How does a reaction path branching take place? A classification of bifurcation events

Valley–ridge-inflection points (VRI) of a potential energy surface (PES) may have a strong relation to bifurcations of chemical reaction pathways. We explain how a reaction path has to be defined to describe the bifurcation of a ‘valley’ of the PES. We propose a classification of different VRI events: valley bifurcation, ridge bifurcation, and the mixed case in between. Chemical implications of the different cases are discussed. q 2004 Elsevier B.V. All rights reserved.