Orientation dependence of the F + H2 reaction. Analysis of the angle-dependent line-of-centres model

Abstract

The orientation dependence of the F + H₂→ HF + H reaction on the Muckerman 5 potential-energy surface has been investigated. Extensive quasiclassical trajectory (QCT) calculations in 1D (collinear), 2D (coplanar) and 3D have been performed and have been used to assess the validity and limitations of the angle-dependent line-of-centres model (ADLOC). Four different angle-dependent barrier functions have been employed in the ADLOC calculations, together with two different choices of the collision diameter. The QCT results are used to investigate whether there exists a set of ADLOC parameters that relate the ADLOC model in a consistent way to the potential surface and collision properties of the reaction. Although there are quantitative discrepancies with the QCT results, the ADLOC model is able to give a satisfactory qualitative description of orientational effects on reaction cross-sections and opacity functions. A method for determining an effective barrier function by inversion of QCT data is described. Some new analytical results in 2D and 3D have also been obtained for the ADLOC model.