## Wikipedia - Molteplicità di spin multiplicity (spin multiplicity)

https://doi.org/10.1351/goldbook.M04062
The number of possible orientations, calculated as $$2\ S+1$$, of the spin @A00353@ 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 @D01853@ has $$S=\frac{1}{2}$$, $$2\ S+1=2$$, etc. Note that when $$S>L$$ (the total orbital @A00353@ possible) there are only $$2\ L+1$$ orientations of total @A00353@ possible.
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2255 [Terms] [Paper]