Atoms have Terms Symbols such as S (L=0), P (L=1), D (L=2), etc...In case of molecules, L no longer exists as other symbols are uesd: which ones?
I often see: Sigma [itex]\Sigma[/itex], Pi [itex]\Pi[/itex], etc. Often with a subscript g or u. The meaning are given in various books. For example, Landau and Lifgarbagez "Quantum Mechanics".