Internal dynamics of subunits and bending force constants in weakly bound dimers
Two models for the bending motions of weakly bound dimers which use different coordinate systems have been considered and inter-related. The first approach uses standard internal coordinates and the second uses a model based on the oscillation of each monomer subunit about its centre of mass. The inter-relationship of the two treatments allows information from vibration–rotation spectroscopy and amplitudes, obtained from high resolution investigations of hyperfine structure in dimer spectra, to be combined in the evaluation of bending force constants and in the understanding of internal dynamics of dimers. The procedures developed are first applied to the CH3CN ⋯ HF dimer, for which both types of spectroscopic information are now available, and are then extended to related dimers. Oscillation amplitudes βHav for the HF subunit and the corresponding oscillation force constants kββ are reported for a series of B ⋯ HF dimers as follows: [graphic omitted].