Energies of metastable ⁴S^o states in the alkaline-earth sequence

Theoretical binding energies have been obtained for the metastable np³⁴S^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 Be^- and within 10 meV for Mg^-. The binding energies of the p³⁴S^o state in Mg^-, Ca^-, and Sr^- are larger than the one in Be^- by roughly 250 meV due to the stronger interactions with the d²p configurations. For Ca^-, the ⁴S^o binding energy is determined to be 555.5 meV, including a contribution of -70 meV due to dielectronic core polarization. For Sr^- the ⁴S^o binding energy is 557.9 meV, including a decrease of only 6 meV due to dielectronic core polarization. This behavior for the ⁴S^o states in Ca^- and Sr^- is ascribed to the different neutral-atom states to which the ⁴S^o states are bound.