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

从核/物理化学的角度来看，正μ子及其μ 鎓原子（Mu=u+e-）具有两个关键方面：（i）在其环境中的μ子极化，初始为100%，这可以被灵敏地监测，以及（ii）μ原子的质量，其是H原子的1/9（但在其他方面化学上相同），从而提供化学反应性中量子质量效应的独特测试。第一方面表现在使用μ介子作为分子相互作用的自旋探针和沸石催化环境中μ介子化自由基的超精细耦合常数。拟议的研究是研究芳基（例如，取代的环己二炔基）和烷基（例如，从顺式-2-丁烯，或μ-叔丁基自由基）在八面沸石中的μ-离子化自由基，以探索催化感兴趣的温度。有很少或没有ESR研究的H-加合自由基，可以形成从酸性沸石（HY），从而可以作为这些重要的工业催化剂的反应中间体。第二个方面表现在测量轻氢原子同位素μ 鎓的化学反应速率。尽管测量的单碰撞反应速率在化学反应动力学领域中的重要性，但仍然是体速率常数影响生命过程和工业化学。此外，从科学的角度来看，对体速率常数的持续测量通常提供了对潜在势能面性质的最佳测试，其中量子质量效应，特别是隧道效应和零点能漂移在阈值附近被探测，对于Mu原子来说最引人注目。我们小组目前的研究重点是在宽的压力和温度范围内研究理论和大气化学（CO，NO，N2 O，CO2，NO2）感兴趣的小分子的复合率，包括超临界CO2的研究。 在这些努力中，超轻μ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.