Calculation of the van der Waals force constant from oscillator strength sums

It is shown that the van der Waals force constant may be computed accurately and directly from oscillator strength sums S ( k ). In particular, for pairs of the atoms H, He, Ne, Ar, Kr and Xe the van der Waals force constant can be obtained to within an error of about 4% from accurate values of S (-2), S (-4) and S (-6), each of which may be derived from accurate refractive index measurements.