Manifestation of the collective effects in the rotational motion of molecules in liquids

The Lagrange approach to the theory of thermal hydrodynamic fluctuations is developed. The rotational motion of a Lagrange particle is studied in deta il. The apparent expression for the angular velocity autocorrelation functi on (AVACF) at arbitrary times is derived. The obtained results are used to explain the specificity of the behaviour of the AVACF for a molecule. The c ollective contribution to the rotational self-diffusion coefficient as well as the manifestation of collective effects in the frequency dispersion of the dielectric permittivity are discussed. The peculiarities of the AVACF f or two-dimensional liquids are considered.