Alkali oxide diatomics: Explanation of the change in ground state symmetry from LiO(2Π) CsO(2Σ+)

The ground state of CsO is 2Σ+, whereas the ground state of LiO is 2Π. Using purely ionic wave functions, we explain the origin of this effect in terms of a balance between Pauli repulsion (favoring 2Σ) and quadrupole attractions (favoring 2Π) and provide spectroscopic parameters (Re, ωe, De) on LiO, NaO, KO, RbO, and CsO from ab initio correlated wave functions.