Orbital alignment dependence of electron transfer cross sections

his paper reports experimental results for the influence of target excitation and orbital alignment on the charge exchange process for the systems Ne⁺, Ar⁺-Na(3s,3p) for impact energies in the 1-15 keV range. The cross section parameters are found to depend sensitively on collision velocity and choice of projectile. Using earlier results by Aumayr et al (Z. Phys. D 6(1987) 145-153) for the Na(3s) target, the relative cross sections are put on an absolute scale. A strong dependence of the total electron transfer cross section on the target state is observed, most dramatically for low energy Ar⁺ impact for which the cross section for a Na(3p) target is more than 200 times larger than for Na(3s). Time-of-flight spectra show that electron transfer channels with energy defects near zero are strongly preferred. Cross section estimates based on the Demkov-Olson model account well for the major trends observed, but not for the detailed behavior.