Electron Correlations for Adiabatic Electrochemical Electron Transfer Reactions in a Model for an Electrode with an Infinitely Wide Conduction Band

Fresh general relationships for adiabatic free-energy surfaces (AFES) and corresponding diagrams of kinetic modes for adiabatic electrochemical electron transfer reactions are derived in the framework of an exactly solvable model for a metallic electrode with an infinitely wide conduction band. The model is a limiting case of the Anderson model applicable to the sp metals. In contrast to earlier studies of adiabatic reactions in a model for an electrode with an infinitely wide conduction band, this work accounts for the electron–electron correlation effects exactly. As an illustration, an AFES is calculated and a diagram of kinetic modes is constructed for a special case corresponding to the equilibrium electrode potential of a two-electron reaction. The exact AFES is compared with the AFES computed in the Hartree–Fock approximation and a spinless model. The correlation effects are shown to play a substantial role and lead to a considerable decrease in the activation free energy.     

Effects of Electron Correlations in a Simple Model for Adiabatic Electrochemical Reactions: The General Relationships

General relationships for adiabatic free-energy surfaces (AFES) for electrochemical reactions of electron transfer are derived in the framework of exactly solvable model of the so-called surface molecule, which is a limiting case of Anderson's Hamiltonian and may be applied to transition metals. As opposed to earlier models for adiabatic reactions, the model exactly allows for the effects of electron–electron correlations. The obtained results constitute a basis for calculating AFES and plotting diagrams that correspond to different kinetic regimes of one- and two-electron processes.     

Effects of Electronic Correlations for Adiabatic Electrochemical Reactions of Electron Transfer in Electrode Models with Nearly Empty and Nearly Filled Conduction Bands: General Relationships

Expressions for the calculation of the adiabatic free energy surfaces (AFES) and average number of electrons in the valence orbital of the reagent for adiabatic electrochemical reactions of electron transfer are obtained in terms of exactly solved models for a metal electrode with nearly empty and nearly filled conduction bands. The models are extreme cases of the Anderson model, which account exactly for the electron–electron correlation effects. In particular, the electrode model with a nearly filled conduction band can be applied to transition metals of Group VIII in the periodic table. Exact relationships connecting AFES and diagrams of kinetic modes (DKM) for electrodes with symmetric position of Fermi levels relative to the conduction band center are obtained. Two characteristic functions for analyzing the role of electron–electron correlation effects in the system under consideration are proposed and calculated. The results form a basis for calculating AFES and studying correlation effects in adiabatic electrochemical reactions of electron transfer and constructing DKM that would correspond to different electron transfer modes.     

Effects of Electronic Correlations for Adiabatic Electrochemical Reactions of Electron Transfer in Electrode Models with Nearly Empty and Nearly Filled Conduction Bands: Adiabatic Free Energy Surfaces

Adiabatic free energy surfaces (AFES) for adiabatic electrochemical reactions of electron transfer (ARET) are computed with exact allowance for electron–electron correlation effects (EECE) in models of electrode with nearly empty and almost filled conduction bands and analyzed on the basis of a diagram of kinetic modes obtained earlier. The EECE role in ARET for an electrode with an arbitrary Fermi level in a conduction band of an arbitrary width is discussed. In the general case, allowing for EECE gives at some model parameters results other than for the Fermi level coinciding with the conduction band center (model of a surface molecule, MSM). As in the case of MSM considered previously, EECE considerably reduce activation free energies and at some model parameters give qualitatively different AFES.     

Electron correlation effects in the adiabatic charge transfer reactions at the metal/polar liquid interface

New simple expressions for average number of electrons in the valence orbital of a reacting ion and the charge susceptibility are obtained that allow one to calculate adiabatic free energy surfaces (AFES) and corresponding kinetic regime diagrams (KRD) for adiabatic processes of electron transfer from the ion, located in a polar liquid, to a metal within the framework of the exactly solvable (in the limit T-->0) model of the metal with the infinitely wide conduction band. This model represents one of limiting cases of the Anderson model that may be applied to s-p metals. Unlike previous studies of the adiabatic reactions in the model of the metal with the infinitely wide conduction band, the present work takes into account the electron-electron correlation effects in an exact manner. General results are illustrated with KRD which determine the regions of the physical parameters of the system corresponding to various types of electron transfer processes. AFES are calculated for some typical parameters sets. The exact AFES are compared with those calculated within the Hartree-Fock approximation. It is shown that the correlation effects are of importance and results not only in a considerable decrease of the activation free energy but also to qualitatively different shapes of AFES in some regions of the system parameters.     

Organic Reactions at Alumina Surfaces

Recent examples are given to emphasize that alumina can cause many different and often unexpected chemical reactions of adsorbed organic molecules. Recent developments are summarized to publicize that reagent-doped alumina can be used deliberately to achieve some very mild and highly selective organic transformations. The scope and limitations of organic reactions at alumina surfaces are discussed, and the advantages of these heterogeneous reactions over the corresponding homogeneous ones are pointed out. The role of the alumina and future problems are discussed briefly.     

