Journal of Physical Chemistry B, Vol.101, No.51, 11119-11128, 1997
Methyl formate on Ag(111). 2. Electron-induced surface reactions
Methyl formate, HCOOCH3, molecularly adsorbed at 120 K on Ag(111), readily undergoes electron-induced chemistry. Working mainly with monolayer coverages and 50 eV electrons, we have characterized the products ejected during electron irradiation and desorbed thermally after irradiation. Controlled electron irradiation at 120 K dissociates HCOOCH3, but more than 95% of the C and O is retained, even when the original monolayer is completely dissociated. H-2, CH4, CH2O, CO2, and HOCH2CHO (glycolaldehyde) desorb as the temperature is raised. Heating to 450 K leaves a clean Ag(111) surface as measured by X-ray photoelectron spectroscopy and work function change measurements. Primary products are themselves altered by electron irradiation; no new products appear in desorption, but the distribution changes. The data support a two-channel electron dissociation model, one forming methyl (H3C(a)) and formates (HCOO(a) and HCO(a)O-(a)), the second forming methoxy (CH3O(a)) and formyl (HC(a)O).