Ethynyl radical
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Preferred IUPAC name
Ethynyl radical
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Systematic IUPAC name
Ethynyl
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3D model (Jmol)
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| 1814004 | |||
| ChEBI | |||
| ChemSpider | |||
| 48916 | |||
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PubChem CID
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| Properties | |||
| C2H | |||
| Molar mass | 25.03 g·mol−1 | ||
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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 | |||
The ethynyl radical (systematically named λ3-ethyne and hydridodicarbon(C—C)) is an organic compound with the chemical formula C≡CH (also written [CCH] or C
2H). It is a simple molecule that does not occur naturally on Earth but is abundant in the interstellar medium. It was first observed by electron spin resonance isolated in a solid argon matrix at liquid helium temperatures in 1963 by Cochran and coworkers at the Johns Hopkins Applied Physics Laboratory. It was first observed in the gas phase by Tucker and coworkers in November 1973 toward the Orion Nebula, using the NRAO 11m radio telescope. It has since been detected in a large variety of interstellar environments, including dense molecular clouds, bok globules, star forming regions, the shells around carbon-rich evolved stars, and even in other galaxies.
Observations of C2H can yield a large number of insights into the chemical and physical conditions where it is located. First, the relative abundance of ethynyl is an indication of the carbon-richness of its environment (as opposed to oxygen, which provides an important destruction mechanism). Since there is typically insufficient quantities of C2H along a line of sight to make emission or absorption lines optically thick, derived column densities can be relatively accurate (as opposed to more common molecules like CO, NO, and OH). Observations of multiple rotational transitions of C2H can result in estimates of the local density and temperature. Observations of the deuterated molecule, C2D, can test and extend fractionation theories (which explain the enhanced abundance of deuterated molecules in the interstellar medium). One of the important indirect uses for observations of the ethynyl radical is the determination of acetylene abundances. Acetylene (C2H2) does not have a dipole moment, and therefore pure rotational transitions (typically occurring in the microwave region of the spectrum) are too weak to be observable. Since acetylene provides a dominant formation pathway to ethynyl, observations of the product can yield estimates of the unobservable acetylene. Observations of C2H in star-forming regions frequently exhibit shell structures, which implies that it is quickly converted to more complex molecules in the densest regions of a molecular cloud. C2H can therefore be used to study the initial conditions at the onset of massive star formation in dense cores. Finally, high spectral resolution observations of Zeeman splitting in C2H can give information about the magnetic fields in dense clouds, which can augment similar observations that are more commonly done in the simpler cyanide (CN).
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