Atomic Negative Ions. Second Period

Abstract

Results of Hartree-Fock calculations on the ions ${\mathrm{Na}}^{\ensuremath{-}}$, ${\mathrm{Al}}^{\ensuremath{-}}$, ${\mathrm{Si}}^{\ensuremath{-}}$, ${\mathrm{P}}^{\ensuremath{-}}$, and ${\mathrm{Cl}}^{\ensuremath{-}}$ in states of the lowest electronic configuration, along with correlation and relativistic corrections, are given. The data are used to compute electron affinities for the atoms of the second row of the periodic table, and the stability of the excited states of the ions relative to the neutral ground-state atoms. The computed electron affinities for atoms on which experimental determinations are not available are 0.78 eV for Na, 0.52 eV for Al, 1.39 eV for Si, and 0.78 eV for P. The computed electron affinities for S and Cl are 2.12 and 3.56 eV in fair agreement with the experimental values of 2.07\ifmmode\pm\else\textpm\fi{}0.07 and 3.613\ifmmode\pm\else\textpm\fi{}0.003 eV, respectively. For the second-row negative ions, several excited states are lower in energy than the corresponding ground-state neutral atoms; the computed stabilities for the species ${\mathrm{Al}}^{\ensuremath{-}}(^{1}D)$, ${\mathrm{Si}}^{\ensuremath{-}}(^{2}D)$ and ${\mathrm{Si}}^{\ensuremath{-}}(^{2}P)$ are 0.23, 0.58, and 0.08 eV, respectively. While the $^{1}D$ state of ${\mathrm{P}}^{\ensuremath{-}}$ is estimated to be very close to that of $\mathrm{P}(^{4}S)$, our estimates are not accurate enough to say definitely whether it is above or below.