Electronic excitation of metal carbonyls on Ag(111): The role of surface-mediated quenching

Abstract

The electronic excitation of adsorbed Fe(CO)5 on clean Ag(111) has been studied using both ultraviolet light (4.8 eV) and electron impact (3–132 eV). Comparisons to photoreaction measurements for Fe(CO)5 adsorbed on an inert spacer layer show that substrate-adsorbate quenching effects of electronically excited Fe(CO)5 on Ag(111) are essentially nonexistent. These results suggest that the CO ligands of Fe(CO)5 themselves act as a spacer layer for electronically excited Fe(CO)5 (ads) species. Both photodissociation and electron impact dissociation of Fe(CO)5 on Ag(111), causing loss of one or more CO ligands, produce new metal carbonyl species which are more strongly bound to Ag(111) than the parent Fe(CO)5 molecule. These new species exhibit a lower cross section for further photodissociation compared to the parent Fe(CO)5 molecule. This is postulated to be due to an increased Ag–Fe interaction for the coordinately unsaturated species produced by photolysis, causing enhancement of adsorbate-substrate quenching. Comparisons are also made between electron impact studies of Fe(CO)5, Ni(CO)4, and C6D6Cr(CO)3 adsorbed on Ag(111). All three carbonyls exhibit similar behavior upon the loss of CO or benzene ligands.