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1.
The influence of deposited potassium on the oxidation and NO reactivity of a Co(0 0 0 1) surface was studied using X-ray photoelectron spectroscopy. The formation of surface CoO was observed when the clean Co(0 0 0 1) surface was exposed to O 2 at 500 K. In contrast, the Co atoms on the K-deposited Co(0 0 0 1) surface remained at a lower oxidation state, CoO x (0 < x < 1). No adsorption or dissociation of NO occurred on the CoO/Co(0 0 0 1) surface at 320 K, whereas a NO 2− species formed on the oxidized K/Co(0 0 0 1) surface. This species is considered to be an intermediate in NO decomposition. It was concluded that the role of potassium was (i) to form the NO 2− intermediate, and (ii) to keep the Co surface partially oxidized (CoO x) as the active site for the dissociation of the NO 2− species. 相似文献
2.
Adsorbed ionic NO x species formed upon the interaction of NO 2 with dehydrated or hydrated Na- and Ba-Y, FAU zeolites were characterized using FT-IR/TPD, solid state NMR, and XANES techniques. NO 2 disproportionates on both dehydrated catalyst materials forming NO + and NO 3− species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na + and Ba 2+), respectively. Although the nature of the adsorbed NO x species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO + and H 2O, and NO 2 and H 2O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and NO 2 on these zeolite catalysts. 相似文献
3.
The electrical conductivities of NaBPh 4, NBu 4I, NaI, NaCl, NaBr and NaClO 4 have been studied in the mixtures of propan-1-ol with water. The obtained results were analysed using the Fuoss–Justice equation. The individual limiting ionic conductivities of Na +, NBu 4+, BPh 4−, I −, Cl −, Br −, ClO 4− ions have been determined using the Fuoss–Hirsch assumption. The dependencies of the limiting molar conductances Λo and Walden products Λoη versus mixed solvent composition have been discussed. 相似文献
4.
This paper reports the first attempt to use L-band spectroscopy for estimating the sensitivity of whole teeth to fast neutrons and gamma-rays. Three teeth were successively irradiated first with fast neutrons with a wide energy spectrum (mean energy around 30 MeV) up to 160 Gy and then with gamma-rays up to 14 Gy. After each irradiation, L-band (1 GHz) EPR spectra of each whole tooth surrounded by the surface–coil resonator were recorded, yielding a single composite line principally due to CO 2− and native radicals. The sensitivities are estimated by the slopes of the linear dose response curves of the dosimetric CO 2− radicals. The ratios of the gamma/neutron sensitivities were found to be in the range 8–9 (±2) for the three teeth. 相似文献
5.
Molecular CO 2 adsorption is observed on an Fe(111) surface at 85 K. For the main fraction of molecules the relative binding energies of the valence ion states as determined by ARUPS are consistent with those in the gas as well as in the condensed phase, and indicate that the electronic structure of that fraction of adsorbed molecules is only slightly distorted upon adsorption. There is a fraction of adsorbed molecules at 85 K that can be identified as bent, anionic CO 2− species. While the weakly adsorbed, linear CO 2 molecules desorb at low temperature, the CO 2− species is stable up to 160–180 K. The latter is proposed to be a precursor to dissociation. Above this temperature adsorbed carbon monoxide and oxygen are observed on the surface, and at room temperature the CO 2− signals have disappeared. Heating above room temperature dissociates the CO molecules into carbon and oxygen. 相似文献
6.
Three luminescence bands in the yellow and red spectral region, which are related to the 1Δ g1Δ g→ 3Σ g− 3Σ g− double electronic transition of O 2, have been investigated in the , β, and γ phase of solid oxygen. The temperature dependence of the intensity of the yellow band is strongly influenced by emission from higher vibrational levels of O 2( 1Δ g), which are populated by anharmonic V–V pumping. The broken mirror symmetry of the luminescence and absorption bands in the phase of solid O 2 points to an interaction between the electrons and the elementary excitations of the crystal, which is different in the ground and excited electronic states, e.g., a quadratic electron–phonon interaction. 相似文献
7.
