气相中Nb＋活化CS2中的C-S键

以Nb＋与CS2反应作为第二前过渡金属离子与CS2反应生成金属硫化物离子和CS的范例体系．采用密度泛函UB3LYP方法,对于Nb＋采用Stuttgart赝势基组,对于C和S采用6—311＋G（2d）基组,计算研究了Nb＋在基态和激发态时与CS2气相反应的机理．全参数优化了反应势能面上各驻点的儿何构型,并且用频率分析方法和内禀反应坐标方法对过渡态进行了验证．结果表明Nb＋与CS2的反应是插入-消去反应,在反应过程中会发生系间窜越,并且找到了两个势能面的能量最低交叉点．     

Optimizing the structures of minimum and transition state on the free energy surface

Presented here is the application of a scheme for optimizing the structures of minima and transition states on the free energy surface (FES) for a path along a fixed reaction coordinate with the aid of ab initio molecular dynamics (AIMD) simulation. In the direction of the reaction coordinate, the values corresponding to the stationary points were optimized using the quasi-Newton method, in which the gradient of the free energy along the reaction coordinate was obtained by a constraint AIMD method, and the Bofill Hessian update scheme was used. The equilibrium values for the other directions were taken as the corresponding averages in the dynamic simulation. This scheme was applied to several elementary bimolecular addition reactions: (A) BH(3) + H(2)O --> H(2)O.BH(3); (B) BF(3) + NH(3) --> FB(3).NH(3); (C) SO(3) + NH(3) --> O(3)S.NH(3); (D) C(2)H(4) + CCl(2) --> H(4)C(2).CCl(2); (E) Ni(NH(2))(2) + PH(3) --> (NH(2))(2)Ni.PH(3); (F) W(CO)(5) + CO --> W(CO)(6). For reactions A, B, C, and F, no transition state (TS) exists on the potential energy surface (PES). However there is a TS on the FES. This stems from the curvature difference of the PES and -TDeltaS as a function of the reaction coordinate. For all reactions, it is found that the TS shifts toward the complexation product with increasing temperature because of the curvature increase of -TDeltaS. The equilibrium bond distances for the inactive coordinates perpendicular to the reaction coordinate always increase with temperature, which is due to the thermal excitation and anharmonicity of the PES.     

Au+(1S, 3D)与N2O(1Σ+)反应机理的理论研究

采用密度泛函B3LYP方法, O和N用6-311+G*基组, Au+用赝势基组(8s7p6d)/[6s5p3d], 研究了Au+(1S, 3D)离子和N2O(1Σ+)分子的反应机理. 报道了在基态单重态和激发三重态势能面上各反应物、中间体和过渡态的构型特征及能量. 结果表明, 两个主反应通道Au+(1S)+ N2O(1Σ+)→1NA-Complex-1→1NA-TS1→1NA-Complex-2→1NA-Crossing→[3OAuNN]+和Au+(1S)+ N2O(1Σ+)→1NB-Complex→1NB-Crossing→[AuNN(1Σ+)]++O(3P)都需经过反应交叉势能面, 出现“系间窜越”. 用内禀坐标单点计算垂直激发态的方法确定了势能面交叉点, 并用含时密度泛函TD-B3LYP方法进一步探讨了自旋翻转机理.     

A unified perspective on the hydrogen atom transfer and proton-coupled electron transfer mechanisms in terms of topographic features of the ground and excited potential energy surfaces as exemplified by the reaction between phenol and radicals

The relation between the hydrogen atom transfer (HAT) and proton-coupled electron transfer (PCET) mechanisms is discussed and is illustrated by multiconfigurational electronic structure calculations on the ArOH + R(*) --> ArO(*) + RH reactions. The key topographic features of the Born-Oppenheimer potential energy surfaces that determine the predominant reaction mechanism are the conical intersection seam of the two lowest states and reaction saddle points located on the shoulders of this seam. The saddle point corresponds to a crossing of two interacting valence bond states corresponding to the reactant and product bonding patterns, and the conical intersection corresponds to the noninteracting intersection of the same two diabatic states. The locations of mechanistically relevant conical intersection structures and relevant saddle point structures are presented for the reactions between phenol and the N- and O-centered radicals, (*)NH2 and (*)OOCH3. Points on the conical intersection of the ground doublet D0 and first excited doublet D1 states are found to be in close geometric and energetic proximity to the reaction saddle points. In such systems, either the HAT mechanism or both the HAT mechanism and the proton-coupled electron transfer (PCET) mechanism can take place, depending on the relative energetic accessibility of the reaction saddle points and the D0/D1 conical intersection seams. The discussion shows how the two mechanisms are related and how they blend into each other along intermediate reaction paths. The recognition that the saddle point governing the HAT mechanism is on the shoulder of the conical intersection governing the PCET mechanism is used to provide a unified view of the competition between the two mechanisms (and the blending of the two mechanisms) in terms of the prominent and connected features of the potential energy surface, namely the saddle point and the conical intersection. The character of the dual mechanism may be understood in terms of the dominant valence bond configurations of the intersecting states, which are zero-order approximations to the diabatic states.     

