Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Ethynyl radical: Difference between pages

{{Short description|Hydrocarbon compound (•CCH)}}

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 461097706

| ImageSizeL1 = 121

| ImageNameL1 = Structural formula of the ethynyl radical

| ImageSizeR1 = 121

| ImageNameR1 = Spacefill model of ethynyl radical

| PIN = Ethynyl

|Section1={{Chembox Identifiers

| CASNo = 2122-48-7

| CASNo_Ref = {{cascite|changed|??}}

| PubChem = 123271

| ChemSpiderID = 109883

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChEBI_Ref = {{ebicite|correct|EBI}}

| SMILES = C#[C]

| SMILES1 = [C]#C

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| InChI = 1/C2H/c1-2/h1H

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

| InChIKey = XEHVFKKSDRMODV-UHFFFAOYAZ

| Beilstein = 1814004

| Gmelin = 48916}}

|Section2={{Chembox Properties

| C=2 | H=1 }}

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 {{Chem|C|2|H}}). 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 paramagnetic resonance|electron spin resonance]] isolated in a [[Matrix isolation|solid argon matrix]] at liquid helium temperatures in 1963 by Cochran and coworkers at the [[Applied Physics Laboratory|Johns Hopkins Applied Physics Laboratory]].<ref name=Cochran1964>{{cite journal|last1=Cochran |first1=E. L. |last2=Adrian |first2=F. J. |last3=Bowers |first3=V. A. |title=ESR Study of Ethynyl and Vinyl Free Radicals |journal=Journal of Chemical Physics |volume=40 |page=213 |date=1964 |issue=1 |bibcode=1964JChPh..40..213C |doi=10.1063/1.1724865}}</ref> It was first observed in the gas phase by Tucker and coworkers in November 1973 toward the [[Orion Nebula]], using the [[National Radio Astronomy Observatory|NRAO]] 11-meter radio telescope.<ref name=Tucker1974>{{cite journal|last1=Tucker |first1=K. D. |last2=Kutner |first2=M. L. |last3=Thaddeus |first3=P. |title=The Ethynyl Radical C₂H – A New Interstellar Molecule |journal=Astrophysical Journal |volume=193 |page=L115–L119 |date=1974 |bibcode=1974ApJ...193L.115T |doi=10.1086/181646}}</ref> It has since been detected in a large variety of interstellar environments, including dense [[molecular cloud]]s, [[bok globule]]s, [[Star formation|star forming regions]], the shells around [[Carbon star|carbon-rich evolved stars]], and even in other [[Galaxy|galaxies]].

==Astronomical Importance==

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).<ref name=Huggins1984>{{cite journal|last1=Huggins |first1=P. J. |last2=Carlson |first2=W. J. |last3=Kinney |first3=A. L. |title=The distribution and abundance of interstellar C₂H |journal=Astronomy & Astrophysics |volume=133 |page=347–356 |date=1984 |bibcode=1984A&A...133..347H}}</ref> Since there are typically insufficient quantities of C₂H along a line of sight to make [[Spectral line|emission or absorption lines]] optically thick, derived column densities can be relatively accurate (as opposed to more common molecules like [[Carbon monoxide|CO]], [[Nitric oxide|NO]], and [[Hydroxide|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).<ref name=Vrtilek1985>{{cite journal|last1=Vrtilek |first1=J. M. |last2=Gottlieb |first2=C. A. |last3=Langer |first3=W. D. |last4=Thaddeus |first4=P. |last5=Wilson |first5=R. W. |title=Laboratory and Astronomical Detection of the Deuterated Ethynyl Radical CCD |journal=Astrophysical Journal |volume=296 |page=L35–L38 |date=1985 |bibcode=1985ApJ...296L..35V |doi=10.1086/184544|doi-access=free }}</ref> One of the important indirect uses for observations of the ethynyl radical is the determination of [[acetylene]] abundances.<ref name=Fuente1998>{{cite journal|last1=Fuente |first1=A. |last2=Cernicharo |first2=J. |last3=Omont |first3=A. |title=Inferring acetylene abundances from C₂H: the C₂H₂/HCN abundance ratio |journal=Astronomy & Astrophysics |volume=330 |page=232–242 |date=1998 |bibcode=1998A&A...330..232F}}</ref> Acetylene (C₂H₂) does not have a [[Electric dipole moment|dipole moment]], and therefore pure rotational transitions (typically occurring in the [[Microwave|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.<ref name=Beuther2008>{{cite journal|last1=Beuther |first1=H. |last2=Semenov |first2=D. |last3=Henning |first3=T. |last4=Linz |first4=H. |title=Ethynyl (C₂H) in Massive Star Formation: Tracing the Initial Conditions? |journal=Astrophysical Journal |volume=675 |page=L33–L36 |date=2008 |issue=1 |arxiv=0801.4493 |bibcode=2008ApJ...675L..33B |doi=10.1086/533412|s2cid=15820346 }}</ref> Finally, high-spectral-resolution observations of [[Zeeman effect|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 [[cyano radical]] (CN).<ref name=Bel1998>{{cite journal|last1=Bel |first1=N. |last2=Leroy |first2=B. |title=Zeeman splitting in interstellar molecules. II. The ethynyl radical |journal=Astronomy & Astrophysics |volume=335 |page=1025–1028 |date=1998 |bibcode=1998A&A...335.1025B}}</ref>

