An analytical potential energy surface of the HClF (2A′) system based on abinitio calculations. Variational transition state theory study of the H+ClF→F+HCl, Cl+HF and F+HCl→Cl+HF reactions and their deuterium isotope variants

Abstract

In this work we have carried out abinitio electronic structure calculations on the ground (²A′) potential energy surface (PES) involved in the H(²S)+ClF and the F(²P)+HCl reactions. Transition states and van der Waals minima have been characterized and have been used along with a grid of approximately 3400 abinitio [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 abinitio 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≈1–2) for the three reactions depending on the temperature and according to the available experimental results.