  We develop an Over Barrier Model for computing charge exchange between ions
and one-active-electron atoms at low impact energies. The main feature of the
model is the treatment of the barrier crossing process by the electron within a
simplified quantum mechanical formulation which takes into account: (a) the
probability of electron reflection even for over-barrier scattering, and (b)
the discreteness of the receiving atom's quantum levels which strongly suppress
captures far from the resonance condition. It is shown that inclusion of these
effects yields a fairly good prediction of experimental data. We discuss also
the probability of electron re-capture by the target.
