Crystalline powder pellets of MoO3 and WO3 were irradiated with 253.7 nm radiation at room temperature in vacuum, in the presence of H2 and in the presence of Hg vapor and H2. Electronic changes induced in the surface of the solids were studied by x-ray photoelectron spectroscopy. In vacuo both MoO3 and WO3 turned blue upon irradiation and the XPS spectra supported the reversible formation of +5 oxidation states which reverted upon exposure to air. When MoO3 was irradiated in the presence of H2, a hydrogen/molybdenum bronze containing Mo in the +6, +5, and +4 oxidation states and hydroxyl groups were irreversibly formed. Exposure to UV radiation in the presence of Hg vapor and H2 enhanced the formation of Mo+4 and hydroxyl groups. Irradiation of WO3 in the presence of H2 and Hg vapor/H2 mixtures produced no further reduction of tungsten compared to irradiation alone. The conclusions based upon core electron emissions from molybdenum, tungsten, and oxygen were supported by changes in the valence band spectra.

The adsorptions of CO and C02 and Pt/Ce02 were studied by infrared and X-ray photoelectron spectroscopy. A heterogeneous distribution of linearly adsorbed CO on Pt at terrace, step, and corner sites was proposed based on changes in the absorption of the CO infrared stretching frequencies from 2084 to 2060 cm-1 upon heating under vacuum from 300 to 473 K. Pretreatment of the sample with 02 above 373 K lead to a blue-shifted peak at 2091 cm"1 11, interpreted as arising from CO adsorbed on Pt with an atom of oxygen at a neighboring site, and a new peak at 2131 cm"1, assigned to CO coadsorbed with an oxygen atom on the same Pt atom. Adsorption of C02 at room temperature resulted in the appearance of an IR band at 2065 cm"1, assigned to CO adsorbed on a Pt atom on a step or corner. The intensity of the CO band from C02 adsorption was sensitive to pretreatment of the sample, being completely suppressed by preoxidation but enhanced by prereduction. Lattice oxygen vacancies in the support, Ce02, in the vicinity of the Pt particles are responsible for the formation of CO from C02. XPS spectra show that Ce3+ is formed by the prereduction treatment, supporting the proposal that lattice oxygen vacancies play an important role in the C02 decomposition. Preoxidation is shown to lead to the formation of Pt2+ XPS (4f) spectra, which is removed by flash heating. Disproportionation of CO to carbon and C02 was shown not to occur by pretreatment of the

The reaction dynamics of the thermal, gas-phase decomposition of vinyl bromide has been investigated using classical trajectory methods on a global, analytic potential-energy surface fitted to the results of ab initio electronic structure calculations and experimental thermochemical, spectroscopic, and structural data. The saddle-point geometries and energies for several decomposition channels are determined using 6-3 lG(d,p) basis sets for carbon and hydrogen and Huzinaga's (4333/433/4) basis set augmented with split outer s and p orbitals and an f orbital for bromine. Electron correlation is incorporated using Mtiller-Plesset fourthorder perturbation theory with all single, double, triple, and quadruple excitations included. The calculated transition-state energies without zero-point energy corrections relative to vinyl bromide are four-center HBr elimination (3.530 eV), three-center HBr elimination (3.196 eV), four-center H2 elimination (4.159 eV), and three-center HZ elimination (4.618 eV). The global potential is written as a sum of the different reaction channel potentials connected by parametrized switching functions. The average absolute difference between AE values for the various decomposition channels obtained from the global surface and experimental measurement is 0.076 eV. Predicted equilibrium geometries for reactants and products are in good to excellent accord with experiment. The average absolute difference between the fundamental harmonic vibrational frequencies predicted by the global surface and those obtained from Raman and IR spectra varies from 10.2 cm-' for HzC=CHBr to 81.3 cm-' for H2C=CH. The potential barriers for six decomposition channels agree with the ab initio calculations to within an average difference of 0.124 eV. The dissociation dynamics of vinyl bromide on the ground-state surface is investigated at several excitation energies in the range 4.0-6.44 eV. The results show the following: (1) The decomposition dynamics follows a first-order rate law.(2) At thermal energies, the only brominated decomposition product is HBr. The results indicate that a previously reported activation energy for this process is too small. (3) As the excitation energy increases, other decomposition channels become important. At E = 6.44 eV, the reaction channels are, in order of importance, HZ elimination (48.1%), HBr formation (44.5%), Br atom elimination (4.6%), and C-H bond fission (2.6%). (4) The percentage of the total excitation energy partitioned into product relative translational motion and HBr internal energy upon HBr elimination is nearly independent of the total excitation energy. (5) Comparison of the calculated and measured relative translational energy distributions for product Br atoms upon C-Br bond fission and time-of-flight spectra for C2H2 upon HBr elimination indicates that in previously reported photolysis experiments Br atom dissociation is occurring on an excited electronic surface but HBr elimination is taking place on the ground-state surface subsequent to internal conversion....

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