THE ADSORPTION GEOMETRY AND ENERGETICS OF FORMALDEHYDE PHYSISORBED ON AG(111) - AN EELS AND TPD STUDY

Formaldehyde (H2CO and D2CO) adsorbed on Ag(111) has been studied in ultrahigh vacuum at submonolayer to multilayer coverages using electron energy loss spectroscopy (in both vibrational and electronic loss regimes) and temperature programmed desorption. It is shown that H2CO is weakly adsorbed on Ag(111) at T < 106 K with little perturbation of its vibrational or electronic properties as compared to the gas-phase molecule. The coverage (c)-dependent desorption activation energy for the monolayer is estimated to be 6.2 + 0.5c kcal/mol. It is demonstrated that the adsorption geometry on the surface can be determined from the relative intensities of the vibrational loss peaks of H2CO and D2CO. The CO axis of formaldehyde is found to be tilted away from the surface normal by 57-degrees +/- 6-degrees. The angle between the molecular plane and the tilt-plane is less well determined, but most likely lies between 0-degrees and 36-degrees.