Temperature-Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates |
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| Authors: | Dr. Rabi Chhantyal-Pun Dr. Max R. McGillen Dr. Joseph M. Beames Dr. M. Anwar H. Khan Dr. Carl J. Percival Prof. Dudley E. Shallcross Prof. Andrew J. Orr-Ewing |
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| Affiliation: | 1. School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS UK;2. School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT UK;3. Jet Propulsion Laboratory, Mail Stop 183-901, 4800 Oak Grove Drive, Pasadena, CA, 92209 USA |
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| 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(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. |
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| Keywords: | atmospheric chemistry Criegee biradical kinetics reactive intermediates trifluoroacetic acid zwitterions |
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