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

The reactants, products, and the transition state for the reaction CHF 3 + OH --> CF3 + H2O have been investigated using ab initio molecular orbital theory at the MP2 level. Geometry optimizations and vibrationa l frequency calculations have been performed on all reactants, product s, and the transition state at both the MP2/3-21G* and MP2/6-311G** l evel. 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 c alculations have been determined and corrected for zero-point energy e ffects. Transition state theory including tunneling contributions has been used to determine a rate constant which was compared with availab le experimental data. The QCISD/6-311G*//MP2/6-311G** calculations le ad 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 c orrection) of 1.034 x 10(-16) cm(3) molecule(-1) s(-1), in excellent a greement with the best experimental value of 2.1 x 10(-16) cm(3) molec ule(-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.