Photodissociation of iron pentacarbonyl adsorbed on Ag(111)

The adsorption states and photochemistry of Fe(CO)5 adsorbed on Ag(111) surface at ∼90 K were studied using IR reflection absorption spectroscopy (IRAS) and thermal desorption spectroscopy (TDS). Fe(CO)5 is molecularly adsorbed on the surface and desorbed around 180 K. A totally symmetric vibrational band appears at 2114 cm−1 in the IRA spectrum, indicating that structural deformation of Fe(CO)5 or charge transfer between the substrate and the adsorbate occurs to some extent upon adsorption. Irradiation of the adsorbed Fe(CO)5 leads to decarbonylation with a high quantum yield, especially around 330 nm. This enhanced photodecomposition is attributable to resonant coupling with excited surface plasmon of Ag. Effect of the surface plasmon on the photodecarbonylation yield was measured as a function of the absorption amount of n-decane preadsorbed on the surface as a spacer layer. The yield was increased with increasing n-decane layer, maximized at around two monolayers, and then decreased to a value twice as large as the initial yield after n-decane coverage is over three monolayers. This result implies that Fe(CO)5 molecules near the surface undergo significant quenching of photoexcited states, and the surface-plasmon induced enhancement lies within ca. 1 nm apart from the surface. The final photo-product exhibits two sharp C–O stretching bands at 2058 and 2068 cm−1 in IRA spectrum, which are assigned to the species produced from the first layer and the overlayer Fe(CO)5, respectively.