Measurements of the frequencies of the normal modes in sodium

The frequencies of the normal modes in sodium with wavevectors in the (001) and (1macron10) symmetry planes have been measured by the inelastic scattering of neutrons. The samples were at room temperature, and about 600 frequencies were recorded. The results have been analyzed in terms of two local pseudopotential models, one a variant on the model of Heine and Abarenkov and the other a simple analytical potential. The latter, involving two adjustable parameters, gave a good fit to the measurements.