O~3＋NH→HNO＋O~2反应机理的量子化学研究

用密度泛函(DFT)的B3LYP方法(6－31++G^*^*)研究了臭氧与NH自由基反应的微观机理,优化得到反应途径上的反应物,过渡态,中间体和产物的构型,通过振动分析对过渡态和中间体进行了确认。对单点用QCISD(T)/6－31++G^*^*方法计算能量,同时进行零点能校正。研究结果表明：NH与O~3反应有两条不同的反应通道,且均表现为亲电反应特征,两条不同的反应均为强放热反应。     

NH2自由基与O3反应机理的从头计算

采用量子化学从头计算的UMP2(full)方法研究了NH2自由基与臭氧的反应机理，优化了反应物、中间体、过渡态和产物的几何构型，并做了频率分析.结果表明, NH2自由基与臭氧反应有两条反应通道，其中一条反应活化能很小，反应极易发生.化学反应热的计算结果与实验结果吻合较好.     

CH_2CH(~2A')自由基与臭氧反应机理的理论研究

用量子化学MP2（full）方法,在6－311+ +G~(**)基组水平上研究了CH_2CH (~2A~＇)自由基与臭氧反应的机理,全参数优化了反应过程中反应物、中间体、过 渡态和产物的几何构型,在QCISD（T,full）/6-311+ +G~(**)水平上计算了它们的 能量,并对它们进行了振动分析,以确定中间体和过渡态的真实性,研究结果表明 ：CH_2CH(~2A~＇)自由基与臭氧反应有两条可行的反应通道,分别为：CH_2CH (~2A~＇)+O_3→TS1→M1→TS2→O_2+OCH_2CH→TS4+O_2→O_2(~3∑_g)+CH_2CHO (~2A~＂)和CH_2CH(~2A~＇)+O_3→M2→TS3→O_2(~3∑_g)+CHO(~2A~＂),后一个反 应通道较容易发生,而且反应活化能小（2.97kJ/mol）,说明CH_2CH(~2A~＇)自由 基与臭氧之间的反应活性很强。     

CH_2CH(~2A')自由基与臭氧反应机理的理论研究

用量子化学MP2（full）方法，在6－311+ +G~(**)基组水平上研究了CH_2CH (~2A~＇)自由基与臭氧反应的机理，全参数优化了反应过程中反应物、中间体、过 渡态和产物的几何构型，在QCISD（T,full）/6-311+ +G~(**)水平上计算了它们的 能量，并对它们进行了振动分析，以确定中间体和过渡态的真实性，研究结果表明 ：CH_2CH(~2A~＇)自由基与臭氧反应有两条可行的反应通道，分别为：CH_2CH (~2A~＇)+O_3→TS1→M1→TS2→O_2+OCH_2CH→TS4+O_2→O_2(~3∑_g)+CH_2CHO (~2A~＂)和CH_2CH(~2A~＇)+O_3→M2→TS3→O_2(~3∑_g)+CHO(~2A~＂),后一个反 应通道较容易发生，而且反应活化能小（2.97kJ/mol），说明CH_2CH(~2A~＇)自由 基与臭氧之间的反应活性很强。     

C_2h_3自由基与O_2反应机理的量子化学研究

用量子化学从头计算中UMP2(full)方法优化了C_2H_3自由基与O_2反应通道上 驻点（反应物、中间体、过渡态和产物）的几何构型，在Gaussian-3(G3)水平上计 算了它们的能量。在此基础上计算了该反应通道上各基元反应的反应活化能。通过 我们的研究发现，C_2H_3自由基与氧气反应存在着三元环、四元环和五元环反应机 理，且分别生成不同的产物，从反应活化能的计算结果扯CH_2O和CHO是反应的主要 产物，其次还可能生成CH_3 + CO_2, CH_2CO_2 + H, C_2H_2 + O_2H和COHCOH + H等产物，且它们生成几率逐渐减少，我们对生成产物CH_2O + CHO, CH_3 + CO_2, C_2H_2 + O_2H和COHCOH + H四条反应通道化学反应热的计算结果与实验吻 合较好。     

H＋CH3NO2→H2＋CH2NO2反应途径和变分速率常数计算研究

采用MP2（FULL）／6－311G**从头算方法，优化了H＋CH3NO2——H2＋CH2NO2反应的过渡态结构，得出该反应的正逆反应的活化位垒分别是82．73和57．14 kJ·mol－1 ．沿IRC分析指出该反应是一个H—H键生成和C—H键断裂的协同反应，而且在反应途径上存在一个引导反应进行的振动模式，这一反应模式引导反应进行的区间在- 0．7～0．2（amu）1/2·a0之间；在 1000～1400 K温度范围内，运用变分过渡态理论（CVT），计算了该反应的速率常数，计算结果与实验相一致．     

