METHYL FORMATE ON AG(111) - 2 - ELECTRON-INDUCED SURFACE-REACTIONS

Methyl formate, HCOOCH3, molecularly adsorbed at 120 K on Ag(111), rea dily undergoes electron-induced chemistry. Working mainly with monolay er coverages and 50 eV electrons, we have characterized the products e jected during electron irradiation and desorbed thermally after irradi ation. Controlled electron irradiation at 120 K dissociates HCOOCH3, b ut more than 95% of the C and O is retained, even when the original mo nolayer 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 spec troscopy and work function change measurements. Primary products are t hemselves altered by electron irradiation; no new products appear in d esorption, but the distribution changes. The data support a two-channe l electron dissociation model, one forming methyl (H3C(a)) and formate s (HCOO(a) and HCO(a)O-(a)), the second forming methoxy (CH3O(a)) and formyl (HC(a)O).