Hund rules

https://doi.org/10.1351/goldbook.H02871
  1. Of the different multiplets resulting from different configurations of electrons in @DT07018@ of an atom those with greatest multiplicity have the lowest energy (multiplicity rule).
  2. Among multiplets having the same multiplicity, the lowest-energy one is that with the largest total orbital @A00353@ (@A00353@ rule) (valid if the total orbital @A00353@ is a constant of motion).
  3. In configurations containing shells less than half full of electrons, the term having the lowest total @A00353@ \(J\) lies lowest in energy, whereas in those with shells more than half filled, the term having the largest value of \(J\) lies lowest (fine structure rule). Hund rules apply if the 'Russell–Saunders' @C01025@ scheme is valid. Sometimes the first rule is applied with questionable validity to molecules.
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2246 [Terms] [Paper]