===== On the Detection of Imidogen, NH, in the Interstellar Medium =====

One and two transitions of the //A// <sup>3</sup>Π – //X// <sup>3</sup>Σ electronic spectrum of imidogen near 335 nm were detected in diffuse clouds toward ζ Per and HD 27778, respectively:\\
D. M. Meyer and K. C. Roth,\\
**[[https://ui.adsabs.harvard.edu/abs/1991ApJ...376L..49M|Discovery of Interstellar NH]]**\\
//Astrophys. J.// **376**, L49–L52 (1991).\\
The transitions involve an //R//(0) component in both cases as well as a //Q//(0) component of the //v// = 0 – 0 vibrational band system near 335.8 and 335.4 nm, respectively.

The detection of one fine struture component of the //N// = 2 – 1 pure rotational transition toward Sgr B2 was reported by\\
J. Cernicharo, J. R. Goicoechea, and E. Caux,\\
**[[https://doi.org/10.1086/312668|Far-Infrared Detection of C<sub>3</sub> in Sagittarius B2 and IRC +10216]]**\\
//Astrophys. J.// **534**, L199–L202 (2000);\\
a second fine structure component of that transition was reported in\\
J. R. Goicoechea, N. J. Rodríguez-Fernández and J. Cernicharo,\\
**[[https://doi.org/10.1086/379704|The Far-Infrared Spectrum of the Sagittarius B2 Region:\\
Extended Molecular Absorption, Photodissociation, and Photoionization]]**\\
//Astrophys. J.// **600**, 214–233 (2004).

A plethora of reports on observations of one or more fine structure components of the //N// = 1 – 0 transition in absorption carried out with //Herschel///HIFI were reported in the HIFI special issue of A&A. In, at least, most instances, the observatioon of absorption lines indicates the presence of NH in diffuse gas. The objects investigated include\\
a photon-dominated region: A. Fuente, O. Berné, J. Cernicharo, et al.:\\
**[[https://doi.org/10.1051/0004-6361/201015093|Herschel Observations in the Ultracompact HII Region Mon R2 – Water in Dense Photon-Dominated Regions (PDRs)]]**\\
//Astron. Astrophys.// **521**, Art. No. L23 (2010);\\
a young stellar object: A. O. Benz, S. Bruderer, E. F. van Dishoeck, et al.:\\
**[[https://doi.org/10.1051/0004-6361/201015111|Hydrides in Young Stellar Objects: Radiation Tracers in a Protostar-Disk-Outflow System]]**\\
//Astron. Astrophys.// **521**, Art. No. L35 (2010);\\
the sight line toward a high-mass star-forminbg region: C. M. Persson, J. H. Black, J. Cernicharo, et al.:\\
**[[https://doi.org/10.1051/0004-6361/201015105|Nitrogen Hydrides in Interstellar Gas – //Herschel///HIFI Observations towards G10.6-0.4 (W31C)]]**\\
//Astron. Astrophys.// **521**, Art. No. L45 (2010);\\
and another young stellar object: P. Hily-Blant, S. Maret, A. Bacmann, et al.:\\
**[[https://doi.org/10.1051/0004-6361/201015253|Nitrogen Cydrides in the Cold Envelope of IRAS 16293-2422]]**\\
//Astron. Astrophys.// **521**, Art. No. L52 (2010).

In this context, also ND was observed in two fine structure components of the //N// = 1 – 0 transition by:\\
A. Bacmann, E. Caux, P. Hily-Blant, et al.\\
**[[https://doi.org/10.1051/0004-6361/201015102|First Detection of ND in the Solar-Mass Protostar IRAS 16293-2422]]**\\
//Astron. Astrophys.// **521**, Art. No. L42 (2010).


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Contributor(s): H. S. P. Müller; 03, 2007; 04, 2011


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