Kinetics and thermochemistry of the reaction of 1-methylpropargyl radicals with oxygen molecules: Experiments and computations

We have used laser-photolysis/photoionization mass spectrometry to measure the kinetics of the reaction of 1-methylpropargyl (but-3-yn-2-yl, ) radicals with oxygen molecules as a function of temperature ( T = 200 − 685 K ) and bath gas density ( 1.2 − 15 × 10 16 cm − 3 ). The low temperature (T ≤ 304 K) kinetics is dominated by oxygen addition to the carbon of the radical to form a peroxyl radical, and the measured bimolecular rate coefficient exhibits negative temperature dependence and depends on bath gas density. At slightly higher temperatures ( 335 − 396 K ), where the redissociation rate of the peroxyl is already observable, we measured the equilibrium constant as a function of temperature. At even higher temperatures ( T = 479 − 685 K ), the loss rate of 1-methylpropargyl is determined by the addition of oxygen to the terminal carbon and the reaction is observed to produce methylketene. The high-temperature bimolecular rate coefficient is independent of bath gas density and the temperature dependence is weakly positive. To explain our experimental findings, we performed quantum chemical calculations together with master equation simulations. By using our experimental data to constrain key parameters, the master equation model was able to reproduce experimental results reasonably well. We then extended the conditions of our simulations up to 2000 K and 100 bar. The results of these simulations are provided in ChemKin compatible PLOG format.