Chemisorption of C₂H₂ on Pd(111) and Pt(111): formation of a thermally activated olefinic surface complex

Ultraviolet photoemission spectroscopy studies indicate that acetylene chemisorbs on Pd(111) and Pt(111) as π-bonded acetylene for T≲ 180 K but upon warming (or room temperature exposure) forms a new surface species. We identify the electronic structure of this new phase as being characteristic of an olefinic C2H2 surface species - the result of rehybridization of the initially chemisorbed molecule. These results are discussed relative to previous work on Ni(111). © 1977.