  Based on fundamental symmetries, molecules cannot have a permanent electric
dipole moment although it is commonly used in the literature to explain the
different molecular spectra for heteronuclear and homonuclear molecules.
Electric-dipole rotational and vibrational spectra can indeed be observed in
heteronuclear molecules while they are missing in molecules with identical
nuclei. I show that the missing spectral features can be explained as an effect
of the exchange symmetry for identical particles.
