ON THE EFFECTS OF AN INTERNAL BARRIER ON FAST 4-ATOM ION-MOLECULE REACTIONS

We investigate the influence of an internal barrier on an exothermic a diabatic reaction model between diatomic ions and molecules. Reaction cross-sections are calculated from quasi-classical trajectories for di fferent initial vibrational and rotational states of the reactants and for relative collision energies in the range from 0.01 to 3 eV. It is shown that the height of a late internal barrier strongly influences both the characteristics of the state-selected cross-sections and the energy distributions of the products. In contrast to complex formation in the entrance region according to the Langevin model our analysis e mphasizes the role of the full potential energy surface for an underst anding of the dynamics of ion-molecule reactions. (C) 1996 American In stitute of Physics.