C_2H_3自由基与O_2反应机理的量子化学研究

Quantum Chemical Study on the Mechanism for the Reaction of C_2H_3 Radical with O_2

用量子化学从头计算中UMP2 (full)方法优化了C2 H3 自由基与O2 反应通道上驻点 (反应物、中间体、过渡态和产物 )的几何构型 ,在Gaussian 3(G3)水平上计算了它们的能量 .在此基础上计算了该反应通道上各基元反应的反应活化能 .通过我们的研究发现 ,C2 H3 自由基与氧气反应存在着三元环、四元环和五元环反应机理 ,且分别生成不同的产物 ,从反应活化能的计算结果看CH2 O和CHO是反应的主要产物 ,其次还可能生成CH3 +CO2 ,CH2 CO2 +H ,C2 H2 +O2 H和COHCOH +H等产物 ,且它们生成几率逐渐减少 ,我们对生成产物CH2 O +CHO ,CH3 +CO2 ,C2 H2 +O2 H和COHCOH +H四条反应通道化学反应热的计算结果与实验吻合较好 .

Ab initio UMP2 (full) method has been used to study the mechanism for the reaction of C2H3 radical with O-2 on the potential energy surface. Energies have been calculated at Gaussian-3 (G3) level. In this paper, we have optimized the geometry configuration of reactants, productions, intermediates and transition states. We have also calculated the activation energies of elementary reactions along the reaction pathways. The results suggest that the reaction mechanism of this reaction involves the formation of three-member, four-member and five-member rings and produces different reaction resultants respectively. According to the calculated activation energies, the CH2O and CHO are the main productions. At the same time, the reaction may form CH3 + CO2, CH2CO2 + H, C2H2 + O2H and COHCOH + H, etc. The probabilities gradually decrease. The reaction heats gained in our study along the four pathways (C2H3 + O-2-->CH2O + CHO, C2H3 + O-2-->CH3 + CO2, C2H3 + O-2-->C2H2 + O2H and C2H3 + O-2-->OHCOH + H) are in good agreement with those of experiments.