【作者】 孙昊；

【导师】 王荣顺；

【作者基本信息】 东北师范大学 ， 无机化学， 2006， 博士

【摘要】 乙烯酮(CH2CO)和氢氟烷(HFCs)与活泼自由基的反应在烃类燃烧过程和大气化学等方面有着举足轻重的作用。然而由于自由基的反应通常速度较快,反应机理复杂,对它们进行结构和动力学的实验研究一般具有相当大的难度。因此对这些反应的理论研究近年来备受关注。本论文利用量子化学计算方法研究了乙烯酮(CH2CO)和氢氟烷与大气中活泼自由基和原子的微观反应机理,并对氢氟烷系列反应的速率常数、产物分支比及其对温度的依赖关系做出了可靠的理论预测,为进一步的实验研究提供了理论依据。所有成果均属首次报道,并得到了国内外专家的普遍认可。本论文最重要的结果有以下六点:1.在QCISD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(d, p)水平上研究了CH2CO +O(3P)反应。结果表明,该反应存在两种反应机理,即羰基碳加成-消除机理和烷基碳加成-消除机理,最终能够生成五种产物,即CH2 + CO2,CO + CH2O,CCO + H2O,H + CO+ HCO和HCO + HCO。其中,CH2 + CO2 (P1)是最佳反应产物,我们的结论与DeMore课题组的结果比较吻合。2.在QCISD(T)/6-311++G (d, p)//B3LYP/6-311+G(d, p)水平上的理论计算结果表明,CH2CO与CN的反应有四种可能的机理:直接氢提取、烷基碳加成-消除、羰基碳加成-消除和氧加成-消除机理,并且每种机理都包括C主导和N主导的进攻。其中,直接氢提取的反应在动力学上是不利的。烷基碳加成消除生成CH2CN+CO的通道能垒低于其他任何通道,从动力学角度看该通道是最佳反应通道。上述两个结论与实验研究结果吻合较好。另外,烷基碳加成-消除生成P4(CH2NC+CO)的通道理论上是可以与该通道竞争的,而这一结论在Edwards的报道中没有体现。3.在QCISD(T)/6-311+G(d, p)//B3LYP/6-311+G(d, p)水平上对CH2CO + NCX (X=O,S)反应的微观机理和可能的反应路径进行了理论研究。计算结果表明:两个反应均包括直接的H提取和烷基碳加成-消除机理。NCX中的三个原子都可以提取CH2CO中的H。但是对于烷基碳加成-消除反应有所不同,两者都存在N进攻的反应通道,但当X=O时没有发现C进攻的通道,当X=S时,却没有发现S进攻的通道。烷基碳加成消除生成CH2NCO + CO的通道所需能垒最低,从动力学角度分析,被认为是CH2CO + NCO反应的最佳反应通道。这一与Edwards的实验结果是一致的。与其相似地,CH2NCS + CO是CH2CO + NCS反应的主要产物。4.利用双水平直接动力学方法研究了CH3CH2F + OH的直接氢提取反应。在MP2/6-311G(d, p)水平上获取相关的势能面信息,再采用G3方法进行高水平的单点能量校正。然后利用内推单点能量的变分过渡态理论(VTST-ISPE, Variational Transition StateTheory with Interpolated Single-Point Energies)计算了在210—3500 K的温度区间内反应更多还原

