Pb氯化反应机理的量子化学研究

本文用量子化学从头计算MP2方法,在SDD基组水平上研究了煤燃烧过程中Pb与HCl、 Cl2在高温条件下两个反应的微观机理,通过优化得到反应物、过渡态、中间体和产物的几何构型。在同一水平上计算能量,同时进行零点能校正,并以此能量计算活化能和反应热效应。采用经典过渡态理论计算反应速率常数。计算结果与相关文献进行了比较,结果比较吻合,表明采用量子化学研究铅等痕量元素与气体反应的机理和动力学参数、热力学参数是可行的。     

用变分过渡态理论对CH3SiH3+O反应体系的动力学研究

用变分过渡态理论对ＣＨ３ＳｉＨ３与氧原子Ｏ的抽提反应进行了理论研究。利用从头算计算了反应体系的构型、振动频率和能量等信息,分析了此反应的反应机理;在２９８～１０００Ｋ计算了主要反应通道的速率常数。结果表明,在低温下,变分对于此反应影响较大,隧道效应较明显;计算得到的室温速率常数和实验符合很好。     

用变分过渡态理论研究CH3SiH3+H→CH3SiH2+H2反应动力学

用变分过渡态理论对ＣＨ３ＳｉＨ３与Ｈ的抽提取应进行了理论研究;利用从头算计算了反应体系的构型、振动频率和能量等信息;计算了温度在２９８￣１７００Ｋ内反应的速率常数和穿透系数。结果表明,在室温下,变分对于此反应影响较大,隧道效应特别明显,计算得到的速率常数和实验值符合得很好。     

异硫氰酸与CF2自由基反应机理的量子化学研究

采用密度泛函理论B3LYP方法研究了CF₂自由基与HNCS的反应机理,并在B3LYP/6-311++G**水平上对反应物、中间体、过渡态进行了全几何参数优化,通过频率分析和IRC确定中间体和过渡态的真实性.为了得到更精确的能量值,又用CCSD（T）/6-311++G**方法计算了在B3LYP/6-311++G**水平优化后的各个驻点的相对能量.根据统计热力学及用Winger校正的Eyring过渡态理论,利用自编程序,计算不同温度下低势垒反应的平衡常数和速率常数.计算结果表明,单重态的CF₂自由基与HNCS的反应有6条可能的反应通道,三重态的CF₂自由基与HNCS的反应有1条反应通道.其中单重态反应通道CF₂+HNCS→IM1→TS1→IM2 HCF₂NCS（P1）为主反应通道.     

SiF2自由基与异硫氰酸反应机理的理论研究

采用密度泛函理论B3LYP 方法研究了CF2 自由基与HNCS 的反应机理, 并在B3LYP/6-311＋＋G**水平上对反应物、中间体、过渡态进行了全几何参数优化. 为了得到更精确的能量值,又用CCSD(T)/6-311＋＋G**方法计算了在B3LYP/6-311＋＋G**水平优化后的各个驻点的相对能量. 根据统计热力学及用Winger校正的Eyring过渡态理论,利用自编程序,计算不同温度下低势垒反应的平衡常数和速率常数.计算结果表明单重态的CF2 自由基与HNCS 的反应有6条反应通道,三重态的CF2 自由基与HNCS 的反应有1条反应通道.其中单重态反应通道CF2＋HNCS→IM1→TS1→IM2 HCF2NCS(P1)为主反应通道.     

SiF_2自由基与异硫氰酸反应机理的理论研究北大核心CSCD

采用密度泛函理论B3LYP方法研究了SiF2自由基与异硫氰酸(HNCS)的反应机理,并在B3LYP/6-311++G**水平上对反应物、中间体、过渡态进行了全几何参数优化,通过频率分析和内禀反应坐标(IRC)确定中间体和过渡态的真实性.为了得到更精确的能量值,又用CCSD(T)/6-311++G**方法计算了在B3LYP/6-311++G**水平优化后的各个驻点的相对能量.根据统计热力学及用Winger校正的Eyring过渡态理论,利用自编程序,计算不同温度下低势垒反应的平衡常数和速率常数,并且通过电子密度拓扑分析讨论了化学反应过程中主要化学键的生成和断裂.计算结果表明,单重态的SiF2自由基与HNCS反应有6条可能的反应通道,其中反应通道SiF2+HNCS→IM1→TS1→IM2HSiF2NCS(P1)为主反应通道.     

