Transition State

The transition state (TS) is the maximum in the reaction path, i.e. along the reaction coordinate.
In the remaining part of this chapter it is explained that a geometry can be characterized by calculating the force constants, the second derivatives of the energy with respect to the normal coordinates.
In a TS, one, and only one, negative eigenvalue should be found, and the corresponding coordinate is the reaction coordinate.

A TS is a stationary point, i.e. all first derivatives are zero, as in minima and maxima.

Back to Chapter 1, part A.