ABSTRACT
The attractive forces between pairs of atoms or molecules are almost always strong enough to support bound vibrational states. The resulting molecular complexes, or Van der Waals molecules, are very weakly bound, and are easily destroyed by collisions with other molecules. They exist in small but significant concentrations in gases and gas mixtures: for example, in Ar gas at 120 K and 1 bar, about 0.4% of the atoms are present as bound dimers [1]. The dimer concentrations decrease with increasing temperature, but are larger for systems with stronger attractive forces, such as most systems containing polar molecules.
