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

Abstract

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