A thin and homogeneous alumina film was prepared by deposition and oxidation of aluminum on a refractory Re(0001) substrate under ultrahigh vacuum conditions. X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and high-resolution electron-energy-loss spectroscopy (HREELS) demonstrate that the oxide film is long-range ordered, essentially stoichiometric and free from surface hydroxyl groups. The chemisorption and thermal decomposition of Mo(CO) 6 on the Al 2 O 3 film were investigated by means of XPS and UPS. Mo(CO) 6 adsorbs molecularly on the oxide film at 100K; however, thermal decomposition of the adsorbate occurs upon annealing at high temperatures. Consequently the metallic molybdenum clusters are deposited on the thin alumina film via complete decarbonylation of Mo(CO) 6 .