The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium
Journal article, 2019

Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, NO, and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS 16293-2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and NO have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 1014 cm in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO, NO+, and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, NO, and NO abundances, but not the NO, HNO, and NHOH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NHOH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures.








IRAS 16293-2422


individual objects


A. Coutens

University of Bordeaux

N. F W Ligterink

University of Bern

J. C. Loison

University of Bordeaux

V. Wakelam

University of Bordeaux

Hannah Calcutt

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

M. N. Drozdovskaya

University of Bern

Jes K. Jørgensen

University of Copenhagen

H. S.P. Müller

University of Cologne

E. F. van Dishoeck

Max Planck Society

Leiden University

S. F. Wampfler

University of Bern

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 623 L13

Protostellar Interferometric Line Survey (PILS)

European Research Council (ERC), 2019-10-30 -- .

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Other Chemistry Topics



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