Reactions at suprathreshold energy: Evidence of a kinematic limit to the internal energy of the products

In numerous state-to-state dynamics studies of atom transfer reactions at e nergies substantially in excess of the barrier height, population is not ob served in many of the energetically accessible product quantum states. Freq uently, the experimental state distributions end for internal energies well below the total energy limit. The lack of observable population in these h igh energy states has led us to conclude that not all of the total availabl e energy is accessible to the rovibrational states of the products. To expl ain this behavior we describe a model in which the internal energy is const rained by kinematic factors. We use this model to show that the energy cons traint is quantitatively determined by the skew angle for the reaction. We apply this model to the results of state-to-state experiments on a large nu mber of reactions and get quantitative agreement between our predictions an d actual observations. (C) 2001 American Institute of Physics.