【Abstract】 The reactions of ketene (CH2CO) and hydrofluorocarbons (HFCs) with active radicalsplay important roles in various fields, such as combustion chemistry and atmosphericchemistry. Due to the short lives of the radicals and the difficulty to obtain the pure species,the experimental research for their structures and reaction features (especially the reactionmechanisms and the dynamics) is very difficult. Therefore, more and more attentions havebeen focused on their theoretical researches in recent years.With the quantum chemistry calculation methods, we studied the reactions of ketene(CH2CO) and hydrofluorocarbons (HFCs) with active radicals or atoms. The reactionmechanisms are theoretically investigated in detail, and rate constants and branching ratios arealso predicted. Our calculations provide the elementary theoretical evidence for furtherexperimental research. The most valuable results in this thesis can be summarized as follows:1. The mechanism for the CH2CO + O(3P) reaction is investigated at theQCISD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(d, p) level. The computational results showthat the reaction proceeds via two possible mechanisms, i.e., carbonyl carbonaddition-elimination mechanism and olefinic carbon addition-elimination mechanism. Fiveproducts, CH2+CO2,CO + CH2O,CCO + H2O,H + CO + HCO and HCO + HCO, aregenerated. With the lowest energy barrier, the pathway producing CH2 + CO2 dominates thetotal reaction and CH2 + CO2 is the main product. Our results provide the theretical evidencefor the experimental report of DeMore group.2. A detailed theoretical survey on the potential energy surface for the CH2CO + CN reactionis carried out at the QCISD(T)/6-311++G(d, p)//B3LYP/6-311+G(d, p) level. The reactionproceeds through four possible mechanism, i.e. direct hydrogen abstraction, olefinic carbonaddition-elimination, carbonyl carbon addition-elimination and side oxygen addition-elimination.Direct hydrogen abstraction is unfavorable kinetically. With the lowest energy, the olefinic carbonaddition-elimination channel to yield CH2CN+CO is most important among all the channels. Theabove conclusions are in good accordance with experimental results. Furthermore, the channelgenerating CH2NC + CO via olefinic carbon addition-elimination mechanism is considerablycompetitive especially as the temperature increases.3. The reactions of CH2CO with NCX(X=O, S) are theoretically investigated at the levelof QCISD (T)/6-311+G(d, p)//B3LYP/6-311+G (d, p). Our computational results suggest thatboth reactions can proceed via direct hydrogen abstraction mechanism and olefinic carbonaddition-elimination mechanism. The direct abstraction of one of the H atoms in CH2COmolecule by NCX may lead to HCCO + HNCX(PX-1), HCCO + HCNX(PX-2) and HCCO +HXCN(PX-3), respectively. There is some difference between their oefinic carbonaddition-elimination reactions. Both N and O can attack the oefinic carbon atom of CH2CO inthe reaction of CH2CO with NCO. As for CH2CO + NCS reaction, C-and N-attack is bothpossible, while S-dominating attack is not found. With the lowest barrier height, the channlegenerating CH2NCO + CO is considered as a kinetically favourable pathway, which was alsosummarized by Hershberger group. Similarly, CH2NCS + CO is theoretically proved to bemain product for CH2CO + NCS reaction.4. The hydrogen abstraction reaction of CH3CH2F + OH is studied by an ab initio directdynamics method. Three feasible channels and the three corresponding transition states, TS1,TS2a and TS2b are identified respectively. The rate constants over the temperature range of210—3500 K are calculated by canonical variational transition state theory (CVT) with thesmall-curvature tunneling correction (SCT) at the G3//MP2/6-311G(d, p) level. Thetheoretical rate constants and branching ratios are in good agreement with the experimentalvalues. The dynamics calculations also exhibit that α-H abstraction dominates the titlereaction from 210 to 800 K, and the reaction proceeds mainly via β-H abstraction in thetemperature higher than 800 K.5. The H-abstraction reaction of CH3CH2F + Cl is investigated by an ab initio directdynamics method. The potential energy surface (PES) information is obtained at theMP2/6-311G(d, p) level, and more accurate energies of stationary points are calculated at thelevel of QCISD(T)/6-311+G(3df, 2p) and G3(MP2). Both α-H abstraction and β-Habstraction are possible, and three transition states, TS1, TS2a and TS2b are identifiedrespectively. The rate constants over the temperature range of 220—2800 K are calculated bycanonical variational transition state theory (CVT) with the small-curvature tunnelingcorrection (SCT). The theoretical rate constants and branching ratio of k1/k agree well withthe experimental values. The dynamics calculations also exhibit that α-H abstractiondominates the title reaction almost over the whole temperature range.6. The potential energy surface (PES) information of the CH3CHF2 + Cl reaction is builtup at the G3(MP2)//MP2/6-311+G(d, p) level. With the ISPE method, the CVT/SCT rateconstants of the reaction are calculated over the temperature range of 200―2500 K. Thebranching ratios are also decided, as well as the dependence on the temperature. Thecalculated rate constant and branching ratios are both in accordance with the experimentalresults. The calculations also indicate that the rate constants over the temperature range 200―2500 K are fitted by the three-parameter expression: k = (4.62× 10-19)T 2.77 exp(-782.89/T).更多还原