Experimental Evidence for the Formation of Solvation Shells by Soluble Species at a Nonuniform Air–Ice Interface

Abstract

Soluble species induce surface premelting at the air–ice interface in the thermodynamic ice stability domain below the liquidus. This quasi-liquid layer is thought to increase in thickness with concentration of impurities and to represent a reservoir into which larger amounts of soluble species dissolve compared to a more rigid ice surface. To directly investigate the response of the quasi-liquid layer to increasing amounts of solutes and to clarify the distribution of these at the ice surface with depth, we use a combination of Auger electron yield X-ray absorption and photoelectron spectroscopies. We studied the adsorption of formic acid to ice at 251 K. These two complementary methods allow concluding that solutes enter the air–ice interface but do not necessarily induce a thicker quasi-liquid layer. Rather, modifications of the hydrogen-bonding network seem to be linked to the formation of solvation shells. We suggest that the flexibility of water molecules in the quasi-liquid layer is essential to fo...