A direct study of the reaction of CH 2( 3B 1)-radicals with toluene in the temperature range 296 K

Abstract

The reaction (1) between CH2-radicals in the triplet electronic ground state,3B1 (≡3CH2), and toluene (T) 3CH2+T→products was studied in the gas phase at temperatures from 296 K≤T≤623 K. The overall rate constant of the reaction was measured between 472 K≤T≤623 K using the discharge flow Laser Magnetic Resonance method. The direct experimental results (±2°) were described by the expression K1exp=(9.4±1.6)·1013·exp[-(4530±100)K/T]cm3/mol·s. Allowing for the [3CH2] decay to occur both via direct reaction with the reactant as well as via partial equilibration between theand ã 1A1 (≡1CH2) excited electronic states followed by reactions of 1CH2 with T, the Arrhenius expression for the direct 3CH2 reaction in the temperature range investigated was found to be (k1b+k1c)=(6.0±1.8)·1013·exp[-(36.8±1.4), kJ mol−1/R·T] cm3/mol·s. The main reaction channels were deduced from the results of an end product study together with a comparison of the Arrhenius parameters to data obtained in this laboratory for related reactions of 3CH2. The end product distribution indicates that at room temperature abstraction of an H-atom from the CH3 group of toluene (reaction 1c) dominates over addition of the 3CH2 to the aromatic ring, whereas for T≥450 K the addition channel (reaction 1b) dominates. In combustion systems the role of 1CH2 has to be taken into account as well.