The effect of iron pentacarbonyl on soot formation during the pyrolysis of propane/Ar and acetylene/Ar mixtures behind reflected shock waves was studied. Time profiles of the soot yield and temperature were obtained. The soot-promoting effect of iron pentacarbonyl was revealed. The results for propane/Fe(CO)(5)lAr mixtures were simulated within the framework of a detailed kinetic model composed of 3390 direct and reverse elementary steps involving 295 species. A novel kinetic mechanism of the thermal decomposition of Fe(CO)(5) and the formation of free iron atoms and iron nanoparticles was tested. This mechanism correctly describes the available experimental data. A qualitative explanation of the experimentally observed effects of Fe(CO)(5) additives on soot formation was proposed. It was suggested that the nascent iron nanoparticles serve as soot precursors for further surface growth with the formation of soot particles. The influence of small Fen(CO) m fragments and small Fen clusters on soot formation is less important because of a rather short lifetime of these species.