multiplicity (spin multiplicity) 

https://doi.org/10.1351/goldbook.M04062
The number of possible orientations, calculated as 2 S+1, of the spin angular momentum corresponding to a given total spin quantum number (S), for the same spatial electronic wavefunction. A state of singlet multiplicity has S=0 and 2 S+1=1. A doublet state has S=12, 2 S+1=2, etc. Note that when S>L (the total orbital angular momentum possible) there are only 2 L+1 orientations of total angular momentum possible.
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2255 [Terms] [Paper]
Citation: 'multiplicity' 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.M04062 RIS BibTex EndNote
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Last revised: February 24, 2014