A theoretical study of the potential energy surface for OH+H2

Abstract

Barrier heights and transition state geometries have been calculated for the reaction OH+H2→H2O+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). The saddle point geometry is found to be coplanar and to resemble OH+H2 as expected because of the large exoergicity (∼16 kcal/mole) of the reaction. The OH distance of the OH moiety is essentially the same as for the OH molecule, while the HH distance of the H2 moiety is 0.10 Å (∼14%) longer than for H2. The distance from the O to the near hydrogen of the H2 moiety is 0.35 Å (∼36%) longer than for the H2O molecule. The HOH angle is 98° and the H2 moiety is tilted from collinearity with the O atom by 15° toward the H of the OH moiety. The calculated barrier height using a [4s3p2d/3s2p] basis set is 6.2 kcal/mole. Transition state theory calculations (including a Wigner tunneling correction) using the theoretically computed surface predict rate constants which are in excellent agreement with experiment over the temperature range of 300–2000 °K.