  Charge transfer in collisions of Na_n^+ cluster ions with Cs atoms is
investigated theoretically in the microscopic framework of non-adiabatic
quantum molecular dynamics. The competing reaction channels and related
processes affecting the charge transfer (electronic excitations, fragmentation,
temperature) are described. Absolute charge transfer cross sections for
Na_n^+(2.7 keV) + Cs --> Na_n + Cs^+ have been calculated in the size range 4
<= n <= 11 reproducing the size dependence of the experimental cross sections.
The energy dependence of the cross section is predicted for n=4,7,9. An exotic
charge transfer channel producing Cs^- is found to have a finite probability.
