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81.
The oxidation of methanol was studied on a Ag(110) single-crystal by temperature programmed reaction spectroscopy. The Ag(110) surface was preoxidized with oxygen-18, and deuterated methanol, CH3OD, was used to distinguish the hydroxyl hydrogen from the methyl hydrogens. Very little methanol chemisorbed on the oxygen-free Ag(110) surface, and the ability of the silver surface to dissociatively chemisorb methanol was greatly enhanced by surface oxygen. CH3OD was selectively oxidized upon adsorption at 180 K to adsorbed CH3O and D218O, and at high coverages the D218O was displaced from the Ag(110) surface. The methoxide species was the most abundant surface intermediate and decomposed via reaction channels at 250, 300 and 340 K to H2CO and hydrogen. Adsorbed H2CO also reacted with adsorbed CH3O to form H2COOCH3which subsequently yielded HCOOCH3 and hydrogen. The first-order rate constant for the dehydrogenation of D2COOCH3 to DCOOCH3 and deuterium was found to be (2.4 ± 2.0) × 1011 exp(?14.0 ± 0.5 · RT)sec?1. This reaction is analogous to alkoxide transfer from metal alkoxides to aldehydes in the liquid phase. Excess surface oxygen atoms on the silver substrate resulted in the further oxidation of adsorbed H2CO to carbon dioxide and water. The oxidation of methanol on Ag(110) is compared to the previous study on Cu(110). 相似文献
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The co-adsorption of H2 and CO on a Cu-Ni (110) surface was studied by thermal desorption spectroscopy (TDS) and ultraviolet photoemission spectroscopy (UPS). Strong interactions between adsorbed CO and hydrogen observed in the CO desorption spectrum and CO valence emissions were attributed to a blockage of certain CO adsorption sites by hydrogen. 相似文献
86.
Le Roy RJ 《Journal of Molecular Spectroscopy》1999,194(2):189-196
A new way of representing vibration-rotation term values for multiple isotopomers of a given electronic state of a diatomic molecule is presented which resolves problems associated with the way the conventional combined isotopomer expansion represents the atomic mass-dependent JWKB and Born-Oppenheimer breakdown correction terms. Its application to infrared and microwave data for HF and DF yields new Dunham expansion coefficients and Born-Oppenheimer breakdown correction terms for this species. This procedure is implemented in a generally available computer program for fitting to various types of data involving one or several electronic states of multiple isotopomers of a diatomic molecule. Copyright 1999 Academic Press. 相似文献
87.
Partition functions for adsorbed hydrogen atoms have been evaluated for Ni(100), Ni(111), Pd(111) and Pt(111) surfaces. These account for the relative order of magnituted of the preexponential factors for associative desorption, νd, including the abnormally low value for the Pt(111)/H system. Furthermore application of transition state theory yields numbers for νd which are in good agreement with experimental data. 相似文献
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A kinetic study of D2 formation from HCOOD decomposition on Ni(110) (2 × 1)C was performed using the flash desorption technique. The surface structure and surface composition were monitored by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Flash curves were obtained using initial coverage and heating rate variations. D2 formation exhibited a single second-order rate-determining step. Three different techniques were employed in obtaining the activation energy, two of which did not require the assumption of reaction order. Using an average value of 12.6 kcal/mole for the activation energy the pre-exponential factor was calculated to be 2.7 × 10?4 cm2 molecules?1 sec?1. Good agreement was achieved with the theoretically generated second-order flash curves only up to the peak temperature. The discrepancy on the high temperature side was explained using the model proposed by Clavenna and Schmidt utilizing a coverage dependent pre-exponential factor. 相似文献
90.
The adsorption/desorption behavior of formic acid from a monolayer of graphite carbon on Ni(110) was studied using AES, LEED and flash desorption spectroscopy. Formic acid adsorbed at 165 K did not form multilayers of adsorbate. Instead, due to strong hydrogen-bonding interactions the formic acid formed a two-dimensional condensed phase on the surface and exhibited zero-order desorption kinetics initially for a 30-fold change in initial coverage. The zero-order desorption rate constant was kd = 1018 exp[?68.2 kJ mol?1/RT]s?1, suggesting a desorption transition state with nearly full translational and rotational freedom on the surface. The desorption kinetics and the coverage limit were consistent with the formation of a surface polymer-monomer equilibrium. 相似文献