Hydrogen atom and free radical chemistry probed with muons

本研究计划采用正介子作为探针，在常规工具不适用的条件下研究氢原子和瞬态有机自由基的化学性质。μ子的意义在于它是类似于氢原子的Muonium （Mu =µ+e-）的原子核。Mu可以作为探针来研究H原子的溶剂化和动力学，也可以作为H的超轻同位素来探索动力学同位素效应。此外，Mu与不饱和分子的反应会产生含有μ子代替质子的自由基。μ子自旋光谱可以确定μ子和其他磁性原子核的超精细常数，提供了类似于传统自由基的电子自旋共振实验的信息。μ子实验是在加拿大国家回旋加速器实验室（TRIUMF）的分子和材料科学中心（CMMS）进行的，这是世界上仅有的四个拥有此类实验设施的地点之一。CMMS由NSERC主要设施访问补助金支持。使用这种奇特的（昂贵的）探针的理由是需要在更传统的工具不适用的极端条件下研究氢原子化学和有机自由基。一个很好的例子就是我们在过热水中进行的化学实验。超临界水焚烧炉（建议用于处理有毒废物）存在这种情况。以及压水堆的热传输系统。μ子光谱学是一种独特的方法，可以在高达400℃的水中获得氢原子反应的直接动力学数据，并在这些极端条件下表征有机自由基。我们的目标包括基础测量（例如确定酮类在过热水中的酮-烯醇平衡常数）和更多应用项目（探索水热降解甲基叔丁基醚（MTBE），一种石油添加剂，在某些地区是严重的地下水污染物）。

This research program employs the positive muon as a probe to investigate the chemistry of hydrogen atoms and transient organic free radicals under conditions where more conventional tools are not applicable.  The significance of the muon is that it is the nucleus of the hydrogen atom analogue Muonium (Mu = µ+e-).  Mu can be used as a probe to investigate H atom solvation and kinetics, and as an ultra-light isotope of H to explore kinetic isotope effects.  In addition, reaction of Mu with an unsaturated molecule results in a free radical incorporating a muon in place of a proton.  Hyperfine constants of the muon and other magnetic nuclei can be determined by muon spin spectroscopy, providing analogous information to electron spin resonance experiments on conventional free radicals.  Muon experiments are performed at the Centre for Molecular and Materials Science (CMMS) at TRIUMF, Canada's national cyclotron laboratory, one of only four sites in the world where there are facilities for such experiments.  CMMS is supported by an NSERC Major Facilities Access grant.  The justification for using such an exotic (and expensive) probe is the need to study H atom chemistry and organic free radicals under the extreme conditions where more conventional tools are not applicable.  A perfect example is our work on chemistry in superheated water.  Such conditions exist in supercritical water incinerators (proposed for the disposal of toxic wastes). and the heat transport systems of pressurized water nuclear reactors.  Muon spectroscopy is unique as a method for obtaining direct kinetic data on hydrogen atom reactions in water up to 400 C, and for characterizing organic radicals under these extreme conditions.  Our goals include both fundamental measurements (e.g. determination of keto-enol equilibrium constants of ketones in superheated water) and more applied projects (exploring the hydrothermal degradation of methyl tert-butyl ether (MTBE), a petroleum additive that is a serious ground-water pollutant in some areas.