共查询到18条相似文献,搜索用时 281 毫秒
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研究了微正则系综下单分子反应速率常数的理论计算公式,并将曲率因子A引入含振动和转动的隧道几率表达式中,进而得到了反应速率常数表达式。应用该式研究了F─C≡C─H反应的氢迁移过程的转动选态及曲率因子对反应速率常数的影响。结果表明:在隧道效应区域内,曲率因子对速率常数的影响比较显著,它将引起速率常数的增加;转动选态对速率的影响不太明显。 相似文献
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用从头算方法计算了反应CH(^4∑^-)+H2O→CH2(^3B1)+OH的反应途径。在此基础上, 计算沿反应途径的动态学性质和正则变分过渡态理论的速率常数, 并进行隧道效应校正。结果表明, 电子相关能对反应活化位垒影响较大; 反应存在返回效应和隧道效应, 用正则变分过渡态方法和小曲率近似的隧道校正是有效的。 相似文献
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采用直接动力学的方法,对多通道反应体系Br+CH3S(O)CH3进行了理论研究.在BH&H-LYP/6-311G(2d,2p)水平下获得了优化几何构型、频率及最小能量路径(MEP),能量信息的进一步确认在MC-QCISD(单点)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(CVT/SCT)方法计算了该反应的两个可行的反应通道在200K~2000K温度范围内的速率常数.在整个反应区间内,生成HBr的反应通道与生成CHa的反应通道存在着竞争,前者是主反应通道,后者是次反应通道.变分效应和小曲率隧道效应对反应速率常数的计算影响都很小.理论计算得到的两个反应通道的反应速率常数与实验值符合得很好. 相似文献
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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。 相似文献
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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。 相似文献
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CH+H_2→CH_3的MCSCF和VTST研究 总被引:1,自引:0,他引:1
用福井的内禀反应坐标理论和MCSCF/6-31G方法计算了CH+H_2→CH_3的反应途径。在此基础上,计算了沿反应途径的动态学行为和变分过渡态理论(VTST)的速率常数(包括CVT,ICVT,/VT和US方法)。结果表明,反应的返回效应不大;但反应途径的曲率效应较大,它对速率常数影响较大,理论研究必须考虑这一因素。 相似文献
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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. 相似文献
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FENG Wen-Lin ZHANG Shao-Wen WANG Yan WU Jun-Nan LI Zong-HeDepartment of Chemistry Beijing Normal University Beijing China 《中国化学》1995,13(5):391-395
The microcanonical rate constants for the hydrogen-transfer process of HCCF (reaction 7) and the fluoro-transfer process of FCCF (reaction 8) are carried out with tunneling correction and curvature correction. The results show that the tunneling effects and curvature effects on the rate constant of reaction 7 is quite different from that of reaction 8. The rate constants for different rotational states are also studied for these reactions. 相似文献
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Shen-Min Li Xin Yu Zhen-Feng Xu Ze-Sheng Li Chia-Chung Sun 《Journal of Molecular Structure》2001,540(1-3):221-229
Ab initio direct dynamics method has been used to study the title reaction. Electronic structure information including geometries, gradients and force constants (Hessians) are calculated at the UQCISD/6-311+G** level. Energies along the minimum energy path are improved by a series of single-point G2//QCISD calculations. The changes of the geometries, vibratioanal frequencies, potential energies and total curvature along the reaction path are discussed. The rate constants in the temperature range 200–3000 K are calculated by canonical variational transition state theory with small-curvature tunneling correction (CVT/SCT) method. The results show that the variational effect is small and in the lower temperature range, the small curvature tunneling effect is important for the reaction. 相似文献
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Ab initio study on the kinetics of hydrogen abstraction for the H+alkene-->H2+alkenyl reaction class
Huynh LK Panasewicz S Ratkiewicz A Truong TN 《The journal of physical chemistry. A》2007,111(11):2156-2165
Kinetics of the hydrogen abstraction reaction class of the H+alkene has been studied using the reaction class transition state theory (RC-TST) combined with the linear energy relationship (LER) and the barrier height grouping (BHG) approach. The rate constants for the reference reaction, H+C2H4, were obtained by the canonical variational transition state theory (CVT) with the small curvature tunneling (SCT) correction in the temperature range of 300-3000 K. Combined with these data, both the RC-TST/LER, where only reaction energy is needed, and RC-TST/BHG, where no other information is needed, are found to be promising methods for predicting rate constants for a large number of reactions in this reaction class. Our analysis indicates that less than 50% systematic errors on the average exist in the predicted rate constants using the RC-TST/LER or RC-TST/BHG method while in comparison to explicit rate calculations the differences are less than 100% or a factor of 2 on the average. 相似文献
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采用双水平直接动力学方法对C2H3与CH3F氢抽提反应进行了研究. 在QCISD(T)/6-311++G(d, p)//B3LYP/6-311G(d, p)水平上, 计算的三个反应通道R1、R2和R3的能垒(ΔE≠)分别为43.2、43.9和44.1 kJ·mol-1, 反应热为-38.2 kJ·mol-1. 此外, 利用传统过渡态理论(TST)、正则变分过渡态理论(CVT)和包含小曲率隧道效应(SCT)的CVT, 分别计算了200-3000 K温度范围内反应的速率常数kTST、kCVT和kCVT/SCT. 结果表明: (1) 三个氢抽提反应通道的速率常数随温度的增加而增大, 其中变分效应的影响可以忽略, 隧道效应则在低温段影响显著; (2) R1反应是主反应通道, 但随着温度的升高, R2反应的竞争力增大, 而R3反应对总速率常数的影响很小. 相似文献
