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]