Wikipedia - Annichilazione (it) annihilation

https://doi.org/10.1351/goldbook.A00366
1. (in radiochemistry) An interaction between a particle and its @A00401@ in which they both disappear.
Source:
Orange Book, 2nd ed., p. 211 [Terms] [Book]
2. (in photochemistry) Two atoms or molecular entities both in an excited @ET07026@ interact often (usually upon collision) to produce one atom or molecular entity in an excited @ET07026@ and another in its ground @ET07026@. This phenomenon (annihilation) is sometimes referred to as @E02111@.
See:
singlet-singlet annihilation
,
spin conservation rule
,
triplet-triplet annihilation
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2228 [Terms] [Paper]