This rule states that for monophotonic radiative transitions in centrosymmetric systems,
the only non-vanishing electric-dipole transition moments are those which connect
an even term (
g) with an odd term (
u).
Source:
PAC, 1996, 68, 2223
(Glossary of terms used in photochemistry (IUPAC Recommendations 1996))
on page 2251