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

Abstract

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 Mo+ 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 O2 show exothermic, barrierless behavior, while Mo+ reacts with O2 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 D0(Y+–O)=7.24±0.18, D0(Y+–C)=2.91±0.12, D0(Zr+–O)=7.76±0.11, D0(Zr+–C)=4.72 ±0.11, D0(Nb+–O)=7.13±0.11, D0(Nb+–C)=5.16±0.15, D0(Mo+–O)=5.06±0.02, and D0(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 D0(MO) and D0(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.