Term Symbol - Others

Others

The term symbol is also used to describe compound systems such as mesons or atomic nuclei, or even molecules (see molecular term symbol). In that last case, Greek letters are used to designate the (molecular) orbital angular momenta.

For a given electron configuration

• The combination of an S value and an L value is called a term, and has a statistical weight (i.e., number of possible microstates) of (2S+1)(2L+1);
• A combination of S, L and J is called a level. A given level has a statistical weight of (2J+1), which is the number of possible micro states associated with this level in the corresponding term;
• A combination of L, S, J and M_J determines a single state.

As an example, for S = 1, L = 2, there are (2×1+1)(2×2+1) = 15 different microstates corresponding to the 3D term, of which (2×3+1) = 7 belong to the 3D₃ (J=3) level. The sum of (2J+1) for all levels in the same term equals (2S+1)(2L+1). In this case, J can be 1, 2, or 3, so 3 + 5 + 7 = 15.