Thermal, Electron, and Photon Induced Chemistry of Acetone on Ag(111)

Abstract

Acetone, (CH3)2CO and (CD3)2CO, adsorbed on Ag(111) at 95 K was studied using using thermal, photon, and electron activation. Adsorption and desorption involve no dissociation. The temperature-programmed desorption (TPD) spectra exhibit three resolvable peaks, two of which (146 and 134 K) are assigned to the first layer and the third (127−134 K) to multilayers. TPD, after sequentially dosing 1 ML of (CD3)2CO followed by 1 ML of (CH3)2CO, shows extensive mixing of the two adsorbates throughout the full width of the desorption peaks. This suggests rapid motion, on the TPD time scale, below the onset of desorption (120 K). RAIRS analysis at 95 K indicates that the orientation of adsorbed acetone is coverage-dependent, but the CO bond remains nearly parallel to the Ag(111) surface at all coverages. At the lowest coverages the average C−C−C plane position is 50° from the surface normal; at higher coverages (up to monolayer) this plane tilts toward the surface normal (22°). Dissociation and desorption of adsorb...