Propene adsorption on clean and oxygen-covered Au(111) and Au(100) surfaces

The adsorption of propene on Au(111) and Au(100) was investigated using temperature-programmed desorption (TPD) and high-resolution energy loss spectroscopy (HREELS). A desorption activation energy of 9.4 kcal/mol and very small shifts of the vibrational frequencies from their gas-phase values indicate that the interaction of propene with the surface is weak. Energy loss spectra suggest that propene adsorbs with its molecular plane tilted slightly with respect to the surface plane. Atomic oxygen, chemisorbed on the gold surfaces, was characterized using TPD and low-energy electron diffraction (LEED), and its reaction with propene investigated. Propene desorption from the oxygen-covered surface occurs at 150 K with a shoulder at 200 K. Only propene and its total oxidation products desorbed from a one monolayer (1 ML) oxygen-covered surface. At an oxygen coverage of similar to 0.4 ML, the higher temperature propene desorption feature at 200 K was maximized. HREEL spectra of propene giving rise to the 200 K desorption feature show shifts in the intensities and frequencies of the -CH2 related vibrational features. Small amounts of product with masses 56 and 58 amu were observed for propene adsorbed onto a 0.4 ML oxygen-covered surface.