Mechanism of the photolysis of iron pentacarbonyl adsorbed on a Pt surface

Photolysis of Fe(CO) ₅ adsorbed on a Pt surface was investigated by IR reflection absorption spectroscopy (IRAS), temperature-programmed desorption (TPD) technique, and X-ray photoelectron spectroscopy (XPS). Although no photoproducts are detected by IRAS, TPD and XPS spectra show that a partly decarbonylated species is formed by irradiation and its Fe/CO ratio is approximately 1:4. Because IRAS is selectively sensitive to vibrational modes perpendicular to a metal surface, these results indicate formation of Fe(CO) ₄ as an intermediate species with a square planar structure parallel to the surface. The intermediate Fe(CO) ₄ species decomposes completely with rise in temperature up to 300 K. Such instability of the intermediate is responsible for the absence of Fe ₂(CO) ₉ or Fe ₃(CO) ₁₂ produced typically by the Fe(CO) ₅ photolysis over insulator surfaces, in the gas or liquid phase, or in low temperature matrices.