Term: col (saddle point)
https://doi.org/10.1351/goldbook.C01145

Definition:
A mountain-pass in a potential-energy (reaction) 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.

Related Terms:
1) potential-energy (reaction) surface (http://doi.org/10.1351/goldbook.P04780).
2) saddle point (http://doi.org/10.1351/goldbook.S05446).
3) gradient (http://doi.org/10.1351/goldbook.G02669).
4) reaction coordinate (http://doi.org/10.1351/goldbook.R05168).

Source: PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 158 (https://doi.org/10.1351/pac199668010149)

Citation: 'col (saddle point)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01145

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