变分过渡态理论对OCS,CO2,CS2体系的研究

本文用变分过渡态理论,首次对无鞍点的释能反应O+CS→CO+S、O+CO→CO+O和S+CS→CS+S进行了动力学研究,考察了反应动力学瓶颈区性质,计算了反应的速度常数,并将O+CS反应的速度常数值与实验值及经典轨迹计算结果进行了比较,三者基本相符.     

3-羟基哒嗪及其CH3, NO2和Cl取代衍生物质子转移过程的理论研究

用密度泛函理论(DFT) B3LYP方法, 在6-311＋G*基组下, 对3-羟基哒嗪及其CH₃, NO₂和Cl取代衍生物分子醇式和酮式结构互变异构化反应进行了研究, 优化化合物的几何构型, 寻找反应的过渡态, 通过振动分析和内禀反应坐标(IRC)分析加以证实, 计算了反应的活化能. 结果表明, 3(2H)-哒嗪酮及其带取代基的衍生物不论是单体, 还是相对应的二聚体, 比其相对应的异构体能量低, 表明在通常情况下是以3(2H)-哒嗪酮及其衍生物形式稳定存在的, 这与前人通过实验数据对3-羟基哒嗪互变异构体的比率进行预测的结果是一致的. 根据计算结果讨论了异构化反应的机理.     

A novel trilinear decomposition algorithm： Three-dimension non-negative matrix factorization

Non-negative matrix factorization(NMF)is a technique for dimensionality reduction by placing non-negativity constraints onthe matrix.Based on the PARAFAC model,NMF was extended for three-dimension data decomposition.The three-dimension non-negative matrix factorization(NMF3)algorithm,which was concise and easy to implement,was given in this paper.The NMF3algorithm implementation was based on elements but not on vectors.It could decompose a data array directly without unfolding,which was not similar to that the traditional algorithms do.It has been applied to the simulated data array decomposition andobtained reasonable results.It showed that NMF3 could be introduced for curve resolution in chemometrics.     

Phosphorescence lifetime of naphthalene and phenanthrene in aggregated aromatic molecule-β-cyclodextrin-precipitant complexes

Aggregated aromatic molecule--cyclodextrin-precipitant complexes exhibit long-lived phosphorescence at room temperature in water after the chemical binding of oxygen. The temperature dependences of the phosphorescence lifetimes of naphthalene-h₈, naphthalene-de, and phenanthrene in the aggregates were measured. For example, the phosphorescence lifetimes of naphthalene-d₈ aggregated with -cyclodextrin and cyclohexane are equal to 25.1, 17.6, and 6.8 s at 77, 276, and 347 K, respectively, and that of phenanthrene aggregated with isooctane and -cyclodextrin are 3.24, 3.06, and 1.26 s at 268, 274, and 335 K, respectively. The temperature dependences of the phosphorescence lifetimes at room temperature are determined by the rate constants of the radiative and nonradiative transitions from the triplet state of an aromatic molecule.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2225–2228, September, 1996.     

Modeling high-pressure densities at wide temperature range with volume scaling: Cyclohexane + n-hexadecane mixtures

High-pressure density data for cyclohexane + n-hexadecane mixtures at a wide temperature range was modeled with several classical equations of state (EOS) and correlative models. A modification for softening the co-volume and another for a volume scaling of the Peng–Robinson EOS (VS-PR) were proposed. The VS-PR model is able to correlate the pure component experimental data employing only five adjustable parameters, with root-mean-square deviation (RMSD) between calculated and experimental densities essentially within the experimental error. This result is superior to widely used approaches, i.e., a six parameter Tait model and six parameter volume translations (temperature and pressure dependent) for Peng–Robinson and Patel–Teja EOS. The VS-PR model also represents well the isobaric thermal expansion and the isothermal compressibility coefficients of the pure cyclohexane, a small naphthenic substance as well as a long chain n-alkane hydrocarbon, n-hexadecane. When modeling the mixture data, the use of VS-PR model of pure components along with the Redlich–Kister expansion, truncated at the first term, the density was correlated within a RMSD only 60% greater than the experimental error. The proposed model is able to accurately represent all the tested mixture data with a relatively small number of parameters.     

Exact electronic properties in the classically forbidden region of a metal surface

