Self-dynamics and collective dynamics of liquid mercury

The low-momentum dynamics of liquid mercury has been investigated by means of inelastic neutron scattering and molecular dynamics (MD) simulations. Because of the rather high incoherent cross-section and the high mass of mercury, the measured dynamic structure factor is dominated by the self-correlation function, although the low-momentum collective dynamics are made accessible by the very good energy resolution of the experiment. Collective modes are clearly visible against the incoherent scattering up to a momentum transfer of 0.4Å−1 and the associated velocity is found to be 2200 ± 200 m s−1, well in excess of the sound velocity which is equal to 1470 m s−1. The self-dynamics, as resulting from either the experiment or the MD simulations, turn out to be characterized by two time scales.