Determination of the bonding and orientation of ethylene on Pd(111) by near-edge X-ray absorption fine structure and photoelectron spectroscopy

The bonding and orientation of ethylene on Pd(111) at low temperature have been characterized by NEXAFS and photoelectron spectroscopy. UPS shows that ethylene is {pi}-bonded to palladium, while NEXAFS demonstrate unequivocally that the molecule adopts a flat-lying geometry on the metal surface, with a slight weakening of the C-C bond. At 100 K the saturation coverage is 0.42 ethylene molecules per surface unit cell. On annealing to 300 K, both XPS and UPS indicate that chemisorbed ethylene desorbs essentially reversibly from the surface with no detectable conversion of decomposition to other species.