Quantum-mechanical continuum solvation study of the polarizability of halides at the water/air interface

In this work, a theoretical study of static polarizabilities of halides (fluoride, chloride, bromide and iodide) at the water/air interface is presented. The study has been carried out employing a new development of the polarizable continuum model (PCM) to treat model interfaces between two different media. Within this framework the water/air interface is modeled as a water/vacuum interface having bulk properties (e.g., density or permittivity) varying smoothly from the bulk water to the vacuum in the interfacial region. The model allows the inclusion of electrostatic and repulsion effects arising from this inhomogeneous environment into the quantum chemical calculation for each of the selected ionic species. Static polarizabilities are then calculated as a function of the ion-interface distance. The results on polarizabilities together with those obtained for other properties and with free energy profiles are finally discussed in relation to the recent simulation results showing a preference of heavier halides for the interface than for bulk water.