Noun
English Wikipedia has an article on:transition stateWikipedia
transition state (plural transition states)
(chemistry) An intermediate state in a chemical reaction that has a higher free energy than the reactants or the products
The transition state of manners and language cannot be too often insisted upon: for this affected the process at both ends, giving the artist in fictitious life an uncertain model to copy and unstable materials to work in. George Saintsbury
Every chemical reaction has a transition state. Derek Barton