spin-statistical factor

in diffusion-controlled reactions
https://doi.org/10.1351/goldbook.ST07482
From the possible @[email protected] 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 @[email protected] reactions, which have an @[email protected] Typical examples are @[email protected] of @[email protected] of aromatic @[email protected] by O2, @[email protected] of triplet states by O2, and triplet–triplet @[email protected]
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 428 [Terms] [Paper]