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 rangeT = 214÷ 283K. 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 c0(Q) and the high frequency value c1�(Q). This finding confirms the existence of a structural (�) 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 ��(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 �-relaxation process is the number of the hydrogen bonds per molecule.