spin multiplicity

Spin multiplicity refers to the number of possible orientations of an atom or molecule's unpaired electrons' spins. It’s calculated as 2S + 1, where S is the total spin (sum of unpaired electrons' spins). For example, if there are no unpaired electrons, the multiplicity is 1 (singlet). With one unpaired electron, it’s 2 (doublet). More unpaired electrons increase the multiplicity, indicating more possible arrangements of their spins. Spin multiplicity impacts the molecule's magnetic properties and reactivity, playing a key role in quantum chemistry and material science.