CH_3S与HCS双自由基反应的密度泛函理论研究  

Density Functional Theory Study on the Biradical Reaction between CH_3S and HCS

作　　者：刘艳[1] 王文亮[1] 王渭娜[1] 罗琼[1] 李前树[1] 

机构地区：[1]陕西师范大学化学与材料科学学院,西安710062

出　　处：《化学学报》2006年第17期1785-1792,共8页Acta Chimica Sinica

基　　金：陕西省自然科学基金(No.2003B05)资助项目.

摘　　要：应用量子化学从头算和密度泛函理论(DFT)对CH3S与HCS双自由基单重态反应进行了研究.在MPW1PW91/6-311G(d,p)水平上优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型,用内禀反应坐标(IRC)计算和频率分析方法对过渡态进行了验证.在QCISD(t)/6-311++G(d,p)水平上计算各物种的单点能,并对总能量进行了零点能校正.研究结果表明,CH3S与HCS反应为多通道反应,有4条可能的反应通道,反应物首先通过S…S弱相互作用形成具有竞争反应机理的五元环硫-硫偶合中间体a和链状硫-硫偶合中间体c,再由此经过氢迁移、离解、异构化等不同机理得到主要产物P1(2CH2S),次要产物P2(CH3SH+CS),P3(CH4+CS2)和P4[CH2(SH)CSH].根据势能面分析,所有反应均为放热反应,生成P1的反应热为-165.55kJ?mol-1.通道R→a→TSa/b→b→P1为标题反应的主通道,其速控步骤a→TSa/b→b在200～2000K温度区间内的速率常数可以表示为k1CVT/SCT=1.75×1010T0.65exp(-907.6/T)s-1.P3及P4的生成需要越过很高的活化能垒,是动力学禁阻步骤,但在反应体系中加入合适催化剂,改变其反应机理,有可能使生成CH2(SH)CSH,CH4及CS2的反应易于进行.A detailed theoretical survey of the potential energy surface （PES） for the reaction CH3S with HCS in gas phase is carried out at the QCISD（t）/6-311＋＋G（d,p）//MPW1PW91/6-311G（d,p） level. The geometries, vibrational frequencies, and energies of all stationary points involved in the title reaction are calculated at the MPW1PW91/6-311G（d,p） level. More accurate energy information is provided by single-point calculations at QCISD（t）/6-311 ＋＋G（d,p） level. Relationships of reactants, intermediates, transition states and products are confirmed by the intrinsic reaction coordinate （IRC） calculations. 8 intermediates and 9 transition states are located and a variety of possible reaction pathways are probed. The association of CH3S with HCS is found to be a barrierless process. Firstly it forms the energy-rich adducts a （five-member ring-type structure） or c （chain structure） through the weak S…S bond. Then, from adducts a and c, the main product P1 （2CH2S） can be produced, as well as secondary important products P2 （CH3SH＋CS）, P3 （CH4＋ CS2） and P4 [CH2（SH）CSH] via the different channels, i.e. hydrogen shift, dissociation and isomerizazion. The reaction pathway leading to the major product 2CH2S is as follows： R→a→TSa/b→b→P1. The rate constant of step a→TSa/b→b is kCVT/SCr=1.75 × 10^10T^0.65 exp（-907.6/T） s^-1 by means of small-curvature tunneling correction in the temperature range of 200-2000 K. By the analysis of the potential energy surface, we can draw the conclusion that all the channels are exothermic reactions and the reaction heat of generating P1 is - 165.55 kJ·mol^-1.

关 键 词：CH3S HCS 密度泛函理论 反应机理 速率常数 

分 类 号：O643.12[理学—物理化学]