Cyano radical

Physical properties

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 (the isocyano radical) is the major contributor. The charge separation in the isocyano radical is similar to that of carbon monoxide. •CN has a dipole moment of 1.45 debyes and a 2Σ+ ground electronic state. The selection rules are:

:\begin{align} N + S &= J \ J + I &= F \end{align}

where N is the angular momentum, S is the electric spin, and I = 1 is the nuclear spin of 14N.

Formation and destruction of ^•CN

Formation

• Dissociative recombination in diffuse clouds:
• :HCN+ + e− → •CN + H•
• Photodissociation in dense clouds:
• :HCN + hν → •CN + H•

Destruction

: + •CN → HCN + H2

Detections of ^•CN

A spectral line of •CN was detected in 1938 in the interstellar medium in the ultraviolet, and was identified in 1940 by Andrew McKellar. The coudé spectrograph and a 100 in telescope were used to observe •CN's interstellar lines and ultraviolet spectra. Use of the spectrograph confirmed McKellar's findings 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 the W51 nebula. 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 = to J = and J = to J = ; N = 7 to N = 8, J = to J = and J = to J = .

References

References

1. (2001). "Comparative chemistry of diffuse clouds: II. CN, HCN, HNC, CH₃CN & N₂H⁺". [[Astronomy & Astrophysics]].
2. (1983). "The millimeter and submillimeter spectrum of CN in its first four vibrational states". [[Journal of Molecular Spectroscopy]].
3. (1996). "Detection of C₂, CN, and NaI D absorption in the AGB remnant of HD 56126". Astronomy and Astrophysics.
4. (1940). "Evidence for the molecular origin of some hitherto unidentified interstellar lines". [[Publications of the Astronomical Society of the Pacific]].
5. Adams, Walter S.. (1941). "Some results with the coudé spectrograph of the Mount Wilson Observatory". [[The Astrophysical Journal]].
6. (1988). "Molecules in external galaxies: The detection of CN, C₂H, and HNC, and the tentative detection of HC₃N". Astronomy and Astrophysics.
7. (1970). "Observation of the CN radical in the Orion Nebula and W51". The Astrophysical Journal.
8. (1995). "Laboratory rotational spectrum of CN in the 1 THz region". Astronomy and Astrophysics.