Reaction Products with Internal Energy beyond the Kinematic Limit Result from Trajectories Far from the Minimum Energy Path: An Example from H + HBr → H2 + Br.

The article demonstrates that trajectories far from a minimum energy path are, in general, responsible for production of highly internally excited products. It suggests that the energy available for internal excitation is constrained to a fraction of the total energy and the magnitude of this constraint depends only on the reaction kinematics (nuclear masses), so the energy available to internal modes is commonly said to be kinematically constrained. It presents an experimental evidence that a small fraction of the H + HBr reactive trajectories do not obey this kinematic constraint. It argues that the usually applicable kinematic limit is broken at high collision energy because some reactive collisions deviate significantly from the minimum energy path.