Production and fragmentation of molybdenum oxide ions

摘要

The production and fragmentation of molybdenum oxide cluster ions MoxO+/minus;yhave been studied by Fourier transform mass spectrometry. The cluster ions were generated by direct laser vaporization (DLV) and fasthyphen;atom bombardment (FAB) of molybdenum trioxide and molybdenum dioxide. The ionization method has a dramatic effect on ion formation with DLV producing primarily MoxO+ywith high oxygenhyphen;tohyphen;metal ratios, while FAB yields Mo+xand MoxO+ywith low oxygenhyphen;tohyphen;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 CO2and Nd:YAG lasers. The spectra obtained are similar; however, differences in (MoO3)+n,n=1ndash;3, production with the two lasers may be related to sample absorption at the CO2wavelength of 10.6 mgr;m. The lowhyphen;energy collisionhyphen;induced dissociation of MoxO+yis dominated by loss of (MoO3)n. In addition, (MoO3)minus;nare the major anionic species produced by FAB and DLV. The prominence of the MoO3unit in both ion production and fragmentation suggests that it may be significant in MoxO+/minus;ystructures.