氢抽提反应CHBr2+HBr→CH2Br2+Br的直接动力学研究

采用直接动力学方法,对CHBr2+HBr→CH2Br2+Br反应通道进行了理论研究,在B3LYP/6-311+G(d,p)水平下获得了优化几何构型、频率以及最小能量路径,更精确的单点能在B3LYP/6-311++G(3df,2pd)水平下完成.利用正则变分过渡态理论,结合小曲率隧道效应校正方法计算了反应通道在220 K～2 000 K温度范围内的速率常数.在整个反应区间,隧道效应对反应的影响比较大;变分效应在低温时有一定的影响,在高温区间的影响很小可以忽略.计算得到的速率常数和已有实验值很好地吻合.     

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;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。     

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298～1000 K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。     

CH_3CN+CH_3→CH_2CN+CH_4氢消除反应的直接动力学研究

采用直接动力学方法,对乙腈与甲基的反应进行了理论研究.在BHandHLYP/6-311G(d,p)和MP2/6-311G(d,p)水平下获得,稳定点的几何结构、振动频率及最小能量路径(MEP),在G3(MP2)和MC-QCISD水平下对能量信息进一步确认.利用正则变分过渡态理论,结合小曲率隧道效应校正(CVT/SCT)方法计算了该反应在220K～2000K的速率常数,与实验值符合得很好.     

CF_2ClC(O)OCH_2CH_3+OH的反应机理及动力学性质的理论研究

利用双水平直接动力学方法,在MCG3-MPWB//M06-2X/aug-cc-pVDZ水平上研究了CF_2ClC(0)OCH_2CH_3+OH的微观反应机理.得到了反应物CF_2ClC(O)OCH_2CH_3的5种稳定构象(RCl~RC5),并对每一构象考察了发生在-CH_3-和-CH_2-基团上的所有可能氢提取反应通道.利用改进的变分过渡态理论(ICVT)结合小曲率隧道效应校正(SCT)计算了各反应通道的速率常数,分析了各构象反应位点选择性.结果表明,对于构象RCl和RC2,低温时氢提取反应主要发生在-CH_2-基团上;而对于构象RC3RC4和RC5,发生在-CH_3基团上的氢提取反应通道在整个温度区间内占绝对优势.根据Boltzmann配分函数计算总包反应速率常数,在298 K温度下计算的体系总包反应速率常数与实验值相符,进而给出200~1000 K温度范围内拟合了速率常数的三参数Arrhenius表达式:k_(overall)=5.45×10~(25)T~(4.54)exp(-685/T).     

CF3CH2CH3+OH的反应机理及动力学性质的理论研究

采用密度泛函理论BB1K/6-31+G(d,p)计算了反应CF₃CH₂CH₃+OH各反应通道上驻点的稳定结构和振动频率, 并分别在BMC-CCSD, MC-QCISD和G3(MP2)水平上进行了单点能校正. 运用变分过渡态理论, 在BMC-CCSD//BB1K, MC-QCISD//BB1K, G3(MP2)//BB1K以及BB1K水平上计算了各反应通道的速率常数, 讨论了-CH₂和-CH₃基团上H提取通道对总反应的贡献, 并与已有实验和理论结果进行了对比. 计算结果表明, BMC-CCSD水平上的速率常数与实验测量值符合得很好, 进而给出了该水平上反应在200~1000 K温度范围内速率常数k(cm³?molecule^-1?s^-1)的三参数表达式: k=1.90×10^-21T^3.21exp(-292.62/T).     

用变分过渡态理论研究NH_3+NH→2NH_2反应动力学

利用变分过渡态理论的“直接动力学”方法对ＮＨ３分子和基态ＮＨ（Ｘ３∑）自由基的反应进行了理论研究；利用从头算计算得到反应体系的电子结构能和能量梯度等信息，计算了２００～２５００Ｋ温度范围该反应的速率常数和穿透系数，分析了影响隧道效应和反应速率常数的一些因素．结果表明，在低温情况下，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．     

H原子和(CH3)2SiH2抽提反应的理论研究

采用UMP2/6-31G(d)理论水平优化了H原子和(CH3)2SiH2抽提反应势能面上的所有驻点,并在此水平基础上进行了内禀反应坐标(IRC)的计算,得到该反应的反应途径(MEP)。应用变分过渡态理论及最小能量途径半经典绝热基态隧道效应校正(MEPSAG)、小曲率半经典绝热基态隧道效应校正(SCSAG)等方法对上述反应进行了动力学研究,期望从理论上提供一套温度范围较宽、精度较高的动力学数据,为阐明反应机理和解释实验结果提供理论依据。     

微正则变分过渡态理论直接动力学计算反应速率常数的一种新方法

在微正则过渡态理论(mTST)和微正则变分过渡态理论(mVT)的基础上, 构造了一种量子变分RRKM速率常数的新算法, 用于计算化学反应的k(E, J), k(E)和k(T). 该算法包括了Beyer-Swinehart的隧道校准方法的微正则速率常数的计算. 在该方法中发展了一种截断式内插法, 可有效的计算热速率常数中的Boltzmann积分. 通过对H(D)2CO→H(D)₂ + CO, CH₂CO→CH₂ + CO和CH₄ + H→CH₃ + H₂反应的检验可看出, 其计算结果与采用更精确计算方法的结果相当符合, 但本方法可节省大量机时.     

