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 modes. The targets (micrometric particles of powdered iron oxides Fe1-xO, Fe3O4 and Fe2O3) were synthesized, on the one hand, from iron 54 isotopes and, on the other hand, from natural iron 56 isotopes. The positive-ion cluster distributions showed a strong correlation with the stoichiometry 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 the distribution of the intensity of clusters. A better understanding of 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 oxygen 1O2 (1Δg). Fourier-transform ion cyclotron resonance mass spectrometry (FT/ICR/MS) has been used to detect the presence of oxygen in the singlet 1O2 (1Δg) state in the plume generated by laser ablation. The in situ identification of iron oxides in biological samples is very important for studying their role as carriers of certain toxic molecules (e.g. PAH). Copyright © 1996 Elsevier Science B.V. All rights reserved.