Contribution of the radical-complex mechanism to the rate of the reaction CH(3) + O(2) (+ M) → CH(3)O(2) (+ M) at high pressures.

Earlier experimental studies of the falloff curves of the reaction CH(3) + O(2) (+ M) → CH(3)O(2) (+ 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 radical-complex (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 = CO(2), 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).