F和CH_3OH多通道反应的速率常数与分支比的研究（英文）

F和CH_3OH有两个夺氢反应通道,分别生成HF+CH_3O和HF+CH_2OH.尽管这两个通道都没有能垒,但前一个通道即生成HF+CH_3O的反应分支比远远高于期望的统计平均值(四分之一).不同实验测得的分支比不仅相去甚远,而且定量上与早期由过渡态理论(稳定点信息在MP2以及G2理论水平下计算得到)得到的计算结果也不符合.此前在CCSD(T)-F12a/AVDZ水平上计算得到了121000个几何构型的能量,采用对易不变多项式结合神经网络的方法拟合得到了该体系的全维高精度势能面.本文采用该势能面,结合准经典轨线动力学方法,对该反应的反应速率常数和反应分支比进行了理论研究,得到的结果与实验吻合.由于反应没有能垒,理论计算结果表明反应速率常数随温度升高而有微弱的下降趋势.     

OH+C2H3F的反应机理及产物支化比反应的理论研究

本文对HOC₂H₃F可能解离通道的势能面进行从头算CCSD(T)/CBS//B3LYP/6-311G(d,p)计算,同时对速率常数进行Rice-Ramsperger-Kassel-Marcus计算. 生成主要产物CH₂CHO+HF最有利的反应途径是OHC₂H₃F→i2→TS14→i6→TS9→i3→TS3→CH₂CHO+HF,其中速率决定步骤是HF通过TS11从CO桥接位置解离,能量比反应物高3.8 kcal/mol. 借助中间态TS14,F原子从C_α迁移到C_β位置生成CH₂O+CH₂F,然后通过中间态TS16,H从O迁移到C_α位置;通过中间态TS5,C-C键断裂生成产物,其能量比反应物低1.8 kcal/mol,比TS11低4.0 kcal/mol.     

对典型多通道反应H+CH3OH的模式特异动力学研究

H+CH₃OH作为典型的多通道反应,在燃烧和星际中起着重要的作用. 本文基于在UCCSD(T)-F12a/AVTZ水平上计算的大量数据点,构建了该体系的全维精确势能面,并基于该势能面,研究了不同产物通道的模式特异动力学. 结果表明,O-H 伸缩、沿C-O轴的扭转以及C$-$H伸缩等模式的振动激发对H₂+CH₃O、H₂+CH₂OH、H₂O+CH₃和H+CH₃OH四个产物通道有着不同的影响. 该研究有助于理解具有多个产物通道的复杂反应的模式特异动力学,进而帮助控制其竞争反应.     

F+H2O→HF+OH反应的高精度速率常数的计算研究

F+H₂O→HF+OH是四原子反应的典型代表,并在环境和天体化学中扮演着重要角色. 基于全维势能面,本文采用环-聚合分子动力学(RPMD)方法计算了该反应的速率常数. 该势能面可以重现高精度理论化学水平(FPA和HEAT)上得到的反应能垒和放热数据,它是目前该体系的最准确势能面. RPMD方法重现了之前半经典过渡态理论结合两维主方程得到的速率常数,二者都与实验结果高度吻合. RPMD方法可以高效可靠地考虑量子效应,如量子隧穿和零点能效应等. 另外,RPMD计算结果随珠子数量增加收敛较快,这些都与之前RPMD的诸多计算应用发现的结论一致.     

全维高精度势能面上F+CH3OH反应的产物振动态分布

甲醇与氟原子之间的抽氢反应可以生成HF和CH₃O、CH₂OH自由基等产物. 该反应在环境化学、燃烧化学、辐射化学和星际化学中都非常重要. 基于之前构建的全维高精度势能面,本文采用准经典轨线方法研究了该典型反应的动力学. 特别是使用正则模式分析方法确定了多原子产物CH₃O和CH₂OH的振动态分布. 研究发现,当反应物处于振转基态时,CH₃O和CH₂OH主要分布在基态. 当反应物CH₃OH的OH伸缩模式激发为第一激发态时,产物CH₂OH的OH伸缩模式、扭转模式、H₂CO 面外弯曲模式及其组合会被有效激发. 在两条通道中,可用能量大部分都流入HF的振动能和产物的平动能,而自由基产物CH₃O或CH₂OH只得到非常少的能量,与实验结果一致,这也表明了自由基的旁观者性质.     

