An XPS and UPS investigation of the adsorption of ethylene on the (111) surface of silver

Monolayer adsorption of pure ethylene on the (111) surface of saver at 80 K has been studied by X-ray (hv = 1486.6 eV) and ultraviolet (hv = 21.2 and 40.8 eV) photoelectron spectroscopy. The density of the adlayer is approximately 5 × 10¹⁴ molecules/cm² at saturation, multilayer formation being prohibited by the ultrahigh vacuum of the spectrometer. The molecular orbitals designated σ¹_CH, σ_CC, σ_CH and 2ss¹ by Demuth are observed at 7.0, 9.0, 10.3 and 13.6 eV below the Fermi level, respectively, but the higher lying π level is obscured by the silver d-band emission. The data are consistent with an undistorted molecule, adsorbed with the molecular axis parallel to the surface. Desorption occurs below 200 K without significant decomposition products remaining on the surface in agreement with the conventional notion that clean silver is relatively inert with respect to olefin adsorption.