Fan Jiwen, Zhang Renyi
Department of Atmospheric Sciences, Texas A&M University, College Station, Texas 77843, USA.
J Phys Chem A. 2008 May 8;112(18):4314-23. doi: 10.1021/jp077648j. Epub 2008 Mar 27.
The OH-initiated oxidation reactions of m-xylene are investigated using density functional theory. The structures, energetics, and relative stability of the OH-m-xylene reaction intermediate radicals have been determined, and their activation barriers have been analyzed to assess the energetically favorable pathways to propagate the oxidation. OH addition occurs preferentially at the two ortho positions with the branching ratios of 0.97, 0.02, and 0.01 for ortho, meta, and ipso additions, respectively. The results reveal that the OH-m-xylene-O2 peroxy radicals preferentially cyclize to form bicyclic radicals under atmospheric conditions rather than reacting with NO to lead to ozone formation, and the decomposition to O2 and the hydroxyl m-xylene adduct is competitive with the cyclization process. The bicyclic radicals of m-xylene formed from the major OH-addition pathways (i.e., ortho positions) are more probable to form bicyclic peroxy radicals by reacting with O2. This study provides thermochemical and kinetic data of the OH-initiated reactions of m-xylene for assessment of the role of aromatic hydrocarbons in photochemical production of ozone, toxic products, and secondary organic aerosols.
采用密度泛函理论研究了间二甲苯的OH引发氧化反应。确定了OH-间二甲苯反应中间体自由基的结构、能量和相对稳定性，并分析了它们的活化能垒，以评估氧化反应的能量有利途径。OH加成优先发生在两个邻位，邻位、间位和本位加成的分支比分别为0.97、0.02和0.01。结果表明，在大气条件下，OH-间二甲苯-O2过氧自由基优先环化形成双环自由基，而不是与NO反应生成臭氧，并且分解为O2和羟基间二甲苯加合物的过程与环化过程相互竞争。由主要OH加成途径（即邻位）形成的间二甲苯双环自由基更有可能与O2反应形成双环过氧自由基。本研究提供了间二甲苯OH引发反应的热化学和动力学数据，用于评估芳烃在臭氧、有毒产物和二次有机气溶胶光化学生成中的作用。
