### 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.