No vibration spectrum for homonuclear diatomic molecules?

[bahamagreen]

Supposed to be because they have a zero dipole moment...

Dipole moment is variously described using neutral systems of pairs of opposite charge, or single items with charge, but I am finding no explanations of same charge pairs I understand..

Wiki states: "To show a vibrational spectrum, a diatomic molecule must have a dipole moment that varies with extension. So, homonuclear diatomic molecules do not undergo electric-dipole vibrational transitions. So, a homonuclear diatomic molecule doesn't show purely vibrational spectra."

How does the dipole moment not vary with extension?

 

[Orodruin]

In a homonuclear diatomic molecule there is no dipole moment because of the additional symmetry. Therefore, the dipole moment is zero regardless of extension and thus independent of the extension.