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

摘要

A 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 + H-2 -> 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 + H-2 PES. We obtain nonrelativistic barrier heights of 1.32 kcal/mol(-1) (bent) and 1.67 kcal/mol(-1) (collinear) that are similar to 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 approximate to 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 + H-2 -> 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.