Collision-induced dissociation of MO + and MO 2+ (M = Ta and W): Metal oxide and dioxide cation bond energies

Abstract

The collision-induced dissociation (CID) of TaO +, WO +, TaO 2 +, and WO 2 + 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 MO 2 + species. The kinetic energy dependences for the CID reactions show endothermic behavior, whereas the MO ++O 2 → MO 2 + + O reactions proceed near the collision limit indicating exothermic processes. Analyses of the endothermic CID reaction cross sections yield 0 K 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 MO 2 + 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 MO 2 + 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 WO 2 + 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.