Infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed desorption study on the absorption and decomposition of Fe(CO)5 over silver surfaces

Abstract

The adsorption and decomposition of Fe(CO)5 over Ag surfaces have been studied using infrared reflection adsorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The thermal desorption spectrum (TDS) showed that Fe(CO)5 is partly chemisorbed at temperatures below 120 K on the Ag surface cleaned by Ar-ion sputtering. The active sites for chemisorption may be defect sites produced by the sputtering. XPS revealed that the chemisorbed species involve a small amount of dissociated species even at 95 K and undergo decarbonylation upon heating the substrate to ca. 180 K to form an intermediate species, Fe(CO)4, which is stable at temperatures up to 280 K and then decomposed completely above 330 K, depositing Fe metal on the surface. An intense C—O stretching band at 2062 cm–1 and a weak band at 2116 cm–1 in the IRA spectra of adsorbed Fe(CO)5 decrease and eventually disappear upon elevating the temperature to 230 K, and a new band grows at 2052 cm–1 upon heating the substrate from 230 to 280 K. These IRAS results were discussed in terms of a surface selection rule for IRAS. The geometry of adsorbed Fe(CO)5 was concluded to be square pyramidal with the square base toward the surface, and the Fe(CO)4 moiety trigonal pyramidal. The deposited Fe metal from Fe(CO)4 was found to dissolve to some extent into the bulk Ag at temperatures below 400 K.