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61.
62.
Dario Del Mazza Manfred G. Reinecke William B. Smith 《Magnetic resonance in chemistry : MRC》1980,14(6):540-542
Diphenyliodonium-2-carboxylate, phenyl 4-methylphenyliodonium-2-carboxylate and phenyl 5-methyl-phenyliodonium-2-carboxylate have been examined by 1H and 13C NMR spectroscopy. Each compound showed one proton considerably upfield from the others. From the two substituted compounds this was deduced to be H-6 on the ring containing the carboxylate group. Shift reagents and relaxation measurements were used to make the 13C chemical shift assignments. These data are most consistent with a cyclic, neutral structure for these iodonium carboxylates. The iodine is in the center of a trigonal bipyramid with the unsubstituted phenyl and carboxylate group apical, which places the C-6 proton in the shielding region of the adjacent phenyl group. 相似文献
63.
U. Cattaneo 《Communications in Mathematical Physics》1969,13(3):226-245
We use cohomology of Lie algebras to analyse the abelian extensions of the Poincaré algebraP. We study particularly the irreducible and truly irreducible extensions: some irreducibility criteria are proved and applied to obtain a classification of types of irreducible abelian extensions ofP. We give a characterization of the minimal essential extensions in terms of truly irreducible extensions. 相似文献
64.
Grazioli C Alfè D Krishnakumar SR Sen Gupta S Veronese M Turchini S Bonini N Dal Corso A Sarma DD Baroni S Carbone C 《Physical review letters》2005,95(11):117201
The occurrence of a noncollinear magnetic structure at a Mn monolayer grown epitaxially on Fe(100) is predicted theoretically, using spinor density-functional theory, and observed experimentally, using x-ray magnetic circular dichroism (XMCD) and linear dichroism (XMLD) spectroscopies. The combined use of XMCD and XMLD at the Mn-absorption edge allows us to assess the existence of ferromagnetic and antiferromagnetic order at the interface, and also to determine the moment orientations with element specificity. The experimental results thus obtained are in excellent agreement with the magnetic structure determined theoretically. 相似文献
65.
Vinyl acetate formation by the reaction of ethylene with acetate species on oxygen-covered Pd(111) 总被引:1,自引:0,他引:1
Stacchiola D Calaza F Burkholder L Tysoe WT 《Journal of the American Chemical Society》2004,126(47):15384-15385
The reaction pathway of vinyl acetate synthesis is scrutinized by reacting gas-phase ethylene (at an effective pressure of 1 x 10-4 Torr) with eta2-acetate species (with a coverage of 0.31 +/- 0.02 monolayer) on a Pd(111)-O(2x2) model catalyst surface in ultrahigh vacuum. It is found that the 1414 cm-1 infrared feature due to the symmetric OCO stretching mode of the acetate species decreases in intensity due to reaction with gas-phase ethylene, while temperature-programmed desorption experiments demonstrate that vinyl acetate is formed. The formation of ethylidyne species is detected when almost all of the acetate species have been removed. The experimental removal kinetics are reproduced by a model in which adsorbed acetates react with an ethylene-derived (possibly ethylene or vinyl) species, where ethylene adsorption is blocked by the acetate present on the surface. 相似文献
66.
We report the partial phonon densities of states (DOS) of iron sulfide, a possible component of the rocky planet's core, measured by the 57Fe nuclear resonant inelastic x-ray scattering and calculate the total phonon DOS under pressure. From the phonon DOS, we drive thermodynamic parameters. A comparison of the observed and estimated compressibilities makes it clear that there is a large pure electronic contribution in the observed compressibility in the metallic state. Our results present the observation of thermodynamic parameters of iron sulfide with the low-spin state of an Fe2+ ion at the high density, which is similar to the condition of the Martian core. 相似文献
67.
We present a novel model for calculating the bit error rate in optical communication systems in the case of on-off keying intensity modulation and optically preamplified direct detection. The model accounts for the intersymbol interference and is based on the Laguerre photon-count probability distribution predicted by photodetection theory. For a non-return-to-zero modulation format an accurate value of the sensitivity for a quantum-limited receiver of 33.9 photons/bit is obtained. 相似文献
68.
Angelamaria Maia Dario LandiniBoguslawa Leska Grzegorz Schroeder 《Tetrahedron letters》2003,44(21):4149-4151
Silicon polypodands 5-7 are found to be powerful complexing agents of alkali metal salts in low polarity solvents and very efficient catalysts in anion-promoted reactions under solid-liquid PTC conditions. The catalytic activity is comparable with that of the cyclic polyether PHDB18C6 8. 相似文献
69.
Braga D Maini L de Sanctis G Rubini K Grepioni F Chierotti MR Gobetto R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(22):5538-5548
Mechanical mixing of solid dicarboxylic acids of variable chain length HOOC(CH(2))(n)COOH (n = 1-7) with solid 1,4-diazabicyclo[2.2.2]octane generates the corresponding salts or co-crystals of the formula [N(CH(2)CH(2))(3)N]-H-[OOC(CH(2))(n)COOH] (n=1-7). Preparation of the same systems from solution has been instrumental for a full characterization of the mechanochemical products by means of single-crystal and powder-diffraction X-ray analyses, as well as by solid-state NMR. The acid-base adducts, whether involving proton transfer from the COOH group to the N-acceptor, that is having ((-))O...H-N((+)) interactions, or the formation of neutral O-H...N hydrogen bonds, show a melting point alternation phenomenon analogous to that shown by the neutral carboxylic acids. The carbon chemical shift tensors of the COOH group obtained from the sideband intensity of low speed spinning NMR spectra provide a reliable criterion for assigning the protonation state of the adducts. 相似文献
70.
The standard Brouwer–Zadeh poset (H) is the poset of all effect operators on a Hilbert space H, naturally equipped with two types of orthocomplementation. In developing the theory, the question occured if (when) (H) fulfils the de Morgan property with respect to both orthocomplementation operations. In Ref.3 the authors proved that it is the case provided dimH<, and they conjectured that if dimH=, then the answer is in the negative. In this note, we first give a somewhat simpler proof of the known result for dimH<, and then we give a proof to the conjecture: We show that if dimH=, then the de Morgan property is not valid. 相似文献