Microscopic dynamics and relaxation processes in liquid Hydrogen Fluoride

TL;DR

This study investigates the microscopic dynamics of liquid hydrogen fluoride using inelastic x-ray and Brillouin scattering, revealing a structural relaxation linked to hydrogen bond network organization and its temperature-dependent activation energy.

Contribution

It provides new insights into the structural relaxation processes in liquid hydrogen fluoride and quantifies the activation energy associated with hydrogen bond network dynamics.

Findings

Positive dispersion of sound velocity observed

Structural ($$) relaxation confirmed

Activation energy follows Arrhenius law

Abstract

Inelastic x-ray scattering and Brillouin light scattering measurements of the dynamic structure factor of liquid hydrogen fluoride have been performed in the temperature range$ T=214\div 283 K$. The data, analysed using a viscoelastic model with a two timescale memory function, show a positive dispersion of the sound velocity $c(Q)$ between the low frequency value $c_0(Q)$ and the high frequency value $c_{\infty \alpha}(Q)$. This finding confirms the existence of a structural ($\alpha$) relaxation directly related to the dynamical organization of the hydrogen bonds network of the system. The activation energy $E_a$ of the process has been extracted by the analysis of the temperature behavior of the relaxation time $\tau_\alpha(T)$ that follows an Arrhenius law. The obtained value for $E_a$, when compared with that observed in another hydrogen bond liquid as water, suggests that the main parameter governing the $\alpha$-relaxation process is the number of the hydrogen bonds per molecule.