Orientational relaxation in hydrogen-bonded systems: liquid water

Abstract

A two-fractional confined rotator/extended diffusion model has been suggested to calculate the wide-band (0 < ν/cm^–1 < 1000) complex permittivity spectra and absorption coefficient of liquid water caused by reorientations of the H₂O polar molecules. The motion of water molecules coupled with ‘normal’ hydrogen bonds is considered from the viewpoint of the confined rotator model, while in the case of the weakened hydrogen bonds, similar motion is described by the extended diffusion model.

It is shown that the experimental dielectric spectra are in qualitative agreement with the theoretical ones calculated for liquid water. The auto-correlation functions (ACFs) of the dipole moment and angular velocity are calculated for liquid water. For the purpose of comparison we also calculate the ACFs for one of the non-associated polar liquids, CH₃F. Both ACFs are interpreted in terms of the molecular models proposed in this paper.