Conservation of spin angular momentum in the reaction $\mathrm{He}\left(2\mathrm{}{}_{}{}^2{}_{}{}^{}S_1^{}{}_{}{}^{}\right)+\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}\right)\to \mathrm{He}(1\mathrm{}{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}+{\mathrm{He}}^{+}+e^{-}$ is demonstrated quantitatively in the afterglow of a helium discharge by measuring the dependence of the electron production rate upon $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ spin-state populations, which are manipulated by an optical-pumping technique.

• Received 21 June 1971

DOI:https://doi.org/10.1103/PhysRevA.5.189