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1.
The multiple channel reaction H + CH(3)CH(2)Cl --> products has been studied by the ab initio direct dynamics method. The potential energy surface information is calculated at the MP2/6-311G(d,p) level of theory. The energies along the minimum energy path are further improved by single-point energy calculations at the PMP4(SDTQ)/6-311+G(3df,2p) level of theory. For the reaction, four reaction channels (one chlorine abstraction, one alpha-hydrogen abstraction, and two beta-hydrogen abstractions) have been identified. The rate constants for each reaction channel are calculated by using canonical variational transition state theory incorporating the small-curvature tunneling correction in the temperature range 298-5000 K. The total rate constants, which are calculated from the sum of the individual rate constants, are in good agreement with the experimental data. The calculated temperature dependence of the branching fractions indicates that for the title reaction, H-abstraction reaction is the major reaction channel in the whole temperature range 298-5000 K. 相似文献
2.
The theoretical investigations were performed on the reaction mechanisms for the title reactions CH(3)C(O)CH(3) + Cl --> products (R1), CH(3)C(O)CH(2)Cl + Cl --> products (R2), CH(3)C(O)CHCl(2) + Cl --> products (R3), and CH(3)C(O)CCl(3) + Cl --> products (R4) by ab initio direct dynamics approach. Two different reaction channels have been found: abstract of the H atom from methyl (--CH(3)) group or chloromethyl (--CH(3-n)Cl(n)) group of chloroacetone and addition of a Cl atom to the carbon atom of the carbonyl group of chloroacetone followed by methyl or chloromethyl eliminations. Because of the higher potential energy barrier, the contribution of addition-elimination reaction pathway to the total rate constants is very small and thus this pathway is insignificant in atmospheric conditions. The rate constants for the H-abstraction reaction channels are evaluated by using canonical variational transition state theory incorporating with the small-curvature tunneling correction. Theoretical overall rate constants are in good agreement with the available experimental values and decrease in the order of k(1) > k(2) > k(3) > k(4). The results indicate that for halogenated acetones the substitution of halogen atom (F or Cl) leads to the decrease in the C--H bond reactivity and more decrease of reactivity is caused by F-substitution. 相似文献
3.
The hydrogen abstract reactions of OH radicals with HOF (R1), HOCl (R2), and HOBr (R3) have been studied systematically by a dual-level direct-dynamics method. The geometries and frequencies of all the stationary points are optimized at the MP2/6-311+G(2d, 2p) level of theory. A hydrogen-bonded complex is located at the product channel for the OH + HOBr reaction. To improve the energetics information along the minimum energy path (MEP), single-point energy calculations are carried out at the CCSD(T)/6-311++G(3df, 3pd) level of theory. Interpolated single-point energy (ISPE) method is employed to correct the energy profiles for the three reactions. It is found that neither the barrier heights (DeltaE) nor the H-O bond dissociation energies [D(H-O)] exhibit any clear-cut linear correlations with the halogen electronegative. The decrease of DeltaE and D(H-O) for the three reactions are in order of HOF > HOBr > HOCl. Rate constants for each reaction are calculated by canonical variational transition-state theory (CVT) with a small-curvature tunneling correction (SCT) within 200-2000 K. The agreement of the rate constants with available experimental values for reactions R2 and R3 at 298 K is good. Our results show that the variational effect is small while the tunneling correction has an important contribution in the calculation of rate constants in the low-temperature range. Due to the lack of the kinetic data of these reactions, the present theoretical results are expected to be useful and reasonable to estimate the dynamical properties of these reactions over a wide temperature range where no experimental value is available. 相似文献
4.
A direct dynamics study is carried out for the hydrogen abstraction reactions Cl + CH(4-n)F(n) (n = 1-3) in the temperature range of 200-1,000 K. The minimum energy paths (MEPs) of these reactions are calculated at the BH&H-LYP/6-311G(d,p) level, and the energies along the MEPs are further refined at the QCISD(T)/6-311+G(2df,2p) and QCISD(T)/6-311+G(d,p) (single-point) level. The rate constants obtained by using the improved canonical variational transition state theory incorporating small-curvature tunneling correction (ICVT/SCT) are in good agreement with the available experimental results. It is shown that the vibrational adiabatic potential energy curves for these reactions have two barriers, a situation similar to the analogous reactions CH(3)X+Cl (X=Cl, Br). The theoretical results show that for the title reactions the variational effect should not be neglected over the whole considered temperature range, while the small-curvature tunneling effect is only important in the lower temperature range. The effects of fluorine substitution on the rate of this kind of reactions are also examined. 相似文献
5.
