MuSR and muonium studies of chemical reactivity and molecular interactions (at TRIUMF)

从核/物理化学的角度来看，正介子及其介子原子（Mu=u+e-）具有两个关键方面：(i)介子在其环境中的极化，最初为100%，可以灵敏地监测；（ii） Mu原子的质量，是h原子的1/9（但其他化学性质相同），从而为化学反应性中的量子质量效应提供了独特的测试。第一个方面表现在使用μ子作为分子相互作用的自旋探针，以及沸石催化环境中mumuated自由基的超精细耦合常数。拟议的研究是研究两种芳基(例如。取代环己二炔)和烷基(如：，从顺-2-丁烯，或mu -t-丁基自由基)在faujasites中，高于RT，以探索催化感兴趣的温度。h -加合物自由基可以由酸性沸石（HY）形成，因此可以作为这些重要的工业催化剂的活性中间体，很少或没有对h -加合物自由基的ESR研究。第二个方面表现在对轻h原子同位素——介子原子的化学反应速率的测量上。尽管测量的单碰撞反应速率在化学反应动力学领域具有重要意义，但影响生命过程和工业化学的仍然是体速率常数。此外，从科学的角度来看，体速率常数的持续测量通常提供了潜在势能表面性质的最佳测试，其中量子质量效应，特别是隧道效应和零点能量位移在阈值附近被探测，最显著的是Mu原子。我们小组目前的研究主要集中在理论和大气化学（CO， NO, N2O,CO2, NO2）在广泛压力和温度范围内的小分子重组率的研究，包括超临界CO2的研究。在这些努力中，超轻介子质量起着关键作用，以协同的方式影响加成、解离和稳定的反应速率。

From a nuclear/physical chemistry perspective, the positive muon and its muonium atom (Mu=u+e-) is endowed with two key aspects: (i) the muon polarization in its environment, initally 100%, which can be sensitively monitored and (ii) the mass of the Mu atom, which is 1/9th that of the H-atom (but otherwise chemically identical), thereby providing for unique tests of quantum mass effects in chemical reactivity. The first aspect finds expression in the use of the muon as a spin probe of the molecular interactions and hyperfine coupling constants of muoniated free radicals in the catalytic environments of zeolites. The proposed research is to study both aryl (eg., substituted cyclohexadieynl) and alkyl (eg., from cis-2-butene, or the Mu-t-butyl radical) muoniated radicals in faujasites , above RT, in order to explore temperatures of catalytic interest. There are little or no ESR studies of H-adduct radicals which could be formed from acidic zeolites (HY)  and which could thereby act as reactive intermediates in these important industrial catalysts. The second aspect finds expression in the measurement of chemical reaction rates of the  light H-atom isotope, muonium. Despite the importance  of measured single-collision reaction rates in the field of chemical reaction dynamics, it is still bulk rate constants that impact on both life processes and industrial chemistry. Moreover, from a scientific perspective, the continued measurement of bulk rate constants often provides the best tests of the nature of the underlying Potential Energy Surface, in which quantum mass effects, notably tunelling and Zero Point Energy shifts are probed near threshold, and most dramatically so for the Mu atom. Current research in our group is focussed on the study of recombination rates with small molecules of interest to both theoretical and atmospheric chemistry (CO, NO, N2O,CO2, NO2) over wide ranges of pressure and temperature, including studies in supercritical CO2.  In these endeavours the ultra-light muon mass plays a pivotal role, affecting the reaction rates for addition, dissociation and stabilization in a synergistic way.