Reaction-path Dynamics and Theoretical Rate Constants for the Reaction of CH3CH2OCF3 with HOOO Radical

A dynamic method is employed to study the reaction mechanisms of CH3CH2OCF3 with the hydrogen trioxy(HOOO) radical. In our paper, the geometries and harmonic vibrational frequencies of all the stationary points and minimum energy paths(MEPs) are calculated at the MPW1K/6-31+G(d,p) level of theory, and the energetic information along MEPs is further refined by the CCSD/6-31+G(df,p) level of theory. The rate constants are evaluated with the conventional transition-state theory(TST), the canonical variational transition-state theory(CVT), the microcanonical variational transition-state theory(μVT), the CVT coupled with the small-curvature tunneling(SCT) correction(CVT/SCT), and the μVT coupled with the Eckart tunneling correction(μVT/Eckart) based on the ab initio calculations in the temperature range of 200 ~ 3000 K. The theoretical results are important in determining the atmospheric lifetime and the feasible pathways for the loss of HFEs.     

Theoretical study and rate constants calculation for the reactions of SiH3 radical with SiH3CH3 and SiH2(CH3)2

The multiple‐channel reactions SiH₃ + SiH₃CH₃ → products and SiH₃ + SiH₂(CH₃)₂ → products are investigated by direct dynamics method. The minimum energy path (MEP) is calculated at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD method. The rate constants for individual reaction channels are calculated by the improved canonical variational transition state theory (ICVT) with small‐curvature tunneling (SCT) correction over the temperature range of 200–2400 K. The theoretical three‐parameter expression k₁(T) = 2.39 × 10⁻²³T^4.01exp(−2768.72/T) and k₂(T) = 9.67 × 10⁻²⁷T^4.92exp(−2165.15/T) (in unit of cm³ molecule⁻¹ s⁻¹) are given. Our calculations indicate that hydrogen abstraction channel from SiH group is the major channel because of the smaller barrier height among eight channels considered. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

H原子与CH3NH2抽氢反应的动力学计算

用QC ISD(T)/6-311 G(3DF,3PD)/MP2/6-311G(D,P)方法研究了H原子与CH3NH2的抽氢反应过程。该反应包含两个反应通道:H分别从CH3基团(R1)和NH2(R2)基团上抽氢。R1势垒比R2势垒低3.42kJ/mol,表明R1是主反应通道。在从头算的基础上,用变分过渡态理论(CVT)加小曲率隧道效应(SCT)研究了各反应温度范围为200~4000K内的速率常数,所得结果与实验值符合的很好。动力计算表明,在所研究的温度范围内,变分效应对速率常数的计算影响不大,而在低温范围内,隧道效应起了很重要的作用。     

Rate constants and hydrogen isotope substitution effects in the CH3 + HCl and CH3 + Cl2 reactions

The kinetics of the CH3 + Cl2 (k2a) and CD3 + Cl2 (k2b) reactions were studied over the temperature range 188-500 K using laser photolysis-photoionization mass spectrometry. The rate constants of these reactions are independent of the bath gas pressure within the experimental range, 0.6-5.1 Torr (He). The rate constants were fitted by the modified Arrhenius expression, k2a = 1.7 x 10(-13)(T/300 K)(2.52)exp(5520 J mol(-1)/RT) and k2b = 2.9 x 10(-13)(T/300 K)(1.84)exp(4770 J mol(-1)/RT) cm(3) molecule(-1) s(-1). The results for reaction 2a are in good agreement with the previous determinations performed at and above ambient temperature. Rate constants of the CH3 + Cl2 and CD3 + Cl2 reactions obtained in this work exhibit minima at about 270-300 K. The rate constants have positive temperature dependences above the minima, and negative below. Deuterium substitution increases the rate constant, in particular at low temperatures, where the effect reaches ca. 45% at 188 K. These observations are quantitatively rationalized in terms of stationary points on a potential energy surface based on QCISD/6-311G(d,p) geometries and frequencies, combined with CCSD(T) energies extrapolated to the complete basis set limit. 1D tunneling as well as the possibility of the negative energies of the transition state are incorporated into a transition state theory analysis, an approach which also accounts for prior experiments on the CH3 + HCl system and its various deuterated isotopic substitutions [Eskola, A. J.; Seetula, J. A.; Timonen, R. S. Chem. Phys. 2006, 331, 26].     

