Formation, structure and bond dissociation thresholds of gas-phase vanadium oxide cluster ions

The formation and structure of gas-phase vanadium oxide cluster anions are examined using a guided ion beam mass spectrometer coupled with a laser vap orization source. The dominant peaks in the anion total mass distribution c orrespond to clusters having stoichiometries of the form (VO2)(n)(VO3)(m)(O -2)(q)(-). Collision-induced dissociation studies of the vanadium oxide spe cies V2O4-6-, V3O6-9-, V4O8-10-, V5O11-13-, V6O13-15-, and V7O16-18- indica te that VO2, VO3, and V2O5 units are the main building blocks of these clus ters. There are many similarities between the anion mass distribution and t hat of the cation distribution studied previously. The principal difference is a shift to higher oxygen content by one additional oxygen atom for the stoichiometric anions (VxOy-) as compared to the cations with the same numb er of vanadium atoms, which is attributed to the extra pair of electrons of the anionic species. The oxygen-rich clusters, VxOy(O-2)(-), are shown to more tightly adsorb molecular oxygen than those of the corresponding cation ic clusters. In addition, the bond dissociation thresholds for the vanadium oxide clusters DeltaE(V+-O)=6.09 +/-0.28 eV, DeltaE(OV+-O)=3.51 +/-0.36 eV , and DeltaE(O2V--O)=5.43 +/-0.31 eV are determined from the energy-depende nt collision-induced dissociation cross sections with Xe as the collision p artner. To the best of our knowledge, this is the first bond dissociation e nergy reported for the breaking of the V-O bond of a vanadium oxide anion. (C) 2001 American Institute of Physics.