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Chemistry

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  • $\begingroup$ Thank you! That makes a lot of sense, and I suspected something similar. The only thing that bothers me is that in my mind, the different vibrational levels lead to a small number of narrow energy bands. I have a hard time imagining that they are numerous enough and close enough to each other to give a broad, "smooth" absorption spectrum overall. But I guess they do? $\endgroup$
    – Bernhard Werner
    Commented Dec 28, 2021 at 16:34
  • $\begingroup$ Yes, in solution, there are so many molecules, with slightly different energies that there are so many transitions, that it looks like a continuous curve. $\endgroup$
    – ACR
    Commented Dec 28, 2021 at 16:42
  • 2
    $\begingroup$ Yes, you could expect some fine structure, and look at the iodine gas phase spectrum in @M.Farooq's answer, there you have it! It is a matter of resolution of the spectrometer if you can see it. However, in condensed phase (liquid) you have additional interactions between the molecules that influence the energy states of the molecules. Thus, so many different transitions occur that no spectrometer can resolve this, and you get your typical smooth absorption bands. You can observe similar effects e.g. in infrared spectroscopy. $\endgroup$
    – Snijderfrey
    Commented Dec 28, 2021 at 16:43