Insights into hydrogen bonding via ice interfaces and isolated water.

Water in a confined environment has a combination of fewer available configurations and restricted mobility. Both affect the spectroscopic signature. In this work, the spectroscopic signature of water in confined environments is discussed in the context of competing models for condensed water: (1) as a system of intramolecular coupled molecules or (2) as a network with intermolecular dipole-dipole coupled O-H stretches. Two distinct environments are used: the confined asymmetric environment at the ice surface and the near-isolated environment of water in an infrared transparent matrix. Both the spectroscopy and the environment are described followed by a perspective discussion of implications for the two competing models. Despite being a small molecule, water is relatively complex; perhaps not surprisingly the results support a model that blends inter- and intramolecular coupling. The frequency, and therefore the hydrogen-bond strength, appears to be a function of donor-acceptor interaction and of longer-range dipole-dipole alignment in the hydrogen-bonded network. The O-H dipole direction depends on the local environment and reflects intramolecular O-H stretch coupling.