Electron-loss cross sections for fast, excited He atoms inH2

By means of an optical detection technique, the electron-loss cross sections for He atoms in the excited states $3{}_{}{}^3{}_{}{}^{}P$, $4{}_{}{}^3{}_{}{}^{}S$, $4{}_{}{}^1{}_{}{}^{}S$, $5{}_{}{}^3{}_{}{}^{}S$, and $5{}_{}{}^1{}_{}{}^{}S$ have been measured in ${\mathrm{H}}_2$ in the energy range 8-160 keV. These cross sections are compared to theoretical cross sections derived by means of the classical impulse approximation of Bates and Walker. In agreement with this theory, the present electron-loss cross sections are found to depend very little on the binding energy and the specific quantum state of the weakly bound electron being removed. Further, they are approximately equal to the total electron-scattering cross section taken at the same impact velocity, as also predicted by the mentioned theory.