ENERGETICS AND MECHANISM OF DECOMPOSITION OF CF3OH

Ab initio calculations are used to examine the energetics of unimolecu lar and water-mediated decomposition of CF3OH into COF2 and HF. The ca lculations indicate that the barrier to unimolecular decomposition is large (42 +/- 3 kcal mol(-1)) and that the rate of this reaction is ne gligible at room temperature. This reaction is of no importance under ambient atmospheric conditions. The calculations also reveal a substan tially lower energy pathway for decomposition that is accessible via a reaction between CF3OH and water. This pathway involves formation of a six-membered-ring transition state, with water acting as a bridge be tween the fluorine and hydrogen of the alcohol. The existence of this lower energy pathway is consistent with experimental evidence for the intermediacy of H2O in the decomposition of CF3OH. From the computatio nal results the second-order rate constant for homogeneous decompositi on can be estimated to lie in the range 10(-27) to 10(-22) cm(3) molec ule(-1) s(-1) at 298 K and is likely too small to be atmospherically s ignificant. The rate for heterogeneous decomposition cannot be estimat ed from the computational results, but the results are consistent with a prominent role for heterogeneous decomposition in the atmospheric c hemistry of CF3OH.