Molecules with Microwave/Rotational spectrum

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SUMMARY

This discussion centers on the microwave (rotational) spectroscopy of various molecules, specifically addressing which molecules possess a microwave spectrum. It is established that diatomic molecules like H2 and N2 lack a permanent dipole moment, thus do not exhibit a purely rotational spectrum in the microwave region. The consensus is that while all molecules can theoretically rotate, only those with a dipole moment, such as H2O and N2O, will interact with microwave radiation due to their ability to change dipole orientation during rotation.

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  • Basic concepts of molecular symmetry and its effects on spectroscopy
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Homework Statement


This question is about microwave (rotational) spectroscopy.
Which of the following molecules have a microwave spectrum?
H2, N2, NO, N2O, CH4, CO2, OCS, H2O, Ethene, Benzene.


The Attempt at a Solution


According to my textbook, it appears that all molecules have a rotational spectrum. However, Wikipedia, "Diatomic molecules such as dioxygen (O2), dihydrogen (H2), etc. do not have a dipole moment and hence no purely rotational spectrum."

I'm not really sure what that's supposed to mean. Do all molecules have a rotational spectrum (I don't see why not, everything with a bond should be able to rotate)?

Is the rotation considered relative to one of the atoms in the molecule, or to the centre of mass?
 
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Have I understood it correctly if I suggest that H2, N2 and O2 all rotate, but (when not considering temporary dipoles) they should not interact with photons in the microwave (nor infrared for that matter) spectrum?
 
That would be my understanding. Both ends of the molecule interact identically, so there is no net force moment that can change rotation.

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