Spectrum of Cyanogen, CN
The spectrum of the molecule cyanogen, CN, is of particular interest because it has been observed in space. It was observed in an interstellar cloud in the constellation Ophiuchus, "The Serpent Bearer". The cloud is illuminated from behind by the star z-Ophiuci, making possible the observation of CN absorption lines.
About measurements made in the early 40's, Rohlf quotes the noted molecular spectroscopist Gerhard Herzberg as saying "From the intensity ratio of the [CN] lines with [j=0 and j=1] a rotational temperature of 2.3 K follows, which has of course a very restricted meaning." It was not as restricted as he thought -- 25 years later, Penzias and Wilson would demonstrate the existence of the cosmic background radiation at 2.7K, an accomplishment for which they received the Nobel Prize. These early spectroscopists had seen evidence of the cosmic background radiation in the relative intensities of observed spectral lines!
Molecular spectra concepts