Strong effects of initial orbital alignment observed for electron capture in keV H sup + -Na(3 p ) collisions

Electron capture in keV collisions of protons with sodium atoms in the excited Na(3{ital p}) state is studied. The initial orbital alignment of the valence electron is controlled by the polarization of the exciting light. Capture into H({ital n}) levels is measured for light polarization parallel and perpendicular to the proton beam direction. For {ital n}=2 the capture cross section is about 35% larger for an orbital aligned parallel than for one perpendicular to the beam direction, at all energies. However, for {ital n}{ge}3 the alignment effect varies dramatically with energy, supporting recent theoretical results.