The molecular structure of liquid water delivered by absorption spectroscopy in the whole IR region completed with thermodynamics data

Absorption spectra of liquid water at various temperatures in the whole IR region (0<ν˜<4000cm-1) are obtained from ATR spectra recorded in the mid-IR region combined with absorption spectra measured in the FIR region. They can be accurately decomposed over two independent spectra. The spectra of the two kinds of H2O (D2O) molecules they suppose are defined as fulfilling spectroscopic constraints and as being in accordance with thermodynamic values. Their enthalpy difference He − Hg is found equal to 11.8 kJ mol−1 for ordinary water and 12.2 kJ mol−1 for heavy water. H2O (D2O) molecules of lower enthalpies Hg, greater than the enthalpy of H2O or D2O molecules in ices by 1.3 kJ mol−1, display vibrations that resemble those of H2O (D2O) molecules in ice. Molecules with enthalpies He reorient without breaking their H-bonds as He appears greater than the potential barrier for rotations around their symmetry axes.

► Experimental spectra of liquid water in the whole IR region at various temperatures. ► Quantitative analysis of the evolution of vibrational spectra with temperature. ► IR spectra of H2O molecules preponderant at low and high temperatures. ► Dynamics and thermodynamics properties of H2O molecules in liquid water.