The O(3P) Methylacetylene Reaction over Wide Temperature and Pressure Ranges

Rate coefficients for the reaction between ground-state O atoms and methylacetylene have been measured using the High-Temperature Photochemistry (HTP) technique at temperatures from 300 to 1350 K and pressures from 100 to 700 mbar. The oxygen atoms were generated by flash photolysis of O 2 or CO 2, and their relative concentrations were monitored by time-resolved resonance fluorescence. The data are independent of pressure and are well-fitted by the expression k (300−1350 K) = 2.9 × 10 -11 exp(−1134 K/ T ) cm 3 molecule -1 s -1 with 2σ precision limits of ±6% to ±12%, depending upon temperature, and corresponding 2σ accuracy limits of about ±22%. An estimation for methyl group H-abstraction yielded k H (300−2500 K) = 5.7 × 10 -20 ( T /K) 2.16 exp(−2429 K/ T ) cm 3 molecule -1 s -1 . This suggests that addition is the only significant initial O-atom attack step even at temperatures as high as those encountered in atmospheric-pressure methylacetylene−air flames.