Calculated reaction rate of fluorinated propanes with hydroxyl radical

Abstract

The reaction rate with hydroxyl radical (OH) is important, since the tropospheric lifetime of a chemical substance is mainly determined by hydrogen abstraction of OH radical. We proposed the new economical method for estimating the reaction rate on the basis of the transition state theory and the molecular orbital method. Our estimation consists of the following three steps. (1) The structure and vibrational frequencies of a reactant and transition states are calculated by MP2/6-31G** method. (2) The energy of a reactant and transition states are corrected by MP-SAC2 method. (3) The reaction rate constants are calculated by the formula of bimolecular reaction. The parameter F2 of MP-SAC2 method was determined to be 0.865 so as to reproduce the observed rate constants of methane, ethane and their fluorides. In order to show the validity of our method, we applied the method to three fluorinated propanes. We calculated the rate constants of hydrogen abstraction and compared them with experimental values. The calculated rate constants agree with observed values within estimation uncertainty of +/-0.4 in log k.