van der Waals interactions in the Cl+HD reaction

The van der Waals forces in the entrance valley of the Cl + HD reaction are shown here to play a decisive role in the reaction's dynamics. Exact quant um mechanical calculations of reactive scattering on a potential energy sur face without Cl-HD van der Waals forces predict that the HCl and DCl produc ts will be produced almost equally, whereas the same calculations on a new ab initio potential energy surface with van der Waals forces show a strong preference for the production of DCl. This preference is also seen in cross ed molecular beam experiments on the reaction. The study of chemical reacti on dynamics has now advanced to the stage where even comparatively weak van der Waals interactions can no longer be neglected in calculations of the p otential energy surfaces of chemical reactions.