The cyano radical is a radical with molecular formula CN, sometimes written ·CN. The cyanido radical was one of the first detected molecules in the interstellar medium. Its detection and analysis was influential in astrochemistry. The first discovery was performed with a coudéspectrograph, which was made famous and credible due to this detection. ·CN has been observed in both diffuse clouds and dense clouds. Usually, CN is detected in regions with hydrogen cyanide, hydrogen isocyanide, and HCHN+, since it is involved in the creation and destruction of these species.
Bonding in the cyano radical can be described as a combination of two resonance structures: the structure with the unpaired electron on the carbon is the minor contributor, while the structure with the unpaired electron on the nitrogen is the major contributor. The charge separation in the isocyano radical is similar to that of carbon monoxide. ·CN has a dipole moment of 1.45Debye and a 2Σ+ ground electronic state. The selection rules are: Where N is the angular momentum, S is the electric spin, and I = 1 is the nuclear spin of 14N.
·CN was first detected In 1941 by A. McKellar In the interstellar medium. The coude spectrograph and a telescope were used to observe ·CN's interstellar lines and ultraviolet spectra. Use of the spectrograph proved McKellar's findings to be correct and also made the spectrograph famous. In 1970, ·CN's first rotational transition from J=0 to J=1 was detected In the Orion Nebula and W51. The first detection of ·CN in extragalactic sources were seen toward Sculptor Galaxy, IC 342, and M82 In 1988. These emission lines seen were from N=1 to N=0 and N=2 to N=1. In 1991, the ·CN vibration-rotational bands were observed in a king furnace at the National Solar Observatory using a McMath Fourier-Transform spectrometer. The observed 2 to 0 lines show an extreme hyperfine structure. In 1995, the rotational absorption spectrum of ·CN in the ground state was observed in the 1 THz region, and most of the lines were measured in the range of 560 to 1020 GHz. Four new rotational transitions were measured; N=8 to N=8, J=15/2 to J=17/2 and J=17/2 to J=19/2; N=7 to N=8, J=15/2 to J=17/2 and J=13/2 to J=15/2.
