Excitation of the(2p2)P3State of Helium near Threshold

Abstract

The trapped-electron method is applied to the excitation by electron impact of the $\left(2\mathrm{}{p}^2\right){}_{}{}^3{}_{}{}^{}P$ state, the lowest doubly excited state of helium which is stable against auto-ionization. The energy of this state, 59.64±0.08 eV, is in good agreement with theory. An estimate of the slope of the total cross section for excitation of the $\left(2\mathrm{}{p}^2\right){}_{}{}^3{}_{}{}^{}P$ state at threshold gives a value of 4 × ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$/eV.