High frequency dynamics of glass forming liquids at the glass transition

The dynamic structure factor of the glass formers glycerol, o-terphenyl, and n-butyl-benzene has been studied by inelastic x-ray scattering across the liquid-glass transition. Data taken at selected temperatures in the 1-8 nm(-1) momentum transfer (Q) range show a propagating sound like mode in both liquid and glass phases. The energy of this mode, studied at fixed Q (approximate to 2 nm(-1)) on a fine temperature grid, shows a cusp behavior in a region either comparable or higher than the macroscopic structural arrest temperature T-c. This suggests the existence of a correlation between the glass structure and the arrest taking place at the molecular scale.