Contribution of the Radical-Complex Mechanism to the Rate of the Reaction CH3 + O-2 (+ M) -> CH3O2 (+ M) at High Pressures

Abstract

Earlier experimental studies of the falloff curves of the reaction CH3 + O-2 M) -> CH3O2 ( M) in the bath gases M = Ar and N-2 (Fernandes et al., J. Phys. Chem. A 2006, 110, 4442), in addition to the usual behavior of the energy-transfer (ET) mechanism, showed first evidence for a participation of the radicalcomplex (RC) mechanism in the reaction at pressures above about 300 bar and at temperatures below 400 K. By extending these measurements to the bath gas M = CO2, more pronounced deviations from the ET mechanism were now observed. This unambiguously confirms the presence of the RC mechanism at high pressures in a medium-sized molecular system, analogous to earlier observations for larger systems such as the dimerization of benzyl radicals (Luther et al., Phys. Chem. Chem. Phys. 2004, 6, 4133).