Nuclear relaxation and molecular properties

The dynamic structure of liquid pyridine has been studied by analysing the deuterium and nitrogen 14N quadrupolar relaxation data of selectively labelled substances. The molecular motions are anisotropic; the anisotropy changes from ‘solid like’ (faster rotation about the axis perpendicular to the molecular plane) to ‘gas like’ (faster rotation about an in-plane axis) behaviour as the temperature increases. The ‘solid like’ region extends over most of the temperature range where pyridine is liquid (at ca. atmospheric pressure). At low temperatures the molecular re-orientations may be described as a rotational diffusion process. Some indication of a possible motional coherence is found.