4fN-15d组态自旋允许与禁戒跃迁能级的研究

通过稀土光谱理论，计算了三价稀土离子的4f^N-15d组态能级的f与d电子间的库仑相互作用，结果表明对于重稀土元素，其自旋允许跃迁能级位置高于自旋禁戒跃迁能级位置，并且两种能级间的能级差随f电子数的增加而依次减小。对于轻稀土元素,则自旋禁戒跃迁能级位置高于自旋允许跃迁能级位置。结果很好地解释了自旋禁戒跃迁能级的光谱现象。     

Emission band shape probes of the mixed-valence excited state properties of polypyridyl-bridged bis-ruthenium(II) complexes

The absorption spectra and emission spectral band shapes of several polypyridine-ligand (PP) bridged bis-ruthenium(II) complexes imply that the Ru(II)/Ru(III) electronic coupling is weak in their lowest energy metal to ligand charge transfer (MLCT) excited states. Many of these PP-bridging ligands contain pyrazine moieties and the weak electronic coupling of the excited states contrasts to the strong electronic coupling inferred for the correlated mixed-valence ground states. Although the bimetallic complexes emit at significantly lower energy than their monometallic analogs, the vibronic contributions to their 77 K emission spectra are much stronger than expected based on comparison to the monometallic analogs (around twofold in some complexes) and this feature is characteristic of bimetallic complexes in which the mixed-valence excited states are electronically localized. The weaker excited state than ground state donor/acceptor electronic coupling in this class of complexes is attributed to PP-mediated super-exchange coupling in which the mediating orbital of the bridging ligand (PP-LUMO) is partly occupied in the MLCT excited states, but is unoccupied in the ground states; therefore, the vertical Ru(III)-PP⁻ (MLCT) energy is larger and the mixing coefficient smaller in these excited states than is found for Ru(II)-PP in the corresponding ground states.     

Solution of periodic Poisson's equation and the Hartree–Fock approach for solids with extended electron states: Application to linear augmented plane wave method

We formulate a Hartree–Fock‐LAPW method for electronic band structure calculations. The method is based on the Hartree–Fock–Roothaan approach for solids with extended electron states and closed core shells where the basis functions of itinerant electrons are linear augmented plane waves. All interactions within the restricted Hartree–Fock approach are analyzed and in principle can be taken into account. In particular, we obtained the matrix elements for the exchange interactions of extended states and the crystal electric field effects. To calculate the matrix elements of exchange for extended states, we first introduce an auxiliary potential and then integrate it with an effective charge density corresponding to the electron exchange transition under consideration. The problem of finding the auxiliary potential is solved by using the strategy of the full potential LAPW approach, which is based on the general solution of periodic Poisson's equation. Here, we use an original technique for the general solution of periodic Poisson's equation and multipole expansions of electron densities. We apply the technique to obtain periodic potentials of the face‐centered cubic lattice and discuss its accuracy and convergence in comparison with other methods. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Electronic structure and chemical bonding in K<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript>

The calculations of the electronic structure of layered polyvanadate K₂V₃O₈ were made employing the spin-polarized tight-binding LMTO method. Calculated magnetic moment for K₄V₆O₁₆ compound phase equals 1.97 μ_B. V-O interactions were established to be dominating in the chemical bonding generation in this polyvanadate according to the estimated crystal orbital overlap population. The covalent bonds V(2)-V(2) in V(2)₂O₇ groups and electron density localization on vanadium atoms in isolated pyramids V(1)O₅ were found.     

Theoretical studies on the band structures of superconducting solid compounds: Nb3X (X=Si, Ge, Sn, Pb)

The band structures of several analogous superconducting A-15 type solid compounds, Nb3X (X=Si, Ge, Sn, Pb), have been calculated by use of the tight-binding method within the Extended Huckel approximation (EHT). By analysis of their energy bands, densities of states and crystal orbital overlap populations, the dependence of the superconducting transition temperatures (Tc) on the electronic structures and bondings is qualitatively elucidated.     

Evaluation of single-ion conductances in nonaqueous solvents at 25°C by the use of tetrabutylammonium tetrabutylboride as a reference electrolyte

Precise conductances for tetrabutylammonium tetrabutylboride (Bu₄NBBu₄) at 25°C have been measured in a number of nonaqueous solvents, and the data have been analyzed by the 1957 Fuoss-Onsager conductance equation. Limiting ion conductances for the Bu₄N⁺ ion at infinite dilution ₀(Bu ₄ N ⁺) in various solvents have been evaluated by dividing ₀ values of the salt into two equal parts. The ₀(Bu ₄ N ⁺) values so obtained are in fairly good agreement (within±0.1–3.5%) with the corresponding values determined from direct transference number measurements in these solvents.     

