Strongly correlated states in the ${\mathrm{Li}}^{-}$ ion

A collinear laser-ion beam apparatus has been used to investigate resonance structure in the $\mathrm{Li}{\mathrm{}\left(3s\right)+e}^{-}\mathrm{}\left(\mathrm{kp}\right)\mathrm{}$ partial photodetachment cross section below the $\mathrm{Li}\mathrm{}\left(6p\right)\mathrm{}$ threshold. A complex rotation calculation was used to identify the strongly correlated, doubly excited states of the quasi-two-electron ion ${\mathrm{Li}}^{-}$ that are responsible for the observed resonances. These represent the most highly excited states of ${\mathrm{Li}}^{-}$ observed thus far. Several members of a strong $“+”$ type series were observed as well as at least one resonance with $“-”$ type character. In particular, we report on an observation of a resonance that violates the $\Delta \nu =0\mathrm{}$ propensity rule.