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UBC Theses and Dissertations

Muonium reactions with aromatics Wu, Zhennan


Positive muons are produced at TRIUMF as pion decay products and form muo nium atoms in media such as water during their two microsecond lifetime. Muo niuin is a hydrogen—like atom with virtually the same Bohr radius and ionization energy as 1H, 2H and 3H, but with a mass one—ninth that of 1H. Its reactions toward solutes are studied by μSR (the muon spin rotation) and LCR (muon level crossing resonance spectroscopy). In this thesis, the reactions of mnuonium with some substituted aromnatics and N-heterocyclic compounds were studied. Reaction rate constants were measured in many cases, and products were identified as mnuonated free radicals formed by muonium addition to a ring-C. Muon hyperfine coupling constants of some muonated cyclohexadienyl-type radicals and all muonated mono- and diazine radicals studied here were determined. The LCR spectra of muonated radicals were recorded and the resonance signals were assigned to particular nuclei of these radicals. Radical isomer distributions and partial rate constants for mono substituted benzenes and N-heterocyclic compounds were estimated. π-electron densities and radical localization energies of neutral aromnatics were calculated by the Huckel MO method. For N-containing compounds LUMO levels as well as these parameters were also calculated by the same method. It was found that there exists a good correlation between partial rate constants and radical localization energies, which implies that muonium addition rates in these systems are mainly governed by an activation barrier proportional to the radical localization energies of the reactants.

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