title: Investigating the role of CH2 radicals in the HACA mechanism.
abstract: Detailed mechanisms of PAH growth involving methylene (CH2) were studied using accurate ab initio density functional theory B3LYP/6-311+G(d,p) calculations, as well as approximate QCISD(T,full)/6-311++G(3df,2pd) calculations. The PAH growth can be divided into five essential reaction steps, namely, addition C2H2 → intramolecular hydrogen migration → addition CH2 → cyclization → H-elimination. The aliphatic species of indene and 1H-phenalene are found in the pathways of PAH growth, which is in accord with the experimental results that reveal the formation of aliphatic species in flames. It was found that the simultaneous removal of two H atoms in one reaction step is feasible in PAH evolution, and this can reasonably interpret the absence of a H atom in the post-flame region. The corresponding rate coefficients at 1 atm were evaluated by using TST and RRKM theory by solving the master equations in the temperature range of 500-2500 K. The calculated branching ratios suggest that the pathways involving CH2 are competitive in PAH growth.
authors.affiliation: Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Liu
authors.affiliation: Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: He
authors.initials: H
authors.lastname: Lin
authors.affiliation: Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Can
authors.initials: C
authors.lastname: Shao
authors.affiliation: Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Guan
authors.affiliation: Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Huang
mesh_terms: D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*
chemical_list: D011084:Polycyclic Aromatic Hydrocarbons; C504223:methylene radical; D008697:Methane