Spin–orbit coupling lifts the degeneracy of the electronic states. This is because the z -component of spin interacts with the z -component of the orbital angular momentum, generating a total electronic angular momentum along the molecule axis J z. This is characterized by the quantum number M J , where M J = M S + M L . Again, positive and negative values of M J are degenerate, so the pairs (M L, M S) and (− M L, − M S) are degenerate. These pairs are grouped together with the quantum number Ω Ω , which is defined as the sum of the pair of values (M L, M S) for which M L is positive: Ω Ω = Λ Λ + M S