PHOTODISSOCIATION OF IRON PENTACARBONYL ADSORBED ON AG(111)

The adsorption states and photochemistry of Fe(CO)(5) adsorbed on Ag(1 11) surface at similar to 90 K were studied using IR reflection absorp tion 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 t o 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 absor ption 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. T his result implies that Fe(CO)(5) molecules near the surface undergo s ignificant quenching of photoexcited states, and the surface-plasmon i nduced enhancement lies within ca. 1 nm apart from the surface. The fi nal photo-product exhibits two sharp C-O stretching bands at 2058 and 2068 cm(-1) in IRA spectrum, which are assigned to the species produce d from the first layer and the overlayer Fe(CO)(5), respectively. (C) 1998 Elsevier Science B.V. All rights reserved.