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August 16, 2022
ALMA Detects Interstellar Propanol and Its Isomer in Milky Way’s Center
Science

ALMA Detects Interstellar Propanol and Its Isomer in Milky Way’s Center

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have detected two complex organic molecules — isopropanol (i-C3H7OH) and its normal isomer, propanol (n-C3H7OH) — in Sagittarius B2, a giant molecular cloud of gas and dust in the constellation of Sagittarius.

Sagittarius B2 is a giant molecular cloud located about 390 light-years from the center of the Milky Way Galaxy. Image credit: ESO / APEX / MSX / IPAC / NASA.

“The detection of a branched alkyl molecule, isopropyl cyanide, in the interstellar medium with ALMA opened a new window into the chemistry that takes place in star forming regions,” said Dr. Arnaud Belloche from the Max-Planck-Institut für Radioastronomie and colleagues.

“The production of such a branched molecule appears to require the addition of a functional group to a nonterminal carbon in the chain forming its backbone.”

“The detection was made in the frame of our earlier imaging spectral line survey called Exploring Molecular Complexity with ALMA (EMoCA) that targeted Sagittarius B2(N).”

“Since the discovery of iso-propyl cyanide, many new complex organic molecules — which are carbon-bearing molecules containing at least six atoms per definition — have been reported in the interstellar medium, including two polycyclic aromatic hydrocarbons, but no other branched molecule has been identified.”

Sagittarius B2 is located approximately 390 light-years from the center of our Milky Way Galaxy.

Also known Sgr B2, this enormous star-forming cloud has a mass of 3 million solar masses.

Its internal structure is complex, with varying densities and temperatures. It is divided into three main cores: north Sgr B2(N), middle or main Sgr B2(M), and south Sgr B2(S).

As part of the new survey, called Re-exploring Molecular Complexity with ALMA (ReMoCA), Dr. Belloche and co-authors searched for iso-propanol and its isomer in the hot core Sgr B2(N2).

They found that iso-propanol is nearly as abundant as normal-propanol, with an abundance ratio of 0.6 which is similar to the ratio of 0.4 that they obtained previously for iso- and normal-propyl cyanide with the EMoCA survey.

“The detection of normal- and iso-propanol and their ratio indicate that the modest preference for the normal form of propyl cyanide determined previously may be a more general feature among similarly sized interstellar molecules,” they said.

“Detecting other pairs of interstellar organic molecules with a functional group attached either to a primary or secondary carbon may help in pinning down the processes that dominate in setting their normal-to-iso ratios.”

“Butanol and its isomers would be the next obvious candidates in the alcohol family, but their detection in hot cores will be challenging.”

A paper on the findings was published in the journal Astronomy & Astrophysics.

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A. Belloche et al. 2022. Interstellar detection and chemical modeling of iso-propanol and its normal isomer. A&A 662, A110; doi: 10.1051/0004-6361/202243575

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