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961.
The combination of hexacyanoferrate(III) anions, [Fe(CN)(6)](3)(-), with nickel(II) complexes derived from the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) affords the enantiopure layered compounds [Ni(trans-(1S,2S)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (1) and [Ni(trans-(1R,2R)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (2). These chiral systems behave as ferromagnets (T(c) = 13.8 K) with a relatively high coercive field (H(c) = 0.17 T) at 2 K. They also exhibit an unusual magnetic behavior at low temperatures that has been attributed to the dynamics of the magnetic domains in the ordered phase.  相似文献   
962.
An equation of state for a multicomponent mixture of nonadditive hard spheres in d dimensions is proposed. It yields a rather simple density dependence and constitutes a natural extension of the equation of state for additive hard spheres proposed by us [A. Santos, S. B. Yuste, and M. Lopez de Haro, Mol. Phys. 96, 1 (1999)]. The proposal relies on the known exact second and third virial coefficients and requires as input the compressibility factor of the one-component system. A comparison is carried out both with another recent theoretical proposal based on a similar philosophy and with the available exact results and simulation data in d=1, 2, and 3. Good general agreement with the reported values of the virial coefficients and of the compressibility factor of binary mixtures is observed, especially for high asymmetries and/or positive nonadditivities.  相似文献   
963.
Pt on mesostructured CeO(2) nanoparticles embedded within ultrathin layers of highly structured SiO(2) binder shows highest activity reported with 80% selectivity for the chemoselective hydrogenation of crotonaldehyde. Characterization by transmission electron microscopy (TEM), CO adsorption, and X-ray photoelectron spectroscopy (XPS) show the presence of small Pt metal particles, preferentially located on CeO(2) (70%) together with the formation of Pt-CeO(2-x) sites at the interface between Pt and CeO(2) (4 nm) nanoparticles. These sites are able to polarize the carbonyl group and facilitate the selective hydrogenation of this with respect to the double bond.  相似文献   
964.
We discuss the failure of commonly used AM1 and PM3 semiempirical methods to correctly describe acid dissociation. We focus our analysis on HCl because of its physicochemical importance and its relevance in atmospheric chemistry. The structure of non-dissociated and dissociated HCl – (H2O) n clusters is accounted for. The very bad results obtained with PM3 (and also with AM1) are related to large errors in gas-phase proton affinity of water and gas-phase acidity of HCl. Indeed, estimation of pKa values shows that neither AM1 nor PM3 are able to predict HCl dissociation in liquid water since HCl is found to be a weaker acid than H3O+. We have proposed in previous works a modified PM3 approach (PM3-MAIS) adapted to intermolecular calculations. It is derived from PM3 by reparameterization of the core–core functions using ab initio data. Since parameters for H–Cl and O–Cl core–core interactions were not yet available, we have carried out the corresponding optimization. Application of the PM3-MAIS method to HCl dissociation in HCl–(H2O) n clusters leads to a huge improvement over PM3 results. Though the method predicts a slightly overestimated HCl acidity in water environment, the overall agreement with ab initio calculations is very satisfying and justifies efforts to develop new semiempirical methods.  相似文献   
965.
In elastic peak electron spectroscopy (EPES), the nearest vicinity of elastic peak in the low kinetic energy region reflects electron inelastic and quasielastic processes. Incident electrons produce surface excitations, inducing surface plasmons, with the corresponding loss peaks separated by 1–20 eV energy from the elastic peak. In this work, X‐ray photoelectron spectroscopy (XPS) and helium pycnometry are applied for determining surface atomic composition and bulk density, whereas atomic force microscopy (AFM) is applied for determining surface morphology and roughness. The component due to electron recoil on hydrogen atoms can be observed in EPES spectra for selected primary electron energies. Simulations of EPES predict a larger contribution of the hydrogen component than observed experimentally, where hydrogen deficiency is observed. Elastic peak intensity is influenced more strongly by surface morphology (roughness and porosity) than by surface excitations and quasielastic scattering of electrons by hydrogen atoms. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
966.
 A very sensitive and selective method for the determination of trace amounts of iron has been developed, based on the reduction of Fe(III) to Fe(II) by ascorbic acid, followed by chromogenic chelation of Fe(II) with ferrozine. The complex Fe(II)-ferrozine is easily sorbed on a dextran-type anion-exchange gel packed in a 1 mm cell, and the absorbance of the gel is measured directly at 569 and 800 nm. The extended linear range of the determination is 0.5–10 ng ml-1 of iron (apparent molar absorptivity=4.4×107 l mol-1 cm-1) and the precision (RSD) 1.3% for a concentration of 5 ng ml-1 of iron (n=10). The detection limit for a sample volume of 1000 ml, using 0.040 g of anion-exchanger, corresponds to 0.12 ng ml-1. The method has been successfully applied to the determination of iron in natural and waste waters, wine, soil extract and previously digested vegetal tissues, drugs and human hair. Received: 20 November 1995/Revised: 23 January 1996/Accepted: 26 January 1996  相似文献   
967.
The properties of precipitate-based copper sulphide electrodes are investigated. Solid-phase studies wre done by x-ray photoelectron spectroscopy and solution-phase studies by combined potentiometric and atomic absorptioni spectrometric techniques. The predominant valence state of copper in the copper sulphide samples is shown to be Cu(I), but Cu(II) can also be identified at the surfaces. The oxidation of the membrane surface results in dissolution of copper ion and a decrease in the Cu/S ratio in the solid phase; reduction of the surface causes sulphide dissolution and an increase in the Cu/S ratio. Application of anodic or cathodic curents was used to study the redox behaviour of the copper suphide memebrane.  相似文献   
968.
Hydrolysis of N,N'-diacyl-1,2-di(4-pyridyl)ethylenediamines 1 in aqueous sulfuric acid gave the corresponding imidazolines 3. 1,2-Di-(4-pyridyl)ethylenediamine 2 was prepared in 61 % yield by treating N,N'-di-t-butyl-oxycarbonyl-1,2-di(4-pyridyl)ethylenediamine 4 with trifluoroacetic acid or in 94% yield by the hydrolysis under basic conditions of N,N'-diphthaloylglycyl-1,2-di(4-pyridy)ethylenediamine 13.  相似文献   
969.
The cross-sections for the production of the short-lived nuclides:26mAl,197mAu,136mBa,79mBr,139mCe,34Cl,167mEr,114m3In,114m2In,38mK,38mCl,26Na,20F,192Re,207mPb,203mPb,46mSc,183mW,90mZr obtained from (n, 2n), (n, n′), (n, alpha), (n,p) reactions using 14 MeV neutrons, were evaluated by the activation method. The experimental results of this work were compared with those obtained by other authors.  相似文献   
970.
The behaviour of iron in the Bayer process has been investigated by neutron activation analysis and Ge(Li) spectrometry, using bauxite samples of various origin. The amount of iron impurities in alumina was found to be independent of the origin of the bauxites. Alumina is contaminated by iron in the process of decomposition of aluminate liquors; regardless whether iron is present in ‘dissolved’ form or as a floating impurity, it will pass into the alumina almost completely.  相似文献   
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