Fingerprints of hydrogen bonding in the terahertz dynamics of ethanol and water: an Inelastic X-Ray Scattering study

We used Inelastic X-Ray Scattering methods to measure the terahertz spectrum of density fluctuations of ethanol in
both liquid and solid phases. The results of a Bayesian inference-based lineshape analysis with a multiple excitation
model and the comparison with a previous similar analysis on water indicate that the different structures induced by
hydrogen bonds in ethanol and water have a profound influence on the respective dynamic responses, the latter being
characterized by longer living and better resolved high-frequency acoustic excitations. Also, we compare these findings
with those obtained with an alternative approach based on the Exponential Expansion Theory and ensuring sum rule
fulfillment, demonstrating that the model's choice directly impacts the number of spectral modes detected.