电子定域函数(ELF)理论方法简介——一种描述化学键的新模型

电子定域函数理论可以清晰和定量化描述理论化学研究的基本对象——化学键,已在原子、分子及固体体系中得到广泛应用。本文系统介绍了电子定域函数(ELF)理论方法的基本物理思想;对ELF函数的一些特点如数值稳定性、ELF与分子中的原子理论(AIM理论)方法的异同及ELF的拓扑分析进行了说明;对电子定域函数在研究原子壳层结构、化学键的性质、孤对电子的位置、反应过程化学键的断裂和生成等方面的应用进行了介绍。     

分子中电子配对能量效应的探讨

“若二个原子各有一个未成对电子,且自旋反平行,则在二个原子接近时这二个未成对电子可以配对,使得能量降低,从而形成化学键。”长期以来,很多化学教科书这样阐述,以致使很多学化学的同学形成了这样的“基本概念“,即“电子配对,能使能量降低,从而形成化学键。”     

卓越的美国化学家和物理学家——欧文·朗缪尔

欧文·朗缪尔(Irving Langmuir)是本世纪卓越的美国化学家和物理学家。他在1906—1956年期间的研究工作包括高温低压下的化学反应、表面化学、原子结构和化学键的电子理论、热离子发射、等离子体物     

磷钼钒酸盐的电子结构与催化性质的研究

本文通过CNDO/2量子化学方法对Keggin型磷钼钒酸盐的电子结构和催化性质的理论研究,导出了该类杂多化合物的价成键轨道结构普适规则,并推广到其他同多杂多化合物。本文根据对前线分子轨道和化学键性质的分析,探讨了随杂阴离子中钒原子数目的变化,磷钼钒酸盐的氧化性质和氧化催化性质变化的规律。     

铀酰配合物的电子结构与化学键

本文采用群分解EHMO计算程序研究了铀酰配合物的电子结构与化学键。计算结果表明,铀酰配合物具有与UO_2~(2+)离子类似的电子结构特征,铀酰基元是典型的共价成键,而第二配体在赤面上密堆积形成离子键。这种电子结构与化学键特点被用来阐明铀酰配合物的立体化学性质以及光谱化学序列。     

光诱导单电子转移反应合成氮杂环脯氨酸肽

以脯氨酸为起始原料合成了四个光反应底物N-(末端三甲基硅苄基脯氨酸肽链)邻苯二甲酰亚胺(4),并在甲醇溶剂中进行了光反应.结果表明,4的光致激发态分子内发生单电子转移反应,生成双离子自由基8,电子沿着化学键在给电子杂原子问转移,达到共振平衡,离去基团离去使平衡向末端杂原子方向移动,高选择性地生成分子内端位双自由基9,自...     

(H)FNO~+异构体的结构及异构化反应的量子化学研究

在CCSD(T)/6-311+G(2d,2p)//B3LYP/6-311+G(2d,2p)水平上对八种(H)FNO+异构体的结构和异构化机理进行了研究.用分子生成密度差结合电子密度拓扑分析方法讨论了FNO质子化过程中的电子转移,结果显示FNO质子化过程中除HFNO+中电荷由N,O原子向H,F原子转移外,其他七种异构体中均是H原子上电荷增加,F原子上电荷减小,说明电子由F向H转移.在八种(H)FNO+异构体中,HFNO+,FNOH-cis,FN(H)O+和FNOH+-trans能量较低,较稳定;异构体间通过H原子迁移、F原子迁移、分子内化学键转动及化学键的相对振动四种过程实现异构化,其中原子迁移过程的反应能垒很高,反应不容易进行.用电子定域函数(ELF)理论讨论了反应过程中化学键的变化.     

硝酸铕与含氮冠醚配合物的电子结构和化学键

本文用XPS和INDO方法研究了硝酸铕与含氮冠醚配合物[Eu(NO3)2(2,2)]NO3的电子结构, 结合能和电荷分布数据指出, 在配位原子中, 电负性低的氮原子N1s结合能的化学位移比电负性高的氧原子O1s的大。在配合物中, 氮原子转移至中心金属离子上的电荷比氧原子转移的多。铕与含氮冠醚配合物的化学键具有一定程度的共价性, 电负性低的氮原子与铕的配位键(N→Eu)的共价性比电负性高的氧原子的配位键(O→Eu)的大。     

密度泛函理论下的分子电负性--Ⅷ. ABEEM方法中封闭体系的电荷极化模式

在密度泛函理论（ＤＦＴ）和原子－键电负性均衡模型（ＡＢＥＥＭ）基础上,给出了建立ＡＢＥＥＭ软度矩阵和封闭体系的电子布居正则模式（ＰＮＭ）的方法．该方法可用于计算和讨论分子体系内部的电荷极化过程,计算结果表明,考虑了孤对电子（ｌｐ）后,原子－键电负性均衡模型下的电子布居正则模式明确地指出了分子内各个部分电荷间的极化．从ＡＢＥＥＭ可以得到与所有化学键电荷极化有关的电子布居正则模式,而这些与化学键电荷极化有关的电子布居正则模式中的最软模式可以正确地预测相应的从头计算结果,但是,方法更简单,结果更明了。     

应用分析电子显微镜考察铂锡催化剂上的积炭

在高分散铂锡催化剂上分别以正丁烷,正己烷及长链烷烃为反应物经催化剂脱氢表面积炭。从电子显微镜图像观察到积炭有多种结构,最小的炭粒呈条纹排列,炭粒集聚形成球状炭黑及不同形状的石墨结晶。选区电子衍射分析炭(002)晶面间距有3.35～4.13A变化表明石墨化程度不同。三种积炭样品的电子能量损失谱相应地亦展示明显的差别。     

Orientation Imaging in Scanning Electron and Transmission Electron Microscopy for Characterization of the Shear Banding Phenomenon

The texture evolution during deformation of high purity fcc single crystals with initial (112) [11 ] orientation has been characterised in detail by transmission (TEM) and scanning (SEM–FEG) electron microscopes. The channel-die deformed samples up to reduction of about 1–1.5, first developing strongly anisotropic layers of elongated cells or twin-matrix plates and then compact clusters of SB. Substantial progress in understanding the mechanism of the SB formation was possible thanks to systematic local orientation measurements (orientation mapping) using SEM and TEM. These two techniques of local orientation measurements have been compared with respect to their applicability for the study of shear banding phenomenon and for characterization of the specific nanostructure of SB in metals with fcc lattice. It was shown that well-developed SB exhibit large orientation spreads up to 35–40° with respect to the adjacent areas outside the band. Most of these misorientations occur by rotations about the TD‖〈110〉 axis with significant further rotations about 〈112〉 poles. This ultimately leads to the formation of the texture components whose occurrence cannot be explained by models homogeneous deformation.     

电子穿梭体介导的微生物胞外电子传递:机制及应用

厌氧条件下微生物将电子传递给胞外电子受体的现象非常普遍,电子穿梭体(electron shuttle,ES)是介导胞外电子传递过程的重要途径之一,但其具体的机制尚未明晰。一部分微生物自身能分泌一些物质作为内生ES,另一部分微生物能利用天然存在或人工合成的某些物质作为外生ES,并将其携带的电子传递至微生物胞外电子受体。ES介导微生物胞外电子传递的基本过程为:氧化态电子穿梭体(ES_ox)接受电子变成还原态(ES_red),ES_red传递电子给胞外电子受体,自身再次氧化成ES_ox,从而循环往复。本文重点介绍不同种类ES及其电子穿梭机制,以及ES的分子扩散、氧化还原电势及电子转移能力对胞外电子传递过程的影响。ES介导的胞外电子传递过程直接影响污染物转化和微生物产电,因此在污染修复及生物能源等方面具有重要的应用前景。     

Monte Carlo Simulation of Electron Transport and X-Ray Generation. I. Electron Elastic and Inelastic Scattering

We present different theoretical approaches to determine differential cross sections for elastic and inelastic interactions of electrons. These cross sections are the basic ingredients for accurate Monte Carlo simulation of electron transport in matter. The considered models range from simple analytical approximations employed in early calculations to purely numerical differential cross sections described by large databases calculated with state-of-the-art theory.     

Organic Electron Donors as Powerful Single‐Electron Reducing Agents in Organic Synthesis

One‐electron reduction is commonly used in organic chemistry for the formation of radicals by the stepwise transfer of one or two electrons from a donor to an organic substrate. Besides metallic reagents, single‐electron reducers based on neutral organic molecules have emerged as an attractive novel source of reducing electrons. The past 20 years have seen the blossoming of a particular class of organic reducing agents, the electron‐rich olefins, and their application in organic synthesis. This Review gives an overview of the different types of organic donors and their specific characteristics in organic transformations.     

Direct Visualization of Electromagnetic Microfields by Superposition of Two Kinds of Electron Holograms

A new electron holographic method is presented to directly visualize pure phase objects such as electromagnetic microfields, which is achieved by superposition of two kinds of electron holograms. The method is very simple and is twice as sensitive as the conventional double-exposure electron holography and the four-electron-wave interference. Using this technique, an electric field around a charged latex sphere and a magnetic field around a barium ferrite particle have been directly observed.     

Monte Carlo Simulation of Electron Transport and X-Ray Generation. II. Radiative Processes and Examples in Electron Probe Microanalysis

Theoretical models for Monte Carlo simulation of radiative processes, i.e. bremsstrahlung and characteristic x-ray emission, are presented. Possible strategies for simulating electron transport are briefly described. For mechanisms involving energy loss and angular deflections, difficulties for strict implementation of accurate numerical differential cross sections still remain due to the strong correlations between these variables. Practical solutions for the case of inelastic collisions and bremsstrahlung emission are described. Comparisons of simulation results with experimental data for several problems of interest in electron probe microanalysis are presented.     

A Novel Micro—hole Electrode Used to Investigate Electron Transfer Reactions at ITIES

A novel micro-hole electrode was fabricated to investigate the electron transfer reaction at the interface between two immiscible electrolyte solutions (ITIES). The electron transfer reaction between feero/ferricyanide in aqueous phase(W) and ferrocene in 1,2-dichloroethane (O) phase was studied as a test experiment. The results showed that the diffusion coefficient obtained from the micro-hole electrode was consistent with that obtained at macro-interface. Due to its simplicity and the very small IR drop it will be a useful tool for the study of ITIES systems.     

基于零价铁的地下水化学还原修复体系中的电子转移有效性和电子竞争机制

近年来,基于零价铁的化学还原技术因其高效性逐渐被应用于受污染地下水的原位修复。但是,该技术在实际应用中仍面临一些亟待解决的问题。零价铁作为一种高活性的电子供体,除了和目标污染物反应外,还可以与地下水中其他的氧化性物质（如O₂、H⁺或NO₃^-等）反应。这些反应所造成的零价铁腐蚀,不仅会降低修复效率还会增加地下水修复成本。此外,同类或多类污染物间也存在对零价铁所释放电子的相互竞争,从而影响各自的去除效率。本文综述了基于零价铁的地下水修复体系中的电子传递过程和氧化物间的电子竞争机制,从零价铁的腐蚀和电子传递、零价铁电子选择性量化指标的提出和量化方法、地下水体中多种共存氧化物间电子竞争作用、电子效率的影响因素以及强化措施等方面进行详细介绍。最后,对该技术今后发展方向作出了展望,以期为其今后实际的地下水修复应用提供参考。     

Imaging and Microanalysis in Environmental Scanning Electron Microscopy

A variety of gas cascade amplification and signal detection strategies have evolved for use in low vacuum and environmental scanning electron microscopy on poorly conducting specimens. These detectors have been optimized to perform well under various limitations on the range of gas pressure and working distance which may be imposed by experimental requirements. All of the detectors must produce high gains, low backgrounds, and generate a sufficient positive ion flux to the specimen to enable charge neutralization. The underlying principles of operation of each detector type are discussed, along with the range of experimental conditions appropriate to each.