A direct dynamics method is employed to study the kinetics of the multiple channel reaction CH(3)OCl + Cl. The potential energy surface (PES) information is explored from ab initio calculations. Two reaction channels, Cl- and H-abstractions, have been identified. The optimized geometries and frequencies of the stationary points and the minimum-energy paths (MEPs) are calculated at the MP2 level of theory using the 6-311G(d, p) and cc-pVTZ basis sets, respectively. The single-point energies along the MEPs are further refined at the G3(MP2)//MP2/6-311G(d, p), G3//MP2/6-311G(d, p), as well as by the multicoefficient correlation method based on QCISD (MC-QCISD) using the MP2/cc-pVTZ geometries. The enthalpies of formation for the species CH(3)OCl and CH(2)OCl are calculated via isodesmic reactions. The rate constants of the two reaction channels are evaluated by using the variational transition-state theory over a wide range of temperature, 220-2200 K. The calculated rate constants exhibit the slightly negative temperature dependence and show good agreement with the available experimental data at room temperature at the G3(MP2)//MP2/6-311G(d, p) level. The present calculations indicate that the two channels are competitive at low temperatures while H-abstraction plays a more important role with the increase of temperature. The calculated k(1a)/k(1) ratio of 0.5 at 298 K is in general agreement with the experimental one, 0.8 +/- 0.2. The high rate constant for CH(3)OCl + Cl shows that removal by reaction with Cl atom is a potentially important loss process for CH(3)OCl in the polar stratosphere. 相似文献
6.
The dynamic properties of the multichannel hydrogen abstraction reactions of CH(3)CH(2)Br + OH --> products and CH(3)CHBr(2) + OH --> products are studied by dual-level direct dynamics method. For each reaction, three reaction channels, one for alpha-hydrogen abstraction and two for beta-hydrogen abstractions, have been identified. The minimum energy paths (MEPs) of both the reactions are calculated at the Becke's half-and-half (BH&H)-Lee-Yang-Parr (LYP)/6-311G(d, p) level and the energy profiles along the MEPs are further refined with interpolated single-point energies (ISPE) method at the G2M(RCC5)//BH&H-LYP level. There are complexes with energies less than those of the reactants or products located at the entrance or exit channels, which indicates that the reactions may proceed via an indirect mechanism. By canonical variational transition-state theory (CVT) the rate constants are calculated incorporating the small-curvature tunneling (SCT) correction in the temperature range of 220-2000 K. The agreement of the rate constants with available experimental values for two reactions is good in the measured temperature range. The calculated results show that alpha-hydrogen abstraction channel is the major reaction pathway in the lower temperature for two reactions, while the contribution of beta-hydrogen abstraction will increase with the increase in temperature. 相似文献
7.
The reaction mechanism of CF(3)CH(2)OH with OH is investigated theoretically and the rate constants are calculated by direct dynamics method. The potential energy surface (PES) information, which is necessary for dynamics calculation, is obtained at the B3LYP/6-311G (d, p) level. The single-point energy calculations are performed at the MC-QCISD level using the B3LYP geometries. Complexes, with the energies being less than corresponding reactants and products, are found at the entrance and exit channels for methylene-H-abstraction channel, while for the hydroxyl-H-abstraction channel only entrance complex is located. By means of isodesmic reactions, the enthalpies of the formation for the species CF(3)CH(2)OH, CF(3)CHOH, and CF(3)CH(2)O are estimated at the MC-QCISD//B3LYP/6-311G (d, p) level of theory. The rate constants for two kinds of H-abstraction channels are evaluated by canonical variational transition state theory with the small-curvature tunneling correction (CVT/SCT) over a wide range of temperature 200-2000 K. The calculated results are in good agreement with the experimental values in the temperature region 250-430 K. The present results indicate that the two channels are competitive. Below 289 K, hydroxyl-H-abstraction channel has more contribution to the total rate constants than methylene-H-abstraction channel, while above 289 K, methylene-H-abstraction channel becomes more important and then becomes the major reaction channel. 相似文献
8.
