Composition of He Metastable Beams Formed by Charge Exchange inHe+-Alkali-Metal Collisions at Medium Energy

The composition of He metastable beams formed by charge exchange on alkali-metal vapors is determined by a time-of-flight analysis. The relative abundance of the two components $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ and $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)$ is measured in the 100-1500-eV energy range. It is shown that a pure $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ beam is obtained with sodium as the exchange target, whereas rubidium is found to be the most efficient target to yield a $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)$ beam. Comparison is made with theoretical predictions.