Hydrogen atom and free radical chemistry probed with muons

这项研究计划使用正Muon作为探针，在更常规工具不适用的条件下研究氢原子和瞬时有机自由基的化学。Muon的意义在于它是氢原子类似物Muonium(Mu=µ+e-)的核心。Muu可以作为探针研究H原子的溶剂化和动力学，作为H的超轻同位素来探索动力学同位素效应。此外，Mu与不饱和分子发生反应，产生一个结合了Muon而不是质子的自由基。Muon自旋光谱可以测定Muon和其他磁核的超精细常数，提供类似于传统自由基的电子自旋共振实验的信息。Muon实验在加拿大国家回旋加速器实验室TRIUMF的分子与材料科学中心(CMMS)进行，世界上仅有的四个拥有此类实验设施的地点之一。CMMS得到了NSERC重大设施准入拨款的支持。使用这种奇特(且昂贵)探测器的理由是需要在更传统工具不适用的极端条件下研究氢原子化学和有机自由基。一个完美的例子是我们在过热水中的化学工作。超临界水焚烧炉中不存在这样的条件(建议用于有毒废物的处置)。我们的目标既包括基础测量(例如，确定酮在过热水中的酮-烯醇平衡常数)，也包括更多的应用项目(探索甲基叔丁基醚(MTBE)的水热降解，这种石油添加剂在某些地区是一种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.