IRAS AND TDS STUDY ON THE PHOTOLYTIC DECARBONYLATION OF IRON PENTACARBONYL ADSORBED ON A SIO2 FILM WITH A BURIED METAL LAYER

IR reflection-absorption spectroscopy (IRAS) is successfully applied t o the observation of surface species formed during the photolytic deca rbonylation of Fe(CO)(5) adsorbed on a SiO2 firm with a buried Al laye r, and thermal desorption spectroscopy (TDS) as well. TDS shows that F e(CO)(5) is molecularly adsorbed on the SiO2 surface at temperatures l ower than 150 K. Irradiation of adsorbed Fe(CO)(5) with synchrotron or bital radiation (SOR) light (>150 nm) leads to CO photo-evolution due to photo-decarbonylation without the photo-desorption of molecular Fe( CO)(5). The average CO/Fe ratio in photo-product obtained from CO evol ution during irradiation and subsequent TDS is close to 4, suggestive of formation of Fe(CO)(4) intermediate, while the photo-product exhibi ts a broad IRAS band and a broad TDS peak with three maxima, indicativ e of formation of oligomer species. The photo-product is, however, unl ikely to be Fe-3(CO)(12), a typical product of the photolysis of Fe(CO )(5) adsorbed on a SiO2 powder, since its IRAS band disappears upon he ating the substrate up to 200 K even though the product remains unchan ged in composition. The disappearance of the band is interpreted in te rms of the surface selection rule of IRAS as a change in the geometry of the product.