Charge exchange in slow collisions of atoms and molecules

The cross section for symmetric charge transfer in ion-atom collisions is usually determined by the adiabatic theory. In this work the adiabatic theory is extended to very low energies, taking into account the curvature of the nuclear motion due to polarization forces. At the very high energy end, the Demkov-Ostrovskii theory is used to compare with the experimental results. The Coulomb force is incorporated into the standard adiabatic theory to determine the cross section for charge transfer between multiply charged ions. The results obtained are in very good agreement with the experimental results. The slight discrepancy between the modified asymptotic theory and the quantum result, in the case of HE/sup */-He+, is studied numerically. Ion-molecule charge transfer is studied using the close coupling method. The relative importance of short and long range electron transfer mechanisms is studied. The merits and demerits of a surface crossing model are discussed. The importance of including the strong electronic-vibrational coupling in any theory dealing with molecular charge transfer is emphasized