Dielectric relaxation in liquid water: two fractions or two dynamics?

Dielectric relaxation in liquid water is studied using molecular dynamics (MD) simulations in the temperature range of 240 to 340 K at atmospheric pressure. The main dielectric and fast relaxation mode are identified in the spectra of dipole moment autocorrelation functions. The microscopic origin of the fast dielectric relaxation process, which takes place on a time scale of subpicoseconds at room temperature, is discussed. A new hypothesis for the fast dielectric mode is presented. It is based on the assumption of the intrawell rotational relaxation taking place during the waiting period between thermally activated large angle jumps occurring in the course of changing H-bond partners.