Analysis of the kinetics and yields of OH radical production from the CH3OCH2 + O2 reaction in the temperature range 195-650 K: an experimental and computational study.
Analysis of the kinetics and yields of OH radical production from the CH3OCH2 + O2 reaction in the temperature range 195-650 K: an experimental and computational study.
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DOI：
10.1021/jp505422e
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发表时间：
2014-08
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通讯作者：
A. Eskola;Scott A. Carr;R. Shannon;B. Wang;M. Blitz;M. Pilling;P. Seakins;S. Robertson
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文献类型：
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作者：
A. Eskola;Scott A. Carr;R. Shannon;B. Wang;M. Blitz;M. Pilling;P. Seakins;S. Robertson
甲氧基甲基自由基CH 3 OCH 2是二甲醚低温燃烧的重要中间体。在195-650 K和5-500 Torr的温度和压力范围内，用CH_3OCH_2Br的准分子激光光解（248 nm）后的激光诱导荧光检测羟基自由基，测定了甲氧基甲基自由基与O_2反应生成OH的动力学和产率。该反应通过形成能量化的CH 3 OCH 2 O2加合物进行，该加合物解离成OH + 2 H2 CO或通过缓冲气体碰撞稳定。在高于550 K的温度下，观察到的OH的第二来源与稳定的CH 3 OCH 2 O2自由基的热分解一致。为了量化CH 3 OCH 2 + O2反应中的OH产生，在与动力学实验相同的（T，P）条件下进行了广泛的相对和绝对OH产率测量。反应在足够低的自由基浓度（10（11）cm（-3）），二次（自由基+自由基）反应是不重要的，速率系数可以从简单的双或三指数分析提取。从头算（CBS-GB 3）/主方程计算（使用程序MESMER）的CH 3 OCH 2 + O2系统也进行了更好地了解这种燃烧相关的反应，以及能够外推实验结果更高的温度和压力。为了获得与实验结果（动力学和产率数据）的一致性，关键过渡态的能量从它们的从头算值大幅降低（20-40 kJ mol（-1）），并考虑了CH 3 OCH 2和CH 3 OCH 2 OO中间体中的受阻旋转的影响。优化的主方程模型被用来产生一组的压力和温度依赖的速率系数的组件9个唯象反应，描述的CH 3 OCH 2 + O2系统，包括4个跳井反应。对于N2和He浴气体，速率系数分别在200至1000 K和1 × 10（17）至1 × 10（23）分子cm（-3）的温度和密度范围内拟合为切比雪夫多项式。与现有自燃机理的比较表明，跳井反应在1巴的压力下是重要的，但在10巴下不显著。主要的差异来自计算的CH 3 OCH 2 OO → CH 2 OCH 2 OOH反应的速率系数，这导致O2 CH 2 OCH 2 OOH的形成速率更快。
The methoxymethyl radical, CH3OCH2, is an important intermediate in the low temperature combustion of dimethyl ether. The kinetics and yields of OH from the reaction of the methoxymethyl radical with O2 have been measured over the temperature and pressure ranges of 195-650 K and 5-500 Torr by detecting the hydroxyl radical using laser-induced fluorescence following the excimer laser photolysis (248 nm) of CH3OCH2Br. The reaction proceeds via the formation of an energized CH3OCH2O2 adduct, which either dissociates to OH + 2 H2CO or is collisionally stabilized by the buffer gas. At temperatures above 550 K, a secondary source of OH was observed consistent with thermal decomposition of stabilized CH3OCH2O2 radicals. In order to quantify OH production from the CH3OCH2 + O2 reaction, extensive relative and absolute OH yield measurements were performed over the same (T, P) conditions as the kinetic experiments. The reaction was studied at sufficiently low radical concentrations (∼10(11) cm(-3)) that secondary (radical + radical) reactions were unimportant and the rate coefficients could be extracted from simple bi- or triexponential analysis. Ab initio (CBS-GB3)/master equation calculations (using the program MESMER) of the CH3OCH2 + O2 system were also performed to better understand this combustion-related reaction as well as be able to extrapolate experimental results to higher temperatures and pressures. To obtain agreement with experimental results (both kinetics and yield data), energies of the key transition states were substantially reduced (by 20-40 kJ mol(-1)) from their ab initio values and the effect of hindered rotations in the CH3OCH2 and CH3OCH2OO intermediates were taken into account. The optimized master equation model was used to generate a set of pressure and temperature dependent rate coefficients for the component nine phenomenological reactions that describe the CH3OCH2 + O2 system, including four well-skipping reactions. The rate coefficients were fitted to Chebyshev polynomials over the temperature and density ranges 200 to 1000 K and 1 × 10(17) to 1 × 10(23) molecules cm(-3) respectively for both N2 and He bath gases. Comparisons with an existing autoignition mechanism show that the well-skipping reactions are important at a pressure of 1 bar but are not significant at 10 bar. The main differences derive from the calculated rate coefficient for the CH3OCH2OO → CH2OCH2OOH reaction, which leads to a faster rate of formation of O2CH2OCH2OOH.