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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >First-Principles Dynamics along the Reaction Path of CH_3CH_2 + O_1 → H_2C = CH_2 + HOO: Evidence for Vibronic State Mixing and Neutral Hydrogen Transfer
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First-Principles Dynamics along the Reaction Path of CH_3CH_2 + O_1 → H_2C = CH_2 + HOO: Evidence for Vibronic State Mixing and Neutral Hydrogen Transfer

机译：CH_3CH_2 + O_1→H_2C = CH_2 + HOO反应路径的第一性动力学：振动态混合和中性氢转移的证据

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We employ Born-Oppenheimer molecular dynamics (BOMD), with forces derived from spin-polarized density functional theory using the B3LYP hybrid exchange-correlation functional, to explore the dynamics of oxidation of ethyl radical to produce ethylene, along the concerted-elimination path CH_3CH_2 + O_2 → CH_3CH_2OO → CH_2 = CH_2 + HOO. The transition state connecting CH_3CH_2OO to CH_2 = CH_2 and HOO has a planar, five-membered-ring structure …C-C-H-O-O… known as TS1. The electronic nature of this saddle point has been the subject of controversy. Recent ab initio calculations have indicated that TS1 has a ~2A" electronic ground state within C_s symmetry. In this state, intramolecular neutral hydrogen transfer from the methyl group of the intermediate ethylperoxy radical (CH_3CH_2OO·) to the terminal oxygen is hindered by the lack of overlap between the 1s orbital of the in-plane hydrogen atom and the singly-occupied 2p (a") orbital of the terminal oxygen. Previous explanations invoked proton transfer, a rather unpalatable process for an alkylperoxy radical. Two other possibilities that both facilitate neutral H-transfer are explored in the present work, namely: (i) an O_2 π~*-resonance mechanism and (ii) ~2A'-~2A" state mixing. First, we show that the structure of TS1 is a "late", loose transition state, consistent with a loosely coupled O_2 that can shift π~*-electrons to aid neutral hydrogen atom transfer. Second, our BOMD trajectories reveal that torsional motion in the ethylperoxy radical and at the transition state causes symmetry-breaking and ~2A'-~2A" state mixing. The low-lying ~2A' excited state, with its in-plane, singly occupied oxygen 2p orbital, can easily transfer a neutral H atom. Not only is vibrationally-induced symmetry-breaking present near (and after crossing) TS1, but also in the CH_3CH_2 and O_2 entrance channel, which again exhibits torsional motion that allows both the ~2A" ground state and the excited ~2A' state to be accessed while forming the ethylperoxy radical. Thus we propose that vibronic state mixing is a key feature of the reaction dynamics of ethane combustion, helping to facilitate dehydrogenation.
机译：我们使用Born-Oppenheimer分子动力学（BOMD），并利用自旋极化密度泛函理论，使用B3LYP杂化交换-相关泛函来推导沿着协同消除路径CH_3CH_2进行乙基氧化生成乙烯的动力学。 + O_2→CH_3CH_2OO→CH_2 = CH_2 + HOO。将CH_3CH_2OO连接到CH_2 = CH_2和HOO的过渡态具有平面五元环结构…C-C-H-O-O…，称为TS1。鞍点的电子性质一直是争议的主题。最近的从头算计算表明，TS1在C_s对称性内具有〜2A“电子基态。在这种状态下，分子间中性氢从中间乙基过氧自由基（CH_3CH_2OO·）的甲基向末端氧的转移受到阻碍平面内氢原子的1s轨道与末端氧的单占据2p（a“）轨道之间的交叠关系。先前的解释调用了质子转移，这对于烷基过氧自由基而言是一种令人不快的过程。在目前的工作中，还探索了两种均有助于中性氢转移的可能性，即：（i）O_2π〜*-共振机制和（ii）〜2A'-〜2A“状态混合。首先，我们证明了TS1的结构是“晚期”的松散过渡态，与松散耦合的O_2一致，O_2可以移动π〜*电子以帮助中性氢原子转移。第二，我们的BOMD轨迹揭示了在乙基过氧自由基中和在过渡态导致对称破坏和〜2A'-〜2A“状态混合。低地〜2A'激发态及其在平面内单占据的氧2p轨道，可以轻松转移中性H原子。不仅在TS1附近（以及穿过TS1之后），而且在CH_3CH_2和O_2入口通道中，都不仅存在振动引起的对称破坏，而且该通道再次表现出扭转运动，允许〜2A“基态和激发〜2A'状态因此，我们认为振动态混合是乙烷燃烧反应动力学的关键特征，有助于促进脱氢。

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