THERMAL AND PHOTOINDUCED DESORPTION AND DECOMPOSITION OF FE(CO)(5) ONCLEAN AND OXYGEN-MODIFIED RU(001)

The thermal and photoinduced desorption and decomposition of Fe(CO)(5) on clean and O-covered Ru(001) surfaces were studied. Adsorption of F e(CO)(5) on Ru(001) is associated with a partial decomposition, result ing in the formation of CO and Fe(CO)(x) fragments. In the thermal des orption spectrum for mass 28, the surface-stabilized decomposition pro duct gives rise to a peak at 270 K, whereas the first and second monol ayers of molecular Fe(CO)(5) desorb at 190 and 160 K, respectively. Th e photochemical studies of Fe(CO)(5) at mono- and multilayered molecul ar coverages on Ru(001) were carried out by UV irradiation at various wavelengths (290-450 nm), Irradiation at wavelengths > 370 nm resulted in photodesorption, while photodecomposition showed significant contr ibution at shorter wavelengths. The total cross sections for the photo chemical process closely follow the UV absorption spectrum of Fe(CO)(5 ) in the gaseous phase, suggesting that the photoreaction is mainly du e to the direct absorption of UV photons by the adsorbed Fe(CO)(5) mol ecule. The photodecomposition yields reactive intermediates that subse quently form Fe-x(CO)(y) clusters. These species thermally decompose, desorbing the CO moieties and depositing Fe atoms on the surface. Diss ociative adsorption of Fe(CO)(5) has also been observed on O-covered R u(001). O adatoms create inhomogeneity in the adsorption sites for Fe( CO)(5), as seen from the broadened desorption peak of the first molecu larly adsorbed layer of Fe(CO)(5). In contrast to the clean surface, i rradiation of Fe(CO)(5) adsorbed on O/Ru(001) at 290 nm produced relat ively lower yields of photodecomposition and a higher extent of photod esorption attributable to the more effective quenching of electronical ly excited Fe(CO)(5) by the O-covered surface.