We derive exact properties of the inhomogeneous electron gas in the asymptotic classically forbidden region at a metal–vacuum interface within the framework of local effective potential energy theory. We derive a new expression for the asymptotic structure of the Kohn–Sham density functional theory (KS‐DFT) exchange‐correlation potential energy v_xc(r) in terms of the irreducible electron self‐energy. We also derive the exact asymptotic structure of the orbitals, density, the Dirac density matrix, the kinetic energy density, and KS exchange energy density. We further obtain the exact expression for the Fermi hole and demonstrate its structure in this asymptotic limit. The exchange‐correlation potential energy is derived to be v_xc(z → ∞) = ?α_KS,xc/z, and its exchange and correlation components to be v_x(z → ∞) = ?α_KS,x/z and v_c(z → ∞) = ?α_KS,c/z, respectively. The analytical expressions for the coefficients α_KS,xc and α_KS,x show them to be dependent on the bulk‐metal Wigner–Seitz radius and the barrier height at the surface. The coefficient α_KS,c = 1/4 is determined in the plasmon‐pole approximation and is independent of these metal parameters. Thus, the asymptotic structure of v_xc(z) in the vacuum region is image‐potential‐like but not the commonly accepted one of ?1/4z. Furthermore, this structure depends on the properties of the metal. Additionally, an analysis of these results via quantal density functional theory (Q‐DFT) shows that both the Pauli W_x(z → ∞) and lowest‐order correlation‐kinetic W(z → ∞) components of the exchange potential energy v_x(z → ∞), and the Coulomb W_c(z → ∞) and higher‐order correlation‐kinetic components of the correlation potential energy v_c(z → ∞), all contribute terms of O(1/z) to the structure. Hence correlations attributable to the Pauli exclusion principle, Coulomb repulsion, and correlation‐kinetic effects all contribute to the asymptotic structure of the effective potential energy at a metal surface. The relevance of the results derived to the theory of image states and to KS‐DFT is also discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Characterization of high-temperature superconductors by electron microprobe analysis

In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y₁Ba₂Cu₃O_6+x (0 < x < 1) HTSC in A1₂O₃ and ZrO₂ crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity.     

Imidazole Coordinated Sandwich-type Antimony Polyoxotungstates Na9[ {Na（H=O2}3{M（C3H4N2）}3（ Sb W9O33）2]·xH=O（M=Ni^Ⅱ, Co^Ⅱ, Zn^Ⅱ, Mn^Ⅱ）

The imidazole covalently coordinated sandwich-type heteropolymngstates Na9[ {Na（H=O2}3{M（C3H4N2）}3（ Sb W9O33）2]·xH=O（M=Ni^Ⅱ, Co^Ⅱ, Zn^Ⅱ, Mn^Ⅱ） were obtained by the reaction of Na2WO4·2H2O, SbCl3·6H2O, NiCl2·6H2O [MnSO4·H2O, Co（NO3）2·6H2O, ZnSO4·7H2O] and imidazole at pH≈7.5. The structure of Na9[{Na（H2O）2}3{Ni（C3H4N2）}3（SbW9O33）2]·32H2O was determined by single crystal X-ray diffraction. Polyanion [{Na（H2O）2}3{Ni（C3H4N2）}3（SbW9O33）2}3]^9- has approximate C3v symmetry, imidazole coordinated six-nuclear duster [{Na（H2O）2}3{Ni（C3H4N2）}3]^9＋ is encapsulated between two （α-SbW9O33）^9-, the three rings of imidazole in the polyanion are perpendicular to the horizontal plane formed by six metals （Na-Ni-Na-Ni-Na-Ni） in the central belt, and x-stacking interactions exist between imidazoles of neighboring polyanions with dihedral angel of 60%. The compounds were also characterized by IR, UV-Vis spectra, TG and DSC, and the thermal decomposition mechanism of the four compounds was suggested by TG curves.     

Separating Ag, B, Cd, Dy, Eu, and Sm in a Gd matrix using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester extraction chromatography for ICP-AES analysis

The separation procedure for Ag, B, Cd, Dy, Eu and Sm as impurities in Gd matrix using ICP-AES technique with an extraction chromatographic column has been developed. The spectral interference of the Gd matrix on the elements was eliminated using a chromatography technique with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) as the mobile phase and XAD-16 resin as the stationary phase. Ag⁺, B₄O₇²⁻, and Cd²⁺ were eluted with 0.1 M HNO₃, while rare earth ions were not. The best eluent for separating Eu and Sm in the Gd matrix was 0.3 M HNO₃. The limit of quantitation for these elements was 0.6-3.0 ng mL⁻¹. The recovery of Ag, B, and Cd was 90-104% using 0.1 M HNO₃ as the eluent, while that of Eu, Gd, and Sm ranged from 100 to 102% with 0.3 M HNO₃. Dy was recovered quantitatively with 4 M HNO₃. The relative standard deviation of the methods for a set of three replicates was between 1.0 and 15.4% for the synthetic and standard Gd solutions. The proposed separation procedure was used to measure Ag, B, Cd, Dy, Eu, and Sm in a standard Gd solution.     

The “Facilitated Transition” hypothesis as an explanation for the gemdialkyl effect

A new technique of searching the conformational space of transition states was used to explore the cause of the rate acceleration in the gem-dialkyl effect in intramolecular cyclization reactions. Several previous hypotheses were discarded and a new hypothesis was advanced based on this new data. This hypothesis, the “Facilitated Transition” hypothesis, states that increased steric hindrance reduces the overall activation energy by facilitating rotation through the transition state. The older “Reactive Rotamer” hypothesis was eliminated by generating all conformations of the starting materials using the and computer programs and demonstrating that no relationship is found between rate increase and a change in the concentration of “reactive rotamers”.