Dimerization Degree of Water Molecules, Their Effective Polarizability, and Heat Capacity of Saturated Water Vapor

Abstract

The properties of water vapor have been studied. The main attention is focused on the physical nature of the effective polarizability of water vapor and the heat capacity of water vapor at a constant volume, with a proper modeling of those parameters being a good test for a correct description of the dimer concentration in various approaches. Thermal vibrations of water dimers are found to be the main factor governing the specific temperature dependences of those characteristics, and the normal coordinates of dimer vibrations are determined. Fluctuations of the dipole moments of dimers and their contribution to the dielectric permittivity of water vapor are considered in detail. The contribution of the interparticle interaction to the heat capacity is taken into account. By analyzing the effective polarizability and the heat capacity, the temperature dependence of the dimer concentration at the vapor-liquid coexistence curve is determined. The noticeable dimerization in saturated water vapor takes place only at temperatures T/Tc > 0.8, where Tc is the critical temperature.