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

Coutens, A.; Ligterink, N. F. W.; Loison, J.-C.; Wakelam, V.; Calcutt, H.; Drozdovskaya, M. N.; Jørgensen, J. K.; Müller, H. S. P.; van Dishoeck, E. F.; Wampfler, S. F. (2019). The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium. Astronomy and astrophysics, 623(L13), L13. EDP Sciences 10.1051/0004-6361/201935040

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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, N₂O, 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 N₂O have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 10¹⁴ cm⁻² in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO₂, 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, N₂O, and NO₂ abundances, but not the NO, HNO, and NH2OH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NH2OH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures.

Item Type:

Journal Article (Further Contribution)


10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Ligterink, Niels Frank Willem; Drozdovskaya, Maria Nikolayevna and Wampfler, Susanne


500 Science > 520 Astronomy
500 Science > 530 Physics




EDP Sciences




Danielle Zemp

Date Deposited:

14 Apr 2020 10:44

Last Modified:

19 Apr 2020 02:53

Publisher DOI:





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