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Kun Wang Jian‐Guo Zhang Tian‐Tian Man Man Wu Shao‐Wen Zhang Tong‐Lai Zhang Li Yang 《International journal of quantum chemistry》2013,113(9):1358-1364
It is believed that the dehydrogenation of LiNH2BH3 (LAB) proceeds through a combination of the decomposition of the LiBH2NH3 (LBA) and LAB isomers. The dehydrogenation of LBA, an isomer of LAB, is discussed in this article. It is demonstrated that the loss of H2 from LBA takes place in a two‐step reaction. Studies of the dehydrogenation process were performed using Møller–Plesset second‐order perturbation theory with a 6‐311++G(3df,2pd) basis set. The intrinsic reaction coordinate was calculated to determine the minimum energy paths. Finally, the rate constants were obtained using the transition‐state theory (TST), TST/Eckart, canonical variational transition‐state theory (CVT), CVT/small‐curvature tunneling correction, and CVT/zero‐curvature tunneling correction methods from 200 to 2500 K. This is the first report on a different dehydrogenation mechanism for an alkali‐metal amidoborane, and the energy barrier of LBA is much lower than that of the traditionally studied LAB. © 2012 Wiley Periodicals, Inc. 相似文献
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The hydrogen abstraction reaction of Cl atoms with CF3CH2Cl (HCFC‐133a) is investigated by using density function theory and ab initio approach, and the rate constants are calculated by using the dual‐level direct dynamics method. Optimized geometries and frequencies of reactants, transition state, and products are computed at the B3LYP/6‐311+G(2d,2p) level. To refine the energetic information along the minimum energy path, single‐point energy calculations are carried out at the G3(MP2) level of theory. The interpolated single‐point energy method is employed to correct the energy profiles for the title reaction. The rate constants are evaluated by using the canonical variational transition state theory with a small‐curvature tunneling correction over a wide range of temperature, 200–2000 K. The variational effect for the reaction is moderate at low temperatures and very small at high temperatures. However, the tunneling correction has an important contribution in the lower temperature range. The agreement between calculated rate constants and available experimental values is good at lower temperatures but diverges significantly at higher temperatures. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 661–667, 2012 相似文献
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Molecules can be exposed to strong local electric fields of the order of 10(8)-10(10) V m(-1) in the biological milieu. The effects of such fields on the rate constant (k) of a model reaction, the double-proton transfer reaction in the formic acid dimer (FAD), are investigated. The barrier heights and shapes are calculated in the absence and presence of several static homogenous external fields ranging from 5.14 × 10(8) to 5.14 × 10(9) V m(-1) using density functional theory (DFT/B3LYP) and second order M?ller-Plesset perturbation theory (MP2) in conjunction with the 6-311++G(d,p) Pople basis set. Conventional transition state theory (CTST) followed by Wigner tunneling correction is then applied to estimate the rate constants at 25 °C. It is found that electric fields parallel to the long axis of the dimer (the line joining the two carbon atoms) lower the uncorrected barrier height, and hence increase the raw k. These fields also flatten the potential energy surface near the transition state region and, hence, decrease the multiplicative tunneling correction factor. The net result of these two opposing effects is that fields increase k(corrected) by a factor of ca. 3-4 (DFT-MP2, respectively) compared to the field-free k. Field strengths of ~3 × 10(9) V m(-1) are found to be sufficient to double the tunneling-corrected double proton transfer rate constant at 25 °C. Field strengths of similar orders of magnitudes are encountered in the scanning tunneling microscope (STM), in the microenvironment of a DNA base-pair, in an enzyme active site, and in intense laser radiation fields. It is shown that the net (tunneling corrected) effect of the field on k can be closely fitted to an exponential relationship of the form k = aexp(bE), where a and b are constants and E the electric field strength. 相似文献