Temperature-dependent kinetics study of the gas-phase reactions of atomic chlorine with acetone, 2-butanone, and 3-pentanone

A laser flash photolysis – resonance fluorescence technique has been employed to study the kinetics of the reactions of atomic chlorine with acetone (CH3C(O)CH3, k1), 2-butanone (C2H5C(O)CH3, k2) and 3-pentanone (C2H5C(O)C2H5, k3) as a function of temperature (210-440 K) and pressure (30-300 Torr N2). No significant pressure dependence is observed for any of the reactions studied. Arrhenius expressions (units are 10-11 cm3 molecule-1 s-1) obtained from the data are k1(T) = (1.53 ± 0.19) exp[(–594 ± 33) / T], k2(T) = (2.77 ± 0.33) exp[(+76 ± 33) / T], and k3(T) = (5.66 ± 0.41) exp[(+87 ± 22) / T] where uncertainties are 2σ and represent precision only. The accuracy of reported rate coefficients is estimated to be ±15% over the entire range of pressure and temperature investigated. The room temperature rate coefficients reported in this study are in good agreement with a majority of literature values. However, the activation energies reported in this study are in poor agreement with literature values, particularly for 2-butanone and 3-pentanone. Possible explanations for discrepancies in published kinetic parameters are proposed, and the potential role of Cl + ketone reactions in atmospheric chemistry is discussed.