现代化学动力学的奠基人—迈克尔.波兰尼

迈克尔·波兰尼(1891-1976),20世纪欧洲卓越的物理化学家和科学哲学家。因在化学动力学领域的开创性工作,尤其是创建了过渡态理论,被称为现代化学动力学奠基人之一。本文就迈克尔·波兰尼的生平及其对物理化学的贡献进行了论述。     

无处不在的化学——化学动力学

Starting from an example of how to extinguish a fire, this article illustrates how chemical dynamics plays a role in our life. It also introduces what is chemical dynamics and the contribution of Dutch chemist Jacobus H. van't Hoff to chemical dynamics. The horse racing analogy is used to illustrate how the amount of reactants, energy, catalysts and other factors affect the chemical reaction rate.     

化学动力学中的补偿效应

据Ａｒｒｈｅｎｉｕｓ方程，阐述了活化能与指前因子两个动力学参数在一定条件下对反应速率常数存在着相互补偿的线性关系，探讨了内在的原理以及研究中存在的问题与有关应用     

分形介质上的化学动力学

经典的化学反应速率理论，在一定程度上讲只适用于均相反应，非均相反应的化学动力学还很不成熟。最近十几年来，人们开始利用分形的概念来描述非均相反应体系中十分复杂的介质形态，并着手研究分形介质上的化学动力学理论，得到了一些大大不同于经典理论的结果。本文综述了该领域的研究成果与现状。     

过渡态理论在化学体系中的2个应用实例*

在大学本科一二年级的物理化学教学中,化学动力学章节的学习涉及到对不同时间尺度的认识。本文利用过渡态理论得到的速率常数表达公式,以乙烷分子碳/碳单键旋转和水分子氢键交换的动力学过程为例,对这2个应用实例的动力学过程所发生的时间尺度做出估算。这些时间尺度的估算对于学生理解不同动力学过程的物理图像至关重要,同时也有助于加强学生对重要公式的理解并能够将这些公式在化学体系中灵活运用。     

过渡态实验研究的进展

过渡态的实验研究是当今化学动力学重要课题之一.从80年代起,应用激光技术于过渡态的实验研究,证实了过渡态的存在。本文从(1)光助过渡区物种的反应.(2)光电子能谱探测过渡态.(3)实时追踪反应过程的飞秒化学诸方面介绍了近十多年来过渡态实验研究的原理及成果.     

甲烷与H02反应的微观动力学研究

应用从头算方法和变分过渡态理论，在B3LYP／6—3ll G^**方法下和300～2000K温度范围内研究甲烷与HO2反应的微观动力学特性，得到由过渡态向反应物方向、向产物方向的能垒分别是11．83和l02．90kJ／mol。理论计算正向反应速率常数与实验值之比为1．08～2．85，用此方法还可以预测没有实验数据的温度点反应的速率常数。     

化学动力学的发展与百年诺贝尔化学奖

探讨了化学动力学三大发展阶段 (宏观反应动力学阶段、元反应动力学阶段和微观反应动力学阶段)中诺贝尔化学奖的 13次颁发对其发展的影响。     

化学动力学的建立与发展概略

回顾了化学动力学的发展历史,介绍了化学动力学的近期研究成果,指出理论与实验的紧密配合是推动这一研究领域持续发展的强大动力。     

Dynamical derivation of Eyring equation and the second‐order kinetic law

Elementary gas‐phase reactions of the bimolecular type A + B → Products are characterized by the second‐order kinetic law , where [A] and [B] are the concentrations of A and B species, t is the time, and k is the rate constant, usually estimated by means of Eyring equation. Here, we show that its dynamical derivation, as such, is not consistent with the second‐order law. This contradiction is however removed by introducing a correlation between what we call potentially reactive pairs. A new presentation of the dynamical derivation of Eyring equation is finally proposed on the basis of the previous findings. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2355–2359, 2010     

Dual-level direct dynamics studies for the reactions of OH radical with bromine-substituted ethanes

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.     

Theoretical study and rate constant calculation for reaction of CF(3)CH(2)OH with OH

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.     

