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)+H 2→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.

The Journal of Chemical Physics
Ottawa-Carleton Chemistry Institute

Wright, J.S, Donaldson, D.J., & Williams, R.J. (Richard J.). (1984). MRD-CI potential surfaces using balanced basis sets. II. O+H2 and F+H2. The Journal of Chemical Physics, 81(1), 397–406.