Observation of 2p3states in the electron-ionization efficiency curve of helium between 58 and 59 eV

High-resolution ionization efficiency curves using electron impact (58–59 eV) on helium are presented. Two previously unknown structures are clearly seen in the spectra at 58.415±0.005 and 58.48±0.02 eV in addition to the large (${\mathrm{He}}^{\mathrm{*}}$ ${)}^{\mathrm{-}}$2s2${\mathrm{p}}^2$ ${(}^2$D) negative-ion resonance. The line-shape parameters for the ${}_{}{}^2{}_{}{}^{}\mathrm{D}$ state obtained by fitting the data to theoretical line profiles are $E_R$=58.283±0.003 eV, Γ=59±4 meV, and Q=-0.70±0.04. The two new structures are tentatively assigned to the (${\mathrm{He}}^{\mathrm{*}}$ ${)}^{\mathrm{-}}$2${\mathrm{p}}^3$ electron configuration.