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

TL;DR

This study models how three-body hydrogen bond defects significantly influence the dielectric properties of the water-vapor interface, highlighting the importance of collective molecular interactions in interfacial water behavior.

Contribution

The paper introduces a simple model linking hydrogen bonding geometries, especially three-body defects, to dielectric properties at the water-vapor interface, supported by atomistic simulations.

Findings

Three-body hydrogen bond defects are crucial for interfacial dielectric properties.

Ideal tetrahedral hydrogen bonding reproduces basic orientational features.

Non-ideal geometries are necessary to explain variations in polarization.

Abstract

In this Letter, 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. By comparing this model to the results of atomistic simulation we show that the anisotropic distribution of molecular orientations at the interface can be understood by considering the behavior of a single water molecule interacting with the average interfacial density field via an empirical hydrogen bonding potential. We illustrate that the depth dependence of this orientational anisotropy is determined by the geometric constraints of hydrogen bonding and we show that the primary features of simulated orientational distributions can be reproduced by assuming an idealized, perfectly tetrahedral hydrogen bonding geometry. We also demonstrate that non-ideal hydrogen bond geometries are required to produce interfacial variations in the average orientational polarization and polarizability. We find that these interfacial properties contain significant contributions from a specific type of geometrically distorted three-body hydrogen bond defect that is preferentially stabilized at the interface. Our findings thus reveal that the dielectric properties of the liquid water-vapor interface are determined by collective molecular interactions that are unique to the interfacial environment.