Vibrational spectroscopic studies of aqueous interfaces: Salts, acids, bases, and nanodrops

Spectroscopic studies of surface water structure as it is affected by salts, acids, and ammonia are reviewed. The review also includes clusters that contribute to understanding the aqueous interface along with studies of aqueous nanodrops. The interfacial structure of water is highly sensitive to the addition of ionic inorganic solutes. The effects of monovalent inorganic anions depend on the polarizability of the ion, which is related to ion size: the more polarizable the anion, the stronger the effect. The interfacial concentration gradients give rise to an increasing interfacial depth as well as with the divalent inorganic anion. However, the larger charge on the polarizable sulfate anion drives an ordering of the water molecules well beyond the immediate solvation shell. For acids, dramatic affects are observed for the dangling OH, as well as possible surface potential effects. The surface potential and interfacial depth increase due to concentration gradients extending deeper into the bulk solution. Overall, cluster and aqueous nanodrop studies are found to significantly contribute to unraveling the effect of ions on the surface.