The adsorption of water on both clean and oxygen-predosed Al(111) has been studied by vibrational spectroscopy using electron energy loss spectroscopy (EELS). At 130 K, adsorption on either surface is competitively associative and dissociative. The dominant dissociation product is a hydroxyl species. On the clean surface, adsorption is predominantly molecular, while in the presence of oxygen, adsorption is predominantly dissociative. In contrast to the low temperature behavior, adsorption of water on clean Al(111) at 300 K is completely dissociative, resulting in oxygen adsorption and surface oxidation. Adsorbed hydroxyl species can be produced at 300 K by prolonged water exposure. Upon heating a low-temperature water layer adsorbed on either surface, molecular water desorption and further decomposition both occur. The production of adsorbed hydroxyl species from water reaches a maximum at 250 K on the clean surface and at 350 K on the oxygen-predosed surface. The hydroxyl species decompose above these temperatures to evolve hydrogen and further oxidize the Al(111) surface.

As a part of a continuing investigation of acetylene reactions on tungsten surfaces covered by ultrathin metal films, the chemistry of acetylene on clean and carbide-modified W(211) surfaces has been investigated using high-resolution electron energy-loss spectroscopy (HREELS) and temperature-programmed desorption (TPD) measurements. Acetylene decomposes between 100 and 450 K on the clean W(211) surface, ultimately forming carbidic carbon and gaseous hydrogen. During this decomposition process, a mixture of different hydrocarbon fragments are formed, most likely vinylidene (CCH 2 ) or vinyl (HCCH 2 ) and acetylide (CCH). On the carbidemodified W(211) surface, acetylene also decomposes to produce carbon and gaseous hydrogen. However, compared to clean W(211), the CH bond activation is suppressed on the carbide-modified W surface, as evidenced by the broadening and significant shifting of the H 2 TPD features toward higher temperatures as well as by the HREEL spectra monitoring the thermal decomposition of acetylene on the carbide-modified W(211) surface.

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