He- 2D weakly bound triply excited resonances: Interpretation of previously unexplained structures in the experimental spectrum
A He plus electron scattering experiment by Gosselin and Marmet [Phys. Rev. A 41, 1335 (1990)] produced the previously known He- 2s2p2 2D resonance at 58.283+/-0.003 eV with a width Γ=59+/-4 meV, and two new structures at 58.415+/-0.005 and 58.48+/-0.02 eV with Γ<2 meV and Γ=70+/-20 meV, respectively. The nature of these last two structures has since remained unexplained. Heuristic analysis of the spectrum of the triply excited states (TES) of He- and of conditions of electron correlation and possible localization, and application of the state-specific theory (SST) for the calculation of electronic structures and properties led to the determination of three resonance states of 2D symmetry that explain quantitatively the experimental data. The implementation of the SST involved the combination of suitable choices of optimized orbitals, of nonorthonormal configuration interaction, and of mixing of bound with scattering configurations. The first two 2D TES contain the 2s2p2 configuration as a major component, but strong radial correlation results in the spatial separation of the two p spin orbitals. The third TES, computed systematically with up to 996 optimized configurations, is an open-channel like localized wave packet.