The Photoionization Spectrum of the Acetyl Radical and the Kinetics of Its Unimolecular and Bimolecular Reactions at Elevated Pressures

The experimental data were simulated using a kinetic model consisting of unimolecular and bimolecular reactions driving CH₃CO formation and decay as well as relevant secondary reactions describing the evolution of the observed intermediates. The measured time profiles showed strong sensitivity to the following reactions involving CH₃CO: (R1) CH₃CO = CH₃ + CO, (R2a) CH₃CO + CH₃CO = (CH₃CO)₂, (R3a) CH₃CO + CH₃ = CH₃COCH₃, and (R5) CH₃CO + Cl = CH₂CO + HCl.

The best-fit bimolecular reaction rate coefficients (<i>k</i>_2a, <i>k</i>_3a, and <i>k</i>₅) differ from the literature values by up to a factor of 2, most likely because the prior works studied each reaction separately, rather than in one unified experimental campaign, and were influenced by other competing reactions. Simulations using the assembled kinetic model enable a direct determination of the rate coefficient of (R1), which is fit to the Arrhenius expression, <i>k</i>₁ = 7.63 × 10¹⁰ exp(−6868/<i>T</i>) s^–1 (336–366 K, 500 kPa, He buffer, and uncertainty of ±40%).

The present study extends the previously available data on CH₃CO dissociation to much higher pressures and provides improved constraints for collisional energy transfer parameters and activation energies from theoretical kinetics studies.