Rate coefficients for the gas-phase reaction CH3CO + O3 ? products (1) were measured between 248 and 403 K at 60–200 Torr (N2). Rate coefficients were measured under pseudo-first-order conditions in CH3CO with CH3CO produced by 248 nm pulsed laser photolysis of acetone and monitored using cavity ringdown spectroscopy at 532 nm. Rate coefficients were found to be pressure independent with a weak neg1 ative temperature dependence k1 ðTÞ = 1:50+0:25 0:30 10
11
exp½ð300 50Þ=T cm3 molecule s1 and k1(296 K) = (4.4 ± 0.5) 1011 cm3 molecule1 s1 where the quoted uncertainties are 2r and include estimated systematic errors.