含铬废物焚烧中CrOH+H→CrO+H2反应机理研究

本文用量子化学密度泛函UB3LYP方法,在6-311 G**基组水平上研究了含铬固体废物焚烧过程中CrOH H→CrO H2的微观反应机理。在相同理论水平上用内禀反应坐标理论(IRC)对最小能量途径进行计算,并进行了详细的讨论。分别计算了正、逆反应的活化能。采用经典过渡态理论计算了正、逆反应的反应速率常数。     

HNCO+HCO→NCO+CH2O氢转移反应的从头算及动力学研究

在UMP2 (Full) /6 311G(d ,p)计算水平上 ,优化了标题反应的反应物、过渡态、产物的几何结构 ,沿最小能量途径讨论了异氰酸 (HNCO)和甲酰自由基 (HCO)发生氢转移反应位能面上驻点的结构以及相互作用分子结构变化 .指出该反应是一个N -H键断裂和C -H键生成的协同反应 .进一步采用UQCISD(T ,Full)方法对反应途径上的驻点进行了单点能量校正 ,得出该反应的计算位垒是 91.4 7kJ/mol,与实验值 10 8.92kJ/mol接近 .在5 0 0～ 2 5 0 0K实验温度范围内 ,运用变分过渡态理论 (CVT)计算得到的速率常数与实验观测值进行了比较 .     

Cr/O2/Ar体系反应机理的量子化学研究

本文用量子化学从头计算法研究了Cr/O2/Ar气相体系所发生的两个反应的机理.在MP2/SDD水平上优化了反应物、过渡态、中间体和产物的几何构型.在同一水平上计算了能量,同时进行零点能校正,并且计算出反应的热效应、熵变、活化能和绝对速率常数,并与文献数据进行了比较.计算结果与文献数据比较吻合,表明量子化学计算是研究铬等痕量元素气相反应机理和计算热力学及动力学参数的一种有效手段.     

CF2自由基与HNCO反应机理的量子化学研究

采用密度泛函理论B3LYP 方法研究了CF2 自由基与HNCO 的反应机理, 并在B3LYP/6-311＋＋G**水平上对反应物、中间体、过渡态进行了全几何参数优化, 通过频率分析和内禀反应坐标(IRC)确定了中间体和过渡态.为了得到更精确的能量值, 又用CCSD(T)/6-311＋＋G**方法计算了在B3LYP/6-311＋＋G**水平优化后的各个驻点的相对能量. 根据统计热力学及用Winger校正的Eyring过渡态理论,利用自编程序,计算不同温度下低势垒反应的平衡常数和速率常数.计算结果表明单重态的CF2 自由基与HNCO 的反应有四条反应通道, 三重态的CF2 自由基与HNCO 的反应有两条反应通道.其中单重态反应通道CF2＋HNCO→1IM1→1TS1→1IM2→1TS2→1IM3→CF2NH＋CO(P1)为主反应通道.三重态反应通道CF2＋HNCO→36IM1→36TS1→36IM2→HCF2+NCO(3P5)为主反应通道.     

The role played by the enthalpy of reactions in the disproportionation of free radicals

A semiempirical model of radical disproportionation was suggested. The reaction was modeled by an intersection of two potential curves describing stretching vibrations of interacting bonds. One of these curves was a parabola (stretching vibration of the attacked bond), and the other, a Morse curve (stretching vibration of the arising bond). Equations describing an increase in the interatomic distance in the reaction center of the transition state of such reactions as a function of the enthalpy of the reaction were obtained. A comparison of the calculation results and experimental data was performed to derive equations that described the rate constant for disproportionation as a function of bond elongation in the transition state and reaction enthalpy. A simple method for calculating interatomic distances in the reaction center of the reactions was suggested. Rate constants for several unstudied radical disproportionation reactions were calculated. The problem of the competition of disproportionation at various reaction centers was considered.     

