Natural Line Shapes Resolved in the Ionization Yield ofHe+below then=2Threshold

Natural line shapes of the states ${\left(2\mathrm{}{s}^{2}2p\right)}^{2}P$ and ${\left(2s2p^2\right)}^{2}D$ of ${\mathrm{He}}^{-}$ are observed in the ionization-efficiency curve of He. The shape factor $q$ and bandwidth $\Gamma$ are determined. The energies of those states are measured, respectively, as 57.15±0.04 and 58.23±0.04 eV. Furthermore, doubly excited levels of He are detected in the ionization-efficiency curve of He as they autoionize and add a contribution to the ${\mathrm{He}}^{+}$ continuum. All nine energy states measured are in very good agreement with values reported using other techniques.