二氧化铬阴离子光电子能谱的理论研究

凭借密度泛函理论,采用不同基组对中性分子CrO2的基态((X)3B1)以及阴离子CrO1-的基态((X)4B1)进行几何优化和振动频率分析;应用量化计算得到的力常数及结构和光谱参数,基于推得的两维四模Franck-Condon重叠积分的代数表示,对CrO2((X)3B1)-CrO2-((X)4B1)的光脱附过程进行Franck-Condon分析和光谱模拟,理论上得到光电子能谱的谱线相对强度及振动结构分布,理论谱与实验测得的二氧化铬阴离子光电子能谱达到一致,并对光电子能谱的振动结构进行归属及热带分析;另外,在光谱模拟过程中通过迭代Franck-Condon分析过程,推得CrO2-((X)4B1)与CrO2((X)3B1)平衡几何结构之差:△R(Cr-O)=0.05A,△∠(O-Cr-O)=12°.     

新型NO2化学传感器:碳化硅纳米管

气体吸附对碳化硅纳米管的电子结构的影响是理解碳化硅纳米管气敏传感器工作机理的基础.基于密度泛函理论,利用CASTEP软件包计算NO₂气体吸附前后的碳化硅纳米管的结构及其电子结构.结果表明,NO₂气体与碳化硅纳米管间形成了稳定的吸附,并明显的增强了碳化硅纳米管的导电特性.碳化硅纳米管是制备气体传感器的理想材料之一,为开发应用于NO₂气体检测的碳化硅纳米管提供必要的理论支持.     

Ta4Cn^-/0(n=0-4)团簇的电子结构、成键性质及稳定性

本文采用尺寸选择的负离子光电子能谱技术,结合密度泛函理论,对Ta4Cn^-/0(n=0-4)团簇电子结构、成键性质以及稳定性进行了研究.实验测得Ta4Cn-(n=0—4)团簇负离子基态结构的垂直脱附能分别为(1.16±0.08),(1.35±0.08),(1.51±0.08),(1.30±0.08)和(1.86±0.08)eV.中性Ta4Cn(n=0—4)团簇的电子亲和能分别为(1.10±0.08),(1.31±0.08),(1.44±0.08),(1.21±0.08)和(1.80±0.08)eV.研究发现Ta4^-/0团簇为四面体结构,Ta4C1-/0团簇中碳原子覆盖在Ta4四面体的一个面上方,Ta4C2^-/0团簇则是两个碳原子分别覆盖在Ta4四面体中的两个面上方.Ta4C3^-/0团簇是一个缺角立方体结构.Ta4C4^-/0团簇则是近似立方体结构,可以看成是α-TaC面心立方晶体的最小晶胞单元.分子轨道分析结果显示Ta4C3团簇的单电子最高占据轨道主要布居在单个钽原子周围,导致Ta4C3^-团簇的垂直脱附能明显低于其相邻团簇.理论研究显示随着碳原子数目的增加,Ta4Cn^-/0(n=0—4)团簇中的钽-钽金属键逐渐被钽-碳共价键取代,单原子结合能逐渐增加且明显高于Ta4+n^-/0(n=0-4)团簇.中性Ta4C4的单原子结合能高达7.13 eV,这说明钽-碳共价键的形成有利于提高材料的熔点,这与碳化钽作为高温陶瓷材料的特性密切相关.     

Chemical ordering in As-Se glasses: X-ray absorption edge and XPES studies

X-ray absorption edge and X-ray photoelectron spectroscopic studies of As-Se glasses seem to support a chemical ordering model. Communication No. 94 from Solid State and Structural Chemistry Unit.     

Photoelectron spectrum of a polycyclic aromatic nitrogen heterocyclic anion: quinoline−

We report a joint photoelectron spectroscopic and theoretical study on the molecular anion, quinoline^?. Analysis of the vibrationally resolved photoelectron spectrum found the adiabatic electron affinity, EA_a(C₉H₇N), to be 0.16 ± 0.05 eV. These findings were supported by density functional theory calculations. Our experimental and computational results demonstrate the unusual electrophilicity for a polycyclic aromatic heterocycle.     

Statistical Mechanics Approach for Uniform and Non-uniform Fluid with Hard Core and Interaction Tail

One recently proposed self-consistent hard sphere bridge functional was combined with an exponential function exp(-cr) and a re-normalized indirect correlation function to construct the bridge function for fluid with hard core and interaction tail. In the present approach, the adjustable parameter α was determined by the thermodynamic consistency realized on the compressibility modulus, the re-normalization of the indirect correlation function was realized by a modified Mayer function with the interaction potential replaced by the perturbative part of the interaction potential. As an example, the present bridge function was combined with the Ornstein-Zernike (OZ) equation to predict structure and thermodynamics properties in very good agreement with the simulation data available for Lennard-Jones (L J). Based on the universality principle of the free energy density functional and the test particle trick, the numerical solution of the OZ equation was employed to construct the first order direct correlation function of the non-uniform fluid as a functional of the density distribution by means of the indirect correlation function. In the framework of the density functional theory, the numerically obtained functional predicted the density distribution of LJ fluid confined in two planar hard walls that is in good agreement with the simulation data.     

