Molecular Dynamics in Liquid Nitrogen and Liquid Bismuth Investigated by Cold Neutron Scattering

The neutron scattering law S(K, ω) for liquid nitrogen at 77.4°K and liquid bismuth at 560°K was determined using a beryllium filter and time-of-flight technique. The scattered neutron spectra at scattering angles between 15° and 90° for liquid nitrogen and between 60° and 90° for liquid bismuth were measured. After making the necessary corrections for multiple scattering, the experimental results were compared with several theoretical models suggested for the scattering law. In the quasi-elastic range, the best agreement was obtained with the effective mass model. For liquid nitrogen it was found necessary to introduce the contribution of rotational diffusion. In the inelastic range, the dispersion law of quasi-phonons for both liquids was determined according to Egelstaff's quasi-crystalline model. (author)