F+H2O/D2O→HF+OH反应的准经典轨迹研究：能垒、反应物转动激发和同位素取代的影响 (cited: 4)

在新构建的含旋轨耦合校正的FH₂O基态势能面上,采用准经典轨迹方法详细研究了F+H₂O/D₂O→HF/DF+OH/OD的反应动态学．氢和氘抽取反应经过较低的类反应物过渡态直接发生反应,生成振动激发的HF/DF和内能较低的OH/OD产物．由于新构建的势能面能垒较低,得到的积分反应截面与实验值吻合．但新势能面对产物态分布和模式选择性影响较小．理论计算结果显示H2O的转动态激发对反应有很强的促进作用,说明其与反应坐标耦合紧密．     

密度泛函理论研究α-MoC(100)在甲醇水蒸汽重整中的催化作用

本文通过密度泛函理论计算方法探究了α-MoC催化甲醇水蒸气重整(CH₃OH+H₂O→CO₂+3H₂)反应,系统地研究了甲醇水蒸气重整反应中相关中间体的吸附行为和基本步骤的动力学. 结果表明,在α-MoC(100)表面,甲醇容易裂解形成CH₃O中间体,CH₃O进一步脱氢为CH₂O. 通过比较CH₂O和OH缔合过程和CH₂O直接分解过程,发现CH₂O和OH之间更容易形成CH₂OOH而不是分解成CHO和H. 计算结果表明,CH₂OOH中间体的连续脱氢对CO₂有很高的选择性. 相反,在α-MoC(111)表面,由于CH₂O中间体的强吸附使其更偏向于脱氢生成CHO,最后生成产物CO. 此外,高水解离产生的OH物种可以促进中间体O-H键的断裂,并显著降低反应能垒. 本文不仅揭示了α-MoC(100)晶面在甲醇水蒸气重整反应中的催化作用,也为α-MoC基催化剂的设计提供了理论指导.     

氘代烷基卤化物CD3CH2F光解动态学的理论研究

在燃烧或大气化学多通道反应中,理解不同产物之间的产品分支比与反应的总速率,对这类基元反应同样重要. 在CCSD(T)/CBS/B3LYP/aug-cc-pVDZ理论水平上,计算所有氘代烷基卤化物CD₃CH₂F物种的基态势能面. 在CD₃CH₂F的解离反应中,C-F键解离反应与分子(HF、DF、H₂、D₂与HD)消除反应存在着争议. 本文使用RRKM方法计算各个步骤的速率常数,并使用稳态方法计算解离产物的相对产物分支比. 在不同的能量下,RRKM方法预测CD₃CH₂F的1,2-消除DF或HF的主要通道是通过四中心过渡态消除,而1,1-消除D₂或H₂的主要通道是通过三中心过渡态消除. 在266、248和193 nm光解时,主产物CD₂CH₂+DF分支比分别为96.57%、91.47%和48.52%;然而,在157 nm光解时,产物分支比计算为16.11%. 基于这些过渡态结构和能量,提出了以下光解离机制：在266、248和193 nm,CD₃CH₂F→吸收光子→TS5→形成产物→CD₂CH₂+DF;在157 nm,CD₃CH₂F→吸收光子→D/F交換的TS1→CDH₂CDF→H/F交换的TS2→CHD₂CHDF→形成产物CHD₂+CHDF.     

硫酸催化乙二醛气体相水化反应机理和速率常数理论计算研究

采用M06-2X和CCSD(T)高阶量化计算和传统过渡态理论研究硫酸催化乙二醛气体相水化反应.对HCOCHO+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O...H₂SO₄和HCOCHO+H₂O+H₂SO₄五个路径的反应机理和速率常数进行了研究.计算结果表明硫酸具有较强的催化能力,能显著减小乙二醛水化反应的能垒,在CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)理论水平,当硫酸分子参与乙二醛水化反应时,反应能垒从37.15 kcal/mol减少至7.08 kcal/mol.在室温条件下,硫酸催化乙二醛水化反应的反应速率1.34×10^-11 cm³/(molecule.s),是等量水分子参与乙二醛水化反应的速率的10¹²倍,大于乙二醛与OH自由基反应的反应速率1.10×10^-11 cm³/(molecule.s).这表明大气条件下,硫酸催化乙二醛水化反应可以发生,同乙二醛与OH自由基反应相竞争.     

