Intermolecular forces in van der waals dimers

Abstract

Abstract For several van der Waals molecules, the results of ab initio intermolecular perturbation theory are compared with the simple Buckingham‐Fowler model. A selection of dimers is studied, with emphasis on cases where the experimental structure is not reliably predicted by the hard‐sphere electrostatic model. Cases are reported where the electrostatic term dominates, in agreement with the model: HF···HF, H 3 N···HF, N 2 O···HF, and H 2 CO··· HF; cases where the electrostatic term dominates but the molecular shapes are not well described by hard spheres: CO 2 ···H 2 O and CIF···HF; and cases where there is a delicate balance between the electrostatic and other terms:H 2 O···HF, H 2 O···HCCH, CO 2 ···HF, CO 2 ···N, and CH 3 CN···HCN. It is concluded that, in general, the electrostatic interaction is central to the strength and orientation dependence of the forces between molecules and that the model provides a useful approximation to this interaction, while perturbation theory gives a more complete picture.