==Formation and destruction==

The formation and destruction mechanisms of the ethynyl radical vary widely with its environment. The mechanisms listed below represent the current ({{as of|2008|lc=1}}) understanding, but other formation and destruction pathways may be possible, or even dominant, in certain situations.

===Formation===

In the laboratory, C₂H can be made via [[photolysis]] of acetylene (C₂H₂) or C₂HCF₃,<ref name=Fahr2003>{{cite journal|last1=Fahr |first1=A. |title=Ultraviolet absorption spectrum and cross-sections of ethynyl (C₂H) radicals |journal=Journal of Molecular Spectroscopy |volume=217 |page=249 |date=2003 |issue=2 |doi=10.1016/S0022-2852(02)00039-5|bibcode=2003JMoSp.217..249F }}</ref> or in a [[glow discharge]] of a mixture of acetylene and helium.<ref name="Müller2000">{{cite journal|last1=Müller |first1=H. S. P. |last2=Klaus |first2=T. |last3=Winnewisser |first3=G. |title=Submillimeter-wave spectrum of the ethynyl radical, CCH, up to 1 THz |journal=Astronomy & Astrophysics |volume=357 |page=L65 |date=2000 |bibcode=2000A&A...357L..65M}}</ref> In the envelopes of carbon-rich evolved stars, acetylene is created in the thermal equilibrium in the stellar photosphere. Ethynyl is created as a photodissociation product of the acetylene that is ejected (via strong [[stellar wind]]s) into the outer [[circumstellar envelope|envelope]] of these stars. In the cold, dense cores of molecular clouds (prior to star formation) where ''n'' > 10⁴&nbsp;cm⁻³ and ''T'' < 20&nbsp;K, ethynyl is dominantly formed via an electron recombination with the [[vinyl radical]] ({{chem|C|2|H|3|+}}).<ref name=Woodall2007>{{cite journal|last1=Woodall |first1=J. |last2=Agúndez |first2=M. |last3=Markwick-Kemper |first3=A. J. |last4=Millar |first4=T. J. |title=The UMIST database for astrochemistry 2006 |journal=Astronomy & Astrophysics |volume=466 |page=1197 |date=2007 |issue=3 |bibcode=2007A&A...466.1197W |doi=10.1051/0004-6361:20064981|arxiv=1212.6362 }}</ref> The neutral-neutral reaction of [[propynylidyne]] (C₃H) and atomic oxygen also produces ethynyl (and [[carbon monoxide]], CO), though this is typically not a dominant formation mechanism. The dominant creation reactions are listed below.

*{{chem|C|2|H|3|+}} + e⁻ → C₂H + H + H

*{{chem|C|2|H|3|+}} + e⁻ → C₂H + H₂

*CH₃CCH⁺ + e⁻ → C₂H + CH₃

*C₃H + O → C₂H + CO

===Destruction===

The destruction of ethynyl is dominantly through neutral-neutral reactions with O₂ (producing carbon monoxide and [[formyl]], HCO), or with atomic nitrogen (producing atomic hydrogen and C₂N). Ion-neutral reactions can also play a role in the destruction of ethynyl, through reactions with HCO⁺ and [[Trihydrogen cation|{{chem|H|3|+}}]]. The dominant destruction reactions are listed below.

*C₂H + O₂ → HCO + CO

*C₂H + N → C₂N + H

*C₂H + HCO⁺ → {{chem|C|2|H|2|+}} + CO

*C₂H + {{chem|H|3|+}} → {{chem|C|2|H|2|+}} + H₂

==Method of observation==

The ethynyl radical is observed in the microwave portion of the spectrum via pure rotational transitions. In its ground electronic and vibrational state, the nuclei are [[Line (geometry)|collinear]], and the molecule has a permanent dipole moment estimated to be ''μ'' = 0.8&nbsp;[[Debye (unit)|D]] = {{val|2.7e-30|u=C·m}}.<ref name="Tucker1974" /> The ground vibrational and electronic (vibronic) state exhibits a simple [[Rigid rotor#The quantum mechanical linear rigid rotor|rigid rotor]]-type rotational spectrum. However, each rotational state exhibits [[Fine structure|fine]] and [[hyperfine structure]], due to the spin-orbit and electron-nucleus interactions, respectively. The ground rotational state is split into two hyperfine states, and the higher rotational states are each split into four hyperfine states. Selection rules prohibit all but six transitions between the ground and the first excited rotational state. Four of the six components were observed by Tucker ''et al.'' in 1974,<ref name="Tucker1974" /> the initial astronomical detection of ethynyl, and 4 years later, all six components were observed, which provided the final piece of evidence confirming the initial identification of the previously unassigned lines.<ref name=Tucker1978>{{cite journal|last1=Tucker |first1=K. D. |last2=Kutner |first2=M. L. |title=The Abundance and Distribution of Interstellar C₂H |journal=Astrophysical Journal |volume=222 |page=859 |date=1978 |bibcode=1978ApJ...222..859T |doi=10.1086/156204}}</ref> Transitions between two adjacent higher-lying rotational states have 11 hyperfine components. The molecular constants of the ground vibronic state are tabulated below.