Theoretical study and rate constants calculation for the reactions X + CF3CH2OCF3 (X = F,Cl, Br)

The multiple‐channel reactions X + CF₃CH₂OCF₃ (X = F, Cl, Br) are theoretically investigated. The minimum energy paths (MEP) are calculated at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for major reaction channels are calculated by canonical variational transition state theory (CVT) with small‐curvature tunneling (SCT) correction over the temperature range 200–2000 K. The theoretical three‐parameter expressions for the three channels k_1a(T) = 1.24 × 10^?15T^1.24exp(?304.81/T), k_2a(T) = 7.27 × 10^?15T^0.37exp(?630.69/T), and k_3a(T) = 2.84 × 10^?19T^2.51 exp(?2725.17/T) cm³ molecule^?1 s^?1 are given. Our calculations indicate that hydrogen abstraction channel is only feasible channel due to the smaller barrier height among five channels considered. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012     

CH3O·2+NO气相反应的密度泛函理论研究

用密度泛函方法分别研究了单态和三态 CH3 O·2 NO CH3 O· NO2 气相反应 .结果表明 ,反应中 NO进攻 CH3 O·2 经过了一个顺反异构化的过程 ,摘取 CH3 O·2 的端基氧 .整个反应是吸热反应 ,理论计算吸热值为 5 0 .93k J/ mol,单态为多通道多步骤反应 ,决定速度步骤的能垒为 1 90 .6 1 k J/ mol.而三态为单通道反应 ,其决定速度步骤的能垒为 1 6 3.31 k J/ mol.三态反应为最佳反应通道 .该反应的研究将为保护臭氧层及大气环境提供重要的理论依据 .     

CH3CH2O+HCHO反应机理及主通道速率常数

采用CCSD(T)/cc-pVDZ//B3LYP/6-311++G(d,p)双水平计算方法研究了CH₃CH₂O+HCHO反应的微观反应机理. 结果表明, 标题反应主要存在5个抽氢和3个氢迁移异构化反应通道, 其中抽氢通道R→ IMa(CH₃CH₂O…CH₂O)→TS1→ IM1b→P1(CH₃CH₂OH+CHO)为优势通道, 其表观活化能为14.65 kJ/mol. 利用变分过渡态理论(CVT)并结合小曲率隧道效应模型计算了主通道R1在275~1000 K温度范围内的速率常数k^TST, k^CVT和k^CVT/SCT, 在此温度区间内表观反应速率常数三参数表达式为k^CVT/SCT=2.26×10^-17 T^0.57 exp(-1004/T), 显示具有正温度系数效应.     

CH_3SO+HO_2气相反应机理与主通道速率常数

在MPW1PW91/6-311G(d,p)水平上优化了标题反应各驻点物种的几何构型,并在相同水平上通过频率计算和内禀反应坐标(IRC)分析对过渡态结构及连接性进行了验证.采用QCISD(T)/6-311G(d,p)方法对所有驻点及反应路径的部分选择点进行单点能校正,分别构建了CH3SO+HO2反应体系的单、三重态反应势能剖面.研究结果表明,CH3SO+HO2反应体系存在6条反应通道7条路径,优势通道(1)R→3IM→P1(CH3SOH+3O2)发生在三重态势能面上,此通道包含两条路径,其表观活化能分别为12.01和-30.04kJ?mol-1,主路径(2)R→3IM→3TS2→P1(CH3SOH+3O2)是一个无势垒氢迁移过程.利用经典过渡态理论(TST)与变分过渡态理论(CVT)并结合小曲率隧道效应模型(SCT),分别计算了主路径(2)在200～2500K温度范围内的速率常数kTST,kCVT和kCVT/SCT,在此温度区间内的表观反应速率常数三参数表达式为kCVT/SCT=4.08×10-24T3.13exp(8012.2/T)cm3imolecule-1is-1,具有负温度系数效应.速率常数计算结果显示,变分效应在计算温度段内影响较小,而量子力学隧道效应在低温段有显著影响.     

