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An account is given of the characters of static and dynamic liquid structures through angular molecular motions studies in dipolar liquids. It recapitulates the main features of torques, velocities, reorientations and angular correlations that have been observed in rotational absorption spectra, and illustrates the role of directional forces induced by permanent dipoles interactions. The discussion considers alternately features in the frequency domain or in the time domain, by considering correlation functions and memory functions of the molecular motions. Comparisons are carried out regularly with the results of numerical simulations, since these provide deeper insight into the details at a molecular level.Intermolecular torques are scrutinized as for their strengths, durations and recurrence, showing their dependence on two timescales (both sensitive to dipolar forces), the short-time collisional components recurring, while the long-lived structural torques persist. Angular velocities are derived from their power spectrum in the far-infrared and their relationship to the torques is studied in a generalized Langevin formalism.Following this review a new coherent process is considered in the frame of concerted molecular rotations among local microclusters. The process illustrates the interdependence of dynamics and the intermolecular forces, with emphasis on the role of dipole interactions. |