Luminescence characterization and electron beam induced chemical changes on the surface of ZnAl2O4:Mn nanocrystalline phosphor

Luminescence characteristics and surface chemical changes of nanocrystalline Mn²⁺ doped ZnAl₂O₄ powder phosphors are presented. Stable green cathodoluminescence (CL) or photoluminescence (PL) with a maximum at ∼512 nm was observed when the powders were irradiated with a beam of high energy electrons or a monochromatic xenon lamp at room temperature. This green emission can be attributed to the ⁴T₁ → ⁶A₁ transitions of the Mn²⁺ ion. Deconvoluted CL spectra resulted in two additional emission peaks at 539 and 573 nm that may be attributed to vibronic sideband and Mn⁴⁺ emission, respectively. The luminescence decay of the Mn²⁺ 512 nm emission under 457 nm excitation is single exponential with a lifetime of 5.20 ± 0.11 ms. Chemical changes on the surface of the ZnAl₂O₄:Mn²⁺ phosphor during prolonged electron beam exposure were monitored using Auger electron spectroscopy. The X-ray photoelectron spectroscopy (XPS) was used to determine the chemical composition of the possible compounds formed on the surface as a result of the prolonged electron beam exposure. The XPS data suggest that the thermodynamically stable Al₂O₃ layer was formed on the surface and is possibly contributing to the CL stability of ZnAl₂O₄:Mn phosphor.     

Oxovanadium (IV) complexes of bidentate [N,O] donor Schiff-base ligands: synthesis and mesomorphism

A series of new oxovanadium(IV) Schiff-base complexes of the type [VO(L)₂], [L?=?N-(4-n-alkoxysalicylaldimine)-4′-dodecyloxyaniline, n?=?6, 8, 16, and 18] have been synthesized. The compounds were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, UV-Vis, FAB-mass, and magnetic susceptibility measurements. The mesomorphic behavior of the compounds was studied by polarized optical microscopy and differential scanning calorimetry. The compounds are all highly thermally stable exhibiting smectic mesomorphism. Non-electrolytic nature of the complexes was ascertained by solution electrical conductance measurements. Cyclic voltammetry revealed a quasireversible single-electron response for VO(V)/VO(IV) couple. A ν_V=O stretching mode at ～970?cm^?1 indicates absence of any intermolecular V=O?···?V=O interactions. Density functional theory study was carried out using DMol3 at BLYP/DNP level to determine energy optimized structure revealed a distorted square pyramidal geometry for the vanadyl complexes.     

An XPS Study of the Effect of La2O3 Dopant on the Dispersion and Thermal Stability of Pt/Al2O3 Catalysts

The Pt(4d)/Al(2s) XPS intensity ratio for Pt/Al₂O₃ catalysts increases with the addition of La₂O₃ as a dopant. The Pt(311) line in the X-ray diffraction pattern also broadens with the addition of La₂O₃. These data imply that doping the Pt/Al₂O₃ catalyst with La₂O₃ increases the dispersion of the platinum which in turn would be expected to increase the activity and thermal stability of the catalyst.     

Surface composition of ordered intermetallic compounds PtBi and PtPb

The surface composition of bulk electrodes made from the ordered intermetallic phases PtBi and PtPb has been studied by ex-situ X-ray photoelectron spectroscopy (XPS) after being subjected to various electrochemical treatments. Analysis of the freshly polished surfaces showed that in the surface and near surface regions the less-noble metals; Bi and Pb are oxidized to a significant extent (28% and 41%, respectively). Upon cycling to increasingly positive potentials, the fraction of oxidized to metallic forms of Bi and Pb decreased gradually to reach the minimal values of 7% and 6% at +400 mV vs. Ag/AgCl (saturated KCl). The observed decrements are due to leaching of surface oxides; Bi₂O₃ on PtBi and PbCO₃ or Pb(OH)₂ on PtPb. When the potential sweep was extended to more positive values, there was a linear decrease in the surface concentration of the less-noble metal, along with a slight increase in the amount of the species in their oxidized state (Bi₂O₃ for PtBi and PbSO₄ for PtPb). Leaching of Bi from the electrode surface occurs in accordance to the Pourbaix diagram for elemental bismuth, indicating no significant increase in stability arising from the formation of an intermetallic phase with platinum. In the case of PtPb, however, the Pb starts to dissolve away at potentials significantly more positive (+800 mV) than what was anticipated from the Pourbaix diagram. The results obtained here are in accord with our previous observations on the effects of electrochemical pre-treatment on these intermetallic phases for the electrocatalytic oxidation of formic acid and other potential fuel cell fuels.     

