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Capturing roaming molecular fragments in real time
Science ( IF 56.9 ) Pub Date : 2020-11-26 , DOI: 10.1126/science.abc2960
Tomoyuki Endo 1, 2 , Simon P. Neville 3 , Vincent Wanie 1 , Samuel Beaulieu 1 , Chen Qu 4 , Jude Deschamps 1 , Philippe Lassonde 1 , Bruno E. Schmidt 5 , Hikaru Fujise 6 , Mizuho Fushitani 6 , Akiyoshi Hishikawa 6, 7 , Paul L. Houston 8, 9 , Joel M. Bowman 10 , Michael S. Schuurman 3, 11 , François Légaré 1 , Heide Ibrahim 1
Affiliation  

Roaming dynamics in real time Roaming is distinct from conventional reaction channels because of the unusual geometries that chemical systems use to bypass the minimum energy pathway. It is a relatively new phenomenon that is usually determined in experiments through spectroscopic characterization of the roaming products. Using a combination of time-resolved Coulomb explosion imaging and quasiclassical trajectory analysis, Endo et al. report real-time observation of individual fragments of the prototypical reaction of deuterated formaldehyde (D2CO) dissociation as they roam on ultrafast time scales. They show that roaming not only occurs several orders of magnitude earlier than previously expected but also that it can terminate in a radical (D + DCO) rather than the well-known molecular (D2 + CO) product channel. Science, this issue p. 1072 Femtosecond time-resolved Coulomb explosion imaging reveals the real-time dynamics of roaming in deuterated formaldehyde (D2CO) dissociation. Since the discovery of roaming as an alternative molecular dissociation pathway in formaldehyde (H2CO), it has been indirectly observed in numerous molecules. The phenomenon describes a frustrated dissociation with fragments roaming at relatively large interatomic distances rather than following conventional transition-state dissociation; incipient radicals from the parent molecule self-react to form molecular products. Roaming has been identified spectroscopically through static product channel–resolved measurements, but not in real-time observations of the roaming fragment itself. Using time-resolved Coulomb explosion imaging (CEI), we directly imaged individual “roamers” on ultrafast time scales in the prototypical formaldehyde dissociation reaction. Using high-level first-principles simulations of all critical experimental steps, distinctive roaming signatures were identified. These were rendered observable by extracting rare stochastic events out of an overwhelming background using the highly sensitive CEI method.

中文翻译:

实时捕捉漫游分子片段

实时漫游动力学漫游不同于传统的反应通道,因为化学系统使用不寻常的几何形状来绕过最小能量路径。这是一种相对较新的现象,通常通过漫游产品的光谱表征在实验中确定。Endo 等人结合使用时间分辨库仑爆炸成像和准经典轨迹分析。报告了氘代甲醛 (D2CO) 解离原型反应的单个片段在超快时间尺度上漫游时的实时观察。他们表明,漫游不仅比先前预期的提前几个数量级,而且可以终止于自由基 (D + DCO) 而不是众所周知的分子 (D2 + CO) 产物通道。科学,这个问题 p。1072 飞秒时间分辨库仑爆炸成像揭示了氘代甲醛 (D2CO) 解离中漫游的实时动态。自从发现漫游作为甲醛 (H2CO) 中另一种分子解离途径以来,它已在许多分子中间接观察到。这种现象描述了碎片在相对较大的原子间距离上漫游而不是遵循传统的过渡态解离的受挫解离;来自母体分子的初始自由基自反应形成分子产物。漫游已通过静态产品通道解析测量以光谱学的方式被识别,但不是在漫游片段本身的实时观察中。使用时间分辨库仑爆炸成像 (CEI),我们在原型甲醛解离反应的超快时间尺度上直接对个体“漫游者”进行成像。使用所有关键实验步骤的高级第一性原理模拟,识别出独特的漫游签名。通过使用高度敏感的 CEI 方法从压倒性的背景中提取罕见的随机事件,这些事件变得可观察。
更新日期:2020-11-26
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