INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, cilt.308, ss.265-274, 2011 (SCI İndekslerine Giren Dergi)
The collision-induced dissociation (CID) of TaO+, WO+, TaO2+, and WO2+ with Xe along with reactions of TaO+ and WO+ with O-2 are studied as a function of kinetic energy using guided ion beam tandem mass spectrometry in order to elucidate the thermochemistry of the MO2+ species. The kinetic energy dependences for the CID reactions show endothermic behavior, whereas the MO++O-2 -> MO2++O reactions proceed near the collision limit indicating exothermic processes. Analyses of the endothermic CID reaction cross sections yield OK threshold energies in eV of E-0(Ta+-O) = 7.01 +/- 0.12, E-0(W+-O) = 6.72 +/- 0.10, E-0(OTa+-O) = 6.08 +/- 0.12, and E-0(OW+-O) = 5.49 +/- 0.09. The nature of the bonding in MO+ and MO2+ is discussed and compared for Ta and W and analyzed using theoretical calculations at the B3LYP/HW+/6-311 + G(3df) level of theory. Bond energies for all MO and MO2+ species are calculated using geometries calculated at this level as well as BHLYP and CCSD(T) levels and the Stuttgart-Dresden (SDD) and the Def2TZVPP basis sets. Reasonable agreement between the theoretical bond energies and experimental CID threshold energies for TaO+, WO+, Tao(2)(+), and WO2+ is found. Potential energy surfaces for the reaction of the metal cations with O-2 are also calculated at the B3LYP level of theory and reveal additional information about the reaction mechanisms. (C) 2011 Elsevier B.V. All rights reserved.