4s Orbitals in sulphur: the perturbation by ligands in SF4 and SF6

Abstract

Valence states of sulphur involving 4s and 3d_σ orbitals in the field of four and six fluorine atoms were investigated. The calculations were made with neglect of interatomic exchange terms. The results indicate a participation of 3d_σ orbitals larger than that of 4s orbitals to molecular valence states. The importance of exchange terms involving 1s orbitals of the ligands is discussed. It is estimated that the inclusion of these repulsive terms affects only marginally energy sequences and excited orbital radii as obtained from the electrostatic approach, the most significant feature being a reduction of the energy gap between states involving 3d_σ and 4s orbitals. It is inferred that if properly antisymmetrized wavefunctions are used, configurations involving 4s orbitals may to some extent become competitive with those involving 3d_σ orbitals.