Resonances in Ca+ + Rb nonadiabatic collisions at ultralow energies

Nonadiabatic inelastic collision cross sections have been computed at low and ultralow energies, focusing in the present work on the Ca+(4s(2)S) + Rb(5s S-2) -> Ca(4s4p P-3) + Rb+(S-1) charge-exchange process at ultralow collision energies (E <= 10(-6) eV) induced by spin-orbit nonadiabatic coupling terms. The calculations reveal a wealth of sharp resonances which can substantially enhance charge-exchange probabilities over a specific energy window of around 10(-6) to 10(-8) eV. Such resonances are analyzed in detail, and the corresponding molecular mechanism is discussed for a specific example, where the nonadiabatic transition probabilities are seen to increase by nearly 2 orders of magnitude.