Temperature and density dependence of the refractive index of pure liquids

Abstract

The refractive indices and densities of benzene, methanol, and carbon tetrachloride have been determined in the temperature range between 8 and 50°C. The data were fitted to an empirical extension of the Lorentz-Lorenz equation previously proposed, which takes into account the change of the polarizability α with temperature and density. The density dependence of α at constant temperature (piezo-optic effect) for the three liquids is quite similar to that previously observed for water and heavy water, and may be qualitatively understood in terms of changes in molecular electronic structure upon compression. In contrast to water and heavy water, which exhibit a significant thermo-optic effect, α is essentially independent of temperature at constant density for all three liquids studied here. A model based on the temperature dependence of librational motion in the liquid appears to account for what now seems to be the anomalously large thermo-optic effect in water and heavy water.