Quantum-chemical calculation of Born–Oppenheimer breakdown parameters to rotational constants

Abstract

The paper describes how Born–Oppenheimer breakdown parameters for the rotational constants of diatomic molecules can be determined via quantum-chemical computations. The deviations from the Born–Oppenheimer equilibrium values are accounted for by considering the adiabatic correction to the equilibrium bond distances, the electronic contribution to the rotational constant via the rotational g tensor, and the so-called Dunham correction, which can be computed directly from a polynomial expansion of the potential curve around the equilibrium distance. Calculations for HCl, SiS, and HF demonstrate the accuracy that can be achieved in the theoretical treatment of the considered Born–Oppenheimer breakdown parameters and the usefulness of such calculations is illustrated for highly accurate spectroscopic measurements in the field of rotational spectroscopy.

Keywords:

• quantum chemistry
• rotational spectroscopy
• Born–Oppenheimer breakdown

Acknowledgements

This work was supported in Mainz by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie and in Bologna by the University of Bologna (RFO funds).