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Rate coefficients, k, for the gas-phase reaction CH3CO + Cl2 → products (2) were measured between 253 and 384 K at 55–200 Torr (He). Rate coefficients were measured under pseudo-first-order conditions in CH3CO with CH3CO produced by the 248-nm pulsed-laser photolysis of acetone, CH3C(O)CH3, or 2,3-butadione, CH3C(O)C(O)CH3. The loss of CH3CO was monitored by cavity ring-down spectroscopy (CRDS) at 532 nm. Rate coefficients were determined by first-order kinetic analysis of the CH3CO temporal profiles for [Cl2] < 1 × 1014 molecule cm−3 and the analysis of the CRDS profiles by the simultaneous kinetics and ring-down method for experiments performed with [Cl2] > 1 × 1014 molecule cm−3. k2(T) was found to be independent of pressure, with k2(296 K) = (3.0 ± 0.5) × 10−11 cm3 molecule−1 s−1. k2(T) showed a weak negative temperature dependence that is well reproduced by the Arrhenius expression k2(T) = (2.2 ± 0.8) × 10−11 exp[(85 ± 120)/T] cm3 molecule−1 s−1. The quoted uncertainties in k2(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 CH3CO + Cl2 reaction is presented. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 543–553, 2009 BIBLIOGRAPHY