A theoretical study of the potential energy surface for O(3<i>P</i>)+H2

Abstract

Barrier heights and transition state geometries have been calculated for the reaction O(3P)+H2→OH+H using large scale POL-CI wave functions (based on GVB wave functions using basis sets of up to triple zeta valence plus double zeta polarization quality). A detailed study was made of the effects on the calculated barrier height and saddle point geometry of (i) basis set, (ii) choice of orbitals, and (iii) choice of reference configurations. Calculations using a [4s3p2d/3s2p] basis lead to a collinear saddle point with rHH=0.92 Å and rOH=1.23 Å with a corresponding barrier height of 12.5 kcal/mole. There are two surfaces which connect the reactants with the products: one of 3A′ symmetry and one of 3A″ symmetry (these correspond to the two degenerate components of the 3Π state in collinear geometries). In the transition state region, the 3A′ surface has a steeper bending curve than the 3A″ surface leading to significantly different reaction rates on the two surfaces.