THE O(P-3) METHYLACETYLENE REACTION OVER WIDE TEMPERATURE AND PRESSURE RANGES

Rate coefficients for the reaction between ground-state O atoms and me thylacetylene have been measured using the High-Temperature Photochemi stry (HTP) technique at temperatures from 300 to 1350 K and pressures from 100 to 700 mbar. The oxygen atoms were generated by flash photoly sis of O-2 or CO2 and their relative concentrations were monitored by time-resolved resonance fluorescence. The data are independent of pres sure and are well-fitted by the expression k(300-1350 K) = 2.9 x 10(-1 1) exp(-1134 K/T) cm(3) molecule(-1) s(-1) with 2 sigma precision limi ts of +/-6% to +/-12%, depending upon temperature, and corresponding 2 sigma accuracy limits of about +/-22%. An estimation for methyl group H-abstraction yielded k(H)(300-2500 K) = 5.7 x 10(-20)(T/K)(2.16) exp (-2429 K/T) cm(3) molecule(-1) s(-1). This suggests that addition is t he only significant initial O-atom attack step even at temperatures as high as those encountered in atmospheric-pressure methylacetylene-air flames.