Role of O2 + QOOH in Low-Temperature Ignition of Propane. 1. Temperature and Pressure Dependent Rate Coefficients

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• 作者：C. Franklin Goldsmith ; William H. Green ; Stephen J. Klippenstein
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：April 5, 2012
• 年：2012
• 卷：116
• 期：13
• 页码：3325-3346
• 全文大小：956K
• 年卷期：v.116,no.13(April 5, 2012)
• ISSN：1520-5215

文摘

The kinetics of the reaction of molecular oxygen with hydroperoxyalkyl radicals have been studied theoretically. These reactions, often referred to as second O₂ addition, or O₂ + QOOH reactions, are believed to be responsible for low-temperature chain branching in hydrocarbon oxidation. The O₂ + propyl system was chosen as a model system. High-level ab initio calculations of the C₃H₇O₂ and C₃H₇O₄ potential energy surfaces are coupled with RRKM master equation methods to compute the temperature and pressure dependence of the rate coefficients. Variable reaction coordinate transition-state theory is used to characterize the barrierless transition states for the O₂ + QOOH addition reactions as well as subsequent C₃H₆O₃ dissociation reactions. A simple kinetic mechanism is developed to illustrate the conditions under which the second O₂ addition increases the number of radicals. The sequential reactions O₂ + QOOH 鈫?OOQOOH 鈫?OH + keto-hydroperoxide 鈫?OH + OH + oxy-radical and the corresponding formally direct (or well skipping) reaction O₂ + QOOH 鈫?OH + OH + oxy-radical increase the total number of radicals. Chain branching through this reaction is maximized in the temperature range 600鈥?00 K for pressures between 0.1 and 10 atm. The results confirm that n-propyl is the smallest alkyl radical to exhibit the low-temperature combustion properties of larger alkyl radicals, but n-butyl is perhaps a truer combustion archetype.