Experimental and Modeling Studies of the Pressure and Temperature Dependences of the Kinetics and the OH Yields in the Acetyl + O2 Reaction

The acetyl + O-2 reaction has been studied by observing the time dependence of OH by laser-induced fluorescence (LIF) and by electronic structure/master equation analysis. The experimental OH time profiles were analyzed to obtain the kinetics of the acetyl + O-2 reaction and the relative OH yields over the temperature range of 213-500 Kin helium at pressures in the range of 5-600 Torr. More limited measurements were made in N-2 and for CD3CO + O-2. The relative OH yields were converted into absolute yields by assuming that the OH yield at zero pressure is unity. Electronic structure calculations of the stationary points of the potential energy surface were used with a master equation analysis to fit the experimental data in He using the high-pressure limiting rate coefficient for the reaction, k(infinity)(T), and the energy transfer parameter, <Delta E-d > as variable parameters. The best-fit parameters obtained are k(infinity) = 6.2 x 10(-12) cm(-3) molecule(-1) s(-1), independent of temperature over the experimental range, and <Delta E-d >(He) = 160(T/298 K) cm(-1). The fits in N-2, using the same k(infinity)(T), gave <Delta E-d >(N-2) = 270(T/298 K) cm(-1). The rate coefficients for formation of OH and CH3C(O)O-2 are provided in parametrized form, based on modified Troe expressions, from the best fit master equation calculations, over the pressure and temperature ranges of 1 <= p/Torr <= 1.5 x 10(5) and 200 <= T/K <= 1000 for He and N-2 as the bath gas. The minor channels, leading to HO2 + CH2CO and CH2C(O)OOH, generally have yields <1% over this range.