FTIR-smog chamber techniques were used to determine rate constants for the gas-phase reaction of Cl and F atoms with CH3C(O)C(O)CH3 and F atoms with CH3C(O)F of (4.0 +/- 0.5) x 10(-13), (4.9 +/- 0.7) x 10(-11), and (3.6 +/- 0.4) x 10(-12) cm(3) molecule(-1) s(-1), respectively. Two pathways for the reaction of Cl and F atoms with CH3C(O)C(O)CH3 were found : (1a) Cl + CH3C(O)C(O)CH3 --> HCl + CH3C(O)C(O)CH2., (1b) Cl + CH3C(O)C(O)CH3 --> CH3C(O)Cl + CH3C(O)., (2a) F + CH3C(O)C(O)CH3 --> HF + CH3C(O)C(O)CH2., (2b) F + CH3C(O)C(O)CH3 --> CH3C(O)F + CH3C(O)., with branching ratios of k(1b)(k(1b) + k(1a)) = 0.23 +/- 0.02 and k(2b)/(k(2b) + k(2a)) = 0.56 +/- 0.09. It was determined that the atmospheric fate of CH3C(O)C(O)CH2O . radicals is decomposition to give HCHO, CO, and CH3C(O). radicals. Pulse radiolysis coupled to UV absorption spectroscopy was used to study the kinetics of the reaction of F atoms with CH3C(O)C(O)CH3 as well as spectra of CH3C(O)C(O)CH2. and CH3C(O)C(O)CH2O2. radicals over the wavelength range 220-400 nm at 295 K. The rate constant for the reaction of F atoms with CH3C(O)C(O)CH3 was determined to be (4.6 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1). The absorption cross sections of CH3C(O)C(O)CH2. and CH3C(O)C(O)CH2O2. radicals were (5.4 +/- 1.0) x 10(-18) at 250 nm and (2.0 +/- 0.5) x 10(-18) cm(2) molecule(-1) at 320 nm, respectively. Results are discussed with respect to the available databaae concerning the reaction of Cl and F atoms with organic compounds.