The OH stretching spectrum of liquid water: A random network model interpretation

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Abstract
We report the results of an analysis of the OH‐stretching region of the vibrational spectrum of liquid water. The random network model is realized by time‐averaged molecular dynamics configurations of ST‐2 water. The hydrogen bond network is defined using a geometric definition of bonded pairs of molecules. Force constants are calculated using empirically derived formulas relating the shifts of the intramolecular frequency and anharmonic potential energy coefficients with a hydrogen bond strength parameter. The strength parameter is related to the separation in a molecular pair, hence, it has a distribution of values defined by the molecular configuration in the model liquid. Fermi resonance between the OH stretching mode and the bending overtone is shown to be an important second‐order effect in the spectral band shape. The calculated spectra compare well with experimental results and support the contention that the spectral features are dominated by intermolecular interactions.