Clustered water adsorption on the NaCl(100) surface

The adsorption dynamics of water on NaCl(100) is studied by molecular dynamics calculations as a function of coverage. We find that, starting from a critical coverage of about 1/2 monolayer, a coupling of the water dipoles sets in and the interaction between the water molecules wins over the interaction between adsorbate and substrate leading via percolation to formation of infinite cluster networks. This effect is confirmed qualitatively by surface sensitive optical second harmonic measurements with well-controlled water exposure. At a coverage of one bilayer, a two-dimensional ‘‘ice’’ structure is found to be stable. Simulated low-energy electron diffraction (LEED) patterns for this configuration are in excellent agreement with recent observation of a c(4×2) overstructure.