Why is ΔJ = −1 for rotational emission spectra?

[avkr]

The selection rule for rotational spectra $ΔJ = ±1$. Is it always true for the emission part of rotation spectra $ΔJ = -1$ and how?

 

[Charles Link]

There recently was a related question posted on Physics Forums. You might find the discussion as well as the "links" that were provided of some interest. https://www.physicsforums.com/threa...ational-transitions-rant.931312/#post-5879837