Reaction between H₂O and Cs on the Ru(001) surface

H2O adsorption on Cs predosed Ru(001) surfaces (with θCs = 0.08, 0.25 and 0.33 (= Cs monolayer)) at 90 and 300 K has been investigated using high resolution electron energy loss spectroscopy (HREELS). For θCs = 0.08, H2O adsorbs molecularly at 90 K and monomeric H2O is observed at small H2O exposures. H2O reacts with the metallic Cs layer for θCs = 0.25 and 0.33. While for θCs = 0.25 dissociation into Had+OHad is observed, complete dissociation into 2Had + Oad occurs for θCs = 0.33. The chemical reactivity of the Cs adlayer increases according to its gain of metallicity with the increase of atomic density. Possible structural models for the (2 × 2)-(Cs + OH + H) overlayer on the Ru(001) surface are discussed