Rare Find: Odd type of ammonia detected in space

An unusual form of ammonia has turned up in space, upending scientists’ long-held belief that this substance is too rare to detect there. The finding could help astronomers better understand the complex chemistry of dark clouds in star-forming regions of space.

A molecule of ammonia consists of one nitrogen atom linked to three hydrogen atoms. Unlike ordinary ammonia used for household cleaning, however, the newly found molecule doesn’t contain typical hydrogen. Instead, it has three atoms of deuterium, a heavy isotope of hydrogen. Throughout the galaxy, there’s about 1 atom of deuterium for each 100,000 atoms of ordinary hydrogen.

An international team of scientists, including Darek Lis of the California Institute of Technology in Pasadena, identified the unusual ammonia in the Milky Way’s Barnard 1 cloud, located about 1,000 light years from Earth. By using the Caltech Submillimeter Observatory on Hawaii’s Mauna Kea, the researchers detected triply deuterated ammonia’s characteristic radio emissions.

Once in ammonia, deuterium atoms “prefer” to stay there when temperatures are extremely low, says Lis. Nonetheless, “it’s surprising that molecules can get so heavily deuterated,” comments Alwyn Wootten of the National Radio Astronomy Observatory in Charlottesville, Va.

The radio signature of ammonia incorporating three deuteriums was first determined more than 3 decades ago in laboratory experiments. It was “known and forgotten,” comments Eric Herbst of Ohio State University in Columbus. No one has previously used the signature to look for the molecule in space because astronomers didn’t believe a measurable concentration of the heavy ammonia was out there. That bias gave way several years ago, when astrochemists discovered molecules of ammonia and formaldehyde containing two deuterium atoms, adds Lis.

The discovery of heavily deuterated molecules in space could help scientists understand the chemistry of star-forming regions, says Herbst. “Molecules tell us more than anything else about these regions,” he notes. Yet before triply deuterated ammonia can provide information on chemistry in space, astronomers must determine how widespread the molecule is, says Wootten.

Lis and his coworkers, who reported their discovery in the May 20 Astrophysical Journal Letters, now plan to look for the molecule elsewhere in the universe and also measure less-deuterated versions of ammonia in the Barnard 1 cloud. In another logical step, says Herbst, researchers will probably start searching for molecules, such as methanol, containing four deuterium atoms.

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