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 ${\mathrm{B}}^{2+}$(1${\mathit{s}}^2$2p) state in ${\mathrm{B}}^{3+}$(1${\mathit{s}}^2$)+He(1${\mathit{s}}^2$) 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.