Microscopic dynamics and relaxation processes in liquid hydrogen fluoride

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--2830.3em0exK. The data, analyzed using a viscoelastic model with a two time-scale memory function, show a positive dispersion of the sound velocity $c(Q)$ between the low frequency value c₀(Q) and the high frequency value c_∞α(Q). This finding confirms the existence of a structural (α) relaxation directly related to the dynamical organization of the hydrogen bonds network of the system. The activation energy Eₐ of the process has been extracted by the analysis of the temperature behavior of the relaxation time τ_α(T) that follows an Arrhenius law. The obtained value for Eₐ, when compared with that observed in another hydrogen bond liquid as water, suggests that the main parameter governing the α-relaxation process is the number of hydrogen bonds per molecule.