Accurate Determination of Barrier Height and Kinetics for the F + H2O → HF + OH Reaction

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 117; no. 36; pp. 8864 - 8872
• Main Authors: Nguyen, Thanh Lam, Li, Jun, Dawes, Richard, Stanton, John F, Guo, Hua
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 12.09.2013
• Subjects: Ab initio calculations; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Coupled cluster theory; Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; Physics; Electron correlations; Isotope effects; Theoretical study; Potential energy surfaces; Classical trajectory; MR CI method; Ab initio calculations; Kinetics; Excitation; Rate constant; Coupled cluster method
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp4069448

The reaction energy and barrier height of the title reaction are investigated using two high-level ab initio protocols, namely Focal Point Analysis (FPA) and modified High Accuracy Extrapolated Ab Initio Thermochemistry (HEAT) methods. It is concluded from these calculations that despite some multireference character, dynamic electron correlation plays a dominant role near the reaction barrier. Thus, the coupled-cluster method with higher excitations than singles and doubles gives a better description than the multireference configuration interaction method for the barrier height. The FPA and HEAT classical barrier heights, including the spin–orbit and other corrections, are 1.919 and 2.007 kcal/mol, respectively. The rate constants and H/D kinetic isotope effect for the title reaction are determined by semiclassical transition-state theory based on the anharmonic potential energy surface near the saddle point, and the agreement with experiment is excellent. The rate constants are also computed using a quasi-classical trajectory method on a global potential energy surface scaled to the FPA barrier height and a similar level of agreement with experimental data is obtained.