What is the ground electronic state of KO?

Abstract

High-level, restricted coupled cluster with singles, doubles, and perturbative triples calculations are performed to determine the ground electronic state of KO. In the absence of spin–orbit coupling, we find that the ground state is a ²Σ⁺ state, with a² Π state lying just over 200 cm⁻¹ higher in energy. We ascertain that basis set extension, higher-order correlation energy, mass-velocity, and Darwin relativistic terms do not change this ordering. We then calculate the low-lying Ω states when spin–orbit coupling is turned on. The ²Σ⁺ ₁/₂state undergoes an avoided crossing with the 2Π ₁/₂state, and we therefore designate the ground state as X ½. This state is essentially ²Σ⁺ ₁/₂at short R, but essentially 2Π ₁/₂at long R; there is a corresponding A ½ state with the opposite behavior. These states have significantly different shapes and so spectroscopy from the adiabatic states. Finally, we calculate the dissociation energy D ₒ, of KO as 66±1 kcal mol⁻¹ and derive ΔH[sub f](KO, 0 K) as 13.6±1 kcal mol⁻¹.