CH3NHNH2 + OH reaction: Mechanism and dynamics studies

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 k_T = 1.6 × 10^?24T^4.03exp (1411.5/T) cm³ molecule^?1 s^?1 between 200–1000 K. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

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 and rate constant calculations of the reactions C2F5CHO with OH radicals and Cl atoms

The hydrogen abstraction reactions of C₂F₅CHO with OH radicals and Cl atoms have been investigated theoretically by a dual-level direct dynamics method. In this study, the optimized geometries and frequencies of the stationary points are calculated at the MP2/cc-pVDZ level of theory. The energies of the stationery points and the selected points along the minimum energy paths are further refined at the MC-QCISD level using the MP2 geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of the two reactions. This result indicates that both of reactions proceed via indirect reaction mechanisms. The enthalpies of formation for the reactant C₂F₅CHO and the product radical C₂F₅CO are estimated by isodesmic reactions at the MC-QCISD//MP2/cc-pVDZ level. At the same level, the rate constants are calculated by canonical variational transition state theory (CVT) incorporating with the small-curvature tunneling correction (SCT) in the temperature range 200–1000 K. Good agreement between the calculated and experimental rate constants is obtained at the room temperature. Due to the lack of the kinetic data of these reactions, the fitted three-parameter expressions based on the CVT/SCT rate constants within 200–1000 K are k₁ = 1.64 × 10⁻²⁴ T^4.33 exp (−566.1/T) and k₂ = 6.33 × 10⁻¹⁵ T^1.35 exp (550.3/T) cm³ molecule⁻¹ s⁻¹, respectively.     

Theoretical study on the Br + CH3SCH3 reaction

The multiple-channel reactions Br + CH(3)SCH(3) --> products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6-31+G(d,p) level, and energetic information is further refined by the G3(MP2) (single-point) theory. The rate constants for every reaction channels, Br + CH(3)SCH(3) --> CH(3)SCH(2) + HBr (R1), Br + CH(3)SCH(3) --> CH(3)SBr + CH(3) (R2), and Br + CH(3)SCH(3) -->CH(3)S + CH(3)Br (R3), are calculated by canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200-3000 K. The total rate constants are in good agreement with the available experimental data, and the two-parameter expression k(T) = 2.68 x 10(-12) exp(-1235.24/T) cm(3)/(molecule s) over the temperature range 200-3000 K is given. Our calculations indicate that hydrogen abstraction channel is the major channel due to the smallest barrier height among three channels considered, and the other two channels to yield CH(3)SBr + CH(3) and CH(3)S + CH(3)Br are minor channels over the whole temperature range.     

Theoretical study for the reaction of CH3OCl with Cl atom

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.     

Ab initio direct dynamics studies on the reactions of chlorine atom with CH3-nFnCH2OH (n = 1-3)

The hydrogen abstraction reactions of Cl atom with a series of fluorinated alcohols, i.e., CH(3-n)F(n)CH(2)OH + Cl (n = 1-3) (R1-R3) have been studied systematically by ab initio direct dynamics method and the canonical variational transition state theory (CVT). The potential energy surface information is calculated at the MP2/6-311G(d,p) level. Energies along the minimum energy paths are improved by a series of single-point calculations at the higher modified GAUSSIAN-2 (G2M) level of theory. Theoretical analysis shows that three kinds of hydrogen atoms can be abstracted from the reactants CH(2)FCH(2)OH and CHF(2)CH(2)OH, and for CF(3)CH(2)OH, two possible pathways are found. The rate constants for each reaction channel are evaluated by CVT with the small-curvature tunneling correction (SCT) over a wide range of temperature from 200 to 2000 K. The calculated CVT/SCT rate constants are in good agreement with the available experimental values for the reactions CHF(2)CH(2)OH + Cl and CF(3)CH(2)OH + Cl. However, for the reaction CH(2)FCH(2)OH + Cl, there is negative temperature dependence below 500 K, which is different from the experimental fitted. It is shown that in the low temperature ranges, the three reactions all proceed predominantly via H-abstraction from the methylene positions, and with the increase of the temperature the H-abstraction channels from the fluorinated-methyl positions should be taken into account, while the H-abstraction channels from the hydroxyl groups are negligible over the whole temperature ranges. Also, the reactivity decreases substantially with fluorine substitution at the methyl position of alcohol.