Van der Waals Forces

Theoretical and experimental values of electric dipole oscillator strengths are used to calculate the coefficients of the leading terms in the series representations of the long range interactions between pairs of atoms. Values are obtained for pairs selected from the alkali metals, the inert gases, H, H - , He + and Li + and are then employed to assess the accuracy of various approximate formulae. Where possible, comparison is made with experimental data and it is shown that the polarizabilities derived from molecular beam measurements are unreliable. A discussion is given of the measurements of elastic scattering of the alkali metals by the inert gases and it is concluded that the normal van der Waals interaction does not suffice to explain the observations at very low scattering angles.