Rate of Association of Methyl Radicals

Abstract

The recombination rate constant of methyl radicals has been redetermined by the intermittent illumination method as 3.7×1013 cc/mole sec at 165°, after a correction for the concurrent formation of methane. The recombination rate constant of deuterated methyl radicals has been found to have a substantially identical value. The dependence of these second-order rate constants on total pressure was studied over the range of 1- to 10-mm acetone pressure. Both rate constants were found to decrease identically with pressure. The form of their pressure dependence agrees with deductions from the ``third-body'' stabilization theory. It is shown that the absolute magnitude of the recombination rate constants, their near-identity and their identical decrease with pressure are all consistent with theoretical predictions, provided the methyl radicals form a loosely bound critical complex, in which they carry out essentially unhindered rotations. Recent literature data on the recombination of methyl radicals are reviewed, and it is shown that they are not in serious disagreement with the present measurements.