Calculation of adiabatic free energy surfaces in the case of electrochemical tunneling microscopy of redox systems

A method of adiabatic (infinitely slow) switching-on of interaction of the reactant with the electrode and the tip of a tunneling microscope at a bias voltage other than zero is used to derive expressions for the average number of electrons in the valence orbital of the reactant, the current passing through the valence orbital of the reactant at fixed values of coordinates of the slow subsystem of the solvent, and the electronic contribution to an expression that describes the adiabatic free energy surface (AFES) of the electrode-reactant-tip of the tunneling microscope system. The derived expressions are the same that had already been obtained in a Kuznetsov-Schmickler work, by a not-quite-correct method, though. Relationships that link the AFES corresponding to the opposite signs of the bias voltage are deduced. Examples of calculations of AFES and a current for a number of characteristic sets of parameters of the system are presented.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 259–272.Original Russian Text Copyright © 2005 by Medvedev.     

Reactions of antimicrobial species to imidazole-microwave plasma reacted poly(dimethylsiloxane) surfaces

Microwave plasma reactions of imidazole, 2-methylimidazole, and 2-ethylimidazole on poly(dimethylsiloxane) (PDMS) surfaces resulted in the formation of species containing conjugated surface domains which can be utilized for further reactions. When imidazole and its derivatives were used, polymerization of imidazole and the formation of C=C and CN conjugated species occurred. However, the extent of reactions for each monomer depends on not only the reaction time but also the molecular structure. For methyl- and ethyl-substituted imidazole, more stable radical species are generated and sustain their excited state in the high-energy plasma environments. Specifically, dehydrogenated 2-methyl, 2-ethylimidazole radicals and (*)N=CR-NH(*) (R = -CH(3), -CH(2)CH(3)) species exhibit higher stability than dehydrogenated imidazole radicals and (*)N=CH-NH(*) species under plasma reaction conditions. Such prepared surfaces are capable of attaching antimicrobial drugs via the Pinner synthesis. These studies show that it is possible to react antimicrobial species such as chloramphenicol, and this promising approach offers numerous applications of microwave plasma reactions in biotechnology. Quantitative analysis of the depth of surface reactions was accomplished by using variable angle ATR FT-IR spectroscopy.     

Ab Initio Construction of Quasiadiabatic Potential-Energy Surfaces for Cycloaddition Reactions of Ethene and Substituted Allylic Cations

The nature of some well known 2π + 2π cycloaddition reactions was studied by explicit construction of the quasiadiabatic potential-energy surfaces for the cycloaddition of ethene and various monosubstituted allylic cations. Such surfaces determined by ab initio MO computations are particularly suitable for analysis of symmetry selection rules. By examining the characteristics of such surfaces, we have studied the substituent effect and the role played by the positive charge in such systems. Qualitative discussion based on simplified MO, involving fewer electrons, is also given.     

Electron Correlation Effects for Adiabatic Electrochemical Reactions of Electron Transfer in a Model for an Electrode with an Infinitely Wide Conduction Band: Computing Adiabatic Free Energy Surfaces

The adiabatic free energy surfaces for adiabatic electrochemical reactions of electron transfer are calculated in a model for an electrode with an infinitely wide conduction band with exact allowance for electron–electron correlations. The surfaces are analyzed on the basis of a diagram of kinetic modes obtained earlier. It is shown that, as in a surface-molecule model for these reactions, the correlation effects play an essential role and lead to a considerable decrease in the activation free energies and to qualitatively different forms of adiabatic free energy surfaces in certain ranges of model parameters.     

On‐Surface Reactions

On‐surface synthesis constitutes a rapidly growing field of research due to its promising application for creating stable molecular structures on surfaces. While self‐assembled structures rely on reversible interactions, on‐surface synthesis provides the potential for creating long‐term stable structures with well‐controlled properties, for example superior electron transport for future molecular electronic devices. On‐surface synthesis holds the promise for preparing insoluble compounds that cannot be produced in solution. Another highly exciting aspect of on‐surface synthesis is the chance to discover new reaction pathways due to the two‐dimensional confinement of the reaction educts. In this review, we discuss the current state‐of‐the‐art and classify the reactions that have been successfully performed so far. Special emphasis is put on electrically insulating surfaces, as these substrates pose particular challenges for on‐surface synthesis while at the same time bearing high potential for future use, for example, in molecular electronics.     

