Near infrared spectra and the disrupted network model of normal and supercooled water

The near IR (overtone) spectra of water, H₂O-D₂O solutions, and a glass-forming glycerol +D₂O solution have been measured in the temperature range 80 to -30 °C (-120 °C for the glycerol +D₂O solution) using emulsion samples to gain access to the deep supercooling range. At -30 °C the intensity attributed to weakly hydrogen bonded -OH is greatly diminished and a small extrapolation in the latter case leads to a spectrum closely similar to that of the vitreous glycerol +D ₂O solution. This is a very broad spectrum, extending from 1.4-1.65 μm, which we associate with a fully bonded and immobile quasilattice in which there is a distribution of hydrogen bond strengths. The changes in intensity which occur with rise in temperature are seen to be consistent with an "exciting across the centroid" model (a weak bond⇄strong bond exchange) suggested by Stillinger and Rahman on the basis of MD calculations. The enthalpy change for this process is found to be 3.0 kcal/mol, consistent with light-scattering data for the hydrogen bond-breaking energy.