The non-reactive j_z-conserving approximation as a probe for the entrance-channel dynamics in reactive collisions: H + H₂

Using the non-reactive classical j_z-conserving approximation we explore the approach of H to H₂. The purpose is to examine the dynamical consequences of several possible modifications of the intermediate- and long-range part of the SLTH potential-energy surface. The reason for the possible need of modification is the present disagreement between experiment and theory for resonances in the H + H₂ collision. It is shown how the stretching of the molecule determines the number of long-lived trajectories and its energy dependence. The influence of initial H₂ rotation is also studied. Several novel aspects of the j_z-conserving approximation, applicable to a wider set of systems, are introduced.