Experimental and theoretical study of the kinetics and mechanism of the reaction of OH radicals with dimethyl ether.
Experimental and theoretical study of the kinetics and mechanism of the reaction of OH radicals with dimethyl ether.
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DOI：
10.1021/jp4070278
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发表时间：
2013-10
期刊：
影响因子：
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通讯作者：
Scott A. Carr;T. Still;M. Blitz;A. Eskola;M. Pilling;P. Seakins;R. Shannon;B. Wang;S. Robertson-S.-R
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文献类型：
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作者：
Scott A. Carr;T. Still;M. Blitz;A. Eskola;M. Pilling;P. Seakins;R. Shannon;B. Wang;S. Robertson-S.-R
用激光闪光光解-激光诱导荧光法研究了195 ~ 850 K温度范围内OH与二甲醚（CH_3 OCH_3）的反应。速率系数可用修正的Arrhenius公式k =（1.23 ± 0.46）× 10（-12）（T/298）（2.05±0.23）exp（（257 ± 107）/T）cm（3）molecule（-1）s（-1）表示。在195-1423 K范围内，结合文献数据，给出了修正的Arrhenius公式：k1 =（1.54 ± 0.48）× 10（-12）（T/298 K）（1.89±0.16）exp（（184 ± 112）/T）cm（3）molecule（-1）s（-1）。各种同位素组合的反应也进行了研究与氘代二甲醚导致正常的同位素效应。羟基的氘化导致小的逆同位素效应。为了深入了解反应机理并支持实验工作，还进行了理论研究，使用高水平从头算方法计算过渡态和络合物的能量和结构。计算还确定了反应前和反应后的复合物。计算表明，预反应络合物的结合能约为22 kJ mol（-1）。稳定到络合物中可能会影响反应的动力学，特别是在低温（<300 K）下，但在本研究的实验条件下没有直接证据表明会发生这种情况。实验数据已被建模使用最近开发的MESMER（主方程求解器的多能量阱反应）代码;计算的速率系数位于16%的实验值在200-1400 K的温度范围内的模型基于一个单一的过渡态。该模型还定性地再现了所观察到的同位素效应，在~600 K以上接近一致，但在低温下高估了它们。低的温度差可能来自隧道效应的不充分处理和/或来自导致预反应络合物的外部过渡态的增强作用。
The reaction of OH with dimethyl ether (CH3OCH3) has been studied from 195 to 850 K using laser flash photolysis coupled to laser induced fluorescence detection of OH radicals. The rate coefficient from this work can be parametrized by the modified Arrhenius expression k = (1.23 ± 0.46) × 10(-12) (T/298)(2.05±0.23) exp((257 ± 107)/T) cm(3) molecule(-1) s(-1). Including other recent literature data (923-1423 K) gives a modified Arrhenius expression of k1 = (1.54 ± 0.48) × 10(-12) (T/298 K)(1.89±0.16) exp((184 ± 112)/T) cm(3) molecule(-1) s(-1) over the range 195-1423 K. Various isotopomeric combinations of the reaction have also been investigated with deuteration of dimethyl ether leading to a normal isotope effect. Deuteration of the hydroxyl group leads to a small inverse isotope effect. To gain insight into the reaction mechanisms and to support the experimental work, theoretical studies have also been undertaken calculating the energies and structures of the transition states and complexes using high level ab initio methods. The calculations also identify pre- and post-reaction complexes. The calculations show that the pre-reaction complex has a binding energy of ~22 kJ mol(-1). Stabilization into the complex could influence the kinetics of the reaction, especially at low temperatures (<300 K), but there is no direct evidence of this occurring under the experimental conditions of this study. The experimental data have been modeled using the recently developed MESMER (master equation solver for multi energy well reactions) code; the calculated rate coefficients lie within 16% of the experimental values over the temperature range 200-1400 K with a model based on a single transition state. This model also qualitatively reproduces the observed isotope effects, agreeing closely above ~600 K but overestimating them at low temperatures. The low temperature differences may derive from an inadequate treatment of tunnelling and/or from an enhanced role of an outer transition state leading to the pre-reaction complex.