The chemistry of alkali atoms on solid water:: a study with MIES and UPS

The chemistry of Na atoms in a multilayer aqueous environment was studied with metastable impact electron spectroscopy (MIES) and ultraviolet photoemission spectroscopy (UPS) under UHV conditions. Films of solid water were grown at 130 K on a rutile, 1 x 1 reconstructed, TiO2(100) single crystal, and exposed to Na. The Na-water interaction was studied between 10 and 130 K. At small exposures, Na-induced water dissociation takes place whereby the Na gets ionized. Initially the outermost water layer remains intact. The number of OH species seen at the surface increases with exposure; finally, no molecular water, but only OH species can be detected with MIES and UPS. At sufficiently large exposures Na atoms are detected at the surface. We find that efficient water dissociation and Na solvation take place only above about 100 K. Under annealing, the mixed film is destroyed around 200 K; the titania surface is then covered by Na+ and hydroxyl groups which desorb around 400 K. (C) 2003 Elsevier Science B.V. All rights reserved.