Observation of orientation propensity for electron capture in multiply-charged-ion–atom collisions

We have measured the circular polarization of photons emitted after electron capture into the B²⁺(1s²2p) state in B³⁺(1s²)+He(1s²) collisions in a planar scattering experiment, using the polarized-photon--scattered-ion coincidence technique. The energy is 1.5--12 keV and scattering angles {θ} are less than 1.5^∘{}. For large impact parameters a strong propensity for orientation is observed, with the sense of electron orbiting in the same direction as the rotation of the internuclear axis being favored by more than a factor of 2 compared to the opposite orientation. This is in qualitative agreement with recent theoretical predictions.