Photochemical activity of iron pentacarbonyl on Ag(111): photofragmentation, quenching and wavelength-dependent effects

Abstract

The UV photon induced decomposition of Fe(CO) 5 on Ag(111) was examined with temperature programmed desorption (TPD), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). In the absence of UV irradiation, Fe(CO) 5 thermally desorbed from Ag(111) with minimal decomposition. The temperature difference between the monolayer and multilayer states (12 K) suggests that the monolayer was physisorbed. Photodecomposition of adsorbed Fe(CO) 5 with 256 or 365 nm light produced unidentified surface species, presumably Fe x (CO) y clusters, which thermally decomposed near 330 K in TPD, evolving gas-phase CO and depositing a pure Fe film on the Ag surface. The photochemical properties of monolayer and multilayer Fe(CO) 5 were investigated separately by isolating multilayers of Fe(CO) 5 from the Ag(111) surface with a chemically and photolytically inert buffer layer (n-decane). Photodecomposition near the threshold energy (3.4 eV) was five times as efficient for monolayer Fe(CO) 5 as for multilayer Fe(CO) 5, presumably due to a red-shifted absorption threshold for the monolayer. The Photodecomposition cross sections with 4.8 eV light were similar to gas-phase values, suggesting that the excited Fe(CO) 5 species were not significantly quenched by the surface. Quenching of energetic Fe x (CO) y fragments was more pronounced in the monolayer than for Fe(CO) 5 as inferred by the low cross section for Fe x CO x Photodecomposition.