CH_3S与HO_2气相反应机理的理论研究

Theoretical Study on the Reaction Mechanism of CH_3S with HO_2 under Atmospheric Conditions

采用密度泛函理论的B3LYP方法,在6-311++G(d,p)基组水平上研究了CH3S自由基与HO2自由基的微观反应机理,全参数优化了反应势能面上各驻点的几何构型,振动分析和内禀反应坐标(IRC)分析结果证实了中间体和过渡态的真实性,计算所得的键鞍点电荷密度的变化情况也确认了反应过程.找到了五条可能的反应通道,对结果的分析表明:单线态反应通道(5)CH3S+HO2→CH3SOOH(1P),是所有通道中的主要反应通道.该通道不需要克服过渡态能垒,属于放热反应,在动力学和热力学上都是最为有利的.对于三线态反应通道来说,通道(1)CH3S+HO2→COM11→TS1→COM12→CH3SH+O2(3P)为主要反应通道,控制步骤的活化能为53.5 kJ/mol,能垒最低,属于放热反应,在动力学和热力学上都是有利的.

A density functional theory （DFT） B3LYP method was employed to study the mechanism of the reaction of CH3S with HO2 at the 6-311 ＋＋G（d,p） basis sets. Geometries of the stationary points were completely optimized. The transition states were validated by the vibrational analysis and the internal reaction coordinate （IRC） calculations, which testified the authenticity of intermediates and transition states. Five feasible reaction pathways of this reaction have been studied. The results indicate that the main reaction pathway is the singlet spin pathway CH3S＋HO2→CH3SOOH （1P）, which has no activation energy and is beneficial from the aspects of reaction kinetics and thermodynamics. For the triplet spin reaction pathway, CH3S→ HO2→COM11→TS 1→COM 12→CH3SH＋ O2 （3P） is the main route, and the corresponding activation energy is 53.5 kJ/mol. This exothermic pathway has the lowest activation energy, which is beneficial from the aspects of reaction kinetics and thermodynamics.