Term: activated state
https://doi.org/10.1351/goldbook.08141

Definition:
In theories of unimolecular reactions an energized chemical species, often characterized by the superscript \(^{\ddagger}\), where the excitation is specific and the molecule is poised for reaction.

Notes:
1) Often used as a synonym for activated complex or transition state, but not restricted to transition-state theory.
2) This is distinct from an energized molecule, often characterized by the superscript \(^{*}\), in which excitation energy is dispersed among internal degrees of freedom.
3) This is not a complex according to the definition in this Glossary.

Source: PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 357 (https://doi.org/10.1515/pac-2018-1010)

Citation: 'activated state' 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.08141

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