| Summary: | Current understanding of the underlying mechanisms of muonium and Mu-radical spin relaxation
in the gas phase is presented. Models and formulae describing the effects of the three contributing
processes, spin exchange, chemical reaction and collisional relaxation, on the muon spin
polarization are developed and employed to extract reaction rate constants, cross sections and
other kinetic parameters in reactions of Mu with atoms and small molecules; notably Mu + Cs,
Mu + NO, Mu + N₂O and Mu + CO. The experimental data obtained are consistent with theory
and the models so introduced. The radical relaxation rates obtained for larger molecules ( MuC₂H₄
and MUC₄H₈) are well described by the phenomenological model presented, which serves as a
useful bridge linking the observed relaxation rates and the physical, chemical and magnetic
properties of the reactants and offers invaluable insight into the underlying mechanisms causing
muon spin relaxation. The ratios of thermal spin-flip cross sections (σ[sup H]/σ[sup Mu]) in electron spin
exchange interactions (Mu + Cs and Mu + NO) are found to be about 3, consistent with previous
experimental measurements for Mu + NO and Mu + O₂ systems. Reaction rates for Mu + NO,
Mu + N₂O and Mu + CO were measured over a wide range of pressures (1 to 60 atm, up to 272
atm for CO) and in one case (N₂O) over a range of temperatures (300-600 K). Dramatic kinetic
isotope effects are observed in all of these systems: a small "inverse" effect ([sup k]Mu/[sup k]H=0.23) in the
Mu + NO reaction and large "normal" effects (([sup k]Mu/[sup k]H > 100) for the Mu + N₂O and Mu + CO
reactions at room temperature. These kinetic isotope effects can be qualitatively understood
within the trends indicated by reaction rate theory and the experimental results of the analogous
H(D) reactions, but a quantitative comparison with theory must await specific calculations of the
Mu reaction rates. This thesis data represents the first observation of large tunneling effects at
room temperature in H-isotope addition reactions in the gas phase.
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