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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Analysis of HO2 and OH formation mechanisms using FM and UV spectroscopy in dimethyl ether oxidation
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Analysis of HO2 and OH formation mechanisms using FM and UV spectroscopy in dimethyl ether oxidation

机译：使用FM和UV光谱分析二甲醚氧化中HO2和OH的形成机理

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摘要

Product formation pathways in the photolytically initiated oxidation of CH3OCH3 have been investigated as a function of temperature (298-600 K) and pressure (20-90 Torr) through the detection of HO2 and OH using Near-infrared frequency modulation spectroscopy, as well as the detection of CH3OCH2O2 using UV absorption spectroscopy. The reaction was initiated by pulsed photolysis with a mixture of Cl-2, O-2, and CH3OCH3. The HO2 and OH yield is obtained by comparison with an established reference mixture, including CH3OH. The CH3OCH2O2 yield is also obtained through the procedure of estimating the CH3OCH2O2/HO2 ratio from their UV absorption. A notable finding is that the OH yield is 1 order of magnitude larger than those known in C-2 and C-3 alkanes, increasing from 10% to 40% with increasing temperature. The HO2 yield increases gradually until 500 K and sharply up to 40% over 500 K. The CH3OCH2O2 profile has a prompt rise, followed by a gradual decay whose time constant is consistent with slow HO2 formation. To predict species profiles and yields, simple chlorine-initiated oxidation model of DME under low-pressure condition was constructed based on the existing model and the new reaction pathways, which were derived from this study. To model rapid OH formation, OH direct formation from CH3OCH2 + O-2 was required. We have also proposed that a new HCO formation pathway via QOOH isomerization to HOQO species and OH + CH3OCH2O2 -> HO2 + CH3OCH2O are to be considered, to account for the fast and slow HO2 formations, as well as the total yield. The constructed model including these new pathways has successfully predicted experimental results throughout the entire temperature and pressure ranges investigated. It was revealed that the HO2 formation mechanism changes at 500 K, i.e., HCO + O-2 via HCHO + OH and the above proposed direct HCO formation dominates over 500 K, while a series of reactions following CH3OCH2O2 self-reaction and OH + CH3OCH2O2 reaction mainly contribute below 500 K. The pressure dependent rate constant of the CH3OCH2 thermal decomposition reaction has been separately measured since it has large negative sensitivity for HO2 formation and is essential to eliminate the ambiguity in the CH3OCH2 + O-2 mechanism at higher temperature.
机译：通过使用近红外频率调制光谱法检测HO2和OH，研究了CH3OCH3的光解引发氧化过程中产物形成途径与温度（298-600 K）和压力（20-90 Torr）的关系。紫外吸收光谱法检测CH3OCH2O2通过用Cl-2，O-2和CH3OCH3的混合物进行脉冲光解来引发反应。通过与建立的参比混合物（包括CH3OH）进行比较，可获得HO2和OH的收率。 CH3OCH2O2的产率也可以通过从其UV吸收量估算CH3OCH2O2 / HO2比的过程中获得。一个值得注意的发现是，OH的收率比C-2和C-3烷烃中的已知收率大1个数量级，随温度的升高从10％增加到40％。 HO2的产量逐渐增加直至500 K，在500 K上急剧增加40％。CH3OCH2O2曲线迅速上升，随后逐渐衰减，其时间常数与缓慢的HO2形成相一致。为了预测物种分布和产量，基于现有模型和新的反应途径，在低压条件下构建了简单的氯引发的二甲醚氧化模型。为了模拟快速OH的形成，需要从CH3OCH2 + O-2直接形成OH。我们还提出要考虑通过QOOH异构化为HOQO种类和OH + CH3OCH2O2-> HO2 + CH3OCH2O的新HCO形成途径，以说明快速和缓慢的HO2形成以及总产率。包含这些新途径的构建模型已成功预测了所研究的整个温度和压力范围内的实验结果。结果表明，HO2的形成机理在500 K时发生变化，即HCO + O-2经由HCHO + OH发生，上述提议的直接HCO形成在500 K以上起主导作用，而CH3OCH2O2自反应和OH + CH3OCH2O2之后的一系列反应CH3OCH2热分解反应的压力依赖性速率常数是独立测定的，因为它对HO2的形成具有较大的负敏感性，并且对于消除高温下CH3OCH2 + O-2机制的歧义性至关重要。

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