Complex Susceptibility of Liquid Water as a Two-Potential System of Reorienting Polar Molecules

The theory elaborated in ref. 1 and 2 is applied to the calculation of the liquid water wide-band (0 < ν/cm^(-1) < 1000) dielectric spectra. These comprise the Debye relaxation region at the centimetre/millimetre wavelengths and the two-humped absorption coefficient frequency dependence in the far infrared (FIR) region. It is supposed that a major part of H2O molecules, called [L]-particles or [L]-molecules, are bonded by relatively strong H-bonds; [L]-molecules perform librations of relatively small amplitude β (β is about 20°). The remaining molecules called R-molecules have more rotational / translational mobility. A new microscopic molecular confined rotator / doble well potential (CR DWP) model of liquid water is developed. The contributions of [L]-and [R]-molecules to the complex permittivity ε are found on the basis of the confined rotator (CR) and the double well potential (DWP) models, with rectangular and cos^2(θ) intermolecular potential profiles, respectively. It is shown that the CR/DWP model gives a good description of the Debye relaxation and a qualitative description of FIR the dielectric spectra of water

Dielectric Response and a Phenomenon of a Narrow Band Absorption for a Classical Rotor in a Double Well Potential

The theory of dielectric relaxation in a planar ensemble of polar molecules is presented for a model where dipoles rotate in an intermolecular conservative double well potential, having a profile U = U_0*sin^2(θ). The evolution of the wide band dielectric spectra is demonstrated when the potential depth U_0 is varied; an isotropic and anisotropic medium being taken as examples. The spectra comprise the Debye relaxation and the quasi-resonant Poley absorption region. The rigorous theory is compared with a simplified one which was called the hybrid quasi-elastic bond / extended diffusion model. This approximation is valid for a qualitative description and also for the quantitative one at the large field parameter p = (U_0/((k_B)T))^(1/2). For P >> 1 the spectrum comprises one narrow absorption band and one Debye relaxation region considerably shifted to low frequencies. It is show that in the long lifetime limit τ there exists a minimum absorption band Δν_0(p). The quantity Δν_0 becomes small if the parameter p >> 1.The dielectric relaxation in ice 1 is discussed with regards to this phenomenon