===== Reports on Hydrogen Isocyanide in the ISM/CSM =====

Hydrogen isocyanide, HNC was among the early molecules detected in space. Moreover, it was one of the molecules detected in space before laboratory spectroscopic information was available for its identification. Two reports appeared at about the same time.\\
L. E. Snyder and D. Buhl,\\
reported on the\\
**[[https://doi.org/10.1111/j.1749-6632.1972.tb12687.x|Detection of Several new Interstellar Molecules]]**\\
//Ann. N Y Acad. Sci.// **194**, 17–24 (1972).\\
An emission line at 90.665 GHz was detected with the 11 m radio telescope of the NRAO toward the massive star-forming regions Sgr B2 and W 51 as well as toward the hot core DR21(OH). The line was assigned somewhat tentatively to the //J// = 1&nbsp:– 0 transition of HNC.\\
B. Zuckerman, M. Morris, P. Palmer, and B. E. Turner,\\
also used the 11 m radio telescope of the NRAO for\\
**[[https://ui.adsabs.harvard.edu/abs/1972ApJ...173L.125Z|Observations of CS, HCN, U89.2, and U90.7 in NGC 2264]]**\\
//Astrophys. J.// **173**, L125–L129 (1972).\\
NGC 2264 is a Galactic open cluster and may, as broader source type, be viewed as photon-dominated region (PDR). U90.7 was not assigned here.\\
The molecule was identified unambiously by the laboratory work of\\
G. L. Blackman, R. D. Brown, P. D. Godfrey, and H. I. Gunn,\\
**[[https://doi.org/10.1038/261395a0|The Microwave Spectrum of HNC: Identification of U90.7]]**\\
//Nature// **261**, 395–396 (1976).

R. D. Brown, P. D. Godfrey, J. W. V. Storey, and F. O. Clark, reported on\\
**[[http://dx.doi.org/10.1038/262672a0|Detection of Interstellar HN<sup>13</sup>C]]**\\
//Nature// **262**, 672–674 (1976).\\
The 11 m radio telescope of the NRAO was used to detect //J// = 1&nbsp:– 0 transition of this isotopolog near 87.1 GHz and of the main isotopolog toward W 51, Sgr B2 and DR21(HCN peak).\\
The authors also reported the detection of HNC toward the circumstellar envelope of the carbon-star CW Leo, aka IRC +10216; the detection of HN<sup>13</sup>C in that source was tentative.

R. D. Brown, P. D. Godfrey, H. I. Gunn, G. L. Blackman, and J. W. V. Storey published\\
**[[https://ui.adsabs.harvard.edu/abs/1977MNRAS.180P..83G|Detection of Interstellar DNC – Difficulties of Chemical Equilibrium Hypothesis for Enrichment]]**\\
//Mon. Not. R. Astr. Soc.// **180**, 83–86 (1977).\\
The //J// = 1&nbsp:– 0 transition near 76.3 GHz was detected toward NGC 2264 again with the 11 m radio telescope of the NRAO.\\
Shortly thereafter, the //J// = 2&nbsp:– 1 transition near 152.6 GHz was detected with the 5 m MWO radio telescope towards a diverse ensemble of sources: NGC&nb1p;1333, Ori A, NGC 2264, and L134 by\\
R. L. Snell and H. A. Wootten,\\
**[[https://ui.adsabs.harvard.edu/abs/1977ApJ...216L.111S|Detection of Interstellar DNC]]**\\
//Astrophys. J.// **216**, L111–L114 (1977).\\


HNC was also detected toward dark clouds:\\
L. E. Snyder and J. M. Hollis,\\
**[[https://ui.adsabs.harvard.edu/abs/1976ApJ...204L.139S|HCN, X-ogen (HCO<sup>+</sup>), and U90.66 Emission Spectra from L134]]**\\
//Astrophys. J.// **204**, L139–L142 (1976).

HNC was detected in the complete set of 38 translucent clouds (11 cirrus, 27 CB) in which it was searched for by:\\
B. E. Turner, L. Pirogov, and Y. C. Minh,\\
**[[https://doi.org/10.1086/304228|The Physics and Chemistry of Small Translucent Molecular Clouds. VIII. HCN and HNC]]**\\
//Astrophys. J.// **483**, 235–261 (1997).\\
DNC was also found in CB 17 by:\\
B. E. Turner,\\
**[[https://doi.org/10.1086/322536|Deuterated Molecules in Translucent and Dark Clouds]]**\\
//Astrophys. J. Suppl. Ser.// **136**, 579–629 (2001).\\


HNC was also seen in absorption in diffuse clouds:\\
H. Liszt and R. Lucas,\\
**[[https://doi.org/10.1051/0004-6361:20010260|Comparative Chemistry of Diffuse Clouds. II. CN, HCN, HNC, CH<sub>3</sub>CN, and N<sub>2</sub>H<sup>+</sup>]]**\\
//Astron. Astrophys.// **370**, 576–585 (2001).

Rotational transitions of HNC in its //v//<sub>2</sub> = 1 excited vibrational state have been detected in the protoplanetary nebula V353 Aur, also known as CRL 618, by:\\
P. Schilke, C. Comito, and S. Thorwirth,\\
**[[https://doi.org/10.1086/367628|First Detection of Vibrationally Excited HNC in Space]]**\\
//Astrophys. J.// **582**, L101–L104 (2003).\\
The CSO was used to detect both //l//-components of the //J// = 3 – 2 and 4 – 3 transitions.

J. Cernicharo, F. Daniel, A. Castro-Carrizo, M. Agundez, N. Marcelino, C. Joblin, J. R. Goicoechea, and M. Guélin\\
were\\
**[[https://doi.org/10.1088/2041-8205/778/2/L25|Unveiling the Dust Nucleation Zone of IRC+10216 with ALMA]]**\\
//Astrophys. J.// **778**, Art. No. L25 (2013).\\
In the process, they detected emission pertaining to several //J// = 3 – 2 transition in excited vibrational states up to the CH stretching mode with //E//<sub>vib</sub> of about 5300 K in the circumstellar envelope of CW Leonis. Even higher states will likely be detected with longer integration time or more dishes. The observations were made in cycle 0.


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Contributor(s): H. S. P. Müller; 04, 2012; 01, 2014

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