Mass spectrometric characterization of iron clusters produced by laser pyrolysis and photolysis of Fe(CO)₅ in a flow reactor

Abstract

Laser-induced decomposition of iron pentacarbonyl in a flow reactor has been used to produce iron clusters and nanoparticles. The as-synthesized species are extracted from the reaction zone by a conical nozzle and expanded into the source chamber of a cluster beam apparatus where, after having traversed a differential chamber, they are analyzed in situ with a time-of-flight mass spectrometer. Three different lasers have been employed to accomplish decarbonylation of the Fe(CO)₅ molecules. A pulsed CO₂ laser (λ = 10.6 μm) was used to excite a mixture of SF₆ and Fe(CO)₅ and to pyrolyze the iron pentacarbonyl. Laser photolysis was performed by directly dissociating the Fe(CO)₅ molecules with UV radiation. For this purpose, we used the tripled (λ = 355 rim) and quadrupled (λ = 266 um) Nd:YAG laser as well as an ArF excimer laser (λ = 193 nm). The mass spectrometric analysis showed that only the Nd:YAG laser produced high purity iron clusters which were essentially free of contamination.