Energy dependence of the differential cross sections for simple models of ion-induced dipole capture collisions

At low relative kinetic energies, the product angular distributions characteristic of the short range part of a reactive scattering event may become distorted by a long range attractive force. We examine this behavior for several different simple models of direct, short range encounters, each of which is coupled at long range to an attractive potential term proportional to r-4. The long range attraction does not generally lead to symmetric angular distributions for low-energy capture collisions. The anisotropy of the differential cross section which is observed at high energies may be preserved at extremely low kinetic energies, or it may be substantially altered toward either more symmetric or less symmetric distributions. It is even possible for a distribution which is forward-peaked at high energy to become backward-peaked at low energy, and vice versa. These results suggest that caution is warranted when one wishes to interpret a change in the product angular distribution, in going from high kinetic energies to low kinetic energies, as due to a change in the short range reaction mechanism