The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6 - 0.4 in order to improve our understanding of the interstellar chemistry of nitrogen .
We report observations of absorption in NH N = 1 \leftarrow 0 , J = 2 \leftarrow 1 and ortho -NH _ { 2 } 1 _ { 1 , 1 } \leftarrow 0 _ { 0 , 0 } .
We also observed ortho -NH _ { 3 } 1 _ { 0 } \leftarrow 0 _ { 0 } , and 2 _ { 0 } \leftarrow 1 _ { 0 } , para -NH _ { 3 } 2 _ { 1 } \leftarrow 1 _ { 1 } , and searched unsuccessfully for NH ^ { + } .
All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities .
All spectra show similar , non-saturated , absorption features , which we attribute to diffuse molecular gas .
Total column densities over the velocity range 11 – 54 km s ^ { -1 } are estimated .
The similar profiles suggest fairly uniform abundances relative to hydrogen , approximately 6 \times 10 ^ { -9 } , 3 \times 10 ^ { -9 } , and 3 \times 10 ^ { -9 } for NH , NH _ { 2 } , and NH _ { 3 } , respectively .
These abundances are discussed with reference to models of gas-phase and surface chemistry .