The effect of long-range forces on the behaviour of electron-atom scattering cross sections near excitation thresholds II. Results for some simple models

The method developed in a previous paper has been used to determine the effect of long-range dipole forces on the threshold behaviour of cross sections for three different mathematical models. Results are obtained for systems with degenerate as well as non-degenerate channels. It is found that for the non-degenerate case the α/ r 2 potentials do not alter Wigner's law for short-range forces. However, the range of energy over which the short-range behaviour is maintained decreases progressively with the decrease of energy difference between the non-degenerate levels. For the exactly degenerate case Wigner's law is violated and the cross section tends to a finite value at the threshold.