Van der Waals molecule

A van der Waals molecule is a stable cluster consisting of two or more molecules held together by van der Waals forces. van der Waal's forces include momentary attractions between molecules, diatomic free elements, and individual atoms. They differ from covalent and ionic bonding in that they are not stable, but are caused by momentary polarization of particles. Because electrons have no fixed position in the structure of an atom or molecule, but rather are distributed in a probabilistic fashion based on quantum probability, there is a non-negligible chance that the electrons are not evenly distributed and thus their electrical charges are not evenly distributed. See Schrodinger Equation for the theories on wave functions and descriptions of position and velocity of quantum particles.

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van der Waals molecules are usually very rigid and different geometries are separated by low energy barriers, so that tunneling splittings, observable in far-infrared spectra, are relatively large. Thus, in the far-infrared one may observe intermolecular vibrations, rotations, and tunneling motions of vdW molecules. Examples of well-studied vdW molecules are Ar₂, H₂-Ar, benzene-Ar, (H₂O)₂, and (HF)₂