气相中Cu＋和Zn＋与SCO反应的理论研究

为更清晰地揭示M^＋与SCO基元反应的机理, 采用密度泛函B3LYP方法, 在6-311＋＋G**基组水平上研究了Cu^＋＋SCO和Zn^＋＋SCO反应体系. 对反应势能面上各驻点的几何构型进行了全优化, 用频率分析方法和内禀反应坐标(IRC)方法对过渡态进行了验证. 在Cu^＋与SCO的反应中, 对影响反应机理和反应速率的势能面交叉现象进行了讨论, 运用Hammond假设和Yoshizawa等的内禀反应坐标垂直激发的计算方法找到了势能面交叉点. 计算结果表明, C—S和C—O键的活化都是通过插入消去机理, 但C—S键的活化在能量上更占优势. 计算确认了标题反应的主通道, 所有的计算结果与实验吻合.     

Modeling reaction pathways of low energy particle deposition on polymer surfaces via first principle calculations

The chemical processes that lead to polystyrene surface modification via low energy deposition of C(2)H(+), C(2)F(+), CH(2), CH(2)(+), and H(+) radicals and ions are examined using first principles calculations. Specifically, the reaction mechanisms responsible for products identified in classical molecular dynamics with reactive empirical bond-order potentials are examined using density functional theory. In addition, these calculations consider how the presence of charges on the incident particles changes the result for the CH(2) system through the comparison of barriers, transition states, and final products for CH(2) and CH(2)(+). The structures of the reaction species and energy barriers are determined using the B3LYP hybrid functional. Finally, CCSD/6-31G(d,p) single point energy calculations are carried out to obtain optimized energy barriers. The results indicate that the large variety of reactions occurring on the polystyrene surface are a consequence of complex interactions between the substrate and the deposited particles, which can easily be identified and characterized using advanced computational methodologies, such as first principle calculations.     

Semiclassical nonadiabatic dynamics based on quantum trajectories for the O(3P,1D) + H2 system

The O(3P,1D) + H2 --> OH + H reaction is studied using trajectory dynamics within the approximate quantum potential approach. Calculations of the wave-packet reaction probabilities are performed for four coupled electronic states for total angular momentum J = 0 using a mixed coordinate/polar representation of the wave function. Semiclassical dynamics is based on a single set of trajectories evolving on an effective potential-energy surface and in the presence of the approximate quantum potential. Population functions associated with each trajectory are computed for each electronic state. The effective surface is a linear combination of the electronic states with the contributions of individual components defined by their time-dependent average populations. The wave-packet reaction probabilities are in good agreement with the quantum-mechanical results. Intersystem crossing is found to have negligible effect on reaction probabilities summed over final electronic states.     

激发态Ti＋(3d14s2)与丙炔醇气相反应理论研究

用量子化学密度泛函(DFT)方法研究了激发态Ti^＋(3d¹4s²)与丙炔醇(PPA)气相反应的机理. 在B3LYP/DZVP水平上, 优化了反应的两个通道的反应物、中间体、过渡态和产物的几何构型, 并在MP4/[6-311＋G**(C,H,O)＋Lanl2dz (Ti)]水平上计算了各驻点的单点能量. 为了确证过渡态的真实性, 在B3LYP/DZVP水平上进行了内禀坐标(IRC)计算和频率分析, 获得了二重态反应势能面, 确定了反应机理. 研究结果表明生成产物为[C₃H₃O]^＋和Ti—H的通道是主要反应途径.     

Reaction of bare VO+ and FeO+ with ammonia: a theoretical point of view

The potential energy surfaces corresponding to the dehydration reaction of NH(3) by VO(+) ((3)Sigma, (1)Delta, (5)Sigma) and FeO(+) ((6)Sigma, (4)Delta) metal oxide cations have been investigated within the framework of the density functional theory in its B3LYP formulation and by employing new optimized basis sets for iron and vanadium. The reaction is proposed to occur through two hydrogen shifts from the nitrogen to the oxygen atom giving rise to multicentered transition states. Possible spin crossing between surfaces at different spin multiplicities has been considered. The energy profiles are compared with the corresponding ones for the insertion of bare cations to investigate the influence on reactivity of the presence of the oxygen ligand. The topological analysis of the gradient field of the electron localization function has been used to characterize the nature of the bonds for all the minima and transition states along the paths.     

