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.
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996))
on page 158