Atomic scattering in the diffraction limit: electron transfer in keV Li+–Na(3s, 3p)collisions

Abstract

We measure angle differential cross sections (DCS) in Li+ + Na → Li + Na+electron transfer collisions in the 2.7–24 keV energy range. We do thiswith a newly constructed apparatus which combines the experimentaltechnique of cold target recoil ion momentum spectroscopy with a laser-cooledtarget. This setup yields a momentum resolution of 0.12 au, an order ofmagnitude better angular resolution than previous measurements on thissystem. This enables us to clearly resolve Fraunhofer-type diffractionpatterns in the angle DCS. In particular, the angular width of the ringstructure is given by the ratio of the de Broglie wavelength λdB = 150 fm at avelocity v = 0.20au and the effective atomic diameter for electron capture 2R = 20 au.Parallel AO and MO semiclassical coupled-channel calculations of the Na(3s, 3p)→Li(2s, 2p) state-to-state collision amplitudes have been performed, and quantumscattering amplitudes are derived by the eikonal method. The resultingangle-differential electron transfer cross sections and their diffraction patternsagree with the experimental level-to-level results over most scattering angles inthe energy range.