Theoretical study on the mechanism and kinetics of atmospheric reactions NH2OH + OOH and NH2CH3 + OOH

Mechanism and kinetics of NH₂OH + OOH and NH₂CH₃ + OOH reactions were studied at the B3LYP and M062X levels of theory using the 6-311++G(3df, 3pd) basis set. The NH₂OH + OOH and NH₂CH₃ + OOH reactions proceed through different paths which lead to different products. Transition state structure and activation energy of each path were calculated. The calculated activation energies of hydrogen abstraction reactions were smaller than 25 kcal/mol and of substitution reactions are in the range of 50–70 kcal/mol. The rate constants were calculated using transition state theory (TST) modified for tunneling effect at 273–2000 K.     

Competition between the concerted and nonconcerted addition of ozone to a double bond

Quantum chemistry methods are used to investigate the mechanism of the reaction of ozone with the double bond of ethylene. It is shown that there are two possible reaction mechanism; concerted addition through a symmetrical transition state (Criegee mechanism) and nonconcerted addition through a biradical transition state (DeMore mechanism). In the single-determinant approximation, both mechanisms were described by using the QCISD, CCSD, and B3LYP methods. These methods give a reasonable ratio between the rates of the two reaction channels, with the rate constants being closer to the experiment when calculated by the CCSD and B3LYP methods. Multiconfiguration calculations are performed at the MRMP2 level. They also show the presence of both channels of the reaction and yield reasonable values of the rate constants for reaction channels and the ratio thereof. It is shown that the reaction of ethylene with ozone via the concerted addition mechanism is much faster.     

Quantum chemical calculations on Al-CVD using DMEAA: surface reaction mechanism of AlH3 on Al(111)

An investigation has been made of the elementary surface reactions of alane and its surface dissociation products using density functional theory and a cluster model to elucidate the reaction mechanism of the deposition of aluminium in aluminium chemical vapour deposition (Al-CVD) using dimethylethylamine alane (DMEAA). Molecular structures, potential energies, and normal mode frequencies of the reactants, the products, and the transition states were calculated for each of the surface elementary reactions. Based on transition state theory, rate constants were estimated from the calculation results. The proposed reaction mechanism is the following. DMEAA is adsorbed onto an aluminium surface without any dissociation in the gas phase; DMEAA dissociates into dimethylethylamine (DMEA) and alane on the surface; DMEA is desorbed and alane remains adsorbed; the adsorbed alane molecules dissociate to AlH₂, AlH, and H on the surface; hydrogen molecules to be desorbed are produced from the hydrogen atoms of AlH whose aluminium atoms form a quasi-aluminium surface on the original surface. The cluster size and structure dependence in quantum chemical calculations has also been considered using model clusters.     

Quantum dynamics and kinetics of the abstraction reactions by H atoms of primary and secondary hydrogens in C3H8

The abstraction reaction of H atoms with propane molecules presents two concurrent channels. In this work we have determined the specific rate constants and the product branching ratios (BRs) between the two channels using quantum chemistry calculations and reduced dimensionality quantum dynamics. The potential energy surfaces were computed by treating explicitly the forming and breaking bonds during the reaction, and optimizing the geometries of all the remaining degrees of freedom. In this way, the dynamics of the reaction occurs on an effective reduced dimensionality hyper-surface accounting for the zero-point energy of the optimized degrees of freedom. Energies are calculated with the CCSD(T) method and the cc-pVTZ basis set, while frequencies are calculated with the MP2 method and the same basis set. The calculations give barrier heights of 0.46 (0.36) eV and the reactions are exothermic by 0.13 (0.25) eV for primary (secondary) hydrogens in C3H8. At room temperature, quantum tunnelling and zero-point effects are found to contribute more than one order of magnitude to the rate constants, when compared to purely classical transition state theory (TST) computations. The branching ratios show the importance of abstraction of secondary hydrogen in propane more significantly at a lower temperature in accord with experimental investigations.     

