where i ≠ j, and  and  represent the spatial configuration of the states. The validity of the El-Sayed rule for different point groups follows the conditions in Table . Thus, it is strictly valid for C2v and D2 molecules only. It may occasionally be valid for Dn (n > 2), Cnv (n > 2), Dnh, Dnd, and cubic groups, depending on the particular state's irreducible representations. Depending on how close the molecule is to a higher symmetry group, it may be approximately invoked for C1, C2, and Cs groups.