Let the strength of the nth multipole term of electromagnetic radiation be denoted and
The strength of multipole radiation most commonly decreases in the following order: (1) electric dipole, (2) electric quadrupole, magnetic dipole, (3) electric octupole, magnetic quadrupole, etc. An exception is rotational transitions of the O2 molecule, which has stronger magnetic dipole radiation (due to its unpaired electrons) than electric dipole (since it is a symmetric, homonuclear molecule).
