Distribution, structure, and dynamics of cesium and iodide ions at the H2O-CCl4 and H2O-vapor interfaces

Molecular dynamics simulations utilizing many-body potentials of H2O-CCl4 and H2O-vapor interfaces were carried out at different cesium and iodide ion concentrations to compare ion distribution, interfacial orientational and structural properties, and dynamics. It was found that cesium was repelled by both interfaces, and iodide was active at both interfaces, but to a much greater degree at the H2O-vapor interface. At the interface, the iodide dipole was strongly induced, orienting perpendicular to the interface for both systems, leading to stronger hydrogen bonds with water. For the H2O-CCl4 interface, though, there was a compensation between these strong hydrogen bonds and short to moderate ranged repulsion between iodide and CCl4. Hydrogen bond distance and angular distributions showed weaker water-water hydrogen bonds at both interfaces, but generally stronger water-iodide hydrogen bonds. Both translational and rotational dynamics of water were faster at the interface, while for CCl4, its translational dynamics was slower, but rotational dynamics faster at the interface. For many of the studied systems and species, translational diffusion was found to be anisotropic at both interfacial and bulk regions.