Term: dividing surface https://doi.org/10.1351/goldbook.D01823 Definition: A surface, usually taken to be a hyperplane, constructed at right angles to the minimum-energy path on a potential-energy (reaction) surface. In conventional transition-state theory it passes through the highest point on the minimum-energy path. In generalized versions of transition-state theory the dividing surface can be at other positions; in variational transition-state theory the position of the dividing surface is varied so as to get a better estimate of the rate constant. Related Terms: 1) minimum-energy path (http://doi.org/10.1351/goldbook.M03931). 2) potential-energy (reaction) surface (http://doi.org/10.1351/goldbook.P04780). 3) transition-state theory (http://doi.org/10.1351/goldbook.T06470). 4) variational transition-state theory (http://doi.org/10.1351/goldbook.V06603). 5) rate constant (http://doi.org/10.1351/goldbook.O04322). Source: PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 163 (https://doi.org/10.1351/pac199668010149) Citation: 'dividing surface' 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.D01823 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.