Triply excitedP2andD2resonance ofHe−

Abstract

The ${}_{}{}^2{}_{}{}^{}P$ ($2s2s2p$) and ${}_{}{}^2{}_{}{}^{}D$ ($2s2p2p$) resonance structure observed in the electron-helium scattering experiments has been investigated using a saddle-point technique. For ${}_{}{}^2{}_{}{}^{}P$ we obtain for the energy — 0.796 93 a.u. with an 82-term wave function. This agrees well with the experimental result. In the past, the ${}_{}{}^2{}_{}{}^{}D$ structure was thought to be a Feshbach resonance. In this calculation, we show that the $2s2p$ ${}_{}{}^3{}_{}{}^{}P$ target is repulsive to the third $p$ electron in the sense that the variational energy of the ${\mathrm{He}}^{-}$ system is monotonically increased as the $p$ electron approaches the target. Hence, the Feshbach resonance cannot be formed for this state. Some comments will be made concerning earlier theoretical calculations in the literature.