Vibrational corrections to dipolar coupling constants: an alternative for determining equilibrium distances from rotational spectroscopy.

The main interaction between the spins of two nuclei is the dipole-dipole coupling between their magnetic moments. The importance of these interactions lies in the facts that a) dipolar coupling constants should be considered for the proper analysis of the hyperfine structure in rotational spectra and b) that dipolar-coupling tensors provide an alternative way for determining bond distances (based either on the analysis of rotational or NMR spectra). In principle, the determination of the dipolar coupling constants just require knowledge of the molecular equilibrium geometry, though quantum-chemical investigations are necessary to evaluate the vibrational corrections. In this presentation we will compare computed dipolar coupling constants for several small to medium-sized molecules to experiment, and demonstrate the importance of including vibrational corrections for accurate predictions. In addition, we will show how experimental dipolar coupling constants together with computed vibrational corrections can be used to derive equilibrium bond distances.