Energies of metastable4Sostates in the alkaline-earth sequence

Abstract

Theoretical binding energies have been obtained for the metastable ${\mathrm{np}}^{3}{}^{4}{S}^{o}$ states in the alkaline-earth sequence using a B-spline configuration-interaction approach. The results agree with available experimental and theoretical data within 5 meV for ${\mathrm{Be}}^{\ensuremath{-}}$ and within 10 meV for ${\mathrm{Mg}}^{\ensuremath{-}}.$ The binding energies of the ${p}^{3}{}^{4}{S}^{o}$ state in ${\mathrm{Mg}}^{\ensuremath{-}},$ ${\mathrm{Ca}}^{\ensuremath{-}},$ and ${\mathrm{Sr}}^{\ensuremath{-}}$ are larger than the one in ${\mathrm{Be}}^{\ensuremath{-}}$ by roughly 250 meV due to the stronger interactions with the ${d}^{2}p$ configurations. For ${\mathrm{Ca}}^{\ensuremath{-}},$ the ${}^{4}{S}^{o}$ binding energy is determined to be 555.5 meV, including a contribution of $\ensuremath{-}70$ meV due to dielectronic core polarization. For ${\mathrm{Sr}}^{\ensuremath{-}}$ the ${}^{4}{S}^{o}$ binding energy is 557.9 meV, including a decrease of only 6 meV due to dielectronic core polarization. This behavior for the ${}^{4}{S}^{o}$ states in ${\mathrm{Ca}}^{\ensuremath{-}}$ and ${\mathrm{Sr}}^{\ensuremath{-}}$ is ascribed to the different neutral-atom states to which the ${}^{4}{S}^{o}$ states are bound.