07482 IUPAC Gold Book - spin-statistical factor 10.1351/goldbook.ST07482 ST07482 current 1 From the possible encounter pairs between states of different spin multiplicity, only those conserving multiplicity in going to products are expected to react. 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. 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 PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 428 (https://doi.org/10.1351/pac200779030293) https://goldbook.iupac.org/terms/view/ST07482/html https://goldbook.iupac.org/terms/view/ST07482/json https://goldbook.iupac.org/terms/view/ST07482/plain 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 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. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . 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. 2026-04-28T23:05:11+00:00