Rate coefficients for the reaction of the acetyl radical, CH 3 CO, with Cl 2 between 253 and 384 K

Rate coefficients, k , for the gas‐phase reaction CH 3 CO + Cl 2 → products (2) were measured between 253 and 384 K at 55–200 Torr (He). Rate coefficients were measured under pseudo‐first‐order conditions in CH 3 CO with CH 3 CO produced by the 248‐nm pulsed‐laser photolysis of acetone, CH 3 C(O)CH 3 , or 2,3‐butadione, CH 3 C(O)C(O)CH 3 . The loss of CH 3 CO was monitored by cavity ring‐down spectroscopy (CRDS) at 532 nm. Rate coefficients were determined by first‐order kinetic analysis of the CH 3 CO temporal profiles for [Cl 2 ] < 1 × 10 14 molecule cm −3 and the analysis of the CRDS profiles by the simultaneous kinetics and ring‐down method for experiments performed with [Cl 2 ] > 1 × 10 14 molecule cm −3 . k 2 (T) was found to be independent of pressure, with k 2 (296 K) = (3.0 ± 0.5) × 10 −11 cm 3 molecule −1 s −1 . k 2 (T) showed a weak negative temperature dependence that is well reproduced by the Arrhenius expression k 2 (T) = (2.2 ± 0.8) × 10 −11 exp[(85 ± 120)/T] cm 3 molecule −1 s −1 . The quoted uncertainties in k 2 (T) are at the 2σ level (95% confidence interval) and include estimated systematic errors. A comparison of the present work with previously reported rate coefficients for the CH 3 CO + Cl 2 reaction is presented. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 543–553, 2009