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

Configuration-interaction calculations show the existence of bound ${\mathrm{Li}}^{-}\left(1s2s2\mathrm{}{p}^2\right){}_{}{}^5{}_{}{}^{}P$ and ${\mathrm{Li}}^{-}\left(1s2\mathrm{}{p}^3\right){}_{}{}^5{}_{}{}^{}S_{}^{\circ }{}_{}{}^{}$ states lying 56.910 and 60.460 eV above the Li ground state, respectively. The ${}_{}{}^5{}_{}{}^{}S_{}^{\circ }{}_{}{}^{}$ state decays into the ${}_{}{}^5{}_{}{}^{}P$ state with $\lambda =3489.5\mathrm{}\pm 1.1$ Å and $\tau =2.86\mathrm{}\pm 0.10$ nsec. Experimental and theoretical evidence about an unclassified, cascade-free, medium-intensity line with $\lambda =3489.7\mathrm{}\pm 0.2$ Å and $\tau =2.9\mathrm{}\pm 0.2$ nsec in the beam-foil spectra of doubly excited lithium strongly suggests the presence of core-excited ${\mathrm{Li}}^{-}$ ions in the beam-foil source.