Relation between the OH stretching frequency and the OO distance in time-resolved infrared spectroscopy of hydrogen bonding

A non-empirical theory is presented to study the relation between the OH stretching frequency and the OO distance in ultrafast laser spectra of water. Diluted solutions HDO/D2O rather than pure H2O were considered to switch off resonant vibrational interactions between water molecules; the local structure of water as well as the OO distribution functions remain unchanged in this substitution. Only times superior to 100-200fs are considered to avoid perturbations generated by collisions between water molecules. It is then shown that the Novak-Mikenda type relations between the OH stretching frequency and the OO distance largely survive when going from equilibrium to laser perturbed non-equilibrium systems. It is also shown that temporally varying infrared pump-probe profiles of OH stretching bands in HDO/D2O closely parallel the oxygen-oxygen distribution functions of these solutions. Infrared pump-probe spectroscopy can thus replace time-resolved X-ray diffraction in this particular case.