吡啶光氯化反应过渡态和反应途径的量子化学研究

用量子化学B3LYP方法在3---21G*水平上优化吡啶光氯化反应加成取代反应机理生成邻、间、对位氯代吡啶不同反应途径的过渡态并对反应热和活化能进行了计算,对邻位反应途径进行了IRC反应路解析,计算结果表明邻位反应途径过渡态的能量最低,为－704.830027a.u.,生成2－氯吡啶所需的活化能最低,为114.60kJ/mol。光氯化反应主要产物为2－氯吡啶,与实验结果一致。IRC反应路径显示在反应过程中C(2)---H(7)键的断裂和C(2)-----Cl(8)键的生成是协同但不是同步的。     

Ab initio方法研究CH~3+OClO反应的可能通道

利用abinitio方法研究了CH~3+OClO反应的三个可能通道,首次应用UMP2(full)/6-31G(d,p)方法得到各反应物、产物、中间物及过渡态的优化构型和谐振频率;然后采用G2MP2理论计算各通道反应焓变和势垒高度。理论计算表明产物通道CH~2O+HOCl是最可能发生的途径,反应放热为443.80kJ·mol^-^1。可能的反应过程为：CH~3和OClO自由基先经无垒过程生成了一个富能中间物,继而通过较低的势垒解离成HOCl+H~2CO。     

NH＋O3→ONH＋O2反应热力学和动力学研究

在量子化学对NH自由基与臭氧O3反应计算的基础上，应用统计热力学方法研究了100～1600 K温度范围内NH和O3反应过程的各热力学量的变化及平衡常数，用经Wigner校正的Eyring过渡态理论计算了不同温度下该反应两不同反应通道的活化热力学量、反应速率常数及频率因子.计算表明，相对于反应通道II，反应通道I不仅有很强的反应自发性，而且在动力学上也是较容易实现的反应.     

C_2H_2~＋＋H_2→C_2H_3~＋＋H反应振动选态速率常数的理论研究

用从头计算法辅以能一梯度法优化了反应Ｃ_２Ｈ＋Ｈ_２→Ｃ_２Ｈ＋Ｈ的过渡态，用福井谦一的理论求出反应途径，用反应途径哈密顿理论及正则变分过渡态理论计算沿反应途径的动力学性质和反应速率常数。在此基础上对涉及振动激发的选态反应速率常数进行计算，所得结果与现有的实验结果相符合。     

Ab initio study on the reaction mechanism of ozone with bromine atom

Ab initio calculations of the potential energy surface (PES) for the Br+O₃ reaction have been performed using the MP2, CCSD(T), and QCISD(T) methods with 6‐31G(d), 6‐311G(d), and 6‐311+G(3df). The reaction begins with a transition state (TS) when the Br atom attacks a terminal oxygen of ozone, producing an intermediate, the bromine trioxide (M), which immediately dissociates to BrO+O₂. The geometry optimizations of the reactants, products, and intermediate and transition states are carried out at the MP2/6‐31G(d) level. The reaction potential barrier is 3.09 kcal/mol at the CCSD(T)/6‐311+G(3df)//MP2 level, which shows that the bromine atom trends intensively to react with the ozone. The comparison of the Br+O₃ reaction with the F+O₃ and Cl+O₃ reactions indicates that the reactions of ozone with the halogen atoms have the similar reaction mechanism. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Quantum chemical study of the reaction mechanism of ozone and methane with fluorine and chlorine atoms

Ab initio calculations of the potential energy surface for the F + O₃ and Cl + O₃ reactions have been performed using the G3 and G3MP2 methods, which optimize the geometry configuration of reactants, products, intermediates, and transition states. The results show that fluorine atoms react with ozone as violently as chlorine atoms. At the same time, we have studied the reaction mechanisms of F atoms and Cl atoms with methane. It is found that fluorine atoms prefer to react with methane and chlorine atoms with ozone when there is competition between ozone and methane. Therefore, we can reasonably explain why chlorine atoms play the main role of reactants depleting ozone, while the more active fluorine atoms deplete less ozone. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/qua.10119     

Theoretical study on the reaction mechanism and thermodynamics of tin oxidation by oxygen species and chlorine species

In this work ab initio molecular orbital methods were employed to study the coal combustion reaction mechanisms of tin oxidized by different oxidants, including HOCl, HCl, ClO, ClO₂, NO₃, CO₂, and O₂. Eleven reaction pathways were identified. The results show that Sn can react with HCl, ClOO, CO₂, O₂, and NO₃ to form SnO and SnCl. SnO can be oxidized into SnCl by HOCl and HCl. SnCl can be further oxidized into a soluble compound, SnCl₂. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

用从头算研究Shilov反应的机理

Shilov反应在CH~4活化中占有中心地位,它有氧化加成和σ迁移两种可能的机理。本文用较大基组的从头算研究了这两种机理的反应过程,认为Shilov反应应按氧化加成机理进行。     

Ab initio study of the mechanism of the atmospheric reaction: NO2 + O3 --> NO3 + O2

