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1.
The reaction of carbon monoxide with oxygen chemisorbcd on polycrystalline platinum has been studied using Auger spectroscopy. Two types of chemisorbed oxygen are distinguished on the basis of Auger electron chemical shifts and reactivity towards carbon monoxide. When the substrate is below 800 K, a single very reactive type of chemisorbed oxygen is formed. Above 800 K a new species begins to form which is characterized by an Auger chemical shift of about 6 eV and by low reactivity. The decay of the oxygen Auger signal using several fixed pressures of carbon monoxide was measured. The reaction is first order in carbon monoxide pressure but no clear decision can be made about the order with respect to oxygen coverage. With the reaction operating at steady-state, the oxygen coverage was measured as a function of CO pressure. In the region 363–600 K, the steady state oxygen coverage began to decline measurably when reached 0.1. When pCO>pO2the oxygen coverage became immeasurably small. A simple model is used to relate these phenomena to observed carbon dioxide production rates. 相似文献
2.
At high incident electron energies the 4p core electron energy loss features of clean La, Ce and Gd strongly resemble the corresponding XPS spectrum with evidence of strong 4p-1 ? 4d-2?f giant Coster-Kronig resonance in the “4p” spectrum. The absence of charge transfer screening peaks in the loss of the oxides is attributed to localised 4p → 5d1 excitation. As the primary energy approaches threshold, a satellite on the low energy side of the losses of La and Ce grows in intensity, due to excitations of multiples through non-dipole transitions. 相似文献
3.
Peter Zimmermann Theodore W. Ducas Michael G. Littman Daniel Kleppner 《Optics Communications》1974,12(2):198-201
We present a new technique for selectively populating excited states which are inaccessible by dipole excitation from the ground state. The method uses a static electric field to introduce a component of a dipole-allowed state into the state of interest. We have applied the method to cesium to measure lifetimes and a Stark mixing coefficient. The results are , , and <62D|;ez |72P>/(E7P?E6D)=0.7(3)×10?3 where is in kV/cm. 141 相似文献
4.
The adsorption of oxygen on polycrystalline palladium, the kinetics of the reaction of adsorbed oxygen with carbon monoxide and the amount of adsorbed oxygen present during the catalyzed reaction, , were studied by Auger electron spectroscopy. At temperatures below 783 K, the initial sticking probability is high (~0.8). Adsorbed oxygen and CO react with high probability and low activation energy to form carbon dioxide. The reaction is first order with respect to carbon monoxide pressure and zero order in oxygen coverage. Oxygen coverages measured during the CO-oxidation reaction decrease sharply around PCO ? PO2 and are very small when PCO >PO2. The reaction kinetics are discussed using a modified Eley-Rideal mechanism involving strongly adsorbed oxygen atoms and surface carbon monoxide in a short-lived state. The oxygen adsorption phenomena are correlated with the reaction kinetics. 相似文献
5.
The radiative lifetimes of the 6p2P levels in Hg(II) have been measured to be ns and ns by the beam-gas-Hanle and the beam-foil techniques, respectively. The result for the level differs from recent theoretical calculations, whereas there is good agreement for the level. 相似文献
6.
The Coriolis resonance between ν4 and ν7 in CH3CN and between ν1 and ν5, ν3 and ν6, and ν4 and ν7 in CD3CN has been analyzed, applying the technique developed by DiLauro and Mills, to obtain the signs of [] and the ratio of to for the interacting pairs in CD3CN. For (ν4, ν7) in both CH3CN and CD3CN, the sign of [] is found to be negative as it is also for (ν1, ν5) in CD3CN. For (ν3, ν6) the sign of this interaction term is found to be positive. For a given definition of normal coordinates the signs of these interaction terms give the relative signs of and ; our study also gives approximate values for the corresponding ratio [] 相似文献
7.
Keu Hong Kim Jong Ho Jun Jae Shi Choi 《Journal of Physics and Chemistry of Solids》1985,46(10):1173-1178
The electrical conductivity of the system Y2O3CeO2 was measured in the temperature range 500–1100°C and Po2 range 10–7?10?1 atm. Possible defect models were suggested on the basis of conductivity data, which were investigated as a function of temperature and of Po2. The observed activation energies were 0.40 eV and 1.79 eV in the low- and high-temperature regions, respectively. The observed conductivity dependences on Po2 were in the temperature range 500–750°C and at temperatures from 750–1100°C. It is suggested that the system Y2O3CeO2 shows a mixed ionic plus hole conduction due to an O″i defect and an electronic hole conduction due to a V'''Y defect in the low- and high-temperature regions, respectively. 相似文献
8.
The polarized excitation and emission spectra of the U6+ molecular centers giving the most intense emission lines at 18 940 cm?1 and 19 285 cm?1 are presented and analyzed in detáil. From the polarization experiments, it is shown that the symmetry of the centers is C4v and that the symmetries of the observed electronic states are Γ2, Γ1 and Γ5. Finally, an electronic model is proposed which associates the emission and excitation lines of the U6+ centers in the visible region to transitions between the fundamental state and the states of the excited configuration . 相似文献
9.
