Reactions of iron clusters with oxygen and ethylene: Observation of particularly stable species

Iron clusters have been produced by CO2-laser-induced decomposition of iron pentacarbonyl in a flow reactor. The absorption of CO2 laser photons was a chieved by using SF6 as a sensitizer. By adding an oxidizing gas, N2O, or a hydrocarbon, C2H4, molecules which are also dissociated in the laser field , the iron clusters may react with several radicals. The as-synthesized spe cies are extracted from the reaction zone by a conical nozzle and expanded into the source chamber of a cluster beam apparatus where they are analyzed with a time-of-flight mass spectrometer. In the experiment with N2O, we ob serve a magic peak at m=856 amu which can be readily assigned to the partic ularly stable Fe13O8 cluster. If C2H4 is added to the reactant gas, the mas s spectrum reveals a magic peak at mass m=884 amu. Using deuterated ethylen e, the magic peak shifts by 12 amu to larger masses, indicating that the ma gic cluster contains 12 hydrogen atoms. With the given restrictions, we rea dily derive the molecular formula Fe13C12H12. Chemical stability and symmet ry considerations suggest that the detailed chemical formula of the magic c luster is Fe-13(C2H2)(6) and that its structure corresponds to a Fe-13 icos ahedron with six HC=CH or C=CH2 groups bound to six pairs of the 12 iron su rface atoms. (C) 2000 American Institute of Physics. [S0021-9606(00)01040-0 ].