Mesoscopic Dynamics in Molecular Liquids: Universality of Nondispersive Structural Mode and Its Reflection in Self-Atomic Motions.

Neutron spin echo experiments on deuterated and protonated molecular liquids with different interactions have revealed their coherent and incoherent scattering functions at the mesoscale. The coherent one decays by a nondiffusive exponential relaxation process that can be related to stress fluctuations. For self-dynamics, we show that even though diffusion is, as expected, the predominant relaxation channel at the mesoscale, the process observed for collective dynamics also appears at short times, evidencing the influence of stress fluctuations on translational motions even at high temperatures.