Probes of spin conservation in heavy metal reactions: experimental and theoretical studies of the reactions of Re+ with H2, D2, and HD

A guided ion beam tandem mass spectrometer is used to examine the kinetic energy dependence of reactions of the third-row transition metal cation, Re(+), with molecular hydrogen and its isotopologues. A flow tube ion source produces Re(+) in its (7)S(3) electronic ground state. Reaction with H(2), D(2), and HD forms Re H(+)(Re D(+)) in endothermic processes. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energy of D(0)(Re(+)-H)=2.29+/-0.07 eV (221+/-6 kJ/mol). The experimental thermochemistry is consistent with ab initio calculations, performed here and in the literature. Theory also provides the electronic structures of these species and is used to examine the reactive potential energy surfaces. Results from reactions with HD provide insight into the reaction mechanisms and indicate that the late metal ion, Re(+), reacts largely via a statistical mechanism. This is consistent with the potential energy surfaces which locate a stable Re H(2) (+)((5)B(2)) complex. Results for this third-row transition metal system are compared with the first-row congener (Mn(+)) and found to have much higher reactivity towards dihydrogen and stronger M(+)-H bonds. These differences can be attributed to efficient coupling among surfaces of different spin along with lanthanide contraction and relativistic effects.     

Theoretical Study on Photoisomerization of 2-Methylfuran to 3-Methylfuran

1 INTRODUCTION 2-Methylfuran belongs to the basic heteroaromatic compounds relevant to many fields of modern che- mistry, ranging from the study of natural products and biologically active substances to the develop- ment of building blocks for organic synthesis and conducting polymers[1]. Since the photochemistry ofR-furan was gradually recognized in 1960s[2～7], lots of interest has been aroused. Herein we only study one branch of photoche- mistry of R-furan: the isomerization of 2-methy…     

Electronic structure and solvation of copper and silver ions: a theoretical picture of a model aqueous redox reaction

Electronic states and solvation of Cu and Ag aqua ions are investigated by comparing the Cu(2+) + e(-)--> Cu(+) and Ag(2+) + e(-)--> Ag(+) redox reactions using density functional-based computational methods. The coordination number of aqueous Cu(2+) is found to fluctuate between 5 and 6 and reduces to 2 for Cu(+), which forms a tightly bound linear dihydrate. Reduction of Ag(2+) changes the coordination number from 5 to 4. The energetics of the oxidation reactions is analyzed by comparing vertical ionization potentials, relaxation energies, and vertical electron affinities. The model is validated by a computation of the free energy of the full redox reaction Ag(2+) + Cu(+) --> Ag(+) + Cu(2+). Investigation of the one-electron states shows that the redox active frontier orbitals are confined to the energy gap between occupied and empty states of the pure solvent and localized on the metal ion hydration complex. The effect of solvent fluctuations on the electronic states is highlighted in a computation of the UV absorption spectrum of Cu(+) and Ag(+).     

几个硫-叶立德反应机理的量子拓扑研究

采用MP2(FC)/6-311++G(d,p)对硫叶立德和类硫叶立德自由基反应机理进行了探讨。优化了中间体、过滤态和产物的几何构型。本文侧重从量子拓扑学的角度,对IRC(内禀反应坐标)反应进程中各点进行电子密度拓扑分析,讨论了反应过程中化学键的断裂、生成和化学键的变化规律。找到了这类反应的能量过渡态和结构过渡态,上述两个反应都是先经历一个没有形成三元环拓扑结构的能量过渡态,再经历一个形成了三元环拓扑结构的结构过渡态,最后到达产物。     

邻位吡啶自由基多通道分解反应的动力学和反应机理研究

Utilizing Gaussian94 program package, all species involved in decomposition reactions of o-pyridyl radical were optimized fully at B3LYP/6-311＋＋G^＊＊ level. Intrinsic reaction coordinate calculations were employed to confirm the connections of the transition states and products, and transition states were ascertained by the number of imaginary frequency （0 or 1）. The reaction mechanism was elucidated by the vibrational mode analysis and electronic population analysis, and the reaction rate constants were calculated with transition state theory.     

Guided ion beam and theoretical study of the reactions of Os+ with H2, D2, and HD

Reactions of the third-row transition metal cation Os(+) with H(2), D(2), and HD to form OsH(+) (OsD(+)) were studied using a guided ion beam tandem mass spectrometer. A flow tube ion source produces Os(+) in its (6)D (6s(1)5d(6)) electronic ground state level. Corresponding state-specific reaction cross sections are obtained. The kinetic energy dependences of the cross sections for the endothermic formation of OsH(+) and OsD(+) are analyzed to give a 0 K bond dissociation energy of D(0)(Os(+)-H) = 2.45 ± 0.10 eV. Quantum chemical calculations are performed here at several levels of theory, with B3LYP approaches generally overestimating the experimental bond energy whereas results obtained using BHLYP and CCSD(T), coupled-cluster with single, double, and perturbative triple excitations, levels show good agreement. Theory also provides the electronic structures of these species and the potential energy surfaces for reaction. Results from the reactions with HD provide insight into the reaction mechanism and indicate that Os(+) reacts via a direct reaction. We also compare this third-row transition metal system with the first-row and second-row congeners, Fe(+) and Ru(+), and find that Os(+) reacts more efficiently with dihydrogen, forming a stronger M(+)-H bond. These differences can be attributed to the lanthanide contraction and relativistic effects.     

