Identification of Bound States of Core-Excited Negative Lithium Atoms in Beam-Foil Experiments

Configuration-interaction calculations show the existence of bound Li^-(1s2s2p²)⁵P and Li^-(1s2p³)⁵S^∘ states lying 56.910 and 60.460 eV above the Li ground state, respectively. The ⁵S^∘ state decays into the ⁵P state with λ=3489.5±1.1 {} and τ=2.86±0.10 nsec. Experimental and theoretical evidence about an unclassified, cascade-free, medium-intensity line with λ=3489.7±0.2 {} and τ=2.9±0.2 nsec in the beam-foil spectra of doubly excited lithium strongly suggests the presence of core-excited Li^- ions in the beam-foil source.