==Isotopologues==

Three [[isotopologue]]s of the ¹²C¹²CH molecule have been observed in the interstellar medium. The change in molecular mass is associated with a shift in the energy levels and therefore the transition frequencies associated with the molecule. The molecular constants of the ground vibronic state, and the approximate transition frequency for the lowest 5 rotational transitions are given for each of the isotopologues in the table below.

:{| class="wikitable" border="1"

|+Rotational transitions for ethenyl isotopologues

! Isotopologue || Year<br>discovered || colspan=2|Molecular constants<br>(MHz) || colspan=2|Transition frequencies<br>(MHz)

|-

|align=center| ¹²C¹²CH

|align=center| 1974<ref name="Tucker1974" />

|align=center| ''B<br>D<br>γ<br>b<br>c''

|align=center| {{val|43674.534}}<br>0.1071<br>−62.606<br>40.426<br>12.254

|align=center| ''N'' = 1→0<br>''N'' = 2→1<br>''N'' = 3→2<br>''N'' = 4→3<br>''N'' = 5→4

|align=right| {{val|87348.64}}<br>{{val|174694.71}}<br>{{val|262035.64}}<br>{{val|349368.85}}<br>{{val|436691.79}}

|-

|align=center| ¹²C¹²CD

|align=center| 1985<ref name="Vrtilek1985" /><ref name=Combes1985>{{cite journal|last1=Combes |first1=F. |last2=Boulanger |first2=F. |last3=Encrenaz |first3=P. J. |last4=Gerin |first4=M. |last5=Bogey |first5=M. |last6=Demuynck |first6=C. |last7=Destombes |first7=J. L. |title=Detection of interstellar CCD |journal=Astronomy & Astrophysics |volume=147 |page=L25 |date=1985 |bibcode=1985A&A...147L..25C}}</ref>

|align=center| ''B<br>D<br>γ<br>b<br>c''

|align=center| {{val|36068.035}}<br>0.0687<br>−55.84<br>6.35<br>1.59

|align=center| ''N'' = 1→0<br>''N'' = 2→1<br>''N'' = 3→2<br>''N'' = 4→3<br>''N'' = 5→4

|align=right| {{val|72135.80}}<br>{{val|144269.94}}<br>{{val|216400.79}}<br>{{val|288526.69}}<br>{{val|360646.00}}

|-

|align=center| ¹³C¹²CH

|align=center| 1994<ref name=Saleck1994>{{cite journal|last1=Saleck |first1=A. H. |last2=Simon |first2=R. |last3=Winnewisser |first3=G. |last4=Wouterloot |first4=J. G. A. |title=Detection of interstellar ¹³C¹²CH and ¹²C¹³CH |journal=Canadian Journal of Physics |volume=72 |page=747 |date=1994 |bibcode=1994CaJPh..72..747S |doi=10.1139/p94-098}}</ref>

|align=center| ''B<br>D<br>γ''

|align=center| {{val|42077.459}}<br>0.09805<br>−59.84

|align=center| ''N'' = 1→0<br>''N'' = 2→1<br>''N'' = 3→2<br>''N'' = 4→3<br>''N'' = 5→4

|align=right| {{val|84154.53}}<br>{{val|168306.70}}<br>{{val|252454.16}}<br>{{val|336594.57}}<br>{{val|420725.57}}

|-

|align=center| ¹²C¹³CH

|align=center| 1994<ref name="Saleck1994" />

|align=center| ''B<br>D<br>γ''

|align=center| {{val|42631.3831}}<br>0.10131<br>−61.207

| ''N'' = 1→0<br>''N'' = 2→1<br>''N'' = 3→2<br>''N'' = 4→3<br>''N'' = 5→4

|align=right| {{val|85262.36}}<br>{{val|170522.29}}<br>{{val|255777.36}}<br>{{val|341025.13}}<br>{{val|426263.18}}

|}

==See also==

*[[List of molecules in interstellar space]]

==References==

{{reflist|30em}}

{{Molecules detected in outer space}}

{{Hydrides by group}}

[[Category:Alkynyl groups]]

[[Category:Free radicals]]