Effects of multidimensional tunneling in the kinetics of hydrogen abstraction reactions of O (3P) with CH3OCHO

Quantum tunneling paths are important in reactions when there is a significant component of hydrogenic motion along the potential energy surface. In this study, variational transition state with multidimensional tunneling corrections are employed in the calculations of the thermal rate constants for hydrogen abstraction from the cis‐CH₃OCHO by O (³P) giving CH₃OCO + OH (R1) and CH₂OCHO + OH (R2). The structures and electronic energies are computed with the M06‐2X method. Benchmark calculations with the CBS_D–T approach give an enthalpy of reaction at 0 K for R1 (−2.8 kcal/mol) and R2 (−2.5 kcal/mol) which are in good agreement with the experiment, i.e. −2.61 and −1.81 kcal/mol. At the low and intermediate values of temperatures, small‐ and large‐curvature tunneling dominate the kinetics of R1, which is the dominant path over the range of temperature from 250 to 1200 K. This study shows the importance of multidimensional tunneling corrections for both R1 and R2, for which the total rate constant at 298 K calculated with the CVT/μOMT method is 8.2 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ which agrees well with experiment value of 9.3 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ (Mori, Bull. Inst. Chem. Res. 1981, 59, 116). © 2018 Wiley Periodicals, Inc.     

CH3SH与NO2的反应机理及动力学

在G3B3,CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p)水平上详细研究了CH3SH与基态NO2的微观反应机理.在B3LYP/6-311++G(d,p)水平得到了反应势能面上所有反应物、过渡态和产物的优化构型,通过振动频率分析和内禀反应坐标(IRC)跟踪验证了过渡态与反应物和产物的连接关系.在CCSD(T)/6-311++G(d,p)和G3B3水平计算了各物种的能量,得到了反应势能面.利用经典过渡态理论(TST)与变分过渡态理论(CVT)并结合小曲率隧道效应模型(SCT),分别计算了在200～3000K温度范围内的速率常数kTST,kCVT和kCVT/SCT.研究结果表明,该反应体系共存在5个反应通道,其中N进攻巯基上H原子生成CH3S+HNO2的通道活化势垒较低,为主要反应通道.动力学数据也表明,该通道在200～3000K计算温度范围内占绝对优势,拟合得到的速率常数表达式为k1CVT/SCT=1.93×10-16T0.21exp(-558.2/T)cm3·molecule-1·s-1.     

Reaction‐path dynamics and theoretical rate constants for the reaction CH4 + O3 → HOOO + CH3

We present a direct ab initio dynamics study of thermal rate constants of the hydrogen abstraction reaction of CH₄ + O₃ → HOOO +CH₃. The geometries of all the stationary points are optimized at MPW1K/6‐31+G(d,p), MPWB1K/6‐31+G(d,p), and BHandHLYP/6‐31+G(d,p) levels of theory. The energies are refined at a multi‐high‐level method. The extended Arrhenius expression fitted from the CVT/SCT and μVT/Eckart rate constants of ozonolysis of methane in the temperature range 200–2500 K are k^CVT/SCT(T) = 5.96 × 10^?29T^4.49e^(?17321.3/T) and k^μVT/Eckart(T) = 7.92 × 10^?29T^4.46e^(?17301.7/T), respectively. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

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.     

Variational transition state theory rate constants and H/D kinetic isotope effects for CH3 + CH3OCOH reactions

The rate constants and H/D kinetic isotope effect for hydrogen abstraction reactions involving isotopomers of methyl formate by methyl radical are computed employing methods of the variational transition state theory (VTST) with multidimensional tunneling corrections. The energy paths were built with a dual-level method using the moller plesset second-order perturbation theory (MP2) method as the low-level and complete basis set (CBS) extrapolation as the high-level energy method. Benchmark calculations with the CBS_D-T approach give an enthalpy of reaction at 0 K for R1 (−4.5 kcal/mol) and R2 (−4.2 kcal/mol) which are in good agreement with the experiment, that is, −4.0 and − 4.8 kcal/mol. For the reactional paths involving the isotopomers CH₃ + CH₃OCOH → CH₄ + CH₃OCO and CH₃ + CH₃OCOD → CH₃D + CH₃OCO, the value of k^H/k^D (T = 455 K) using the canonical VTST/small-curvature tunneling approximation method is 6.7 in close agreement with experimental value (6.2). © 2019 Wiley Periodicals, Inc.     

