D1Autoionization Series in Helium

Abstract

Ten states of doubly excited He have been observed in a high-resolution electron-emission spectrum from 30-MeV ${\mathrm{O}}^{5+}$ +He collisions. Five lines can be identified as the $\mathrm{}\left(2pnp\right)\mathrm{}{}_{}{}^1{}_{}{}^{}D+\mathrm{series}$. The excitation mechanism is discussed and compared with results of an identical measurement using 4-MeV proton excitation.