Structure of a Precursor State in Dissociative Chemisorption

Near-edge- and surface-extended-x-ray-absorption fine-structure measurements of ${\mathrm{H}}_2$S on $\mathrm{Cu}\mathrm{}\left(001\right)p(2\mathrm{}\times 2)\mathrm{S}$ have been used to make the first direct structural determination of an intermediate molecular precursor in dissociative adsorption. Our results indicate that population of these precursor states overcomes the kinetic barrier to ${\mathrm{H}}_2$S adsorption and leads to the formation of a $c(2\mathrm{}\times 2)\mathrm{S}$ structure.