Ar、NO和CHBr3对电子激发态CH的淬灭

The collisional quenching rate constants of CH(A, V'=0) by Ar and CHBr_3 and CH(A, B, V'=0) by NO molecule were measured by means of laser photolysis of CHBr_3 molecule at 266 nm generating CH(A, B) radicals and monitoring the time-resolved signal of ethession CH(A, B→X). The dependence of quenching rate constant of CH(A, V'=0) by CHBr_3 on rotational state of CH(A) is presented. It is found that the quenching rate decreases with increasing rotational quantum number of CH(A).     

Temperature-dependent rate constants for the reactions of chlorine atom with methanol and Br2

Kinetics of the reaction of Cl atoms with methanol has been investigated at 2 Torr total pressure of helium and over a wide temperature range 225-950 K, using a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction Cl + CH₃OH → products (1) was determined using both absolute measurements under pseudo-first order conditions, monitoring the kinetics of Cl-atom consumption in excess of methanol and relative rate method, k₁ = (5.1 ± 0.8) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and was found to be temperature independent over the range T = 225-950 K. The rate constant of the reaction Cl + Br₂ → BrCl + Br (3) was measured in an absolute way monitoring Cl-atom decays in excess of Br₂: k₃ = 1.64 × 10⁻¹⁰ exp(34/T) cm³ molecule⁻¹ s⁻¹ at T = 225-960 K (with conservative 15% uncertainty). The experimental data for k₃ can also be adequately represented by the temperature independent value of k₃ = (1.8 ± 0.3) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The kinetic data from the present study are compared with previous measurements.     

CH3CH2+O(3P)反应机理的理论研究

The reaction for CH3CH2+O(3P) was studied by ab initio method. The geometries of the reactants, intermediates, transition states and products were optimized at MP2/6-311+G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single-point calculations for all the stationary points were carried out at the QCISD(T)/6-311+G(d,p) level using the MP2/6-311+G(d,p) optimized geometries. The results of the theoretical study indicate that the major products are the CH2O＋CH3, CH3CHO+H and CH2CH2+OH in the reaction. For the products CH2O＋CH3 and CH3CHO+H, the major production channels are A1: (R)→IM1→TS3→(A) and B1: (R)→IM1→TS4→(B), respectively. The majority of the products CH2CH2+OH are formed via the direct abstraction channels C1 and C2: (R)→TS1(TS2)→(C). In addition, the results suggest that the barrier heights to form the CO reaction channels are very high, so the CO is not a major product in the reaction.     

CH激发态碎片的形成及动力学研究

利用流动余辉技术研究了亚稳态氦与CHBr_3、CH_2Br_2的传能反应。由激发态碎片的发射光谱测定了CH(A,B,C)等碎片的相对布居、形成速率常数和CH(A~2Δ,v'=0)的转动温度,并对传能反应机理进行了初步的讨论。     

Theoretical Investigation of CH3CF2O2+HOO Reaction

The reactions of CH3CF2O2 with HOO are important chemical cyclic processes of photochemical contamination. In this paper, the reaction pathways and reaction mechanism of CH3CF2O2+HOO are investigated extensively with the Gaussian 98 package at the B3LYP/6-311++G** basis sets. The use of vibrational mode analysis and electron population analysis to reveal the reaction mechanism is firstly reported. The study shows that CH3CF2CO2+HOO→IM1→TS1→CH3CF2O2H+O2 channel is the energetically most favorable, CH3CF2CO2H and O2 are the principal products, and the formation of CH3OH and CF2O is also possible.     

Direct dynamic study on the hydrogen abstraction reaction CH3CN + OH-->CH2CN + H2O

The reaction of acetonitrile with hydroxyl has been studied using the direct ab initio dynamics methods. The geometries, vibrational frequencies of the stationary points, as well as the minimum energy paths were computed at the BHandHLYP and MP2 levels of theory with the 6-311G(d, p) basis set. The energies were further refined at the PMP4/6-311+G(2df, 2pd) and QCISD(T)/6-311+G(2df, 2pd) levels of theory based on the structures optimized at BHandHLYP/6-311G(d, p) and MP2/6-311G(d, p) levels of theory. The Polyrate 8.2 program was employed to predict the thermal rate constants using the canonical variational transition state theory incorporating a small-curvature tunneling correction. The computed rate constants are in good agreement with the available experimental data.     

Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

The global environment pollution includes pho-tochemical smog, acid rain and stratospheric ozonedepletion. The short-lived species/radicals in atmos-phere are closely related to these phenomena. Theshort-lived species/radicals bring the photochemicalsmog,…