FORMATION OF IRON-OXIDES CLUSTERS INDUCED BY RESONANT LASER-ABLATION IONIZATION

The present work has been conducted by Time-of-Flight Laser Microprobe Mass Spectrometry (TOF-LMMS) in resonant or non-resonant ionization m odes. The targets (micrometric particles of powdered iron oxides Fe1-x O, Fe3O4 and Fe2O3) were synthesized, on the one hand, from iron 54 is otopes and, on the other hand, from natural iron 56 isotopes. The posi tive-ion cluster distributions showed a strong correlation with the st oichiometry of iron in oxides. This correlation is even more striking when the resonant ionization process of iron at 278.8 nm is used. The dissociation energy of the Fe-O bond in the Fe1-xO bulk also affects t he distribution of the intensity of clusters. A better understanding o f the way cluster ions (Fe-2(+) and Fe2O+) are formed will improve our ability to interpret the mass spectra of iron oxides. Indeed, results show that the way Fe-2(+) dimer and Fe2O+ ions are formed is closely associated with the presence of the neutral species FeO and singlet ox ygen O-1(2)((1) Delta(g)). Fourier-transform ion cyclotron resonance m ass spectrometry (FT/ICR/MS) has been used to detect the presence of o xygen in the singlet O-1(2)((1) Delta(g)) State in the plume generated by laser ablation. The in situ identification of iron oxides in biolo gical samples is very important for studying their role as carriers of certain toxic molecules (e.g. PAH).