Rate coefficients for cycloalkyl + O reactions and product branching in the decomposition of chemically activated cycloalkoxy radicals: an experimental and theoretical study.
Rate coefficients for cycloalkyl + O reactions and product branching in the decomposition of chemically activated cycloalkoxy radicals: an experimental and theoretical study.
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化学活化环烷氧基自由基分解中环烷基 O 反应和产物支化的速率系数：实验和理论研究。
DOI：
10.1039/b925920a
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
T. Zeuch
中科院分区：
文献类型：
--
作者：
K. Hoyermann;Sven Maarfeld;Frank Nacke;Jörg Nothdurft;M. Olzmann;J. Wehmeyer;O. Welz;T. Zeuch
研究了环烷基 + O 反应的速率系数和化学活化环烷氧基分解产物支化比的动力学。环己基 (c-C(6)H(11))、环庚基 (c-C(7)H(13)) 和环辛基 (c-C(8)H(15)) 自由基与氧原子的反应速率系数通过由带有分子束采样和 REMPI/TOF-MS 检测的放电流反应器组成的实验装置确定。获得以下速率系数（单位：cm(3)/mol(-1) s(-1)）：k(c-C(6)H(11) + O) = (1.33 +/- 0.24) x 10(14)(T/298 K)(0.11) (T = 250-600 K), k(c-C(7)H(13) + O) = (1.85 +/- 0.25) x 10(14) (T = 298 K)，k(c-C(8)H(15) + O) = (1.56 +/- 0.20) x 10(14)(T/298 K)(0.66+/-0.15) (T = 268-363 K)。通过定量 FTIR 光谱测定稳定产物。环烷氧基自由基的分解除了导致β-C-H键裂变外（产率：c-C(6)H(11)O为24%，c-C(8)H(15)O为20-25%），主要通过β-C-C键断裂开环生成烷基自由基。这些开链烷基主要通过β-C-C键断裂进一步分解。总压力从 4 mbar 增加到 1 bar 对 c-C(6)H(11) + O 反应的产物分布没有影响，而对于 c-C(8)H(15) + O 反应，开环产物的进一步分解在 1 bar 下受到显着抑制。利用统计速率理论对通道分支及其压力依赖性的实验结果进行了合理化。实验和建模结果的比较表明受阻内旋转（HIR）对开环产物的反应有显着影响。描述这些模式的谐波近似被证明是不够的，而一维 HIR 的处理可以显着改善实验结果和建模结果之间的一致性。讨论了我们的发现对二次有机气溶胶形成和高温燃烧的影响。
The kinetics of cycloalkyl + O reactions were studied with respect to their rate coefficients and the product branching ratios from the decomposition of the chemically activated cycloalkoxy radicals. Rate coefficients for the reactions of cyclohexyl (c-C(6)H(11)), cycloheptyl (c-C(7)H(13)) and cyclooctyl (c-C(8)H(15)) radicals with oxygen atoms were determined with an experimental setup consisting of a discharge flow reactor with molecular beam sampling and REMPI/TOF-MS detection. The following rate coefficients were obtained (units: cm(3)/mol(-1) s(-1)): k(c-C(6)H(11) + O) = (1.33 +/- 0.24) x 10(14)(T/298 K)(0.11) (T = 250-600 K), k(c-C(7)H(13) + O) = (1.85 +/- 0.25) x 10(14) (T = 298 K), k(c-C(8)H(15) + O) = (1.56 +/- 0.20) x 10(14)(T/298 K)(0.66+/-0.15) (T = 268-363 K). Stable products were determined by quantitative FTIR spectroscopy. The decomposition of the cycloalkoxy radicals leads besides beta-C-H bond fission (yields: 24% for c-C(6)H(11)O, 20-25% for c-C(8)H(15)O) mainly to alkyl radicals by ring-opening viabeta-C-C bond cleavage. These open-chain alkyl radicals further decompose mainly by beta-C-C bond scission. An increase of the total pressure from 4 mbar to 1 bar had no effect on the product distribution for the reaction c-C(6)H(11) + O, whereas for the reaction c-C(8)H(15) + O further decomposition of the ring-opening product is significantly suppressed at 1 bar. The experimental results on the channel branching and its pressure dependence were rationalized with the statistical rate theory. A comparison of the experimental and modeling results indicates a significant influence of hindered internal rotations (HIRs) on the reactions of the ring-opening products. The harmonic approximation to describe these modes was shown to be inadequate, while a treatment as one-dimensional HIRs led to a significantly improved agreement between experimental and modeling results. Implications of our findings for the formation of secondary organic aerosol and high-temperature combustion are discussed.