Kinetic Studies of the Reactions CH₃+ NO₂→ Products, CH₃O + NO₂→ Products, and OH + CH₃C(O)CH₃→ CH₃C(O)OH + CH₃, over a Range of Temperature and Pressure

The title reactions were investigated using pulsed laser photolysis combined with pulsed laser induced fluorescence detection of CH 3 O to determine the rate coefficients for CH 3 + NO 2 → products (3) and CH 3 O + NO 2 → products (5) as a function of temperature and pressure, and to estimate the yield of CH 3 (and thus the yield of CH 3 C(O)OH) from the reaction of OH with CH 3 C(O)CH 3 (2) at two different temperatures. Reaction 3 has both bimolecular and termolecular components: a simplified falloff parametrization with F cent = 0.6 gives = (3.2 ± 1.3) × 10 -28 ( T /297) -0.3 cm 6 s -1 and = (4.3 ± 0.4) × 10 -11 ( T /297) -1.2 cm 3 s -1 with CH 3 NO 2 the likely product. The rate constant for the bimolecular reaction pathway to form CH 3 O + NO (3a) was found to be 1.9 × 10 -11 cm -3 s -1 . The low- and high-pressure limiting rate coefficients for reaction between CH 3 O and NO 2 to form CH 3 ONO 2 (5b) were derived as = (5.3 ± 0.3) × 10 -29 ( T /297) -4.4 cm 6 s -1 and = (1.9 ± 0.05) × 10 -11 ( T /297) -1.9 cm 3 s -1, respectively. Although the final result is associated with some experimental uncertainty, we find that CH 3 is formed in the reaction between OH and CH 3 C(O)CH 3 at ≈50% yield at room temperature and 30% at 233 K.