PRODUCTION AND FRAGMENTATION OF MOLYBDENUM OXIDE IONS

The production and fragmentation of molybdenum oxide cluster ions MoxOy+/- have been studied by Fourier transform mass spectrometry. The cluster ions were generated by direct laser vaporization (DLV) and fast-atom bombardment (FAB) of molybdenum trioxide and molybdenum dioxide. The ionization method has a dramatic effect on ion formation with DLV producing primarily MoxOy+ with high oxygen-to-metal ratios, while FAB yields Mo(x+) and MoxOy+ with low oxygen-to-metal ratios. Direct emission appears to be an important mechanism in laser vaporization of molybdenum oxides, while the FAB results are consistent with ion formation by recombination reactions. For molybdenum dioxide, a comparison is made between DLV with pulsed CO2 and Nd:YAG lasers. The spectra obtained are similar; however, differences in (MoO3)n+, n = 1-3, production with the two lasers may be related to sample absorption at the CO2 wavelength of 10.6-mu-m. The low-energy collision-induced dissociation of MoxOy+ is dominated by loss of (MoO3)n. In addition, (MoO3)n- are the major anionic species produced by FAB and DLV. The prominence of the MoO3 unit in both ion production and fragmentation suggests that it may be significant in MoxOy+/- structures.