The characterization of surface acetylene and ethylene species on Pt(111) by angle resolved photoemission using synchrotron radiation

Angle resolved photoemission using synchrotron radiation was employed to elucidate the molecular structure of the species present in the low and high temperature phases of ethylene and acetylene on Pt(111). The plane polarized nature of synchrotron radiation allows the use of simple symmetry arguments to determine the orientation of an adsorbed species relative to the surface. In the low temperature phases of acetylene and ethylene the data are consistent with the carbon-carbon bond axis being parallel to the surface in agreement with earlier work. The high temperature phases of both molecules were found to consist of identical surface complexes where the carbon-carbon bond axis is normal or nearly normal to the surface. The orbital symmetries determined from this study favor the ethylidyne structure originally proposed by Kesmodel et al.