Temperature Dependence of the Rates of Reaction of Trifluoracetic Acid with Criegee Intermediates

The rate coefficients for gas-phase reactions of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240 - 340 K. The rate coefficients k(CH2OO + TFA) = (3.4 ± 0.3) × 10-10 cm3 s-1 and k((CH3)2COO + TFA) = (6.1 ± 0.2) × 10-10 cm3 s-1 at 294 K exceed estimates for collision-limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre-reactive complex. Fits to a model incorporating this complex formation give k [cm3 s-1] = (3.8±2.6)×10-18 T2 exp((1620±180)/T) + 2.5 × 10-10 and k [cm3 s-1] = (4.9±4.1)×10-18 T2 exp((1620±230)/T) + 5.2 × 10-10 for the CH2OO + CF3COOH and (CH3)2COO + CF3COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.