An Etymological Dictionary of Astronomy and Astrophysics
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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.