Hong‐Xia Liu Ying Wang Lei Yang Jing‐Yao Liu Hong Gao Ze‐Sheng Li Chia‐Chung Sun 《Journal of computational chemistry》2009,30(14):2194-2204
A direct dynamics study was carried out for the multichannel reaction of CH3NHNH2 with OH radical. Two stable Conformers (I, II) of CH3NHNH2 are identified by the rotation of the ? CH3 group. For each conformer, five hydrogen‐abstraction channels are found. The reaction mechanisms of product radicals (CH3NNH2 and CH3NHNH) with OH radical are also investigated theoretically. The electronic structure information on the potential energy surface is obtained at the B3LYP/6‐311G(d,p) level and the energetics along the reaction path is refined by the BMC‐CCSD method. Hydrogen‐bonded complexes are presented at both the reactant and product sides of the five channels, indicating that the reaction may proceed via an indirect mechanism. The influence of the basis set superposition error (BSSE) on the energies of all the complexes is discussed by means of the CBS‐QB3 method. The rate constants of CH3NHNH2 + OH are calculated using canonical variational transition‐state theory with the small‐curvature tunneling correction (CVT/SCT) in the temperature range of 200–1000 K. Slightly negative temperature dependence of rate constant is found in the temperature range from 200 to 345 K. The agreement between the theoretical and experimental results is good. It is shown that for Conformer I, hydrogen‐abstraction from ? NH? position is the primary pathway at low temperature; the hydrogen‐abstraction from ? NH2 is a competitive pathway as the temperature increases. A similar case can be concluded for Conformer II. The overall rate constant is evaluated by considering the weight factors of each conformer from the Boltzmann distribution function, and the three‐term Arrhenius expressions are fitted to be kT = 1.6 × 10?24T4.03exp (1411.5/T) cm3 molecule?1 s?1 between 200–1000 K. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
9.
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. 相似文献
10.
Theoretical study and rate constant calculation for the reactions of SH (SD) with Cl2, Br2, and BrCl
The mechanisms of the SH (SD) radicals with Cl2 (R1), Br2 (R2), and BrCl (R3) are investigated theoretically, and the rate constants are calculated using a dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the MP2/6-311G(d,p) and MPW1K/6-311G(d,p) levels. Higher-level energies are obtained at the approximate QCISD(T)/6-311++G(3df, 2pd) level using the MP2 geometries as well as by the multicoefficient correlation method based on QCISD (MC-QCISD) using the MPW1K geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of these reactions, which indicate that the reactions may proceed via an indirect mechanism. The enthalpies of formation for the species XSH/XSD (X = Cl and Br) are evaluated using hydrogenation working reactions method. By canonical variational transition-state theory (CVT), the rate constants of SH and SD radicals with Cl2, Br2, and BrCl are calculated over a wide temperature range of 200-2000 K at the a-QCISD(T)/6-311++G(3df, 2pd)//MP2/6-311G(d, p) level. Good agreement between the calculated and experimental rate constants is obtained in the measured temperature range. Our calculations show that for SH (SD) + BrCl reaction bromine abstraction (R3a or R3a') leading to the formation of BrSH (BrSD) + Cl in a barrierless process dominants the reaction with the branching ratios for channels 3a and 3a' of 99% at 298 K, which is quite different from the experimental result of k3a'/k3' = 54 +/- 10%. Negative activation energies are found at the higher level for the SH + Br2 and SH + BrCl (Br-abstraction) reactions; as a result, the rate constants show a slightly negative temperature dependence, which is consistent with the determination in the literature. The kinetic isotope effects for the three reactions are "inverse". The values of kH/kD are 0.88, 0.91, and 0.69 at room temperature, respectively, and they increase as the temperature increases. 相似文献
11.
