Temperature-dependent branching ratios of deuterated methoxy radicals (CH _2DO?) reacting with O _2

摘要

The methoxy radical is an intermediate in the atmospheric oxidation of methane, and the branching ratio (k _(1a)/k _(1b)) (CH _2DO? + O _2 → CHDO + HO _2 (1a) and CH _2DO? + O _2 → CH _2O + DO _2 (1b)) strongly influences the HD/H _2 ratio in the atmosphere, which is widely used to investigate the global cycling of molecular hydrogen. By using the FT-IR smog chamber technique, we measured the yields of CH 2O and CHDO from the reaction at 250-333 K. Kinetic modeling was used to confirm the suppression of secondary chemistry. The resulting branching ratios are well fit by an Arrhenius expression: ln(k _(1a)/k _(1b)) = (416 ± 152)/T + (0.52 ± 0.53), which agrees with the room-temperature results reported in the only previous study. The present results will be used to test our theoretical understanding of the role of tunneling in the methoxy + O _2 reaction, which is the prototype for the entire class of alkoxy + O _2 reactions.