The reaction of methylidene (CH) with methanol isotopomers

Abstract

The reactions of the methylidene (CH) radical with a variety of methanol isotopomers has been studied using pulsed laser photolysis/laser induced fluorescence, as a function of temperature (298–753 K) and pressure (100–600 Torr helium). The rate coefficient was independent of total pressure and the following rate coefficients were determined:

where the errors represent statistical uncertainties at the 1σ level. The reaction can either proceed ia CH insertion into a C–H bond (as for the reaction with methane) or ia an initial complex with subsequent insertion into either the O–H or C–O bonds (as for the reaction with water). The absence of any significant isotope effect indicates that the reaction proceeds ia the latter mechanism, however, the room temperature rate coefficient is an order of magnitude greater than that for the reaction of CH with water. A correlation between the ionization potential of the substrate and rate coefficient is suggested to rationalise experimental observations. Above an ionization potential of approximately 11 eV, there is an inverse correlation between rate coefficient and ionization energy, below an ionization energy of 11 eV, the rate coefficient reaches a plateau of ∽3×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹.