Alignment in Molecular Excitation for 3.22-keVH2+-He Collisions

Electronic alignment in molecular excitation, relative to a specific internuclear axis orientation, has been observed for the first time, enabling specific detailed checks of the quasidiatomic molecular-orbital model in kiloelectronvolt atom-molecule collisions. The alignment was determined from the polarization of ${\mathrm{L}}_{\alpha }$ radiation, resulting from the collision process ${{\mathrm{H}}_2}^{+}+\mathrm{He}\to {{{\mathrm{H}}_2}^{+}}^{*}+\mathrm{He}\to {\mathrm{H}}^{+}+\mathrm{H}\mathrm{}\left(2p\right)+\mathrm{He}$,, for specific laboratory scattering angles of ${\mathrm{H}}^{+}$. The results suggest that, as in many ion-atom systems, rotational coupling is the dominant excitation mechanism.