The orientation of molecular H2O in a bilayer on defect-free (100), and of chemisorbed OH that was adsorbed at F centers on the (100) surface, was investigated by using angle-resolved near-edge X-ray absorption fine-structure spectroscopy. High-quality monocrystalline thin (100) films of NaCl which were about 4 monolayers thick were grown onto Ge (100). These films were bombarded with 250eV electrons, so that F and F’ centers with a maximum density of about 10% of a monolayer were created. On the defect-free surface, only molecular water was adsorbed, but dissociation occurred at the F centers and the OH- was bound. The near-edge X-ray absorption fine-structure spectroscopic data for molecular water revealed almost no angular dependence; even in the monolayer. This was consistent with the formation of a H-bonded bilayer of H2O. The OH species which formed at the F centers was found to be inclined at 39 to the surface normal.

U.Malaske, H.Pfnür, M.Bässler, M.Weiss, E.Umbach: Physical Review B, 1996, 53[19], 13115-20