Free Radical Chemistry Probed with Muon Spin Spectroscopy

用μ子自旋光谱探测自由基化学

• 批准号: RGPIN-2014-05991
• 负责人: Percival, Paul
• 金额: $ 2.19万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=632515
• 关键词: Free; Radical; Chemistry; Probed; Muon

In this research program the high-tech tools of particle physics are applied to study fundamental chemistry. The simplest chemical species is the hydrogen atom, which has a single electron in orbit around a proton as nucleus. Replacing the proton with a positive muon results in the muonium atom (Mu), which can be thought of as a light isotope of hydrogen (mass 0.11) similar to its heavier cousins deuterium (2) and tritium (3). Just like H, Mu can react with certain types of molecules to form free radicals. Because the muons come from a beam line where their spins are aligned in one direction, it is possible to use magnetic resonance techniques to follow what happens to Mu in its different chemical environments: how fast it reacts, which part of a molecule it reacts with, and the properties of the muoniated free radical formed. The muon spin spectroscopy experiments are performed at TRIUMF, Canada’s national cyclotron laboratory, one of only four sites in the world where there are facilities for such experiments. Why use such an exotic, expensive probe to study “simple” chemistry? It is because muon spin spectroscopy can be applied in situations where more conventional methods are impossible or give confusing results. An example of the former is radiation chemistry in the superheated water used in nuclear power reactors: we have studied reactions in water as high as 470°C and 400 atm. pressure and the results are being used by AECL to guide the development of the “Generation-IV” supercritical-water-cooled reactor. In a new project we are studying the chemistry of guest molecules inside gas hydrates similar to the infamous “ice crystals” that were involved in the Deepwater Horizon oil rig disaster in the Gulf of Mexico. Flames and explosions propagate through free radical reactions, yet almost nothing is known about the diffusion and interactions of atoms and radicals through the cavities of gas hydrate crystal structures. We have demonstrated the ability to detect Mu in hydrates of saturated organic molecules, and muoniated radicals in hydrates of similar unsaturated molecules. We have clear evidence that radicals behave differently in hydrates than in pure liquids at the same temperature. Further studies will involve lower temperatures, to investigate the change of molecular motion and reactivity as a function of temperature. The results will tell us how reactive free radicals behave in hydrate crystals and the conditions under which explosions occur. Our results on diffusion will also aid other researchers who are investigating the potential use of gas hydrates for hydrogen storage and carbon dioxide sequestration. Another project concerns the free radical reactivity of novel organosilicon, organogermanium, and organophosphorus compounds. Synthetic chemists from around the world collaborate with us by sending their new materials because we can provide unique information on how their molecules react with free radicals. These materials are often produced in the search for new catalysts for industrial processes, such as radical-induced polymerization. However, there is no simple means of producing “normal” H atoms without producing many other highly reactive, competing free radicals. Our work provides a direct route to the free radical reactivity of the new candidate catalysts.

在这个研究项目中，粒子物理学的高科技工具被应用于基础化学的研究。最简单的化学物质是氢原子，它有一个电子在轨道上围绕一个质子作为核。用正μ子取代质子会产生μ 鎓原子（Mu），它可以被认为是氢的轻同位素（质量0.11），类似于其较重的表亲氘（2）和氚（3）。就像H一样，Mu可以与某些类型的分子反应形成自由基。由于μ子来自一条束线，它们的自旋在一个方向上对齐，因此可以使用磁共振技术来跟踪Mu在不同化学环境中发生的事情：它反应的速度有多快，它与分子的哪一部分反应，以及形成的μ自由基的性质。μ子自旋光谱实验在加拿大国家回旋加速器实验室TRIUMF进行，该实验室是世界上仅有的四个拥有此类实验设施的地点之一。为什么要用这样一种奇特、昂贵的探针来研究“简单”的化学？这是因为μ子自旋光谱学可以应用于更传统的方法是不可能的或给出混乱结果的情况。前者的一个例子是核反应堆中使用的过热水中的辐射化学：我们研究了高达470°C和400 atm的水中的反应。AECL正在使用这些结果来指导“第四代”超临界水冷反应堆的开发。在一个新的项目中，我们正在研究气体水合物内部客体分子的化学性质，这种气体水合物类似于墨西哥湾深水地平线石油钻井平台灾难中臭名昭著的“冰晶”。火焰和爆炸通过自由基反应传播，但对原子和自由基通过气体水合物晶体结构的空腔的扩散和相互作用几乎一无所知。我们已经证明了在饱和有机分子的水合物中检测Mu的能力，以及在类似的不饱和分子的水合物中检测μ离子化自由基的能力。我们有明确的证据表明，在相同的温度下，自由基在水合物中的行为与在纯液体中的行为不同。进一步的研究将涉及更低的温度，以研究分子运动和反应性随温度的变化。结果将告诉我们活性自由基在水合物晶体中的行为以及爆炸发生的条件。我们关于扩散的研究结果也将有助于其他研究人员研究天然气水合物在储氢和二氧化碳封存方面的潜在用途。另一个项目涉及新型有机硅、有机锗和有机磷化合物的自由基反应性。来自世界各地的合成化学家通过发送他们的新材料与我们合作，因为我们可以提供关于他们的分子如何与自由基反应的独特信息。这些材料通常在寻找用于工业过程的新催化剂时产生，例如自由基诱导聚合。然而，没有一种简单的方法可以在不产生许多其他高度反应性的竞争性自由基的情况下产生“正常”的H原子。我们的工作提供了一个新的候选催化剂的自由基反应性的直接途径。