基于过渡态理论的碳烟成核过程中萘生长路径

Growth Pathways of Naphthalene in Soot Nucleation Process Based on Transition State Theory

采用G3(MP2,CC)方法计算了添加C_2H_2、C_2 H_3和C_4H_4使苯基(C6H5)生长到萘(C10H8)(分别为C_2H_2-路径、C_2 H_3-路径和C_4H_4-路径)以及C5H5和C_5H_4反应生成萘和甘菊环(C10H8)(C_5H_4-路径)的详细多环芳香烃(PAH)生长路径,比较了4个路径的入口势垒和最大反应势垒,考察了反应位点对脱氢和C_2H_2添加反应的影响以及氢原子的存在对脱氢反应的影响,计算了以Arrhenius形式表达的反应速率常数.结果表明:C_5H_4-路径入口势垒极低,即C_5H_5极易与C_5H_4发生反应.与C_2H_2和C_2 H_3相比,C_4H_4更容易与苯基发生反应.C_2 H_3-路径和C_4H_4-路径中所有子路径的限速步骤均为顺反异构化反应.反应位点对有氢原子参与的脱氢反应影响不大,对C_2H_2添加反应影响较大.此外,有氢原子参与的脱氢反应比直接脱氢反应更容易发生.

The reaction mechanisms of polycyclic aromatic hydrocarbon(PAH)growth from phenyl radical(C6H5)to naphthalene via C2H2,C2H3 and C4H4(which were named as:C2H2-path,C2H3-path and C4H4-path in manuscript,respectively)and from C5H5 with C5H4 to naphthalene and azulene(C5H4-path)were investigated by the G3(MP2,CC)method.The entrance barriers and the biggest barriers of these paths were compared.The influence of reactive sites to H-abstraction and C2H2 addition reactions was studied.Besides,the influence of the existence of hydrogen atoms to H-abstractions was also investigated.Rate constants of elementary reactions in the modified Arrhenius equation form were calculated.The results show that,the entrance barrier of C5H4-path is very low,meaning that C5H5 is very easy to react with C5H4.Compared with C2H2 and C2H3,C4H4 is easier to react with C6H5.All rate limiting steps of C2H3-path and C4H4-path are the cis-trans conversion reactions.Different reactive sites have low effect on the Habstraction reactions via hydrogen atoms,but high effect on C2H2 addition reactions.Besides,H-abstraction reactions via hydrogen atoms are easier to occur than H-abstraction reactions directly.