Title: spin-statistical factor
Long Title: IUPAC Gold Book - spin-statistical factor
DOI: 10.1351/goldbook.ST07482
Status: current

Definition
From the possible encounter pairs between states of different spin multiplicity, only those conserving multiplicity in going to products are expected to react.

Note
This factor determines the efficiency of diffusion-controlled reactions, which have an encounter-controlled rate. Typical examples are quenching of fluorescence of aromatic hydrocarbons by $\ce{O2}$, quenching of triplet states by $\ce{O2}$, and triplet–triplet annihilation.

Related Terms
- annihilation: https://goldbook.iupac.org//terms/view/A00366
- diffusion: https://goldbook.iupac.org//terms/view/D01716
- encounter: https://goldbook.iupac.org//terms/view/E02086
- encounter-controlled rate: https://goldbook.iupac.org//terms/view/E02089
- fluorescence: https://goldbook.iupac.org//terms/view/F02453
- hydrocarbons: https://goldbook.iupac.org//terms/view/H02889
- quenching: https://goldbook.iupac.org//terms/view/Q05007

Source
- PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 428 (https://doi.org/10.1351/pac200779030293)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/ST07482/html
- json: https://goldbook.iupac.org/terms/view/ST07482/json
- xml: https://goldbook.iupac.org/terms/view/ST07482/xml

Citation: Citation: 'spin-statistical factor' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.ST07482
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Accessed: 2026-04-28T23:08:20+00:00