ESR Study of the Kinetics of the Reaction of H Atoms with Methane

A wide-temperature-range study using ESR atom detection has been employed to measure the rate of the reaction H + CH4→H2 + CH3. Over the temperature range 426°–747°K, we obtain a specific rate constant for the above reaction of k1 = 6.9 ± 0.6 × 1013exp(−11 800 ± 200) / RT expressed in units of cubic centimeters per mole per second. The value obtained in the present work is compared to a number of other results obtained by various workers. The activation energy we observe is considerably higher than previous values obtained in this temperature range. However, our results coupled with the heat of the reaction predict an activation energy for the reverse reaction which agrees well with experimental values. In addition, the pre-exponential factor we obtain agrees with absolute rate theory predictions as well as with entropy considerations. We do not agree with literature results which give very low pre-exponential factors suggesting steric factors of the order of 10−3–10−5 for this reaction.