ABSTRACT
This chapter discusses the reaction dynamics not by relying upon the transition state theory and its extensions, but by providing a connection with the transition state through the concept of potential ridge. It summarizes the hyperspherical coordinate approach and the corresponding scattering equations, and defines the basic physical quantities. The conventional transition state plays an important role in the chemical reaction, but it does so particularly as a reaction barrier. The chapter describes the role of potential ridge, and presents some examples to demonstrate its significance for a qualitative understanding of reaction dynamics under the regime of the reduced dimensionality approximations. It also discusses the quantum mechanically accurate treatments of triatomic systems. Progress in theoretical methodologies and supercomputer capability has made it possible to clarify the correct dynamics of tri-and tetra-atomic reaction systems.
