The University of Liverpool maintains a ChemTube 3D page, where it says
*> Highly symmetric polyatomic molecules, such as carbon dioxide, also
have no net dipole moment - the dipoles along the C-O bonds are always equal and opposite and cancel each other out. It is important to recognise also that if a molecule has a permanent dipole, but this dipole lies along the main rotation axis, then the molecule will not have a rotational spectrum - such as for a water molecule.
1) A chemistry student brought this question to me, and I am also surprised by their claim. Why can't water have a rotational spectrum? It defies the very purpose of microwave oven and the gas phase rotational spectrum of water is all over the spectroscopic literature. I would like to confirm the with the opinion of spectroscopists that this is incorrect or not.
2) Another question from the student electromagnetic waves have an sinusoidal electric and a magnetic field of microwaves. How does the magnetic field interact with the permanent electric dipole moment of a molecule say HCl? I have checked many physical chemistry texts and they are quiet about the interaction from varying magnetic component and the dipole moment of the molecule. Electric field interaction is discussed in detail.