page_title: Ammonia
section_title: Interstellar formation mechanisms
hierarchical_section_title: Ammonia / In astronomy / Interstellar space / Interstellar formation mechanisms
context_page_description: Ammonia is a compound of nitrogen and hydrogen with the formula NH₃. A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a characteristic pungent smell. It is a common nitrogenous waste, particularly among aquatic organisms, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceutical products and is used in many commercial cleaning products. It is mainly collected by downward displacement of both air and water.
  Although common in nature—both terrestrially and in the outer planets of the Solar System—and in wide use, ammonia is both caustic and hazardous in its concentrated form. It is classified as an extremely hazardous substance in the United States, and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
  The global industrial production of ammonia in 2018 was 175 million tonnes, with no significant change relative to the 2013 global industrial production of 175 million tonnes.
context_section_description: The interstellar abundance for ammonia has been measured for a variety of environments. The [NH₃]/[H₂] ratio has been estimated to range from 10⁻⁷ in small dark clouds up to 10⁻⁵ in the dense core of the Orion Molecular Cloud Complex. Although a total of 18 total production routes have been proposed, the principal formation mechanism for interstellar NH₃ is the reaction:
  NH₄⁺ + e⁻ → NH₃ + H·
  The rate constant, k, of this reaction depends on the temperature of the environment, with a value of 5.2×10⁻⁶ at 10 K. The rate constant was calculated from the formula . For the primary formation reaction, a = 1.05×10⁻⁶ and B = −0.47. Assuming an NH₄⁺ abundance of 3×10⁻⁷ and an electron abundance of 10⁻⁷ typical of molecular clouds, the formation will proceed at a rate of 1.6×10⁻⁹ cm⁻³s⁻¹ in a molecular cloud of total density 10⁵ cm⁻³.
  All other proposed formation reactions have rate constants of between 2 and 13 orders of magnitude smaller, making their contribution to the abundance of ammonia relatively insignificant. As an example of the minor contribution other formation reactions play, the reaction:
  H₂ + NH₂ → NH₃ + H
  has a rate constant of 2.2×10⁻¹⁵. Assuming H₂ densities of 10⁵ and [NH₂]/[H₂] ratio of 10⁻⁷, this reaction proceeds at a rate of 2.2×10⁻¹², more than 3 orders of magnitude slower than the primary reaction above.
  Some of the other possible formation reactions are:
  H⁻ + NH₄⁺ → NH₃ + H₂
  PNH₃⁺ + e⁻ → P + NH₃
caption: Ball-and-stick model of the diamminesilver(I) cation, [Ag(NH3)2]+
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