锐钛矿TiO2及其掺Fe所导致的红移现象研究：赝势计算和紫外光谱实验

采用平面波超软赝势方法研究了锐钛矿型TiO2及Fe掺杂TiO2的晶体结构和能带结构，计算表明Fe掺杂导致TiO2电子局域能级的出现及禁带变窄，从而导致吸收光谱红移.研究发现，t2g态在红移现象中起了重要作用.紫外透射光谱实验证实了TiO2掺Fe后吸收光谱红移和禁带变窄的理论预言. 关键词： 密度泛函理论 TiO2 Fe掺杂 红移     

Temperature and pressure dependence of Raman active lattice mode frequencies of cubic C8H6(Br)2, evidence of a phase transition

The temperature dependence of the Raman active frequencies of the lattice modes of dibromocubane is measured below room temperature. The frequencies are linearly dependent on the temperature decreasing with increased temperature with a marked change in slope occurring at 200?K indicative of a structural phase transition. The pressure dependence of the frequencies measured at room temperature up to 24?KBar shows no evidence of a phase change. Density functional calculations of the structure and Raman frequencies of the internal modes of an isolated molecule of C₈H₆(Br)₂ indicate the molecule is slightly distorted from a cubic carbon structure.     

XPS and ab initio study of the interaction of PbTe with molecular oxygen

Density functional (B3LYP) calculations have been performed to investigate the adsorption of molecule on the surface of cluster (PbTe)₄. To study the influence of point defects (namely, impurity atoms and cation and anion vacancies) on the reactivity of PbTe surface, clusters (PbTe)₃GeTe, (PbTe)₃GaTe, (PbTe)₃Te, and (PbTe)₃(Pb) were investigated. The adsorption of oxygen on the surface of (PbS)₄ cluster was calculated to evaluate the role of anions in the adsorption process. It was shown that the formation of the peroxide-like complex is the first step of adsorption. The calculated tendency to surface oxidation increases in sequence: PbTe with cation vacancies <PbS < pure PbTe < PbTe doped with Ga < PbTe doped with Ge < PbTe with anion vacancies. The results of quantum-chemical calculations correlate with X-ray photoelectron spectroscopy data.     

Electronic structure of non-centrosymmetric AgCd2GaS4 and AgCd2GaSe4 single crystals

X-ray photoelectron core-level and valence-band spectra for pristine and Ar⁺-ion irradiated (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals grown, respectively, by the Bridgman method and the method of direct crystallization have been measured in the present work. The X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals. Electronic structure of AgCd₂GaS₄ has been calculated employing the full potential linearized augmented plane wave method. For the AgCd₂GaS₄ compound, the X-ray emission bands representing the energy distribution of the valence Ag d-, Cd d-, Ga p- and S p-like states were recorded and compared on a common energy scale with the XPS valence-band spectrum. The theoretical and experimental data regarding the occupation of the valence band of AgCd₂GaS₄ were found to be in excellent agreement to each other. Second harmonic generation (SHG) efficiency of AgCd₂GaS₄ by using the 320 ns CO laser at 5.5 μm has been recorded within the temperature range 80–300 K. Substantial increase of the photoinduced SHG which in turn is substantially dependent on the temperature has been detected for the AgCd₂GaS₄ compound.     

室温合成硫化银纳米粒子及其X射线光电子能谱表征

在常温常压下制备了硫化银纳米粒子,选用廉价的氧化银和硫粉为原料,采用多聚甲醛为还原剂,并在乙二胺体系中完成了反应。所得产物用X射线光电子能谱、X射线粉末衍射和透射电镜进行了表征。X射线粉末衍射表明：产物为单斜相的硫化银;透射电子显微镜表明：产物为直径约为100nm的棒状纳米粒子,其对应的电子衍射斑点可以指标成(120)和(303),说明产物的结晶较好;X射线光电子能谱分析表明：产物中Ag属 1价而S属-2价,它们的原子个数比为Ag：S=1：0．453。对比实验表明：多聚甲醛和无水乙二胺都起了很关键的作用;多聚甲醛起了多重作用,它既是溶剂,又是中和剂,用以除去反应的副产物多个点-甲酸,从而加速了反应的进行。     

2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面的裂解机理

本文研究了2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面解离的可能微观反应机理,使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态.采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法,优化了2-丙醇和1,1,1-三氟-2-丙醇裂解反应过程各物种在Ni(100)表面的top,hollow和bridge位的吸附模型,计算了能量,并对布局电荷进行了分析,得到了各物种的有利吸附位.结果表明:2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面都存在β-H和γ-H两个平行竞争的解离过程,其中2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为64.7 k J·mol-1猯,而γ-H解离速控步骤活化能为233.1 k J·mol-1猯,故β-H解离过程占优势,主要产物是CH3COCH3;相反,1,1,1-三氟-2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为257.1 k J·mol-1猯,而γ-H解离速控步骤活化能为148.1 k J·mol-1猯,故γ-H解离过程占优势,主要产物是CF3CH=CH2.由此说明,电负性更大的氟原子取代2-丙醇中的氢原子之后,2-丙醇在Ni表面的解离机理发生了改变.理论预测结果与实验结论一致.     

