Theoretical Electron Affinities for Some of the Alkali and Alkaline-Earth Elements

The ${\mathrm{}\left(\mathrm{ns}\right)\mathrm{}}^2$ correlation energies for the negative ions ${\mathrm{Li}}^{-}$, ${\mathrm{Na}}^{-}$, and ${\mathrm{K}}^{-}$ have been calculated by the method of superposition of configurations. Comparisons with Hartree-Fock calculations of the neutral species yield electron affinities of 0.62, 0.54, and 0.47 eV, respectively. A study of the computed ionization potentials of the neighboring isoelectronic atoms and ions suggests a maximum uncertainty of 0.1 eV. Similar calculations of the $\mathrm{ns}{\mathrm{}\left(\mathrm{np}\right)\mathrm{}}^2{}_{}{}^4{}_{}{}^{}P$ states of ${\mathrm{Be}}^{-}$ and ${\mathrm{Mg}}^{-}$ indicate that they are metastable, with electron affinities, relative to the $\mathrm{nsnp}{}_{}{}^3{}_{}{}^{}P$ state of the neutral atom, of 0.24 and 0.32 eV, respectively.