Bending force constants for weakly bound dimers AB (A = symmetric top, B = linear molecule) from centrifugal distortion in rotational spectra

The contribution of the harmonic intermolecular bending force field to the quartic centrifugal distortion constants of weakly bound dimers AB (where A is a symmetric-top molecule and B is a linear molecule) has been examined. Approximate formulae are derived that relate the force constant and the vibrational wavenumber for the oscillation of the A subunit to the combination 2DJ + DJK of distortion constants. These formulae are applied to 35 dimers, and a generalisation is made.