Dissecting the stabilization of iodide at the air–water interface into components: A free energy analysis

Recent experiments and simulations show that large chaotropic anions favor solvation at the water surface, mainly due to induction interactions dominated by ionic polarizabilities. We compare the solvation free-energy components of iodide at the water surface and bulk with a recent, polarizable force field. The bulk position is stabilized by the interaction between the iodide permanent charge and the solvent permanent dipole moments; the surface is favored by the iodide polarizability and the reduced cavity accommodating the solute. The ionic solvation is not described satisfactorily by linear response; the non-linearity of the iodide induced dipole moment is discussed.