Heavier alkali-metal monosulfides (KS, RbS, CsS, and FrS) and their cations

Abstract

The heavier alkali-metal monosulfides (KS, RbS, CsS, and FrS) have been studied by high-level ab initio calculations. The RCCSD(T) method has been employed, combined with large flexible valence basis sets. All-electron basis sets are used for potassium and sulfur, with effective core potentials being used for the other metals, describing the core electrons. Potential-energy curves are calculated for the lowest two neutral and cationic states: all neutral monosulfide species have a Π2 ground state, in contrast with the alkali-metal monoxide species, which undergo a change in the electronic ground state from Π2 to Σ+2 as the group is descended. In the cases of KS, RbS, and CsS, spin-orbit curves are also calculated. We also calculate potential-energy curves for the lowest Σ-3 and Π3 states of the cations. From the potential-energy curves, spectroscopic constants are derived, and for KS the spectroscopic results are compared to experimental spectroscopic values. Ionization energies, dissociation energies, and heats of formation are also calculated; for KS, we explore the effects of relativity and basis set extrapolation on these values. © 2005 American Institute of Physics.