A laser photolysis/LIF study of the reactions of O(3P) atoms with CH3 and CH3O2 radicals
Abstract
Kinetics and mechanisms of the reactions CH3+ O → CH2O+ H (1), and CH3O2+ O → CH3O+ O2(2) at 298 K have been investigated using 193 nm laser co-photolysis of N2O–azomethane mixtures for the simultaneous generation of O(3P) atoms and CH3(N2 as diluent)-CH3O2(O2 as diluent) radicals combined with LIF for the time-resolved detection of reaction products. From measurements of CH2O formation the rate coefficients k1 was determined as k1=(1.1 ± 0.4)× 10–10 cm3 s–1. Concurrent yield studies suggest that CH2O accounts for the total loss of CH3. The rate coefficient k2 was determined from observation of CH3O formation to be k2=(4.3 ± 2.0)× 10–11 cm3 s–1. Although in this reaction OH radicals and CH2O were also observed, a detailed product analysis combined with computer simulation suggests that these result from unavoidable parallel and consecutive reactions. Hence it is concluded that CH3O + O2 is the dominant product channel of reaction (2). Energy diagrams are presented which suggest that the dynamics of both reactions are determined by primary capture mechanism forming highly vibrationally excited adducts and followed by rapid subsequent decomposition, viz. CH3+ O → CH3O*→ CH2O + H (1) CH3O2+ O → CH3O*3→ CH3O + O2. (2) As a result of high excitation energies and low exit barriers k1 and k2 are not expected to be pressure-dependent.