Département de chimie moléculaire

A review. Autoionization of water which gives rise to its pH is one of the key properties of aq. systems. Surfaces of water and aq. electrolyte solns. are traditionally viewed as devoid of inorg. ions; however, recent mol. simulations and spectroscopic expts. show the presence of certain ions including hydronium in the topmost layer. This raises the question of what is the pH (defined using proton concn. in the topmost layer) of the surface of neat water. Microscopic simulations and measurements with atomistic resoln. show that the water surface is acidic due to a strong propensity of hydronium (but not of hydroxide) for the surface. In contrast, macroscopic expts., such as zeta potential and titrn. measurements, indicate a neg. charged water surface interpreted in terms of preferential adsorption of OH-. Here we review recent simulations and expts. characterizing autoionization at the surface of liq. water and ice crystals in an attempt to present and discuss in detail, if not fully resolve, this controversy. [on SciFinder(R)]