Structural Evolution of Water on ZnO(10 $\bar{1}$ 0): From Isolated Monomers via Anisotropic H-Bonded 2D and 3D Structures to Isotropic Multilayers

The surface chemistry of water on zinc oxides is an important topic in catalysis and photocatalysis. Interaction of D₂ O with anisotropic ZnO(10 $\bar{1}$ 0) surfaces was studied by IR reflection absorption spectroscopy using s- and p-polarized light incident along different directions. Interpretation of the experimental data is aided using isotopologues and DFT calculations. The presence of numerous species is revealed: intact monomers, a mixed 2D D₂ O/OD adlayer, an anisotropic bilayer, and H-bonded 3D structures. The isolated water monomers are identified unambiguously at low temperatures. The thermally induced diffusion of water monomers occurs at elevated temperatures, forming dimers that undergo autocatalytic dissociation via proton transfer. Polarization- and azimuth-resolved IR data provide information on the orientation and strength of H-bonds within the 2D and 3D structures. Ab initio molecular dynamics simulations reveal strong anharmonic couplings within the H-bond network.