RELATION BETWEEN THE ELECTRON-SCATTERING LENGTH AND THE VAN-DER-WAALSAPPROXIMATION TO THE EQUATION OF STATE

A theoretical relation between the electron scattering length and the van der Waals approximation to the equation of state is described. The theory provides a simple calculation for the scattering length of neu tral atomic scatterers such as rare gases, using two experimental para meters: the hard-core radius (calculated from the van der Waals equati on of state, using critical data) and the atomic polarizability. The r esults' for the calculated electron scattering length agree with measu red values derived either from the energy shifts of highly excited mol ecular Rydberg states, perturbed by He, Ne, Ar, Kr, and Xe, or from sw arm electron cross-section data for the same gases.