Quantum-chemical determination of Born–Oppenheimer breakdown parameters for rotational constants: the open-shell species CN, CO+ and BO

Abstract

The quantum-chemical protocol for computing Born–Oppenheimer breakdown corrections to rotational constants in the case of diatomic molecules is extended to open-shell species. The deviation from the Born–Oppenheimer equilibrium rotational constant is obtained by considering three contributions: the adiabatic correction to the equilibrium bond distance, the electronic contribution to the moment of inertia requiring the computation of the rotational g-tensor, and the so-called Dunham correction. Values for the Born–Oppenheimer breakdown parameters of CN, CO+, and BO in their 2Σ+ electronic ground states are reported based on coupled-cluster calculations of the involved quantities and compared to available experimental data.