The cyano radical (or cyanido radical) is a
radical with molecular formula CN, sometimes written
•CN. The cyano radical was one of the first detected molecules in the
interstellar medium, in 1938. Its detection and analysis was influential in
astrochemistry
Astrochemistry is the study of the abundance and reactions of molecules in the Universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar Syst ...
. The discovery was confirmed 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.
Usually, CN is detected in regions with
hydrogen cyanide,
hydrogen isocyanide
Hydrogen isocyanide is a chemical with the molecular formula HNC. It is a minor tautomer of hydrogen cyanide (HCN). Its importance in the field of astrochemistry is linked to its ubiquity in the interstellar medium.
Nomenclature
Both ''hydroge ...
, and
HCNH+, since it is involved in the creation and destruction of these species (see also ''
Cyanogen
Cyanogen is the chemical compound with the formula ( C N)2. It is a colorless and highly toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecu ...
'').
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
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
.
•CN has a
dipole moment of 1.45
debyes and a
2Σ
+ ground electronic state. The
selection rule
In physics and chemistry, a selection rule, or transition rule, formally constrains the possible transitions of a system from one quantum state to another. Selection rules have been derived for electromagnetic transitions in molecules, in atoms, in ...
s are:
:
where ''N'' is the
angular momentum
In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...
, ''S'' is the electric spin, and = 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
+ + H
2
Detections of •CN
A spectral line of
•CN was detected in 1938 in the
interstellar medium in the
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
, and was identified in 1940 by
Andrew McKellar
Andrew McKellar, MBE, FRSC (February 2, 1910 – May 6, 1960) was a Canadian astronomer who first detected the presence of molecular matter in interstellar space, and found the first evidence of the cosmic radiation left over from the Big Bang. ...
. The
coudé spectrograph and a 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.
[ The first detection of •CN in extragalactic sources were seen toward ]Sculptor Galaxy
The Sculptor Galaxy (also known as the Silver Coin, Silver Dollar Galaxy, NGC 253, or Caldwell 65) is an intermediate spiral galaxy in the constellation Sculptor. The Sculptor Galaxy is a starburst galaxy, which means that it is currently underg ...
(NGC 253), IC 342
IC 342 (also known as Caldwell 5) is an intermediate spiral galaxy in the constellation Camelopardalis, located relatively close to the Milky Way. Despite its size and actual brightness, its location behind dusty areas near the galactic equator m ...
, 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
The National Solar Observatory (NSO) is a United States public research institute to advance the knowledge of the physics of the Sun. NSO studies the Sun both as an astronomical object and as the dominant external influence on Earth.
NSO is headq ...
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
{{DEFAULTSORT:Cyano Radical
Free radicals
Cyanides