Applications of molecular spectra

    (1) Identify molecules in interstellar space

    (2) 3o background radiation

     Famous example of rotational spectra:  Absorption (Fraunhofer) lines from constellation ζ Ophiucius

    CN molecules in constellation Ophiucius illuminated from behind by UV light from another constellation

    UV photon λ = 387.5 nm:              Electronic transition + rot. (L = 0 -> L=1)

    2nd UV photon Δλ = - 0.061 nm:    Electronic transition + rot. (L = 1 -> L=2)

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