Abstract
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(CH(2) OO + CF(3) COOH)=(3.4±0.3)×10(-10) cm(3) s(-1) and k((CH(3) )(2) COO + CF(3) COOH)=(6.1±0.2)×10(-10) cm(3) 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 [cm(3) s(-1) ]=(3.8±2.6)×10(-18) T(2) exp((1620±180)/T) + 2.5×10(-10) and k [cm(3) s(-1) ]=(4.9±4.1)×10(-18) T(2) exp((1620±230)/T) + 5.2×10(-10) for the CH(2) OO + CF(3) COOH and (CH(3) )(2) COO + CF(3) COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.