气相中自由基OH在不同催化剂下对甲酰氟FCHO进行提氢反应的理论性研究

分别在水、甲酸和硫酸存在的情况下,通过CCSD(T)//M06-2X/6-311++G(3df,3pd)的理论方法,对大气中自由基OH提取甲酰氟FCHO上的氢进行了反应机理和动力学的研究.计算结果表明相对于反应物,加入催化剂的过渡态的能垒从3.64 kcal/mol分别下降到-2.89、-6.25和-7.76 kcal/mol,表明水、甲酸和硫酸在甲酰氟FCHO和自由基OH提氢反应中起了重要作用.通过运用具有Eckart隧道校正的传统过渡态理论计算出的动力学数据表明通道X...FCHO+OH(X=H₂O, HCOOH,或者H₂SO₄)要比通道X...OH+FCHO更有利于反应的发生.催化剂水、甲酸和硫酸的加入使甲酰氟FCHO 和自由基OH提氢反应的速率常数要比不加催化剂时小,说明了催化剂的加入不能促进大气中甲酰氟FCHO和自由基OH的反应.     

Use of cw-CRDS for studying the atmospheric oxidation of acetic acid in a simulation chamber

The coupling between cavity ring-down spectroscopy (CRDS) and an environmental chamber in the investigation of photo-induced reaction mechanisms is demonstrated for the first time. The development of the CRDS device and the corresponding analytical performances are presented. The first application is devoted to the investigation of the branching ratio of the ^?OH radical reaction of CH₃C(O)OH and CH₃C(O)OD under tropospheric conditions. An environmental chamber coupled to two complementary detection systems is used:

gas chromatography with FTIR spectroscopy for quantitative detection of acetic acid;

CRDS for quantitative detection of CO₂.

Investigation of the reaction kinetics of ^?OH+CH₃C(O)OH gives a rate constant of (6.5±0.5)×10^-13 cm³?molecule^-1?s^-1 (296 K) and shows good agreement with literature data. The product study indicates that the H-abstraction channel from the acid group is the dominant pathway with a branching ratio of (78±13)%, whereas the corresponding D-abstraction channel in the ^?OH+CH₃C(O)OD reaction represents only (36±7)%. This result could be attributed to a strong kinetic isotope effect. Glyoxylic acid has also been detected for the first time as by-product. These results illustrate the high interest of the CRDS technique in the investigation of atmospheric relevant problems.     

Direct ab initio molecular dynamics study of F atom reaction with methane

The dynamics of the F + CH₄ → HF + CH₃ and F + CD₄ → DF + CD₃ reactions have been investigated using classical trajectory calculations at the MP2/cc-pvdz level of theory. The trajectories were calculated directly from electronic structure computations, and a Hessian based method with updating was used to integrate the trajectories. Using this method, product rovibrational populations and internal energy distributions were obtained for the F + CH₄ and F + CD₄ reactions. The theoretical results were compared with the available experimental data and previous calculations results. The state distributions of the reaction F + CH₄ in these calculations are in reasonable agreement with the experimental results, which indicates that the experimental behavior of the reaction could be well reproduced by the direct classical trajectory calculations at MP2/cc-pvdz level. As such, the product rovibrational populations and internal energy distributions for the reaction F + CD₄ were predicted. The same degree of agreement between theory and experiment as the F + CH₄ reaction is expected.     

Theoretical study of the hydrogen abstraction reaction of CH3OH with NCO

A direct dynamics method is employed to study the mechanism and kinetics of the hydrogen abstraction reaction of CH₃OH with NCO. The optimized geometries and frequencies of the stationary points and the minimum-energy paths (MEPs) are obtained at the MP2/6-311G(d,p) level. In order to obtain more accurate potential energy surface (PES) information and provide more credible energy data for kinetic calculation, the single-point energies along the MEPs are further computed at QCISD(T)/6-311+G(d,p) and G3MP2 levels. The rate constants for two channels, the methyl-H abstraction channel and hydroxyl-H abstraction channel, are calculated by canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over the wide temperature region 220–1500?K. The theoretical overall rate constants are in good agreement with the available experimental data. For the title reaction, the methyl-H abstraction channel is dominant, while the hydroxyl-H abstraction channel is negligible over the whole temperature region.     

A computational perspective on the kinetics and thermochemistry of the gas phase reactions of 1, 1-dichlorodimethylether (DCDME) with OH radical at 298 K

Kinetics and thermochemistry of the gas phase reactions between CH₃OCHCl₂ (DCDME) and OH radical are investigated theoretically. The geometries and all the stationary points on the potential energy surface are calculated at BHandHLYP/6-311G(d,p) method. The energy information is further refined at CCSD(T)/6-311G(d,p) level of theory. Reaction profiles are modelled including the formation of two pre-reactive and post-complexes. The rate constants, which are evaluated by Canonical Transition State Theory (CTST) including tunnelling correction at 298 K, are in very good agreement with the available experimental data. The percentage contributions of both reaction channels are also reported at 298 K. The hydrogen abstraction reaction from the –CHCl₂ group is found to be dominant leading to the formation of CH₃OCCl₂ + H₂O. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CH₃OCHCl₂, CH₃OCCl₂ and CH₂OCHCl₂ are also reported.     

