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
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
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,
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
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 HN13C in that source was tentative.

R. D. Brown, P. D. Godfrey, H. I. Gunn, G. L. Blackman, and J. W. V. Storey published
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,
Detection of Interstellar DNC
Astrophys. J. 216, L111–L114 (1977).

HNC was also detected toward dark clouds:
L. E. Snyder and J. M. Hollis,
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,
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,
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,
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 v2 = 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,
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
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 Evib 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.

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

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