SOME OBSERVATIONS ON THE THEORY OF DIELECTRIC RELAXATION IN ASSOCIATED LIQUIDS

Abstract

The theory of absolute reaction rates is examined for the case of relaxation in associated polar liquids where the activation process is probably an excitation of a librational motion to one of complete rotation over a rotational potential energy barrier. The rotational barriers in water are calculated using the point-charge model of the water quadrupole and the effect of thermal bond bending is examined. The experimental heats of activation for dielectric relaxation in water and deuterium oxide are discussed and their temperature dependence examined; the heat capacity change for rotational activation is derived. Isotopic effects in the heats of activation, the relaxation times, and frequency factors are discussed. A qualitative explanation is sought for the homogeneity of relaxation times in water; rotation of water molecules in the fields of the hydroxonium and hydroxide ions present in water may account for the narrow distribution of relaxation times observed experimentally. This mechanism is shown to be consistent with other theoretically derived quantities and with the mechanism of proton mobility in water. A different mechanism is indicated in ice, where the proton concentration is lower, but in ice containing extra protons, the mechanism probably reverts to that existing in water.