June 2008

Cyano radical

To mark the 5th anniversary of The Astrochymist, this months's featured molecule is one of the most widely distributed and best known species, CN. The cyano radical was just the second interstellar molecule to be identified, going back to the 1940 work of McKellar and 1941 work of Adams. Both of these studies detected features in the near-UV or UV region of the electromagnetic spectrum due to electronic transitions, and both found CN in absorption toward the bright star ζ Ophiuchi. A microwave detection in the Orion nebula and W51 by Jefferts et al. followed in 1970. Turner & Gammon provided confirmation several years later and found CN in many other sources. CN was also one of the earliest molecules to be detected in other galaxies, beginning with the 1988 work of Henkel et al.

But the study of extraterrestrial CN goes back another 60 years before the first interstellar observations, to its 1881 detection by Huggins in the Great Comet of that year, distinguished as only the second comet to be photographed but certainly the first to be studied spectroscopically. A dominant feature is the violet band at 3883 Å from an electronic transtion. Later, CN was observed in Comet Hale-Bopp via rotational spectroscopy by Lis et al.

CN is also found in sunspots in our sun, other G-type stars, and in carbon stars.

The triple bond between C and N leaves one electron available in the CN radical, which is very reactive. Reactions between CN and unsaturated hydrocarbons like acetylene and ethylene have been shown to be efficient even at very cold temperatures. Organic molecules with the -CN group are known as nitriles. They are potential source of prebiotic amino acids, which can be formed through Strecker synthesis or other pathways.

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