F. Pourarian M.V. Satyanarayana W.E. Wallace 《Journal of magnetism and magnetic materials》1981,25(1):113-116
Magnetostrictive strain and thermal expansion measurements in an oriented assembly of NdCo5 particles along the c-axis were carried out between 77 and 330 K. The measurement strains in the c-derection and transverse to the c-direction exhibited anomalous behavior at 285 and 245 K, which are assoiciated with the spin reorientation process in this temperature range. The estimated magnetostrictive energy is comparable to the anisotropy energy at 285 K. There is also a pronouced anomaly in ther thermal expansion in the spin reorientation temperature region. 相似文献
10.
R.P. Goddard 《Nuclear Physics A》1977,291(1):13-20
Deuteron-nucleus optical model calculations which include two types of tensor spin-orbit interactions are compared. The interactions considered are of the forms where the operators Tr and Tp are defined as . Here, are the deuteron spin, position, and momentum operators, respectively. If a physically reasonable radial dependence VTP(r) is used, the S-matrix elements (and hence all observables) calculated using a Tp tensor potential are found to be similar to those calculated using a suitably chosen Tr potential, provided that the incident deuteron energy is small compared to the real central potential. At higher deuteron energies, the differences between the effects of Tr and Tp potentials are more pronounced. 相似文献
11.
A direct measurement of the diffusion distance of the state excitation in NdP5O14 along the crystallographic a-axis is reported. At room temperature an upper limit of 32 nm is found which is 20 times shorter than an earlier estimate. 相似文献
12.
A study of BaO has been made by use of thermogravimetric analysis, oxygen concentration analysis, and X-ray lattice parameter measurements in the temperature range 850°C ? T ? 1420°C and oxygen pressure range 7 × 10-6 atm ? pO2 ? 0·820 atm. Both the weight gain by the BaO samples and subsequently determined excess oxygen concentration were found to be directly proportional to . The enthalpy of incorporation oxygen in the lattice was determined to be ?0·395 ± 0·034 eV. Creation of vacancies on cation sites or of oxygen interstitials are consistent with the experimental results. As an alternative, the formation of O22? ions, (as in BaO2) as a result of incorporation of excess oxygen in the lattice, has been suggested. 相似文献
13.
Oscillations in the rate of CO2 production have been observed for the first time over Pd and Ir catalysts. The experiments were conducted near atmospheric pressure in a clean flow reactor system using polycrystalline Pd or Ir wire. For Pd, sustained oscillations were found over a wide range of gas compositions and temperatures (230 < Tg < 350°C), where PCO and PO2 are the respective partial pressures of carbon monoxide and oxygen in the gas stream, and Tg is the temperature of the gas. For Ir, oscillations were found for and 180 < Tg < 250°C. As proposed for CO oxidation over a Pt catalyst, it is believed that the oscillations occur between two branches of a Langmuir-Hinshelwood reaction mechanism, and that the slow formation and removal of subsurface oxygen drives the reaction between these two branches. These experiments suggest that oscillations in surface reactions are more general than previously suspected. 相似文献
14.
Metastable He2 molecules are produced by a dc discharge in a flowing He stream. Laser excitation downstream of the discharge produces excitation spectra for a number of He2 states. LIF spectra are observed for the series for n = 4–9, excepting 5 and the series for n = 5–15. 相似文献
15.
The cross-relaxation of YAG:Tb3+ has investigated by analysis of the 5D3 decay curve as a function of Tb3+ concentration. This technique is a more sensitive test of the mechanism than relative intensity measurements alone. It is shown that the relaxation is predominantly dipole-dipole in character (R0 ~ 1.3nm), and insensitive to temperature. The population of the 5D4 state following high energy excitation occurs almost entirely via cross-relaxation from the 5D3 state. 相似文献
16.
Stephen Bomar Elliott Bay H.-G Kraft J.W Bevan 《Journal of Molecular Spectroscopy》1981,87(2):482-489
The R band (26.5–40 GHz) microwave spectrum of 2,4-dioxabicyclo[3.1.0]hexan-3-one is reported. Rotational constants for the ground vibrational state of the common 12C41H416O3 and 13C1, 13C6 isotopically substituted species (the latter observed in natural abundance) have been evaluated. In addition rotational constants of the VB = 1 to VB = 5 quanta associated with the bending vibration of the five membered ring have been determined. A partial rs structure has been calculated: , . With certain assumed molecular information a least squares fit yields the following parameters: , , . 相似文献
17.
18.
The excitation functions of have been measured in the energy range Ep = 14.2 to 17.4 MeV in 50 keV steps at θlab = 120°, 140° and 160°. The isobaric analog resonances of the parent states in 209Pb up to Ex = 2.5 MeV and the optical-model background were fit simultaneously at all energies and angles. The spreading widths and the values of a parameter β2, which measures the isospin purity of the IAR, were determined for the , and resonances. An average value of the isospin purity of β2 = 66% was found. 相似文献
19.
20.
M. Taniguchi S. Suga S. Shin K. Inoue M. Seki H. Kanzaki 《Solid State Communications》1982,44(1):85-88
Reflectance spectra due to 3d core-levels of Ge have been measured in the photon-energy region from 29 to 38 eV by means of synchrotron radiation. Second-energy-derivative spectra have newly shown pairs of doublet structures with energy separation of the Ge core-level splitting. The observed doublet structures are assigned to the transitions from the and core-levels to the flat regions of the conduction band around the particular symmetry points of Δ6c and L(3c(L6c, L4,5c). 相似文献