Relations between the association of liquid water molecules and the dielectric and raman spectra of H2O

A two-fraction model that makes it possible to analytically calculate the complex dielectric permittivity of liquid water in wide frequency and temperature ranges is described. The far IR spectrum of water is found as a dielectric response of vibrating H 2 O monomers and dimers, while the spectrum of low-frequency (Debye) relaxation is found as a response of collective reorientations of associated water molecules. It is shown that the dielectric spectra of water calculated at −5.6, 27, and 81.4°C agree well with its experimental spectra. The low-frequency Raman spectrum of water is calculated for the same set of model parameters as the spectrum of the complex dielectric permittivity. These spectra are found to correlate with each other, and the physical nature of the difference between them is clarified. An interpretation of the well-known anomaly of water at a temperature of T = 300 K is presented. It is shown that the number of water molecules that compose an associate at this temperature is minimal.