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

点击翻译按钮获取中文摘要

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.