  Imidogen (NH) is a reactive molecule whose presence in astrochemical
environments is of interest due to its role in the formation of
nitrogen-containing molecules and as a potential probe of nitrogen abundance.
Spectroscopic NH monitoring is useful for Earth-based combustion and photolysis
processes of ammonia and other nitrogen-containing species. NH is also relevant
to ultracold molecular physics and plasma studies. To enable these diverse
applications, high-quality molecular spectroscopic data is required. Here, a
new line list with significant advantages over existing data is presented. Most
notably, this line list models isotopologue spectroscopy and forbidden
transitions (important for NH visible absorption), alongside some overall
improvements to accuracy and completeness. This approach takes advantage of
existing experimental data (from a previous MARVEL compilation) and
perturbative line lists together with new MRCI ab initio electronic data. These
are used to produce a novel variational spectroscopic model and trihybrid line
list for the main 14N1H isotopologue, as well as isotopologue-extrapolated
hybrid line lists for the 14N2H, 15N1H and 15N2H isotopologues. The new 14N1H
ExoMol-style trihybrid line list, kNigHt, comprises 4,076 energy levels (1,078
experimental) and 327,014 transitions up to 47,500 cm-1 (211 nm) between five
low-lying electronic states (X 3{\Sigma}-, a 1{\Delta}, b 1{\Sigma}+, A 3{\Pi}
and c 1{\Pi}). For most anticipated applications aside from far-IR studies,
this line list will be of sufficient quality; any improvements should focus on
the b 1{\Sigma}+ energies, and the a 1{\Delta} - A 3{\Pi} and b 1{\Sigma}+ - A
3{\Pi} spin-orbit couplings.
