Infrared-Thermodynamics Conversion as a Function of Temperature: Towards Confined Water

Abstract : An experimental method has been developed to calculate the thermodynamic properties of water from its vibrational properties, relevant to study (in near future) the properties of adsorbed or confined water. The infrared absorption of the intra-molecular OH stretching mode of liquid water has been measured over a wide range of temperature (from -10°C to 90°C). The corresponding large band has been decomposed into three Gaussian components standing for three different water connectivities (percolation model) that feature the liquid state as a function of temperature: network, intermediate, multimer, water. Measurements evidenced that the components are differently shifted with temperature, giving a quantitative insights into the internal energy change of liquid. A vibrational partition function has been used to calculate the corresponding thermodynamic properties, neglecting all energy components except the present intra-molecular vibrational mode. Interestingly, the vibrational free enthalpy thus computed differs of the total free enthalpy only by a multiplicative constant all along the thermal range.