Rate Coefficients for the Reaction of OH with CF3CH2CH3 (HFC-263fb) Between 200 and 400 K: Ab Initio, DFT, and Transition State Theory Calculations

摘要

Rate coefficients for the reaction of the hydroxyl radical with CF3CH2CH3 (HFC-263fb) were computed using ab initio methods, viz. MP2, G39P2, and G3B3 theories between 200 and 400 K. Structures of the reactants in the ground state (GS) and transition state (TS) were optimized at MP2(FULL)/6-31G*. MP2(FULL)/6-311++G**, and B3LYP/6-31G* level of theories. Seven TSs were identified for the title reaction in the above theories. However, five out of seven TSs were found to be symmetrically distinct. The kinetic parameters due to these five different TSs are presented in this manuscript. Intrinsic reaction coordinate (IRC) calculations were performed to confirm the existence of transition states. The contributions of all the individual hydrogens in the substrate for the reaction are estimated and compared with the results obtained using Structure Additivity Relationships. The rate coefficients for the title reaction were computed to be k = (7.96 +/- 0.93) X 10(-13) exp [-(2245 +/- 30)/T] cm(3) molecule(-1) s(-1) at MP22, k = (9.50 +/- 0.93) X 10(-13) exp [-(1162 +/- 30)/T] cm(3) molecule(-1) s(-1) at G3MP2, and k = (7.01 +/- 0.88) X 10(-13) exp [-(753 +/- 35)/T] cm(3) molecule(-1) s(-1) at G3B3 theories. The theoretically computed rate coefficients are found to be in excellent agreement with the experimentally determined ones. The OH-driven atmospheric lifetimes of this compound are computed to be 132, 2.2, and 0.7 years at, MP2, G3MP2, and G3B3 level of theories, respectively.