One and two transitions of the A ³Π – X ³Σ 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,
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,
Far-Infrared Detection of C₃ 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,
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.:
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.:
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.:
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.:
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.
First Detection of ND in the Solar-Mass Protostar IRAS 16293-2422
Astron. Astrophys. 521, Art. No. L42 (2010).

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