MRD-CI potential surfaces using balanced basis sets. II. O+H2 and F+H2

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Abstract
Multireference configuration interaction (MRD‐CI) methods are used to calculate ground state potential surfaces for three triatomic systems at frozen bond angles: H2O→OH+H at 104.5°, O(3P)+H2→OH+H at 180°, and F(2P)+H2→HF+H at 180°. The ‘‘balanced basis sets’’ are of double‐zeta plus polarization quality, augmented by (s, p) bond functions optimized for the diatomic hydrides. The CI data points are computed along rays of constant θ and the data on each ray are fitted by generalized Morse functions. The fits are excellent over a wide range of the potential. Cubic splines interconnect each ray, forming a smooth, continuous surface. Reaction energetics in each case are accurate to 2 kcal/mol or better, and force constants are reasonable. Barrier heights are 12.8 kcal/mol for 0+H2 and 0.1 kcal/mol for F+H2. The OH2 barrier lies near the best theoretical estimate. The FH2 barrier disagrees with previous estimates, but may resolve a conflict between theory and experiment for this reaction.