A dual-level direct dynamic method is employed to study the reaction mechanisms of CF3CH2OCHF2 (HFE-245fa2; HFE-245mf) with the OH radicals and Cl atoms. Two hydrogen abstraction channels and two displacement processes are found for each reaction. For further study, the reaction mechanisms of its products (CF3CH2OCF2 and CF3CHOCHF2) and parent ether CH3CH2OCH3 with OH radical are investigated theoretically. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the B3LYP/6-311G(d,p) level. The energetic information along the MEPs is further refined at the G3(MP2) level of theory. For reactions CF3CH2OCHF2 + OH/Cl, the calculation indicates that the hydrogen abstraction from --CH2-- group is the dominant reaction channel, and the displacement processes may be negligible because of the high barriers. The standard enthalpies of formation for the reactant CF3CH2OCHF2, and two products CF3CH2OCHF2 and CF3CHOCHF2 are evaluated via group-balanced isodesmic reactions. The rate constants of reactions CF3CH2OCHF2 + OH/Cl and CH3CH2OCH3 + OH are estimated by using the variational transition state theory over a wide range of temperature (200-2000 K). The agreement between the theoretical and experimental rate constants is good in the measured temperature range. From the comparison between the rate constants of the reactions CF3CH2OCHF2 and CH3CH2OCH3 with OH, it is shown that the fluorine substitution decreases the reactivity of the C--H bond. 相似文献
12.
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. 相似文献
13.
14.
Calculation of microcanonical rate constants has been an important field in chemical dy-namic studies for many years because it can be used not only to give good prediction of rate con-stants in microcanonical assembly, but also to calculate rate constants with certain conserved quantum numbers such as the total angular momentum, and in turn, can be easily converted into thermal rate constants[1—3]. The widely used method for calculating microcanonical rate constants of unimolecular reac-tions… 相似文献
15.
We present a direct ab initio and hybrid density functional theory dynamics study of the thermal rate constants of the unimolecular decomposition reaction of C2H5O-->CH2O + CH3 at a high-pressure limit. MPW1K/6-31+G(d,p), MP2/6-31+G(d,p), and MP2(full)/6-31G(d) methods were employed to optimize the geometries of all stationary points and to calculate the minimum energy path (MEP). The energies of all the stationary points were refined at a series of multicoefficient and multilevel methods. Among all methods, the QCISD(T)/aug-cc-pVTZ energies are in good agreement with the available experimental data. The rate constants were evaluated based on the energetics from the QCISD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) level of theory using both microcanonical variational transition state theory (microVT) and RRKM theory with the Eckart tunneling correction in the temperature range of 300-2500 K. The calculated rate constants at the QCISD(T)/aug-cc-pVTZ/MPW1K/6-31+G(d,p) level of theory are in good consistent with experimental data. The fitted three-parameter Arrhenius expression from the microVT/Eckart rate constants in the temperature range 200-2500 K is k = 2.52 x 10(12)T(0.41)e(-8894.0/T) s(-1). The falloff curves of pressure-dependent rate constants are performed using master-equation method within the temperature range of 391-471 K. The calculated results are in good agreement with the available experimental data. 相似文献
16.
Wu Y Ding YH Xiao JF Li ZS Huang XR Sun CC 《Journal of computational chemistry》2002,23(14):1366-1374
Direct ab initio dynamic calculations are performed on the reactions of atomic hydrogen with GeD(n)(CH(3))(4-n) (n = 1-4) over the temperature range 200-2000 K at the PMP4SDTQ/6-311 +G(3df,2p)//MP2/6-31 +G(d) (for n = 2-4) and G2//MP2/6-31 +G(d) (for n = 1) levels. The corresponding k(H)/k(D) ratios are then calculated in order to determine the kinetic isotope effect for the four reactions. For the simplest GeD(4) +H reaction, the only one that has available experimental data, the calculated canonical variational transition state theory incorporates small-curvature tunneling correction (CVT/SCT) thermal rate constants, and the k(H)/k(D) values are in good agreement with the experimental values within the experimental temperature range 293-550 K. For the four GeD(n)(CH(3))(4-4) (n = 1-4) reactions, the variational effect is small over the whole temperature range, whereas the small-curvature effect is important in the lower temperature range. Finally, the overall rate constants are fitted to the three-parameter expression over the whole temperature range 200-2000 K as 5.8 x 10(8)T(1.68)exp(-929/T), 1.7 x 10(8)T(1.80)exp(-691/T), 2.58 x 10(8)T(1.71)exp(-706/T), and 1.0 x 10(7)T(2.08)exp(-544/T) cm(3) mol(-1) s(-1) for the n = 4, 3, 2, and 1 reactions. Our work may represent the first theoretical study of the kinetic isotope effect for the H-attack on the G-H bonding. 相似文献
17.
