Helium Negative Ions from Metastable Helium Atoms

Helium negative ions were produced from ${\mathrm{He}}^{+}$ by a two-step process in which $\mathrm{He} \mathrm{}\left(1s2s\right)\mathrm{}{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ was first produced by a nearly resonant charge transfer and then ${\mathrm{He}}^{-}$ was produced by capture of a $2p$ electron. Both collisions were with cesium atoms. The maximum yield of ${\mathrm{He}}^{-}$ was 1.2% of the incident ${\mathrm{He}}^{+}$ when the energy of the ${\mathrm{He}}^{+}$ was 3 keV. The cross sections relevant to these processes were obtained.