The atmospheric reaction NO2 + O3 --> NO3 + O2 (1) has been investigated theoretically by using the MP2, G2, G2Q, QCISD, QCISD(T), CCSD(T), CASSCF, and CASPT2 methods with various basis sets. The results show that the reaction pathway can be divided in two different parts at the MP2 level of theory. At this level, the mechanism proceeds along two transition states (TS1 and TS2) separated by an intermediate, designated as A. However, when the single-reference higher correlated QCISD methodology has been employed, the minimum A and the transition state TS2 are not found on the hypersurface of potential energy, which confirms a direct reaction mechanism. Single-reference high correlated and multiconfigurational methods consistently predict the barrier height of reaction (1) to be within the range 2.5-6.1 kcal mol(-1), in reasonable agreement with experimental data. The calculated reaction enthalpy is -24.6 kcal mol(-1) and the reaction rate calculated at the highest CASPT2 level, of k = 6.9 x 10(-18) cm(3) molecule(-1) s(-1). Both results can be regarded also as accurate predictions of the methodology employed in this article.     

五氧化二氮和水反应的从头算研究

在臭氧空洞形成过程中,极地云是一个重要的条件。为了理解极地云的形成和性质,采用不同水平的从头计算方法对N~2O~5+H~2O→2HNO~3反应进行了理论研究。在QCISD(T)//MP2/6-311G(d,p)理论水平上,该气相反应的焓变△H^0=-39.5kJ·mol^-^1,自由能变化△G^0=-36.1kJ/mol,活化能E~a=88.2kJ·mol^-^1(298K)。计算的结果与五氧化二氮易潮解的性质相符。     

Ab initio study on the mechanism of reaction HNCO+NH_2

Ab initio UMP2 and UQCISD(T) calculations, with 6-311G** basis sets, were performed for the titled reactions. The results show that the reactions have two product channels: NH2+ HNCO→NH3+NCO (1) and NH2+HNCO-N2H3+CO (2), where reaction (1) is a hydrogen abstraction reaction via an H-bonded complex (HBC), lowering the energy by 32.48 kJ/mol relative to reactants. The calculated QCISD(T)//MP2(full) energy barrier is 29.04 kJ/mol, which is in excellent accordance with the experimental value of 29.09 kJ/mol. In the range of reaction temperature 2300-2700 K, transition theory rate constant for reaction (1) is 1.68 × 1011- 3.29 × 1011 mL · mol-1· s-1, which is close to the experimental one of 5.0 ×1011 mL× mol-1· s-1 or less. However, reaction (2) is a stepwise reaction proceeding via two orientation modes, cis and trans, and the energy barriers for the rate-control step at our best calculations are 92.79 kJ/mol (for cis-mode) and 147.43 kJ/mol (for trans-mode), respectively, which is much higher than     

Theoretical study on the mechanism of the reaction acetone + OH: channels towards the formation of methanol

Two possible pathways for the acetone + OH reaction towards the formation of methanol have been examined theoretically. Our results show that both channels are characterized by a substantial activation barrier and reject the possibility of a significant CH₃CO + CH₃OH channel. This revised version was published online in August 2006 with corrections to the Cover Date.     

Catalytic reaction mechanism of L-lactate dehydrogenase: an ab initio study

Studies on the catalytic reaction mechanism of L-lactate dehydrogenase have been carried out by using quantum chemical ab initio calculation at HF/6-31G* level. It is found that the interconversion reaction of pyruvate to L-lactate is dominated by the hydride ion HR- transfer, and the transfers of the hydride ion HR and proton HR are a quasi-coupled process, in which the energy barrier of the transition state is about 168.37 kJ/mol. It is shown that the reactant complex is 87.61 kJ/mol lower, in energy, than the product complex. The most striking features in our calculated results are that pyridine ring of the model cofactor is a quasi-boat-like configuration in the transited state, which differs from a planar conformation in some previous semiempirical quantum chemical studies. On the other hand, the similarity in the structure and charge between the HR transfer process and the hydrogen bonding with lower barrier indicates that the HR transfer process occurs by means of an unusual manner. In addition,     

A theoretical ab initio study on the H(2)NO + O(3) reaction

The deviation of the NH(2) pseudo-first-order decay Arrhenius plots of the NH(2) + O(3) reaction at high ozone pressures measured by experimentalists, has been attributed to the regeneration of NH(2) radicals due to the subsequent reactions of the products of this reaction with ozone. Although these products have not yet been characterized experimentally, the radical H(2)NO has been postulated, because it can regenerate NH(2) radicals through the reactions: H(2)NO + O(3) --> NH(2) + O(2) and H(2)NO + O(3) --> HNO + OH + O(2). With the purpose of providing a reasonable explanation from a theoretical point of view to the kinetic observed behaviour of the NH(2) + O(3) system, we have carried ab initio electronic structure calculations on both H(2)NO + O(3) possible reactions. The results obtained in this article, however, predict that of both reactions proposed, only the H(2)NO + O(3) --> NH(2) + O(2) reaction would regenerate indeed NH(2) radicals, explaining thus the deviation of the NH(2) pseudo-first-order decay observed experimentally.