Quantum Effects on Global Structure of Liquid Water

The structure difference between light and heavy liquid water has been systematically in-vestigated by high precision Raman spectroscopy over the temperature range of 5-85 oC. Distinct difference between the Raman spectral profiles of two different liquid waters is clearly observed. By analyzing the temperature-dependent Raman spectral contour using global fitting procedure, it is found that the micro-structure of heavy water is more ordered than that of light water at the same temperature, and the structure difference between the light and heavy water decreases with the increase of the temperature. The temperature off-set, an indicator for the structure difference, is determined to vary from 28 oC to 18 oC for the low-to-high temperature. It indicates that quantum effect is significantly not only at low temperature, but also at room temperature. The interaction energy among water moleculeshas also been estimated from van't Hoff's relationship. The detailed structural information should help to develop reliable force fields for molecular modeling of liquid water.