The adsorption of acetylene on W(110) at room temperature: An electron spectroscopic study

Acetylene adsorbed as C 2H radicals with the C-C axis parallel to the surface and to the [1̄10] surface direction. Up to 0.5 L a poorly ordered p(2 × 2) structure was formed and a poorly ordered c(2 × 2) thereafter. Electron bombardment caused C-H bond scission, as did heating to 500 K. Scission of the C-C bond started at 650 K. Saturation of the surface carbide produced molecular C 2H 2 similar to that formed on W(100), but less stable to either electron bombardment or to heating indicative of a species lying closer to the W(110) surface in comparison with its W(100) counterpart. Carbon could diffuse below the crystal surface without raising the temperature above 1000 K. A schematic energy diagram is proposed to rationalize this effect.