The entrance complex, transition state, and exit complex for the F + H2O → HF + OH reaction. Definitive predictions. Comparison with popular density functional methods.

Following the H + H(2) and F + H(2) reactions, the fluorine atom - water system has the potential to become one of the best understood chemical reactions. Stationary points for the F + H(2)O potential energy surface have been located with the "Gold Standard" CCSD(T) method using the Dunning correlation consistent basis sets through quintuple zeta. The CCSD(T)/cc-pV5Z barrier height is prediced to be 2.5 kcal mol(-1), less than previous estimates of 4-7 kcal mol(-1). From higher level theoretical studies of the prototypical F + H(2) reaction, this barrier should be less than 0.5 kcal mol(-1) above the exact, nonrelativistic classical barrier height. 41 of the 49 DFT methods applied to F + H(2)O predict no barrier at all. The eight DFT methods that do predict a barrier show exothermicities that are somewhat too small. The CCSD(T)/cc-pV5Z entrance complex is bound by 3.4 kcal mol(-1) relative to separated F + H(2)O. The analogous exit complex is bound by 5.9 kcal mol(-1) relative to separated HF + OH.