Electronic Structure and Ground State of Scandium Monofluoride

Abstract

Recent experiments have shown that the electronic ground state of ScF is 1Σ+, contrary to the 3Δr ground state known for the isoelectronic TiO molecule. Previous theoretical calculations have shown that the 1Σ+ state of TiO lies above 3Δr, in agreement with experiment. Truncated matrix Hartree—Fock wavefunctions for ScF have been calculated here to study the apparent ground-state term inversion of the 1Σ+ and 3Δr levels of this molecule. The ab initio calculations are based on the LCAO expansion method of Roothaan and employ an extended basis that contains the essential functions necessary to represent uncorrelated ground states reliably when there are close-lying valence states. The basis is larger than those used in previous calculations on related monoxides to ensure that the computed ground state and qualitative ordering of ther low-lying states are stationary to further improvements in the basis. For reference purposes, similar extended calculations have been carried out on the TiO molecule. It is found that 3Δr of configuration δσ is the symmetry restricted Hartree—Fock ground state of both ScF and TiO. A semiempirical estimate of the correlation energy contributions shows that correlation depresses the 1Σ+ state relatively more than 3Δr in both cases and suggests that 1Σ+ is the ground state of ScF, in agreement with experiment. This study provides additional information on the electronic structures of molecules of the transition metals and demonstrates the possibilities of term inversions in other monoxides of the titanium family.