Wei Tian Wenliang Wang Yue Zhang Weina Wang 《International journal of quantum chemistry》2009,109(7):1566-1575
A theoretical study of the mechanism and the kinetics for the hydrogen abstraction reaction of methylamine by OH radical has been presented at the CCSD(T)/6‐311 ++G(2d,2p)//CCSD/6‐31G(d) level of theory. Our theoretical calculations suggest a stepwise mechanism involving the formation of a prereactant complex in the entrance channel and a preproduct complex in the exit channel, for the two hydrogen abstraction channels involving the methyl and amine groups. For clarity, the diagram of potential for the reaction is given. The calculated standard reaction enthalpies are ?98.48 and ?76.50 kJ mol?1 and barrier heights are 0.36 and 25.25 kJ mol?1, respectively. The rate constants are evaluated by means of the improved canonical variational transition state theory with small‐curvature tunneling correction (ICVT/SCT) in the temperature range of 299–3000 K. The calculated results show that the rate constants at experimentally measured temperatures are in good agreement with the experimental values. It is shown that the calculated rate constants exhibit a non‐Arrhenius behavior. Moreover, the variational effect is obvious in the calculated temperature range. The dominant product channel is to form CH2NH2 and H2O via hydrogen abstraction from the CH3 group of CH3NH2 by OH in the calculated temperature range. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
18.
The dual-level direct dynamics approach is employed to study the dynamics of the CH(3)OCH(3) + H (R1) and CH(3)OCH(3) + CH(3) (R2) reactions. Low-level calculations of the potential energy surface are carried out at the MP2/6-311+G(d,p) level of theory. High-level energetic information is obtained at the QCISD(T) level of theory with the 6-311+G(3df,3pd) basis set. The dynamics calculations are performed using variational transition state theory (VTST) with the interpolated single-point energies (ISPE) method, and small-curvature tunneling (SCT) is included. It is shown that the reaction of CH(3)OCH(3) with H (R1) may proceed much easier and with a lower barrier height than the reaction with CH(3) radical (R2). The calculated rate constants and activation energies are in good agreement with the experimental values. The calculated rate constants are fitted to k(R1) = 1.16 x 10(-19) T(3) exp(-1922/T) and k(R2) = 1.66 x 10(-28) T(5) exp(-3086/T) cm(3) mol(-1) s(-1) over a temperature range 207-2100 K. Furthermore, a small variational effect and large tunneling effect in the lower temperature range are found for the two reactions. 相似文献
19.
Qing Zhu ZHANG Chun Sheng WANG Yue Shu GU* School of Chemistry Chemical Engineering Shandong University Jinan Abstract: The 《中国化学快报》2002,13(12)
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… 相似文献
20.
Putikam Raghunath Yun‐Min Lee Shang‐Ying Wu Jong‐Shinn Wu Ming‐Chang Lin 《International journal of quantum chemistry》2013,113(12):1735-1746
Hydrogen atoms and SiHx (x = 1–3) radicals coexist during the chemical vapor deposition (CVD) of hydrogenated amorphous silicon (a‐Si:H) thin films for Si‐solar cell fabrication, a technology necessitated recently by the need for energy and material conservation. The kinetics and mechanisms for H‐atom reactions with SiHx radicals and the thermal decomposition of their intermediates have been investigated by using a high high‐level ab initio molecular‐orbital CCSD (Coupled Cluster with Single and Double)(T)/CBS (complete basis set extrapolation) method. These reactions occurring primarily by association producing excited intermediates, 1SiH2, 3SiH2, SiH3, and SiH4, with no intrinsic barriers were computed to have 75.6, 55.0, 68.5, and 90.2 kcal/mol association energies for x = 1–3, respectively, based on the computed heats of formation of these radicals. The excited intermediates can further fragment by H2 elimination with 62.5, 44.3, 47.5, and 56.7 kcal/mol barriers giving 1Si, 3Si, SiH, and 1SiH2 from the above respective intermediates. The predicted heats of reaction and enthalpies of formation of the radicals at 0 K, including the latter evaluated by the isodesmic reactions, SiHx + CH4 = SiH4 + CHx, are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and unimolecular reactions have been predicted with tunneling corrections using transition state theory (for direct abstraction) and variational Rice–Ramsperger–Kassel–Marcus theory (for association/decomposition) by solving the master equation covering the P,T‐conditions commonly employed used in industrial CVD processes. The predicted results compare well experimental and/or computational data available in the literature. © 2013 Wiley Periodicals, Inc. 相似文献