Orbital alignment dependence of electron transfer cross sections. I: H+-Na(3p) near the matching velocity

This paper reports experimental and theoretical results for the influence of target excitation and orbital alignment on the charge exchange process for the system H+-Na(3s,3p). The experimental velocity range covers for the first time the region around and beyond the "matching velocity" of 0.47 a.u. of the Na(3p) state, i.e. the velocity characteristic of the orbital motion of the valence electron. The cross section parameters are found to depend sensitively on collision velocity, with a qualitatively different behaviour below and above the matching velocity. The results for the orbital alignment dependence support the intuitive picture that, when going beyond the matching velocity, electron transfer becomes increasingly favoured when the orbital velocity of the active electron has a component parallel to the collision velocity. Agreement with earlier experimental and theoretical results at lower velocities is good and allows conclusions about the quality of theoretical approximations in the various velocity regimes.