Structure and dynamics of acetonitrile: Molecular simulation and neutron scattering

We examine the interplay between organization and dynamics in bulk liquid acetonitrile. Using angularly resolved radial distribution functions, g(r,?), derived from molecular simulations, we identify a complex microscopic structure which most molecules are associated with one or more neighboring an antiparallel, “octupole-paired” configuration and/or offset, head-to-tail configuration. A detailed analysis of these structural motifs reveals that offset dimers prevalent. time-dependent pairing corroborates this picture robust associations favoring dimers, last longer than antiparallel dimers. This organization, is times (?ps) typical rotational time constant, cannot be explained on basis Coulomb interactions dimer, so must arise collective effects neither strong nor specific. Finally, using both neutron-scattering techniques study acetonitrile over scales ranging subpicosecond (the vibrational density states) to picosecond (rotational/translational motions generalized tens picoseconds (self-diffusivity Fickian regime).