Term: non-crossing rule
https://doi.org/10.1351/goldbook.NT07425

Definition:
Electronic states of the same symmetry cannot cross along a reaction coordinate.

Note: Only applies to diatomic molecules and not to polyatomic molecules.

Related Terms:
1) reaction coordinate (http://doi.org/10.1351/goldbook.R05168).

Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 374 (https://doi.org/10.1351/pac200779030293)

Citation: 'non-crossing rule' 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.NT07425

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