Application of high resolution ICP-spectrometry to the determination of B,Be, Co,Mo and Sn in soils and similar matrices

The most sensitive emission lines for the elements B, Be, Co and Mo are strongly influenced by disturbing emission lines of Fe using normal optical resolution. The advantages of high resolution, applying the new ICP-spectrometer JY 38 Plus (Jobin-Yvon, France) with the 2400 lines/mm grating measuring in the 1st and 2nd order will be discussed. Beside the concentrations in soils, sediments and sludges, applying aqua regia and HF decomposition methods, the detection limits in these matrices will be given. The possibilities of ICP-spectrometry for the determination of the above-mentioned elements are shown at the examples of SRMs (standard reference materials). The materials used here were three soils and three sludges from the BCR (Community Bureau of Reference, European Communities) and one sediment from NBS (National Bureau of Standards, USA). For example, the most sensitive and normally used line for the determination of boron at 249.7733 nm cannot be used in case of this type of matrix due to normally high Fe-concentrations and due to a strong Fe-interference. Therefore, it is necessary to use the line at 249.6778 nm, where an interference-free measurement can be achieved in case of high optical resolution. The measured B-contents in these samples are in the range of 20 to 60 g/g, for Co in the 10 g/g region, for Be well below 1 g/g, for Sn between 3 and 400 g/g. Mo was only detectable in the sludge samples (limit of determination 0.5 g/g).Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Preparation of candidate certified reference materials for the quality control of EDTA-and acetic acid-extractable trace metal determinations in sewage sludge-amended soil and terra rossa soil

The determination of extractable trace metal contents in soil using single extraction procedures is currently performed in many laboratories to assess the bioavailable metal fraction (and related phytotoxic effects) and the accessability to the environment (e.g. contamination of ground waters). Owing to the need for validation of the extraction schemes used and of the analytical techniques, the EC Measurements and Testing Programme (formerly BCR) has organized a project for improving the quality of determination of extractable trace metal contents in soil, the first step being an interlaboratory study to adopt common extraction procedures and the second being a certification campaign to certify two soils for their extractable trace element contents following these procedures. This paper gives a brief overview of the project organisation and describes the preparation, homogeneity and stability studies of two soil candidate reference materials (sewage sludge-amended and terra rossa soils).     

The effect of a coriolis force on Taylor-Couette flow

Taylor-Couette flow subject to a Coriolis force is studied experimentally and numerically. In the experiment, the Couette apparatus is mounted on a turntable with the axis of the cylinders orthogonal to the rotation vector of the turntable. The Coriolis force stabilizes the fluid against the onset of Taylor vortices and alters the velocity fields, both above and below the transition from the initial flow. At small dimensionless turntable frequencies, the transition yields time-independent Taylor vortices which are tilted with respect to the cylinder axis. At larger there is a direct transition to turbulence. We determine the first-order correction to the classical Couette initial flow, to account for the effects of the Coriolis force, by expanding in powers of. We present numerical results for the axial velocity (the only nonvanishing correction term to order) in the infinite-cylinder approximation.     

Two new standard reference materials for the determination of drugs of abuse in human hair

Two new standard reference materials (SRM) for drugs of abuse in human hair have been developed. SRM 2379 consists of hair spiked with cocaine, benzoylecgonine, cocaethylene, phencyclidine, amphetamine, and methamphetamine. SRM 2380 consists of hair spiked with codeine, morphine, monoacetylmorphine, and tetrahydrocannabinol (THC). The SRMs were prepared by soaking the hair in a solution of the target analytes in water-dimethylsulfoxide. The concentration of each analyte was determined using two methods, one based upon gas chromatography/mass spectrometry (GC/MS) and one based upon liquid chromatography/mass spectrometry (LC/MS). Both methods used 0.1 M HCl for extraction of all the analytes from the hair, except for THC, which was extracted with 1 M NaOH. For isolation of the analytes from the extracts, the GC/MS-based methods used different clean-up procedures from those used for the LC/MS-based methods. The results from the two methods were in good agreement with mean differences for the analytes ranging from 4% to 16%. These materials will enable laboratories performing analyses of hair for drugs of abuse to test the accuracy of their methods.