The F + H2(v= 0) →FH (v′⩽ 3>) + H reaction: Quantum collinear reaction probabilities on three different potential energy surfaces

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Abstract
Exact quantum reaction probabilities have been calculated for the collinear reaction F + H2 (v = 0) →FH (v′ ⩽ 3) + H by a modified numerical version of the State Path Sum method. The potential energy surfaces used are the semiempirical LEPS surfaces No. I and No. V of Muckerman, and one based on the ab initio SCF CI surface of Bender et al. In each case, a rotated-Morse cubic-spline representation of the surfaces is used in the calculations. For the Muckerman V surface, the results agree well with those of Schatz et al. For the Muckerman I surface, our results are in fair agreement with the calculations of Wu et al., apart from an energy range where the scattering is sensitive to the number of sectors used to represent the surface. We have also found two new narrow scattering resonances for the Muckerman I surface. Although the three surfaces are quite similar, they give rise to considerably different quantitative scattering results. However, the main qualitative features in the scattering can be correlated in a one-to-one manner for the Muckerman I and V surfaces, and there are also some common features for the Bender et al. surface at low translational energies. At high translational energies the Bender et al. surface gives rise to some qualitatively different features. Comparison of the scattering for the three surfaces suggests that certain regions of an ab initio surface need to be known very accurately if quantitatively meaningful scattering results are to be obtained. These regions include the asymptotic diatomic molecule states, resonance scattering regions (if any) and, at low translational energies, the corner and saddle point regions. It is suggested that potential energy surfaces useful in scattering calculations might be obtained by rescaling ab initio surfaces using additional experimental and theoretical information.