ACETYLENIC COMPLEX-FORMATION AND DISPLACEMENT VIA ACID-BASE REACTIONS ON AG(110)
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abstract
Acetylene reacts with oxygen atoms on the Ag(110) surface via a Brnsted acid-base pathway to form H2O plus adsorbed acetylide intermediates. The reaction occurs with a high probability and proceeds to complete consumption of adsorbed oxygen. Below 250 K oxygen abstracts one proton per acetylene, forming HC2(a) species. The monodentate acetylides disproportionate at 270 K to yield acetylene plus bidentate acetylides C2(a). The bidentate acetylides give rise to LEED patterns which suggest formation of domains of uniform dimension on the surface. The C2 species are stable to 550 K, at which temperature dissociation to amorphous carbon is observed. The identity of the acetylide intermediates was confirmed by titration reactons. HC2(a) species react with CH3COOD to give HC=CD, C2(a) species react to form C2D2. These reactions completely remove the acetylides as acetylene and result in formation of a stoichiometric coverage of adsorbed acetate intermediates. Results of X-ray photoelectron spectroscopy confirm the stoichiometry of the initial proton-transfer, disproportionation, and titration reactions above. Carbon atoms attached to the surface in the acetylide intermediates exhibit a shift to lower binding relative to acetylene, reflecting the formation of the surface bond. Ultraviolet photoelectron spectroscopy shows no evidence for rehybridization of acetylene or acetylides on Ag(110) and further confirms the identity of the C2 species by showing evidence for the C-C and bonding orbitals. 1982.
