be+ 2s+2p transition show a large reduction in the forward-angle differential cross section, and demonstrate that this interference effect is so pronounced that it should be experimentally observable.