April 2024
Cyanomethylidyne radical

The reactive cyanomethylidyne radical (CCN) was detected toward the carbon-rich source IRC +10216 by Anderson & Ziurys, as reported in 2014. CCN is an open-shell molecule with one unpaired electron, giving rise to paired lines known as doublets in its rotational spectrum. Three pairs of lines were detected using the two ARO telescopes: the 12m telescope at Kitt Peak National Observatory and the Submillimeter telescope at Mount Graham International Observatory. The detection was based on new rotational data for the molecule published by the Ziurys group. The use of extrapolated data may account for a previous unsuccessful search for CCN toward IRC +10216 by Fuchs et al.

Researcher Links
JK Anderson
LM Ziurys

The cyanomethylidyne radical has been the subject of a wide variety of studies of its spectra and reactivity relevant to astrochemistry. Volosatova et al. explored the possible formation of CCN from irradiation of acetonitrile (methyl cyanide). Reactions of CCN with various atoms and molecules have been characterized: with H (Loison & Hickson), with N (Stubbing et al), with H2S (Dong et al.), with H2S, PH3, and HCl (Wang et al.), with methane (Wang et al.), with various alcohols (Zhu et al.), and with various alkanes (Zhu et al.). The rovibrational spectrum of CCN was predicted by Hill et al., while its Renner-Teller splitting was studied by both Muzangwa & Reid and Coudert et al.. Chefai et al. chacterized the collisional excitation of CCN by He as well as the impact of He on its fine and hyperfine excitation.

While the bonding in the CCN radical can be viewed as consisting of a single bond between the two C atoms and a triple bond between the C and N atoms, the electrons can also be coupled to give two double bonds as shown in the orbital coupling diagrams in the figure to the right. The existence of a second resonance configuration means that there is unpaired electron character on both of the terminal atoms, as depicted in the orbital shown here. While much of the unpaired electron character is on the terminal C atom, the N atom also has unpaired electron character. Both terminal atoms can form covalent bonds, yield HCCN and CCNH.

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