Temperature‐Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

The rate coefficients for gas‐phase reaction 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 + CF3COOH)=(3.4±0.3)×10−10 cm3 s−1 and k((CH3)2COO + CF3COOH)=(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.