Angular correlation between autoionization electrons and scattered ions in 2000-eVHe+-He collisions

Complex population amplitudes for the excitation of magnetic sublevels of $\mathrm{He}\left(2\mathrm{}{p}^2\right){}_{}{}^1{}_{}{}^{}D$ and $\mathrm{He}\mathrm{}\left(2s2p\right)\mathrm{}{}_{}{}^1{}_{}{}^{}P$ states in 2-keV ${\mathrm{He}}^{+}$ -He collisions have been determined by measuring the energy spectra of the corresponding autoionization electrons ejected at different angles in coincidence with the inelastically scattered ions. It was found that $\mathrm{He}\left(2\mathrm{}{p}^2\right){}_{}{}^1{}_{}{}^{}D$ is excited with a relative probability of 97%. If the direction of the internuclear line at the distance of closest approach is taken as $z$ axis, we find that primarily the $m=0\mathrm{}$ sublevel is populated and that the complete ${}_{}{}^1{}_{}{}^{}D$ excitation can be interpreted as due to pure $m=0\mathrm{}$ excitations with respect to momentary internuclear lines at different points of the trajectory which are symmetric to the turning point. These results are discussed within the framework of the Fano-Lichten promotion model. Quantization along an axis perpendicular to the scattering plane shows an orientation of the excited ${}_{}{}^1{}_{}{}^{}D$ state. From this we find that the angular momentum $L_y$ transferred from the motion of the heavy particles to the electron cloud has an expectation value of $〈L_y〉\approx -\hslash$.