A series of polyacrylonitrile–dimethylsulfoxide–CuX 2 (X=CF 3SO 3−, Cl −, Br −), films (foils) were prepared by means of the solution cast technique. The thickness of the foils was between 0.04 and 0.09 cm and they contained 70–80 wt.% of the solvent. Conductivities of the solid electrolytes were obtained from impedance measurements. The conductivity increases with the increase of the salt content up to 8 wt.%; at higher concentrations (>8 wt.%) the conductivity is more or less stable, and reaches, in the case of Cu(CF 3SO 3) 2 and CuCl 2, the level of ca. 10 −3 Ω −1 cm −1 at room temperature. The foils based on the CuBr 2 show even higher conductivity, close to 10 −2 Ω −1 cm −1 at room temperature, a value comparable to that characteristic for liquid solutions. The temperature variation of the conductivity for all the systems studied is of the Arrhenius type. The activation energy, determined from linear plots ln σ=f( T−1), is of the order ca. 14 kJ mol −1 for the PAN/CuBr 2/DMSO and of ca. 21 kJ mol −1 for the PAN/CuCl 2/DMSO and the PAN/Cu(CF 3SO 3) 2/DMSO systems. 相似文献
8.
An organic molecule isomerizes in viscous solvents when appropriate cavities are formed around it in the course of slow diffusive thermal fluctuations of solvent molecules. The isomerization occurs when fast twisting (vibrational) fluctuations around a bond get to have large amplitudes in such cavities. This situation can be described by the two-reaction-coordinate model of Sumi and Marcus originally proposed for electron transfer reactions. In fact, the rate constant derived from this model fits nicely to that observed for thermal Z→E isomerization of substituted azobenzenes and N-benzylideneanilines. The rate constant is influenced by slow speeds of diffusive motions of solvent molecules, whose relaxation time τ is usually proportional to the solvent viscosity η. It has a form of k = 1/( kTST−1+ kf−1), where kTST, independent of τ, represents the rate constant expected from the transition state theory (TST), while kf ∝ τ − with 0 < ≤ 1 represents the part controlled by solvent fluctuations. An analytic expression of for the isomerization reactions is given in terms of physical parameters underlying the reaction mechanism with cavity formation. This rate-constant formula is a general one applicable widely also to other solution reactions, covering from the TST-validated regime for a small τ to the TST-invalidated one for a large τ. In the former, k approaches kTST since kf kTST, while in the latter, k approaches kf since kf kTST, becoming decreasing with a decrease in the typical speed (∝ τ−1) of solvent fluctuations. The dependence of k ≈ kf ∝ η− in the non-TST regime has often been observed also in biological reactions such as enzymatic ones. In this case, it is not appropriate to say that reactions are controlled by slow speeds of solvent fluctuations, but we should rather say that enzymes utilize this situation, which has been called conformational gating, in the course of solvent-fluctuation-driven conformational fluctuations of proteins. It has important meanings in protein functions. 相似文献
9.
Aqueous solutions of Nal containing CCl 4 and MgCl 2 at various concentrations were irradiated under air with 1 MHz ultrasound and the yield of I 3− was determined. The yield was not affected by MgCl 2 at concentrations up to 0.1 M. This contrasts with the finding of Lepoint and co-workers, who reported a sharp minimum in the yield at a MgCl 2 concentration of 2.5 × 10 −3M, the yield decreased to 60% at 1 M MgCl 2, the reason being the lower solubility of CCl 4 at high MgCl 2 concentrations. In the absence of CCl 4, another dependence on the MgCl 2 concentration was observed: the yield was not affected up to 1 M, and at higher MgCl 2 concentrations the yield rapidly decreased owing to the increased viscosity of the solution. On the basis of these observations, there is no strong reason to postulate an electrical mechanism for the initiation of chemical reactions in the cavitation bubbles. 相似文献
10.
Density functional theory (DFT) calculations (6–311+G(2d,p)/B3LYP level of theory) of 51V electric field gradient (EFG) tensor elements are performed for embedded and isolated cluster models of orthovanadates. The structural models used to calculate the EFGs of 51V are (I) an isolated H 4VO 4+ cluster, (II) an isolated H nVO 4n−3 cluster ( n=number of next-neighbor cations) (III) an isolated orthovanadate anion, VO 4−x, and (IV) a VO 4−x ion embedded in a finite point-charge array whose electrostatic potential, at the embedded ion, is equivalent to that of the infinite lattice. For models III and IV, a charge x is assigned estimating the covalence of the system. Models III and IV provide results in good agreement with the experiment. Calculations, employing the embedded and isolated VO 4−x models, are used to discuss site assignments for AlVO 4. Correlations between quadrupole coupling parameters and deviations of the orthovanadate structure from ideal tetrahedral symmetry are shown. 相似文献
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