Cage diffusion in liquid mercury

TL;DR

This study uses inelastic neutron scattering to investigate cage diffusion in liquid mercury, revealing that both incoherent and coherent parts of the dynamic structure factor are influenced by self-diffusion and cage effects, with an unexpectedly large quasi-elastic response at small wave numbers.

Contribution

It provides experimental evidence of cage diffusion in liquid mercury and suggests a valence fluctuation mechanism amplifies the cage diffusion signal at small wave numbers.

Findings

Energy halfwidth of incoherent S(q,E) is determined by self-diffusion.

Coherent S(q,E) shows behavior characteristic of cage diffusion.

Large quasi-elastic mode at small wave numbers suggests valence fluctuation amplification.

Abstract

We present inelastic neutron scattering measurements on liquid mercury at room temperature for wave numbers $q$ in the range 0.3 $< q <$ 7.0 \AA$^{-1}$. We find that the energy halfwidth of the incoherent part of the dynamic structure factor $S(q,E)$ is determinded by a self-diffusion process. The halfwidth 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 quasi-elastic 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.