The context of my question is rotational spectroscopy (using microwave radiation), where there is the $J = \pm 1$ selection rule. The way I understand spectroscopy is that the sample is irradiated with a range of frequencies. Is it possible, during the irradiation of the sample (say CO), for the molecule to be excited by 2 levels by 2 successive photons of the appropriate frequencies?
Now this does not affect the locations of the peaks per se, because the relaxation of course has to happen one level at a time. I am specifically wondering about the distribution of peaks, which is supposed to follow the Boltzmann distribution. Let us say, for example, we have a sample at absolute zero, where all the molecules are at the ground state $J = 0$. Is it possible for a molecule to be excited twice (or more), leading to the rotational spectrum showing more than one peak?
Thank you in advance.