An analytical potential energy surface of the HCIF (~2A') system based on ab initio calculations. Variational transition state theory study of the H + CIF -> F + HCI, CI + HF and F + HCI -> CI + HF reactions and their deuterium isotope variants

摘要

In this work we have carried out ab initio electronic structure calculations on the ground (~2A') potential energy surface (PES) involved in the H(~2S) + ClF and the F(~2P) + CHl reactions. Transition states and van der Waals minima have been characterized and have been used along with a grid of approximately 3400 ab initio [PUMP2/6-311G(3d2f,3p2d)] points to derive an analytical PES. The global root-mean-square deviation of the fit (2.66 kcal mol~(-1)) is within the range of the estimated ab initio accuracy. The saddle-point energies of this fitted PES were locally scaled to reproduce the thermal rate constants at 300 K of these reactions considering the H isotope. Calculated variational transition state theory rate constants with the inclusion of a microcanonical optimized multidimensional tunneling correction are in good accord with experiments at different temperatures, both for reactions with H and D isotopes. A small H/D kinetic isotope effect is predicted to have a similar extension (k_H/k_D approx= 1-2) for the three reactions depending on the temperature and according to the available experimental results.