AN AB-INITIO INVESTIGATION OF THE REACTION OF TRIFLUOROMETHANE WITH THE HYDROXYL RADICAL

The reactants, products, and the transition state for the reaction CHF3 + OH --> CF3 + H2O have been investigated using ab initio molecular orbital theory at the MP2 level. Geometry optimizations and vibrational frequency calculations have been performed on all reactants, products, and the transition state at both the MP2/3-21G** and MP2/6-311G** level. Single-point energy calculations at the MP2/6-311G** level using the MP2/3-21G** optimized geometries and at the QCISD/6-311G** level using the MP2/6-311G** optimized geometries have also been carried out on all species. Classical barriers corresponding to these different calculations have been determined and corrected for zero-point energy effects. Transition state theory including tunneling contributions has been used to determine a rate constant which was compared with available experimental data. The QCISD/6-311G**//MP2/6-311G** calculations lead to a classical barrier of 9.589 kcal mol(-1) and a rate constant at 298 K (using a nonsymmetric Eckart barrier to compute the tunneling correction) of 1.034 x 10(-16) cm(3) molecule(-1) s(-1), in excellent agreement with the best experimental value of 2.1 x 10(-16) cm(3) molecule(-1) s(-1). This leads to an estimated lifetime for CHF3, based on its reaction with OH radicals in the troposphere, of 65.5 yr.