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UBC Theses and Dissertations

Measurement of the rate of hydrogen atom abstraction from methane and ethane by muonium Snooks, Rodney J.


Reaction rates for the gas-phase reactions Mu+ CH₄ → MuH + CH₃ and Mu + C₂H₆ → MuH + C₂H₅ have been measured using μSR over the temperature ranges 626-821 K and 511-729 K respectively. The usual Arrhenius plots for each data set are linear. The measured parameters A are 5.7 [+4.8 superscript and -2.5 subscript] x 10⁻⁸ and 1.0 [+0.7 superscript and -0.4 subscript] x 10⁻⁹ cm³ molecule⁻¹ s⁻¹, and the parameters E [α subscript], 24.66 [+0.88 superscript and -0.82 subscript] and 15.35 [+0.65 superscript and +0.59 subscript] kcal/mol respectively. The E [α subscript] values are 11.5 and 5.5 kcal/mol higher than for the corresponding H atom reactions. The very large increases in E [α subscript] seem to indicate drastic differences between the Mu and H variants of the title reactions, in location of the transition states on the potential energy surfaces. Also, for the Mu variants, the reaction rates seem to be reduced less for vibrationally excited states of CH₄ and C₂H₆than for the ground states than is the case for the corresponding H atom reactions, an effect which contributes to the large increase in activation energy for Mu.

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