A mountain-pass in a
potential-energy surface is known as a col or
saddle point. It is a point at which the
gradient is zero along all coordinates, and the curvature is positive along all but one coordinate,
which is the
reaction coordinate, along which the curvature is negative.
Source:
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC
Recommendations 1996))
on page 158