2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面的裂解机理

本文研究了2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面解离的可能微观反应机理,使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态。采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法,优化了2-丙醇和1,1,1-三氟-2-丙醇裂解反应过程各物种在Ni(100)表面的top,hollow和bridge位的吸附模型,计算了能量,并对布局电荷进行了分析,得到了各物种的有利吸附位。结果表明： 2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面都存在β-H和γ-H两个平行竞争的解离过程,其中2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为64.7 kJ∙mol-1,而γ-H解离速控步骤活化能为233.1kJ∙mol-1,故β-H解离过程占优势,主要产物是CH3COCH3;相反,1,1,1-三氟-2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为257.1 kJ∙mol-1,而γ-H解离速控步骤活化能为148.1kJ∙mol-1,故γ-H解离过程占优势,主要产物是CF3CH=CH2。由此说明,电负性更大的氟原子取代2-丙醇中的氢原子之后,2-丙醇在Ni表面的解离机理发生了改变。理论预测结果与实验结论一致。     

Interfacial properties of 2D WS2 on SiO2 substrate from X-ray photoelectron spectroscopy and first-principles calculations

Two-dimensional (2D) WS₂ films were deposited on SiO₂ wafers, and the related interfacial properties were investigated by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principles calculations. Using the direct (indirect) method, the valence band offset (VBO) at monolayer WS₂/SiO₂ interface was found to be 3.97 eV (3.86 eV), and the conduction band offset (CBO) was 2.70 eV (2.81 eV). Furthermore, the VBO (CBO) at bulk WS₂/SiO₂ interface is found to be about 0.48 eV (0.33 eV) larger due to the interlayer orbital coupling and splitting of valence and conduction band edges. Therefore, the WS₂/SiO₂ heterostructure has a Type I energy-band alignment. The band offsets obtained experimentally and theoretically are consistent except the narrower theoretical bandgap of SiO₂. The theoretical calculations further reveal a binding energy of 75 meV per S atom and the totally separated partial density of states, indicating a weak interaction and negligible Fermi level pinning effect between WS₂ monolayer and SiO₂ surface. Our combined experimental and theoretical results provide proof of the sufficient VBOs and CBOs and weak interaction in 2D WS₂/SiO₂ heterostructures.     

Electronic Excitations in Pyrrole: A Test Case for Determination of Chromophores in the Chromogenic Effects of Neurotoxic Hydrocarbons by Time-Dependent Density Functional Theory and Single-Excitation Configuration Interaction Methods

Time-dependent density functional theory (TD-DFT) and single-excitation configuration interaction (CIS) calculations on the electronic excitations in pyrrole have been performed to examine the reliability of these first-principles electronic structure methods in predicting electronic excitation spectraof pyrrole-containing compounds. Both the TD-DFT and CIS calculations led to satisfactory results when compared to available experimental data, particularly for low-lying excited states. The TD-DFT and CIS calculations provide lower and upper limits of the excitation energies, respectively, for low-lying singlet excited states. These results suggest that these methods can be used for the prediction of the excitation spectra, particularly the excitation energies for low-lying excited states, of chromophores responsible for the chromogenic effects of neurotoxic hydrocarbons, which are believed to be substituted pyrroles and their adducts with proteins. As an example of a practical application, the spectrum of the widely used 2,5-dimethylpyrrole has been calculated. It is shown that the 2,5-dimethylpyrrole molecule does not have an absorption in the region of the visible spectrum (400-700 nm), suggesting that the absorption observed at 530 nm and the color of 2,5-dimethylpyrrole is due to another species, probably a product of possible 2,5-dimethylpyrrole autoxidation. This suggests that the conclusions from previously reported experimental studies of biochemical reactions of neurotoxic γ-diketones need to be reexamined in terms of the relationship of chromogenicity to neurotoxicity.     

X-ray photoemission spectra measurements of CeNi2Sb2 and CeCu2Sb2

X-ray photoemission spectra, resistivity and susceptibility of CeNi₂Sb₂ and CeCu₂Sb₂ were measured and are discussed. The results indicate that these alloys are Kondo systems. For comparison of the valence band properties, the spectra of the isostructural alloys of RT₂X₂-type with R = La, Gd, T = Cu, Ni and X = Sn, Sb were investigated, too.