Three-Body Hydrogen Bond Defects Contribute Significantly to the Dielectric Properties of the Liquid Water-Vapor Interface.

We present a simple model of aqueous interfacial molecular structure, and we use this model to isolate the effects of hydrogen bonding on the dielectric properties of the liquid water-vapor interface. We show that water's interfacial molecular structure can be understood by considering the orientational preferences of a single molecule immersed in the environment of the average interfacial density field. We illustrate that depth-dependent orientational anisotropy is determined by the geometric constraints of hydrogen bonding, and we show that the primary features of atomistic simulation data can be reproduced by assuming an idealized, perfectly tetrahedral hydrogen bonding geometry. We demonstrate that nonideal hydrogen bond geometries are required to account for variations in the orientational polarization and polarizability of the interface. Finally, we highlight that these properties contain significant contributions from a specific type of geometrically distorted three-body hydrogen bond defect that is preferentially stabilized at the interface.