Near-field influence on barrier evolution in symmetric atom transfer reactions: A new model for two-state mixing

We here consider the fundamental interactions which drive barrier evolution in atom transfer reactions. By applying the functional behavior predicted by second-order nondegenerate perturbation theory to a symmetric linear cur ve crossing model, we are able to derive a simple formula for two-state mix ing in the near-field. It becomes readily apparent that the system property most critically responsible for governing the magnitude of coupling is the diabatic state-to-state overlap. In order to explore this parameter in dep th, we outline a basic strategy for diabatic state construction in the near -field and use the imposed symmetry requirements and phase relations to der ive a functional form which relates the state-to-state overlap to molecular orbital properties of the isolated reactants and the interatomic overlap m atrix. Finally, we show how trends in barrier heights may be analyzed in th e context of combined far-field and near-field effects and how these effect s may be separated in order to provide insight into the underlying physics and broadly applicable mechanistic information.