气相中CrO2+活化甲烷C—H键的理论研究

用密度泛函UB3LYP/6-311＋＋G**方法计算研究了气相中CrO₂⁺ (²A₁/⁴A")活化甲烷C—H键的微观机理, 找到了四条反应通道. 对其中涉及的两态反应(TSR)进行了分析, 并对影响反应机理和反应速率的势能面交叉现象(potential energy surfaces crossing)进行了详细讨论, 进而运用Hammond假设和Yoshizawa等的内禀坐标单点垂直激发计算的方法找出了一系列势能面交叉点[crossing points (CPs)], 并作了相应的讨论. 进一步用碎片分子轨道理论[fragment molecular orbital (FMO)]对TS1中的轨道相互作用进行了分析, 解释了CrO₂⁺活化甲烷C—H键的机理.     

DFT and CASPT2 study on the mechanism of ethylene dimerization over Cr(II)OH+ cation

In this work, the ethylene coordination and dimerization mechanism over Cr(II)OH(+) cation were systematically investigated using density functional theory (DFT) and complete active space second-order perturbation theory (CASPT2). It was found that Cr(II)OH(+) cation can coordinate with up to four ethylene molecules which gives seven possible stable Cr(II)OH(+)·(C(2)H(4))(n) (n = 1-4) π-complexes. We investigated whether ethylene dimerization over Cr(II)OH(+) cation proceeds through either a carbene mechanism or a metallacycle mechanism. The potential energy surfaces were characterized using four different functionals (M06L, BLYP, B3LYP, and M06). It was found that the potential energy profiles calculated at the M06 level agreed well with the CASPT2 energy profiles. Since the intermediates involved in the proposed catalytic cycles showed different ground spin states, a reaction pathway involving a spin crossing between two potential energy surfaces was observed. The minimum-energy crossing points (MECPs) that connect the two potential energy surfaces were successfully located. The two-state metallacycle reaction pathway with the formation of chromacyclopentane as the rate-determining step was found to be energetically more favorable than the carbene reaction pathway. 1-Butene was formed from the chromacyclopentane by a two-step reductive elimination pathway through a chromium(IV) hydride intermediate.     

硫代双烯酮与异氰酸环加成反应的理论研究

采用从头算ＲＨＦ／６－３１Ｇ方法研究了硫代双烯酮与异氰酸之间两种可能的环加成反应的机理,并对反应各驻点进行了电子密度拓扑分析研究．结果表明,这两个生成不同四元杂环产物的平行反应均为非同步的协同反应,但两个反应进行的难易程度不同,形成硫氮杂环的反应更容易一些,而形成氮杂环反应的产物在热力学上更稳定一些     

About the barriers to reaction of CCl4 with HFeOH and FeCl2

The reactions of zerovalent iron with water and carbon tetrachloride are of interest for environmental remediation of contaminated water and soil. Atom-dropping experiments have shown that the reactions of iron atoms with water and CCl(4) may produce HFeOH and FeCl(2), respectively, but these compounds are themselves unreactive toward CCl(4) at the low temperatures under which the atom-dropping experiments were performed. We report a modeling study of these reactions using density functional theory, ab initio Hartree-Fock and couple-cluster theory, and principles of Marcus-Hush theory to characterize the underlying intrinsic barriers and rationalize the experimental results. Electron-correlated CCSD(T) calculations (at B3LYP/TZVP optimized structures) show that the transition state for Cl atom transfer from CCl(4) to HFeOH arises from crossing of electronic states in which the configuration of Fe changes from a quintet high spin state in the Fe(II) reactant to a sextet high spin state in the Fe(III) products. The crossing point is 23.8 kcal/mol above a long-range precursor complex that is 2.1 kcal/mol more stable than the separated reactants. The electronic structure changes in these Cl atom transfer reactions involve unpairing of d electrons in Fe(II) and their recoupling with Cl-C σ bond electrons. These processes can be conveniently described by invoking the self-exchange reactions HFeOH/HFeClOH, FeCl(2)/FeCl(3), and CCl(4)/(?)CCl(3) for which we determined the energy barriers to be 15.5, 13.1, 18.6 kcal/mol, respectively. For the cross reaction FeCl(2)/CCl(4), we estimated a barrier of 16.6 kcal/mol relative to the separated reactants and 21.1 kcal/mol from the precursor complex. The magnitudes of the reaction barriers are consistent with reports of the absence of products in the atom-dropping experiments.