Autoionization of He and Autodetachment ofHe−following Bombardment byH+,H2+,He+, and He Atoms

Presented here are experimental results of a study of the systematics of electron emission from discrete states of He and ${\mathrm{He}}^{-}$ as produced by ${\mathrm{H}}^{+}$, $\mathrm{H}_2^{}{}_{}{}^{+}$, ${\mathrm{He}}^{+}$, and He impacts. The results were obtained by energy analysis of the electrons emitted at angles of 10° to 160°. Projectile energies ranged from 20 to 150 keV. Differential and integrated cross sections are presented for emission of electrons from the $2s^2\left({}_{}{}^1{}_{}{}^{}S\right)$, $2s2p\left({}_{}{}^3{}_{}{}^{}P\right)$, the sum of the $2p^2\left({}_{}{}^1{}_{}{}^{}D\right)$ and $2s2p\left({}_{}{}^1{}_{}{}^{}P\right)$ autoionizing levels of He, and the $1s2s^2\left({}_{}{}^2{}_{}{}^{}S\right)$ autodetaching level of ${\mathrm{He}}^{-}$. The $2s^2\left({}_{}{}^1{}_{}{}^{}S\right)$ cross section is nearly isotropic, while the $2s2p\left({}_{}{}^3{}_{}{}^{}P\right)$ and $2p^2\left({}_{}{}^1{}_{}{}^{}D\right)+2s2p\left({}_{}{}^1{}_{}{}^{}P\right)$ cross sections are in general anisotropic. The ratios of the ${}_{}{}^3{}_{}{}^{}P$ to the ${}_{}{}^1{}_{}{}^{}S$ cross sections follow an approximate $A+B{cos}^2\theta$ form. The peak arising from the ${\mathrm{He}}^{-}$ level has an asymmetric profile with a positive $q$ value which increases as the projectile energy decreases.