An Etymological Dictionary of Astronomy and Astrophysics
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An irritating, colorless, gaseous compound of → nitrogen and → hydrogen (NH₃), which is lighter than air and readily soluble in water. It is formed in nature as a by-product of protein metabolism in animals. Ammonia is used in the preparation of many substances containing nitrogen, such as fertilizers, explosives, refrigerants, and so on.

Coined in 1782 by Swedish chemist Torbern Bergman (1735-1784) for gas obtained from ammoniac, a salt and a gum resin containing ammonium chloride found near temple of Jupiter Ammon in Libya, from Gk. ammoniakos "belonging to Ammon" (Egyptian God).

Âmoniyâk, loan from Fr.

A maser source in which excited → ammonia molecules (NH₃) produce → maser emission. The first device to demonstrate the principle of → stimulated emission of radiation used ammonia molecules (Gordon et al. 1954). The hydrogen atoms of ammonia molecules have a rotation motion whereas the nitrogen atom oscillates between two positions, above and below the plane of the hydrogen atoms. These arrangements do not represent exactly the same energy, and therefore the molecule exists in two energy states. The difference in energy between the states corresponds to a frequency of 23.87 GHz, or 1.25 cm. In astrophysics, ammonia maser emission has been detected toward active star formation regions, such as W51. → interstellar masers.

→ ammonia; → maser.