Flow reactor studies of methyl radical oxidation reactions in methane-perturbed moist carbon monoxide oxidation at high pressure with model sensitivity analysis

New rate constant determinations for the reactions CH3 + HO2 --> CH3O + OH (1) CH3 + HO2 --> CH4 + O-2 (2) CH3 + O-2 --> CH2O + OH (3) were made at 1000 K by fitting species profiles from high-pressure flow rea ctor experiments on moist CO oxidation perturbed with methane. These reacti ons are important steps in the intermediate-temperature burnout of hydrocar bon pollutants, especially at super-atmospheric pressure. The experiments u sed in the fit were selected to minimize the uncertainty in the determinati ons. These uncertainties were estimated using model sensitivity coefficient s, derived for time-shifted flow reactor experiments, along with literature uncertainties for the unfitted rate constants. The experimental optimizati on procedure significantly reduced the uncertainties in each of these rate constants over the current literature values. The new rate constants and th eir uncertainties were determined to be, at 1000 K: k(1) = 1.48(10)(13) cm(3) mol(-1) s(-1) (UF=2.24) k(2) = 3.16(10)(12) cm(3) mol(-1) s(-1) (UF= 2.89) k(3) =2.36(10)(8) cm3 mol(-1) s(-1) (UF = 4.23) There are no direct and few indirect measurements of reactions (1) and (2) in the literature. There are few measurements of reaction (3) near 1000 K. These results therefore represent an important refinement to radical oxidat ion chemistry of significance to methane and higher alkane oxidation. The model sensitivity analysis used in the experimental design was also use d to characterize the mechanistic dependence of the new rate constant value s. Linear sensitivities of the fitted rate constants to the unfitted rate c onstants were given. The sensitivity analysis was used to show that the det erminations above are primarily dependent on the rate constants chosen for the reactions CH3 + CH3 + M --> C2H6 + M and CH2O + HO2 --> HCO + H2O2. Unc ertainties in the rate constants of these two reactions are the primary con tributors to the uncertainty factors given above. Further reductions in the uncertainties of these kinetics would lead to significant reductions in th e uncertainties in our determinations of k(1), k(2), and k(3). (C) 2001 Joh n Wiley & Sons, Inc.