【作者】 许保恩；

【导师】 孟令鹏； 李晓艳；

【作者基本信息】 河北师范大学 ， 物理化学， 2009， 硕士

【摘要】 含硫、含氮物种已成为大气环境污染的一个重要因素,会导致环境的恶化、酸雨的形成和光化学烟雾等,在大气化学和燃烧化学发挥着重要的作用。CH3SH是含硫有机物中的重要瞬态物种,约占大气中有机硫化物的10%。HNCS是同时含硫、含氮的气相小分子,能从燃烧的废气中除去有毒的化合物。因此,对这些含硫、含氮小分子的稳定性及其在大气中的反应活性进行研究有非常重要的意义。本论文以量子化学理论和过渡态理论为基础,利用密度泛函理论、微扰理论、组态相互作用理论、耦合簇理论和分子中原子理论,对CH3SH、HNCS与大气中活泼自由基和原子的几个反应体系进行详细地研究,通过计算反应中各物种的优化构型、振动频率,体系的势能面,各通道的速率常数,深入揭示了反应体系的微观反应机理和动力学特征。论文共分六章。第一章介绍了近年来国内外对CH3SH及其自由基、HNCS的实验和理论研究现状。第二章对现代量子化学基本原理、过渡态理论和量子拓扑学原理进行了简单介绍。第三章对CH3SH与CN自由基反应的微观机理进行了理论研究。第四章对CH3SH与基态NO2的反应机理和动力学进行了研究。第五、第六章分别对HNCS与H原子、Cl原子的反应机理和动力学进行了研究。主要结论和创新点:1.在CCSD//B3LYP/6-311++G(d,p)水平上研究了CH3SH与CN自由基的微观反应机理,找到了三个可能的反应通道,其中生成CH3S+HCN的通道为主通道,并成功地解释了Brian等的实验结论。通过对反应进程中一些重要点的电子密度拓扑分析,讨论了反应进程中化学键的变化规律,发现了六元环状过渡结构。2.在G3B3,CCSD(T)//B3LYP/6-311++G(d,p)水平上研究了CH3SH与基态NO2的微观反应机理,利用正变分过渡态理论(CVT) (SCT),并得到了200～3000 K温度范围内的经小曲率隧道效应模型速率常数校正的速率常数和三参数表达式,解释和补充了Balla等的实验结论。该体系共存在5个反应通道,其中N进攻巯基上H原子生成CH3S + HNO2的通道活化势垒较低,为主反应通道。动力学数据也表明,该通道在200～3000 K计算温度范围内占绝对优势。3.采用QCISD(T)//MP2/6-311++G(d,p)方法研究了HNCS与H原子反应的微观机理。得到了200～2500K温度范围内主反应通道的速率常数。共找到四个反应通道,生成产物H2NCS的通道为主反应通道。反应速率常数随温度升高而增大,在整个温度范围内变分效应对速率常数计算影响较大,而隧道效应在低温区对反应速率影响较显著。4.采用QCISD(T)//B3LYP/6-311++G(d,p)方法研究了HNCS与Cl原子反应的微观机理。计算了200～2500 K温度范围内各反应通道的速率常数。HNCS与Cl原子反应存在3个反应通道。当温度低于294 K时,生成HCl + NCS的夺氢反应是优势通道,温度高于294 K时,生成HNC(Cl)S的加成反应为主反应通道,Cl进攻N的反应通道因能垒较高而难以进行。更多还原

【Abstract】 The species of containing sulfur or nitrogen play an important role in atmospheric chemistry and combustion chemistry , and contribute to environmental problems such as the deterioration of environment, acid rain and photochemical smog. As an important sulfurous organic compound, CH3SH accounts for around 10% of the global flux of sulfur compounds in the atmosphere. HNCS is a potential agent for effectually eliminating nitrogen oxides in exhaust gas streams. So the studies on physical and chemistry properties of containing sulfur or nitrogen are the focuses in atmospherical field.In the thesis, on the basis of quantum chemistry theory and the tradition state theory, the several reactions of CH3SH and HNCS with active radicals or atoms have been investigated by using Density Functional Theory , the Moller-Plesset correlation energy correction, Configuration Interaction, Couple Cluster, and Atoms in Molecules. By analyzing these convincing datum of the optimum geometries and frequencies of all stationary points along the reaction paths, PES, and rate constant, the mechanism and kinetics of these reactions have been investigated deeply.The thesis consists of six chapters.In chapter 1, the experimental and theoretical studies on the reactions of CH3SH and radical, and HNCS in resent years are investigated.In chapter 2, the Quantum Chemistry theory and the tradition state theory are summarized, the content of this part is the basis of our studies and offer us with useful and reliable quantum methods.In chapter 3, reaction mechanism of CH3SH with radical CN has been studied, and the cleavage and formation of the chemical bonds in the reaction process have been discussed by the topological analysis of electronic density.In chapter 4, reaction mechanism and chemical kinetics of CH3SH with NO2 have been investigated.In chapter 5 and 6, the mechanism and kinetics of the reaction HNCS with H and N have been studied.The main conclusions and innovations of this work are listed as following:1. For the first time, the reaction mechanism of CH3SH with radical CN was investigated at CCSD//B3LYP/6-311++G(d,p) level, three reaction channels were found, and the channel leading to CH3S + HCN is the major channel. The calculated results successfully explained the conclusions of Brian’s experimental study. The cleavage and formation of the chemical bonds in the reaction process were discussed by the topological analysis of electronic density, and the transition state with six-member-ring structure (STS) was found.2. The detailed theoretical survey of the potential energy surface (PES) for the reaction of CH3SH with NO2 has been carried out at the G3B3 and CCSD(T)//B3LYP/6-311++G(d,p) level. In the temperature range of 200～3000 K, the rate constants of the reactions were obtained by means of the small-curvature tunneling correction. Five possible reaction channels have been identified. The major reaction channel is the hydrogen abstraction of SH by N atom of NO2, leading to the formation of CH3S and HNO2. The results successfully explain and perfect the conclusions of Balla’s experimental study.3. The mechanism of the reaction of HNCS with H has been investigated at QCISD(T) //MP2/6-311++G(d,p) level. The rate constants were calculated over the temperature range of 200～2500K by using variational transition state theory. The results reveal that four reaction channels have been identified and H2NCS is the main product. It is found that the rate constants of the main reaction channel are positively dependent on the temperature. The variational effect on the calculation of rate constants is very obvious over the whole temperature range and the small-curvature tunnelling effect is very important in the lower temperature range.4. The reaction mechanism of HNCS with Cl has been studied at the level of QCISD(T) //B3LYP/6-311++G(d,p) level of theory. The rate constants of the reactions were calculated over the temperature range of 200-2500 K. According to analysis, there are three reaction channels for the reaction. When temperature is lower than 294 K, the channel (a) is the major channel and HCl + NCS are the main products, while the channel (c) is the major reaction process and HNC(Cl)S is the dominant product when temperature is higher than 294 K. The reaction channel (b) of Cl atom attacking N atom is a difficult process because of a higher energy barrier.更多还原