First-Principle Analysis of the IR Stretching Band of Liquid Water

We provide an interpretation of the complex shape of the infrared (IR) stretching band of neat, heavy water, based on the results of ab initio molecular dynamics simulations. We show that intermolecular dipolar correlations play a key role in determining the shape and width of the band and that these correlations are long-ranged, extending to the second coordination shell. Both hydrogen-bonded and non-hydrogen-bonded molecules contribute to the IR stretching band over the entire frequency range, with no distinctive peak or shoulder associated with each species. Within a molecular orbital picture, we identified specific features of the band arising from correlations of electronic contributions to the IR activity.