Theoretical study on the mechanism of the reaction of FOX-7 with OH and NO2 radicals: bimolecular reactions with low barrier during the decomposition of FOX-7

The decomposition of 1,1-diamino-2,2-dinitroethene (FOX-7) attracts great interests, while the studies on bimolecular reactions during the decomposition of FOX-7 are scarce. This study for the first time investigated the bimolecular reactions of OH and NO₂ radicals, which are pyrolysis products of ammonium perchlorate (an efficient oxidant usually used in solid propellant), with FOX-7 by computational chemistry methods. The molecular geometries and energies were calculated using the (U)B3LYP/6-31++G(d,p) method. The rate constants of the reactions were calculated by canonical variational transition state theory. We found three mechanisms (H-abstraction, OH addition to C and N atom) for the reaction of OH + FOX-7 and two mechanisms (O abstraction and H abstraction) for the reaction of NO₂ + FOX-7. OH radical can abstract H atom or add to C atom of FOX-7 with barriers near to zero, which means OH radical can effectively degrade FOX-7. The O abstraction channel of the reaction of NO₂ + FOX-7 results in the formation of NO₃ radical, which has never been detected experimentally during the decomposition of FOX-7.     

Kinetics of C<Subscript>10</Subscript>H<Subscript>7</Subscript>Br Pyrolysis

The temperature and pressure-dependent rate constants for the process C₁₀H₇Br ? C₁₀H₇+Br were evaluated using the variable reaction coordinate transition state theory VRC-TST. The calculated rate constants and computational fluid dynamics (CFD) calculations were employed to estimate the pyrolysis efficiency of 2-bromonaphthalene in the resistively-heated SiC high-temperature “chemical reactor” at the temperature of about 1500 K. The observed 40% pyrolysis efficiency is reproduced by CFD calculations if the value of the calculated rate constant for the C₁₀H₇Br pyrolysis is increased by a factor of 2.     

The reaction of ozone with hexafluoropropylene: Competition of concerted and nonconcerted addition

The initial stage of the reaction between ozone and hexafluoropropylene (HFP) was studied by the DFT/B3LYP quantum-chemical method using the family of 6-31G basis sets and the cc-pVDZ+ basis set. Two reaction paths were compared, concerted (the Criegee mechanism) and nonconcerted (the DeMore mechanism) addition. For both reaction paths, the geometry and transition state energies, entropy, and thermodynamic and electronic enthalpy were calculated and the rate constants of the reaction were estimated. It was shown that the DeMore mechanism should be given preference for the reaction of HFP with ozone. UB3LYP calculations for the DeMore mechanism give reaction rate constants close to the experimental values.     

ONIOM方法计算胺和二芳基碳正离子的亲核反应的速率常数

利用第一性原理计算了胺和二芳基碳正离子的亲核反应的速率常数. 研究不同的溶剂化模型(PCM、CPCM和COSMORS)、不同类型的原子半径(UA0、UAKS、UAHF、Bondi和UFF)、以及一些单点能计算方法(B3LYP、B3P86、B3PW91、BHANDH、BMKPBEPBE、M06、MP2和ONIOM)在计算这类速率常数时的表现.通过比较速率常数的实验值和计算值,发现ONIOM(CCSD(T)/6-311++G(2df,2p):B3LYP/6-311++G(2df,2p))//B3LYP/6-31G(d)/PCM/UFF方法表现最好. 该方法随后被用于计算更多的胺和二芳基碳正离子的亲核反应的速率常数. 65个反应的速率常数的实验值和计算值之间表现出了相当好的相关性,这表明该方法适用于计算胺二芳基碳正离子的亲核反应的速率常数.     

Computational study on the kinetics of OH initiated oxidation of methyl difluoroacetate (CF2HCOOCH3)

The kinetics of hydrogen atom abstraction reactions of methyl difluoroacetate (CF₂HCOOCH₃) by OH radical has been studied by quantum mechanical method. The geometry optimisation and frequency calculation of the titled compound was performed with density functional theory using hybrid meta density functional MPWB1K with 6-31+G(d,p) basis set. Transition states have been determined and intrinsic reaction coordinate (IRC) calculation has been performed to ascertain that the transition from reactants to products was smooth through the corresponding transition state. Energy values are refined by making single point energy calculation at G3B3 level of theory and an energy level diagram is constructed. The standard enthalpies of formation of reactants and other species formed during the reaction were calculated using isodesmic method. The rate constants are calculated using canonical transition state theory and the overall rate constant is determined to be 1.35×10^?13 cm³ molecule^?1 s^?1 at 298 K and 1 atmospheric pressure. Tunnelling has been taken into account in the determination of the rate constant because it plays a critical role at low temperature especially when transfer of hydrogen takes place. The calculated value is found to be in good agreement with the experimentally determined value of 1.48×10^?13 cm³ molecule^?1 s^?1.