Zheng X L, Sun H Y, Law C K
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA.
J Phys Chem A. 2005 Oct 13;109(40):9044-53. doi: 10.1021/jp058116a.
In recognition of the importance of the isobutene oxidation reaction in the preignition chemistry associated with engine knock, the thermochemistry, chemical reaction pathways, and reaction kinetics of the isobutenyl radical oxidation at low to intermediate temperature range were computationally studied, focusing on both the first and the second O2 addition to the isobutenyl radical. The geometries of reactants, important intermediates, transition states, and products in the isobutenyl radical oxidation system were optimized at the B3LYP/6-311G(d,p) and MP2(full)/6-31G(d) levels, and the thermochemical properties were determined on the basis of ab initio, density functional theory, and statistical mechanics. Enthalpies of formation for several important intermediates were calculated using isodesmic reactions at the DFT and the CBS-QB3 levels. The kinetic analysis of the first O2 addition to the isobutenyl radical was performed using enthalpies at the CBS-QB3 and G3(MP2) levels. The reaction forms a chemically activated isobutenyl peroxy adduct which can be stabilized, dissociate back to reactants, cyclize to cyclic peroxide-alkyl radicals, and isomerize to the 2-hydroperoxymethyl-2-propenyl radical that further undergoes another O2 addition. The reaction channels for isomerization and cyclization and further dissociation on this second O2 addition were analyzed using enthalpies at the DFT level with energy corrections based on similar reaction channels for the first O2 addition. The high-pressure limit rate constants for each reaction channel were determined as functions of temperature by the canonical transition state theory for further kinetic model development.
认识到异丁烯氧化反应在与发动机爆震相关的预点火化学中的重要性，对异丁烯基自由基在低至中温范围内氧化的热化学、化学反应途径和反应动力学进行了计算研究，重点关注异丁烯基自由基与氧气的首次和第二次加成反应。在B3LYP/6-311G(d,p)和MP2(full)/6-31G(d)水平上优化了异丁烯基自由基氧化体系中反应物、重要中间体、过渡态和产物的几何结构，并基于从头算、密度泛函理论和统计力学确定了热化学性质。使用等键反应在DFT和CBS-QB3水平上计算了几种重要中间体的生成焓。使用CBS-QB3和G3(MP2)水平的焓对异丁烯基自由基与氧气的首次加成反应进行了动力学分析。该反应形成一个化学活化的异丁烯基过氧加合物，它可以稳定化、解离回反应物、环化形成环状过氧化物-烷基自由基，以及异构化为2-氢过氧甲基-2-丙烯基自由基，该自由基进一步与另一个氧气分子发生加成反应。使用DFT水平的焓，并基于与异丁烯基自由基与氧气的首次加成反应类似的反应通道进行能量校正，分析了第二次氧气加成反应中异构化、环化和进一步解离的反应通道。通过正则过渡态理论确定了每个反应通道的高压极限速率常数作为温度的函数，以用于进一步的动力学模型开发。
