Cage Diffusion in Liquid Mercury

We present inelastic neutron scattering measurements on liquid mercury at room temperature for wave numbers q in the range 0.3 - 7.0 Å-1. We find that the energy half width of the incoherent part of the dynamic structure factor S(q,E) is determined by a self-diffusion process. The half width of the coherent part of S(q,E) shows the characteristic behavior expected for a cage diffusion process. We also show that the response function at small wave numbers exhibits a quasielastic mode with a time scale characteristic of cage diffusion, however, its intensity is larger by an order of magnitude than what would be expected for cage diffusion. We speculate on a scenario in which the intensity of the cage diffusion mode at small wave numbers is amplified through a valence fluctuation mechanism.