Theoretical Model for Resonances ine−HeScattering near 60 eV

Abstract

The results of close-coupling calculations for electron-helium scattering at incident electron energies between 40 and 70 eV are reported. The calculations were carried out by including in the expansion terms representing both the singly and doubly excited electronic states of the target. The results confirm the suggestion by Fano and Cooper that the narrow resonances at about 57.2 and 58.3 eV can be associated with formation of autoionizing states of ${\mathrm{He}}^{-}$ with dominant configurations $\left(2\mathrm{}{s}^{2}2P\right){}_{}{}^2{}_{}{}^{}p_{}^o{}_{}{}^{}$ and $\left(2s2p^2\right){}_{}{}^2{}_{}{}^{}D_{}^e{}_{}{}^{}$, respectively. The results for total excitation cross sections of the $2{}_{}{}^3{}_{}{}^{}S$ state agree qualitatively with recent measurements, but a discrepancy of a factor of 2 between theory and experiment remains at this time unexplained. The calculated total cross section for scattering by the gound state agrees quite well with experiment. The effect of the resonances on the total cross section and their possible correlation with other resonances observed in electron-helium excitation functions is discussed.