Cl原子与CH3COCH2Cl反应动力学的理论研究

在B3LYP/6-31G(d,p)水平上优化了Cl原子与CH3COCH2Cl反应的各驻点的几何构型,并在相同水平上通过频率计算和内禀反应坐标(IRC)分析对过渡态的结构和反应物、产物的连接性进行了验证。采用高精确模型G3MP2方法进行单点能计算,构建了反应的势能剖面。计算结果表明,标题反应有抽氢反应、加成-消除反应、取代反应3种反应机理6条反应通道。利用经典过渡态理论(TST)和正则变分过渡态理论(CVT)计算了各反应通道在200~2000 K温度范围内的速率常数,并用小区率隧道效应模型(SCT)对抽氢反应进行校正。计算结果显示,反应有一定的变分效应,计算的总反应速率常数与文献报道的实验值符合得较好,速率常数的三参数表达式为k=2.33×10-19T2.54exp(567.07/T)cm3·mol-1·s-1。     

Mechanistic study and kinetic properties of the CF3CHO + Cl reaction

Theoretical investigations have been carried out on the mechanism and kinetics for the reaction of CF 3 CHO + Cl using duallevel direct dynamics method. The potential energy surface information was obtained at the MCQCISD/3//MP2/cc-pVDZ level and the kinetic calculations were done using variational transition state theory with interpolated single-point energy (VTST-ISPE) approach. The calculated results show that the reaction proceeds primarily via the H-abstraction channel, while the Cl-addition channel is unfavorable due to the higher barriers. The improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling correction (SCT) was used to calculate the rate constants. The theoretical rate constants at room temperature are in general agreement with the experimental values. A three-parameter rate constant expression was fitted over a wide temperature range of 200-2000 K.     

Theoretical Investigation for the Abstraction Reaction of H with (CH_3)_3GeH

The reaction of H atom with (CH3)3GeH is considered to play important role in chemical vapor deposition (CVD) processes used in the semiconductor industry 1-2. The reaction mechanism and kinetics nature for this reaction are therefore essential input data for computer-modelling studies directed towards obtaining an understanding of the factors controlling CVD processes. However, despite its importance, the kinetics work about this reaction was very limited. Only two groups studied exper…     

Theoretical study of hydrogen abstraction reactions CH4 + R → CH3 + HR,geometrical, energetical and kinetical aspects

Five hydrogen abstraction reactions, CH₄ + R CH₃ + HR have been studied usingab initio SCF and CI methods. R was successively chosen as H, CH₃, NH₂, OH and F. Geometries were fully optimized at SCF level and energies were computed at CI level for products, reactants and transition states. Quadratic hypersurfaces were fitted in the neighborhood of the most important points of the potential energy hypersurfaces and vibrational analysis were performed thereupon. Wigner's and Christov's approximations were used to obtain an idea of the importance of tunneling of H atoms through the reaction barrier, and this effect was shown to be non-negligible. Finally, rate constant calculation were carried out at different temperatures.Chercheur Qualifié au Fonds National Belge de la Recherche Scientifique.     

Theoretical studies of the reactions of CF3CHCLOCHF2/CF3CHFOCHF2 with OH radical and Cl atom and their product radicals with OH

The mechanisms and dynamics studies of the OH radical and Cl atom with CF(3)CHClOCHF(2) and CF(3)CHFOCHF(2) have been carried out theoretically. The geometries and frequencies of all the stationary points are optimized at the B3LYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies (ISPE) method at the G3(MP2) level of theory. For each reaction, two H-abstraction channels are found and four products (CF(3)CHFOCF(2), CF(3)CFOCHF(2), and CF(3)CHClOCF(2), CF(3)CClOCHF(2)) are produced during the above processes. The rate constants for the CF(3)CHClOCHF(2)/CF(3)CHFOCHF(2) + OH/Cl reactions are calculated by canonical variational transition-state theory (CVT) within 200-2000 K, and the small-curvature tunneling is included. The total rate constants calculated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained. Our calculation shows that the substitution of Cl by F decreases the reactivity of CF(3)CHClOCHF(2) toward OH and Cl. In addition, the mechanisms of subsequent reactions of product radicals and OH radical are further investigated at the G3(MP2)//B3LYP/6-311G(d,p) level, and the main products are predicted in the this article.     

Theoretical Studies on the Abstraction Reaction of Atomic O（^3p） with Si2H6

The hydrogen abstraction reaction of O(^3P) with Si2H6 has been studied theoretially. Two transition states of ^3A″ and ^3A′ symmetries have been located for this abstraction reaction. Geometries have been optimized at the UMP2 leve with 6-311G (d) basis set. G3MP2 has been used for the final single-point energy calculation. The rate constants have been calculated over a wide temperature range of 200-3000K using canonical variational transition-state sheory (CVT) with small curvature tunneling effect(SCT). The calculated CVT/SCT rate constants match well with the experimental value.     

H原子和(CH_3)_2SiH_2抽提反应的理论研究

采用UMP2 / 6- 3 1G(d)理论水平优化了H原子和 (CH3) 2 SiH2 抽提反应势能面上的所有驻点 ,并在此水平基础上进行了内禀反应坐标 (IRC)的计算 ,得到该反应的反应途径 (MEP) .应用变分过渡态理论及最小能量途径半经典绝热基态隧道效应校正 (MEPSAG)、小曲率半经典绝热基态隧道效应校正 (SCSAG)等方法对上述反应进行了动力学研究 ,期望从理论上提供一套温度范围较宽、精度较高的动力学数据 ,为阐明反应机理和解释实验结果提供理论依据