Influence of temperature on wideband water spectra: Semi-phenomenological calculation

The results of analytical calculation of the complex permittivity ε and of the absorption coefficient α are presented for the temperature range extending from −5.6 °C for supercooled water to 81.4 °C. Dielectric response is modeled by two water fractions with lifetimes from 0.1 to 0.25 ps. One fraction comprises rigid permanent dipoles librating rather freely in a narrow and deep hat-like potential well and the other fraction comprises H-bonded charged molecules performing: (a) fast elastic vibrations along the hydrogen bond; (b) elastic reorientations around this bond; and (c) non-harmonic bending vibration perpendicular to the H-bond. At low temperature the latter vibration is characterized by a noticeable association of water molecules. The calculation reveals the break in continuity of some fitted model parameters occurring in water at the temperature ≈300 K.