INFRARED REFLECTION-ABSORPTION SPECTROSCOPY, X-RAY PHOTOELECTRON-SPECTROSCOPY AND TEMPERATURE-PROGRAMMED DESORPTION STUDY ON THE ADSORPTIONAND DECOMPOSITION OF FE(CO)5 OVER SILVER SURFACES

The adsorption and decomposition of Fe(CO)5 over Ag surfaces have been studied using infrared reflection absorption spectroscopy (IRAS), X-r ay photoelectron spectroscopy (XPS) and temperature-programmed desorpt ion (TPD). The thermal desorption spectrum (TDS) showed that Fe(CO)5 i s partly chemisorbed at temperatures below 120 K on the Ag surface cle aned by Ar-ion sputtering. The active sites for chemisorption may be d efect sites produced by the sputtering, XPS revealed that the chemisor bed species involve a small amount of dissociated species even at 95 K and undergo decarbonylation upon heating the substrate to ca. 180 K t o form an intermediate species, Fe(CO)4, which is stable at temperatur es 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 a nd a weak band at 2116 cm-1 in the IRA spectra of adsorbed Fe(CO)5 dec rease and eventually disappear upon elevating the temperature to 230 K , and a new band grows at 2052 cm-1 upon heating the substrate from 23 0 to 280 K. These IRAS results were discussed in terms of a surface se lection rule for IRAS. The geometry of adsorbed Fe(CO)5 was concluded to be square pyramidal with the square base toward the surface, and th e 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 temperatur es below 400 K.