Water Structure in the Contact Layer on the Surface of Crystalline Silver Iodine

Abstract

The basal face of a silver iodide crystal in unsaturated water vapor is covered by a continuous molecular layer which serves as an underlying film. The structure of the film demonstrates long-range molecular order and looks like a honeycomb. Thus, macroscopic manifestations of the substrate wetting are due to the structure of the underlying film rather than the substrate crystal surface as such. A quarter of hydrogen bonds of the film molecules participate in bonding with the ions of the second crystallographic layer of the substrate. Three other quarters ensure the integrity of the film. The interactions with the ions of the first crystallographic layer are antibonding in nature. No free molecules serving as hydrogen bond donors are left on the film surface to keep vapor molecules. The shape of the free energy function associated with the adsorption of vapor molecules indicates its markedly layered nature.