F + H2 → FH + H potential energy surface: Construction of the reference configuration state function space and MR‐ACPF‐2 results

Abstract

AbstractA new electronic configuration reference space (subsequently used in multi‐reference averaged coupled pair functional (MR‐ACPF) or multi‐reference configuration interaction singles and doubles [MR‐CI(SD)] level treatments of electron correlation) is determined using the aug‐cc‐pVQZ basis set as a step toward constructing a new potential energy surface (PES) for the F + H2 → FH + H reaction. We use our new reference space to calculate several chemically important properties (e.g., barriers, exothermicity, van der Waals wells) of the F + H2 PES. We obtain nonrelativistic barrier heights of 1.32 kcal/mol−1 (bent) and 1.67 kcal/mol−1 (collinear) that are ∼0.2–0.3 kcal/mol−1 lower than those obtained from the current best PES. Our nonrelativistic value for the exothermicity is 32.45 kcal/mol−1, which is 0.7–1.1 kcal/mol−1 higher than the values obtained from some other PESs and 0.45 kcal/mol−1 higher than the experimental value. The van der Waals wells we find are slightly deeper (0.05 kcal/mol−1) than the wells on the other PES. The ≈1‐kcal/mol−1 magnitude of the differences among barrier heights, exothermicities, and well depths, obtained in our work and using the most reliable current PESs suggest that to obtain a three‐dimensional (3D) PES for the F + H2 → FH + H accurate to 0.2 kcal/mol−1, we will have to use even higher‐level methods (e.g., explicitly correlated wave functions) and include relativistic corrections. We intend to do so in the next phase of this effort that is currently under way. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006