Adsorption geometry of OH adsorbed at F centers on a NaCl(100) surface

The orientation of molecular (Formula presented)O in a bilayer on defect-free NaCl(100) and of chemisorbed OH adsorbed at F centers on the (100) surface of NaCl was investigated using angle-resolved O K edge near-edge x-ray-absorption fine-structure spectroscopy (NEXAFS). High-quality single crystalline thin films of NaCl(100) of about four monolayers thickness were grown on Ge(100). These films were bombarded with 250 eV electrons so that F and F′ centers of a maximum density of about 10% of a monolayer were created. Whereas on the defect-free surface only molecular water is adsorbed, dissociation occurs at the F centers and (Formula presented) is bound. NEXAFS of molecular water shows almost no angular dependence even in the monolayer. This finding is consistent with formation of a hydrogen bonded bilayer of water suggested earlier. The OH species formed at the F centers is found to be inclined with respect to the surface normal by 39°±4°. An adsorption model is proposed. © 1996 The American Physical Society

Dissociation of Water on the Surface of Organic Salts Studied by X-ray Photoelectron Spectroscopy

Water dissociation has important implications for numerous chemical processes. Although extensively studied on metals and to some extent on inorganic salts, this phenomenon has not yet been shown to occur on organic surfaces. Herein, the ability of two crystalline organic hydrochloride salts to induce water dissociation at their surface was demonstrated. Using a modified X-ray photoelectron spectroscopy setup, the oxygen lacking crystalline organic salts were exposed to high water vapor pressures within an environment sealed from ambient air. Thus, the O(1s) peak resulting from exposure to water vapor at room temperature could be unambiguously assigned to dissociated water, a phenomenon previously unreported with organic material. Both powder and single crystal samples were investigated, to determine the effect of defects on the extent of dissociation. Dissociation was shown to be dependent on the level of defects present at the surface. The presence of highly reactive dissociated water on organic surfaces has important implications for the solid state chemical stability of these substances