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.

The reconstructed anatase TiO2(001) surface has been investigated by low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and angle-resolved mass spectroscopy of recoiled ions (AR-MSRI). Prior investigations have observed or considered only a (1x1) unreconstructed termination for this surface with no detailed structural analysis. Our LEED results indicate a previously unobserved two-domain (1x4) reconstruction after sputtering and annealing the (1x1) surface. The XPS data for this reconstruction indicate the presence of only Ti4+. Simulations of the AR-MSRI experimental data indicate a best fit for a microfaceted surface, revealing both (103) and (1;03) surface planes.

Guided ion beam mass spectrometry is used to examine the kinetic energy dependence of reactions of the second row transition metal cations, Y + , Zr + , Nb + , and Mo + , with molecular hydrogen and its isotopologues. By using a meter long flow tube ion source, we are able to create Zr + , Nb + , and Mo + ions that are believed to be in their electronic ground state terms and primarily in the lowest spin-orbit levels and Y + mostly in its ground state. Corresponding state-specific reaction cross sections are obtained. Analysis of the cross section data yields 0 K bond dissociation energies of D 0 (Y + -H) ) 2.65 ( 0.08 eV, D 0 (Zr + -H) ) 2.26 ( 0.08 eV, D 0 (Nb + -H) ) 2.28 ( 0.07 eV, and D 0 (Mo + -H) ) 1.72 ( 0.06 eV. This thermochemistry is compared with theoretical calculations and previous experimental measurements. Results for the HD reactions indicate that Y + ( 3 D) reacts via a statistical mechanism, Zr + ( 4 F), Nb + ( 5 D), and Mo + ( 6 S) react via largely statistical mechanisms, and Y + ( 1 S) shows complex behavior. The reaction mechanisms and reactivity differences among these ions are explained by using simple molecular orbital concepts and by referring to potential energy surfaces calculated by Das and Balasubramanian. † Present address:

A guided ion beam tandem mass spectrometer is used to measure the kinetic energy dependence of the V+(5D) + CO2 reaction and a reverse pathway, VO+(3∑−) + CO. Two intermediates along these reaction pathways, V+(CO2) and OV+(CO), are examined by threshold collision-induced dissociation experiments with Xe. Thermochemical analyses of the cross sections obtained in these systems allow the measurement of D0(OV+–O) = 3.06±0.40 eV, D0(V+–CO2) = 0.75±0.04 eV, D0(OV+–CO) = 1.05±0.10 eV, and speculative characterization of electronic excitation energies for two states of VO+. Combined with literature information on the electronic states of V+ and VO+, these data enable the potential energy surfaces for this reaction system to be mapped out in some detail. We find that coupling between surfaces of different spin is observed, but that spin conservation plays an important role in both the forward and reverse reactions.