Impact of inter- and intra-molecular interactions on the collective dynamics of liquids and glass-forming systems

In a recent LET experiment with polarization analysis we have disentangled for the first time collective (coherent) and self (incoherent) contributions to the intensity scattered by heavy water. They behave in a strikingly different way in the region of length scales larger than the inter-molecular distances --an almost unexplored territory due to the low intensities and mixing contributions. The collective response at such mesoscales is nearly independent of scattering vector (Q), suggesting the dominance of a Q-independent mode, with the same temperature dependence as the mainly diffusive collective dynamics at inter-molecular scales. Here we will study the impact of inter- and intra-molecular interactions on the collective dynamics of liquids and glass-formers: van der Waals (e. g. tetrahydrofurane) vs H-bonds (previously studied water), and the internal connectivity (polymer melt).