Ab initio molecular orbital calculations on F+H 2→HF+H and OH+H 2→ H 2O+H using unrestricted Møller-Plesset perturbation theory with spin projection

Abstract

The reactions of fluorine atom and hydroxyl radical with molecular hydrogen have been studied by molecular orbital methods using the 6-311G (d, p) and 6-311 + + G (2df, 2pd) basis sets with the unrestricted Hartree-Fock approach and with Møller-Plesset perturbation theory up to fourth order, with and without spin projection. The positions of transition states were optimized with a grid search at the MP n and PMP n levels using the 6-311G(d, p) basis. The projected MP2, MP3 and MP4 barriers are 1–1.5 kcal/mol lower and 0.03–0.05 Å closer to the reactants than the unprojected calculations. At the PMP4SDTQ/ 6-311 + + G(2df, 2pd) level, the classical barriers are 2.6 kcal/mol for F+H 2 and 5.7 kcal/mol for OH+H 2.