Bio-derived isobutanol has been approved as a gasoline additive in the U.S., but our understanding of its combustion chemistry still has significant uncertainties. Detailed quantum calculations could improve model accuracy leading to better estimation of isobutanol’s combustion properties and its environmental impacts. This work examines 47 molecules and 38 reactions involved in the first oxygen addition to isobutanol’s three alkyl radicals located α, β, and γ to the hydroxide. Quantum calculations were mostly done at CCSD(T)-F12/cc-pVTZ-F12//B3LYP/CBSB7, with 1-D hindered rotor corrections obtained at B3LYP/6-31G(d). The resulting potential energy surfaces are the most comprehensive isobutanol peroxy networks published to date. Canonical transition state theory and a 1-D microcanonical master equation are used to derive high-pressure-limit and pressure-dependent rate coefficients, respectively. At all conditions studied, the recombination of α- isobutanol radical with O2 forms HO2 and isobutanal. The recombination of γ-isobutanol radical with O2 forms a stabilized hydroperoxy alkyl radical below 400 K, water and an alkoxy radical at higher temperatures, and HO2 and an alkene above 1200 K. The recombination of β-isobutanol radical with O2 results in a mixture of products between 700-1100 K, forming acetone, formaldehyde and OH at lower temperatures and forming HO2 and alkenes at higher temperatures. The barrier heights, high-pressure-limit rates, and pressure-dependent kinetics generally agree with the results from previous quantum chemistry calculations. Six reaction rates in this work deviate by over three orders of magnitude from kinetics in detailed models of isobutanol combustion, suggesting the rates calculated here can help improve modeling of isobutanol combustion and its environmental fate.

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异丁醇燃烧中形成的过氧自由基的压力依赖性动力学

生物衍生的异丁醇在美国已被批准用作汽油添加剂，但是我们对其燃烧化学的理解仍存在很大的不确定性。详细的量子计算可以提高模型的准确性，从而更好地估计异丁醇的燃烧特性及其对环境的影响。这项工作研究了在异丁醇的三个烷基（分别位于氢氧化物的α，β和γ处）首次加氧时涉及的47个分子和38个反应。量子计算主要在CCSD（T）-F12 / cc-pVTZ-F12 // B3LYP / CBSB7处完成，在B3LYP / 6-31G（d）处获得一维受阻转子校正。由此产生的势能面是迄今为止发布的最全面的异丁醇过氧网络。规范过渡态理论和一维微规范主方程分别用于导出高压极限和压力相关的速率系数。在所有研究的条件下，α-异丁醇自由基与O2的重组形成HO2和异丁醛。γ-异丁醇自由基与O2的重组会形成低于400 K的稳定氢过氧烷基，高温下水和烷氧基以及HO2和高于1200 K的烯烃。β-异丁醇自由基与O2的重组会形成混合物在700-1100 K之间的产物，在较低温度下形成丙酮，甲醛和OH，在较高温度下形成HO2和烯烃。势垒高度，高压极限率和依赖压力的动力学通常与先前的量子化学计算的结果一致。