Cyano radical

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 coudé spectrograph, which was made famous and credible due to this detection. ·CN has been observed in both diffuse clouds and dense clouds.[1] 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.

Cyano radical
Names
Preferred IUPAC name
Cyano
Systematic IUPAC name
Isocyano
Other names
Cyanyl
Nitrile
Identifiers
3D model (JSmol)
1697323
ChEBI
ChemSpider
88
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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 Debye 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.[2]

Formation and destruction of ·CN

Formation
  • Dissociative Recombination In Diffuse Clouds: HCN+ + e− → ·CN + ·H[1]
  • Photo-Dissociation In Dense Clouds: HCN + hv → ·CN + ·H[3]

Destruction
H3+ + ·CN → HCN+ + H2

Detections of ·CN

·CN was first detected In 1941 by A. McKellar In the interstellar medium.[3]

The coude spectrograph and a 100-inch (2.5 m) 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.[4] In 1970, ·CN's first rotational transition from J=0 to J=1 was detected In the Orion Nebula and W51.[5] The first detection of ·CN in extragalactic sources were seen toward Sculptor Galaxy (NGC 253), IC 342, and M82 In 1988. These emission lines seen were from N=1 to N=0 and N=2 to N=1.[6] 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.[7] 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.[8]

References
  1. Liszt, H.; Lucas, R. (2001). "Comparative chemistry of diffuse clouds: II. CN, HCN, HNC, CH3CN & N2H+". Astronomy & Astrophysics. 370 (2): 576–585. Bibcode:2001A&A...370..576L. doi:10.1051/0004-6361:20010260.
  2. Skatrud, David D.; De Lucia, Frank C.; Blake, Geoffrey A.; Sastry, K. V. L. N. (1983). "The millimeter and submillimeter spectrum of CN in its first four vibrational states". Journal of Molecular Spectroscopy. 99 (1): 35–46. Bibcode:1983JMoSp..99...35S. doi:10.1016/0022-2852(83)90290-4.
  3. Bakker, Eric J.; Waters, L. B. F. M.; Lamers, Henry J. G. L. M.; Trams, Norman R.; Van der Wolf, Frank L. A. (1996). "Detection of C2, CN, and NaI D absorption in the AGB remnant of HD 56126". Astronomy and Astrophysics. 310: 893–907. Bibcode:1996A&A...310..893B.
  4. McKellar, Andrew (1940). "Evidence for the molecular origin of some hitherto unidentified interstellar lines". Publications of the Astronomical Society of the Pacific. 52 (307): 187–192. Bibcode:1940PASP...52..187M. doi:10.1086/125159.
  5. Adams, Walter S. (1941). "Some results with the coudé spectrograph of the Mount Wilson Observatory". The Astrophysical Journal. 93: 11–23. Bibcode:1941ApJ....93...11A. doi:10.1086/144237.
  6. Henkel, C.; Mauersberger, R.; Schilke, P. (1988). "Molecules in external galaxies: The detection of CN, C2H, and HNC, and the tentative detection of HC3N". Astronomy and Astrophysics. 201: L23–L26. Bibcode:1988A&A...201L..23H.
  7. Jefferts, K. B.; Penzias, A. A.; Wilson, R. W. (1970). "Observation of the CN radical in the Orion Nebula and W51". The Astrophysical Journal. 161 (2): L87–L89. Bibcode:1970ApJ...161L..87J. doi:10.1086/180576.
  8. Klisch, E.; Klaus, Th.; Belov, S. P.; Winnewisser, G.; Herbst, E. (1995). "Laboratory rotational spectrum of CN in the 1 THz region". Astronomy and Astrophysics. 304: L5–L8. Bibcode:1995A&A...304L...5K.
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