SELECTIVE OXYGEN ADDITION TO ADSORBED CH2 AND CH3 ON PD(100)

The reaction pathways of CH2 and CH3 in the presence of coadsorbed oxy gen atoms on a Pd(100) surface were investigated by means of temperatu re-programmed desorption (TPD) and photoelectron spectroscopy (XPS and UPS). The CHx species were produced by the dissociation of CH2I2 and CH3I. Adsorbed oxygen shifts the dissociation temperature of iodo comp ounds and the temperature of self-hydrogenation of CHx fragments forme d at higher temperatures. Oxygen atoms reacted with CH2 above 150 K to give formaldehyde, which desorbed from the surface after its formatio n. Above 200 K, the oxidalion of CH2 led to the production of H2O and CO, the latter being further oxidized to CO2 above 370 K. The oxidatio n of CH3 species with oxygen atoms also occurred above 200-220 K to yi eld CH2O, H2O and CO, very probably through the transient formation of CH3O species.