Van der Waals molecule

[4] Also in cold equilibrium gases vdW molecules are formed, albeit in small, temperature dependent concentrations.

Van der Waals molecules are usually very non-rigid and different versions are separated by low energy barriers, so that tunneling splittings, observable in far-infrared spectra, are relatively large.

The VRT spectroscopic study of Van der Waals molecules is one of the most direct routes to the understanding of intermolecular forces.

[6] In study of helium-containing van der Waals complexes, the adiabatic or Born–Oppenheimer approximation has been adapted to separate angular and radial motions.

Despite the challenges posed by the weak interactions leading to large amplitude motions, research demonstrates that this approximation can still be valid, offering a quicker computational method for Diffusion Monte Carlo studies of molecular rotation within ultra-cold helium droplets.