Hydrogen atom and free radical chemistry probed with muons

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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.