Topography of potential-energy surfaces. DIM (diatomics-in-molecules) surface for Cl + Cl2

Abstract

Potential-energy surfaces have been calculated over the full range of nuclear configurations for the Cl + Cl₂ reaction using the DIM (diatomics-in-molecules) method with the 28 poly-atomic basis functions of ²A′ symmetry and the 26 of ²A″ symmetry arising from three Cl(²P_u) atoms. The lowest ²A′ surface has its lowest potential-energy barrier E_b≈ 28 kJ mol^–1 in a configuration bent by ca. 35° from the collinear configuration with ²Σ⁺_g symmetry. The lowest ²A″ surface has its lowest barrier E_b≈ 75 kJ mol^–1 in the collinear configuration with ²Π_u symmetry. Comparison with previous calculations on the F + F₂ reaction shows that the barrier heights are lower and the bent configuration more energetically favoured over the collinear configuration on the ²A′ surface, in accord with Walsh molecular-orbital theory. However, the predicted increase in bending of the ²A′ transition state for Cl₃ compared with F₃ is observed to only a small extent (ca. 5°)