Interfacial Reactions of Tetraphenylporphyrin with Cobalt-Oxide Thin Films

We have studied the adsorption and interfacial reactions of 2H-tetraphenylporphyrin (2HTPP) with cobalt-terminated Co₃O₄(111) and oxygen-terminated CoO(111) thin films using synchrotron-radiation X-ray photoelectron spectroscopy. Already at 275 K, we find evidence for the formation of a metalated species, most likely CoTPP, on both surfaces. The degree of self-metalation increases with temperature on both surfaces until 475 K, where the metalation is almost complete. At 575 K the porphyrin coverage decreases drastically on the reducible cobalt-terminated Co₃O₄(111) surface, while higher temperatures are needed on the non-reducible oxygen-terminated CoO(111). The low temperature self-metalation is similar to that observed on MgO(100) surfaces, but drastically different from that observed on TiO₂(110), where no self-metalation is observed at room temperature.     

Computed Potential Energy Surfaces and Minimum Energy Pathways for Chemical Reactions

Computed potential energy surfaces are often required for computation of such observables as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method with the Dunning correlation consistent basis sets to obtain accurate energetics, gives useful results for a number of chemically important systems. Applications to complex reactions leading to NO_x and soot formation in hydrocarbon combustion are discussed.     

Photochemistry of Transition-Metal Atoms: Reactions with Molecular Hydrogen and Methane in Low-Temperature Matrices

Reactions of metal atoms with molecular hydrogen and alkanes are prototypical of more complex systems involving metal-mediated reactions in solution, on supports, and on surfaces. The simplicity of metal-atom reactions makes them particularly attractive for fundamental experimental and theoretical studies. Following the first reports of H₂ and CH₄ activation by photoexcited metal atoms in cryogenic matrices, the behavior of a number of transition-metal atoms in their ground and selected electronically excited states has been examined with molecular hydrogen, methane, and ethane. A wealth of structural, electronic, reactivity, and selectivity information is emerging from these studies and it is now becoming possible to recognize the controlling factors at work in these fundamental chemical reactions. In this article, some experimental results for a number of metal-atom systems, in particular, those involving silver, copper, manganese, and iron atoms, are presented along with a discussion of the factors that are believed to be important in the understanding of the observed physical and chemical behavior.     

Zn片经水热反应和氟硅烷修饰构建超疏水ZnO表面

以乙二胺为溶剂, Zn片在120、140 及160 ℃经水热反应生长出具有蛋糕形、荷叶乳突状、棒状和仙人球状等微结构的ZnO表面. 扫描电镜研究表明, 反应时间越长越有利于形成完整的微纳米结构, 反应温度较高生成的微纳米结构更规整. 140 ℃反应4 h和160 ℃反应5 h的ZnO表面经过氟硅烷修饰后表现出良好的超疏水性, 与水滴的接触角分别达到154.6°和157.3°, 滚动角分别为5°和3°. 该方法因其操作简便、成本低廉, 在锌表面制备特殊微结构和构建超疏水表面具有潜在的应用.     

Reactions of gaseous organic compounds on silica surface. Spectral studies and synthetic aspects

The results of infrared spectroscopic and mass-spectrometric studies on reactions of vapor phase carboxylic acids, polyazamacrocyclic ligands, pyrimidine bases, acetylacetonates and related compounds with hydroxylic, chlorosilylated, halo- and aminoalkylsilylated silica surfaces are analyzed. Application of various reactions for the gasphase derivatization of silica materials and for the gassolid-phase synthesis of 2,5-dioxoperazines is discussed.     

偏二甲肼在氟化镁涂层表面的吸附与反应

The absorption and chemical reactions of 1,1-dimethyl-hydrazine(C2H8N2) on the surface of magnesium fluoride(MgF2) coating was studied. The coating surface is firstly contaminated by liquid or gaseous C2H8N2 , and then it is placed into a vacuum environment for a long period. Contrasting the infrared absorption spectra, X-ray photoelectron energy spectra and diffusive reflectivity of MgF2 coating surfaces before and after experiment, it may be learned that the absorption and chemical reactions occur at the surface. The experimental results show that the molecules of a liquid film of C2H8N2 over MgF2 coating surface take about two hours to desorb adequately in a vacuum environment, after the adequate desorption, there only exists a single chemical absorption layer over the coating surface, with a mass density of about 27 ng/cm2. The diffusive reflectivity of MgF2 coating surface decreases about 10%-15% after the contamination of liquid C2H8N2. For MgF2 coating surfaces immersed in C2H8N2 vapor at the pressure of 3 kPa for ten minutes, there are neither changes in their atomic constitution and diffusive reflectivity, nor characteristic peaks of C2H8N2 appear in their infrared absorption spectrum.     

Reactions of Atoms

Several methods for the quantitative investigation of reactions of free atoms in the gas phase have been developed in recent years. The present article deals with reactions of hydrogen, carbon, oxygen, and halogen atoms with simple molecules. The results of such investigations are of fundamental importance for the understanding of chemical reactions and for many technical applications, such as explosion and combustion processes, halogenations, and chemical lasers.