The muon as a non-perturbing probe of radical kinetics

Mu addition to double bonds places the muon two bonds away from the radical center. Mu is thus not normally directly involved in reactions of the radical, and any kinetic isotope effects are secondary and thus small. This makes the muon a non-perturbing radical kinetics probe. Its advantage is the extraordinary sensitivity of the technique which requires only a single muon in the sample at a given time. This eliminates any radical termination reactions. With on the order of 10 muons needed for an experiment the concentration of the reaction partner does not change, and kinetics is of ideal pseudo-first order. This eliminates a munber of sources for serious errors which often affect the accuracy of conventional radical kinetics. 

More recently, longitudinal muon spin relaxation was used to measure rate constants for the reactions of organic radicals with molecular oxygen and with NO in the gas phase [32, 46]. The reactions are important in combustion processes and for the degradation of organic pollutants in the atmosphere. Accurate determinations by conventional techniques have often proved to be non-trivial, so that the muon technique appears to be a very valuable addition to the tool box of experimental methods. 

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