Metal oxide and carbide thermochemistry of Y+, Zr+, Nb+, and Mo+

Reactions of Y+, Zr+, Nb+, and Mo+ with molecular oxygen and carbon monoxide and the collision induced dissociations of their metal oxides with Xe are studied as a function of kinetic energy using guided ion beam mass spectrometry. A meter-long flow tube ion source is used to create Zr+, Nb+, and Moi ions in their electronic ground state terms and Y+ mostly in its ground state, The kinetic energy dependencies for the reactions of Y+, Zr+, and Nb+ with O-2 show exothermic, barrierless behavior, while Mo+ reacts with O-2 in a process with a small endothermicity. Reactions with CO lead to formation of MC(+) and MO(+) in endothermic processes. Analyses of the reaction cross sections obtained in this study yield 0-K bond dissociation energies (in eV) of D-0(Y+-O)=7.24+/-0.18, D-0(Y+-C)=2.91+/-0.12, D-0(Zr+-O)=7.76+/-0.11, D-0(Zr+-C)=4.72 +/-0.11, D-0(Nb+-O)=7.13+/-0.11, D-0(Nb+-C)=5.16+/-0.15, D-0(Mo+-O)=5.06+/-0.02, and D-0(Mo+-C)=4.31+/-0.20. There is some question whether the YC+ and YO+ bond energies represent the correct adiabatic values. From this thermochemistry and literature values for D-0(MO) and D-0(MC), we also are able to calculate the ionization energies for the metal carbides and oxides (in eV): IE(YO)=6.39+/-0.22, IE(YC)=7.60+/-0.19, IE(ZrO)=6.87+/-0.18, IE(NbO)=7.65+/-0.22, IE(Nbc)=7.45+/-0.20, IE(MoO)=7.79+/-0.22, and IE(MoC)=7.73+/-0.26. These thermochemical values are compared with the literature and the periodic trends discussed. (C) 1996 American Institute of Physics.