On Charge Transfer in Ion-Atom Collisions at Intermediate Collision Velocities

We study charge transfer at intermediate energies for multielectron ion-atom collisions within the coupled-state impact-parameter method. We point out the importance of assumptions about electronic relaxation by comparing various calculations of cross sections for KK charge transfer in F9+ + Si as a test case. In these calculations, either the unrelaxed Hamiltonian of the atomic model or a relaxed molecular Hamiltonian has been employed, and two-state atomic or molecular basis sets have been used. To correct for the inadequacy of atomic orbitals for close collisions at intermediate energies, we propose to add orbitals of the united atom at the two collision centers. With such an atomic basis set, quasimolecular behavior of the system is represented sufficiently well. We report on results for the collision system H+ + He+ for which calculations with large molecular and atomic basis sets exist.