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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Experimental and theoretical study of the kinetics and mechanism of the reaction of OH radicals with dimethyl ether
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Experimental and theoretical study of the kinetics and mechanism of the reaction of OH radicals with dimethyl ether

机译：OH自由基与二甲醚反应动力学和机理的实验和理论研究

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摘要

The reaction of OH with dimethyl ether (CH_3OCH_3) 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 k_1 = (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.
机译：OH与二甲醚（CH_3OCH_3）的反应已在195至850 K范围内使用激光闪光光解法和激光诱导的OH自由基荧光检测进行了研究。这项工作的速率系数可以通过修改后的Arrhenius表达式k =（1.23±0.46）×10〜（-12）（T / 298）2.05±0.23 exp（（257±107）/ T）cm〜3分子来参数化-1 s〜（-1）。包括其他最近的文献数据（923-1423 K）得到的修正的Arrhenius表达式为k_1 =（1.54±0.48）×10〜（-12）（T / 298 K）1.89±0.16 exp（（184±112）/ T）在195-1423 K范围内，cm〜3分子-1 s〜（-1）。还研究了反应的各种同分异构体组合，其中二甲醚氘化导致正常的同位素效应。羟基的氘代导致小的反同位素效应。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，使用高级从头算方法计算了过渡态和配合物的能量和结构。该计算还确定了反应前和反应后的配合物。计算表明，反应前配合物的结合能为〜22 kJ mol〜（-1）。稳定到配合物中可能会影响反应的动力学，尤其是在低温（<300 K）下，但没有直接证据表明在本研究的实验条件下会发生这种情况。实验数据已使用最近开发的MESMER（用于多能井反应的主方程求解器）代码建模;使用基于单个过渡状态的模型，在200-1400 K的温度范围内，计算出的速率系数在实验值的16％以内。该模型还定性地重现了观察到的同位素效应，在〜600 K以上时接近一致，但在低温下高估了它们。较低的温度差异可能源于对隧道的处理不充分和/或源于外部过渡态导致反应前配合物的作用增强。

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