O(1D)和CD4反应的准经典轨线

在新的全域势能面上, 用准经典轨线方法细致地研究了O(¹D)+CD₄多通道化学反应的动力学．这个势能面是用交换不变多项式方法基于MRC+Q/aug-cc-pVTZ从头算点拟合得到的．通过计算得到了产物OD+CD₃、D+CD₂OD/CD₃O和D₂+DCOD/D₂CO的分支比、平动能分布以及角度分布,结果显示理论与实验吻合得较好, 从而说明了这个反应的同位素取代效应很小． 研究表明,O(¹D)+CD₄反应是经过陷入的抽取机理发生的： 最初主要通过D原子的抽取,并不是之前人们认为的直接C-D键的插入形成CD3OD中间物后再进而解离成各个产物通道．     

Theoretical study of the reaction 2,5-dimethylfuran + H → products

The reaction of 2,5-dimethylfuran (DMF) with H-atoms was studied using a potential energy surface calculated at the CBS-QB3 level of theory and master equation/RRKM modeling. Hydrogen abstraction by H-atom and hydrogen additions on DMF were considered. As the decomposition pathways of the initial adducts were unknown, a large number of decomposition routes was explored for these adducts. An important number of interconnected product channels were found and preliminary master equation calculations were performed to select the crucial wells and exit channels. The ipso substitution DMF + H → methylfuran (MF) + CH₃ and the formation of 1,3-butadiene and acetyl radical (CH₃CO) were found to be the major product channels in the addition process. The total calculated rate constant was found in good agreement with experimental data and is nearly pressure-independent. A small sensitivity to pressure was found for the computed branching ratios. At 1 bar, the yields of the two product channels of the addition process are maximal at 1100 K with computed branching ratios of 39% (MF + CH₃) and 27% (1,3-C₄H₆ + CH₃CO). Above 1300 K, hydrogen abstraction by H-atom becomes dominant and reaches a branching ratio of 56% at 2000 K.     

Exploring the reaction channels between arsine and the hydroxyl radical

The aim of this study was to present the reaction mechanism channels between arsine (AsH₃) and hydroxyl (OH) which was evaluated at CCSD(T)/CBS//CCSD/cc-pVTZ level. One potential channel is the hydrogen abstraction pathway (R1), leading to AsH₂ and H₂O products, which occurs due to the formation of an entrance complex (AsH₃OH) followed by a 1,2-hydrogen shift pathway (involving the proton transfer from the arsine group to hydroxyls, with one leading to the products). Additional channels are accessed via H-elimination pathways of the entrance complexes, forming arsinous acid (AsH₂OH; R2) and arsine oxide (AsH₃O; R3). In this respect, R2 is the only exoergic route of the three exit channels, representing the major branching ratio at 200–1000 K and, after 2000 K, R1 increases gradually becoming the major route of this reaction. In contrast, even at 4000 K, R3 is a highly unfeasible pathway. Therefore, the information predicted here provides new insights into the neutral–neutral chemical reaction dynamics regarding the Group V hydrides. On the other side, the R2 pathway may have some potential to solve the arsine oxidation puzzle as a possible primary pathway to the arsenic-oxygen species formation.     

Theoretical study on the mechanism of the reaction of FOX-7 with OH and NO2 radicals: bimolecular reactions with low barrier during the decomposition of FOX-7

The decomposition of 1,1-diamino-2,2-dinitroethene (FOX-7) attracts great interests, while the studies on bimolecular reactions during the decomposition of FOX-7 are scarce. This study for the first time investigated the bimolecular reactions of OH and NO₂ radicals, which are pyrolysis products of ammonium perchlorate (an efficient oxidant usually used in solid propellant), with FOX-7 by computational chemistry methods. The molecular geometries and energies were calculated using the (U)B3LYP/6-31++G(d,p) method. The rate constants of the reactions were calculated by canonical variational transition state theory. We found three mechanisms (H-abstraction, OH addition to C and N atom) for the reaction of OH + FOX-7 and two mechanisms (O abstraction and H abstraction) for the reaction of NO₂ + FOX-7. OH radical can abstract H atom or add to C atom of FOX-7 with barriers near to zero, which means OH radical can effectively degrade FOX-7. The O abstraction channel of the reaction of NO₂ + FOX-7 results in the formation of NO₃ radical, which has never been detected experimentally during the decomposition of FOX-7.