![Ka = 0 rotational transitions of HNCOH+ identified towards G+0.693 and sorted by increasing frequency (see also Table B.1). The LTE fit of HNCOH+ is plotted with a red line, while the blue line depicts the emission from all the molecules identified to date in our survey, including HNCOH+ (observed spectra shown as gray histograms). The molecular structure of HNCOH+ is shown in the bottom right. The quantum numbers of each rotational transition (J + 1 → J) are indicated in the upper left of each panel. Blue labels show the rest of identified species contributing to the observed spectra.-- [astro-ph.GA]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/Detection.png?fit=1200%2C675&ssl=1)
[astro-ph.GA] Only five out of the ∼350 molecules detected in the interstellar medium (ISM) carry the isocyanate functional group (NCO), the essential substructure of peptide bonds in proteins. Among them are isocyanic acid (HNCO) and its most stable N-protonated isomer H2NCO+.
Previous studies have predicted that the O-protonated isomer HNCOH+ should be present in the ISM; yet this species has remained elusive. We search for the metastable HNCOH+ towards the Galactic Center molecular cloud G+0.693-0.027, where H2NCO+ has already been detected. We use an ultra-deep broadband spectral survey carried out towards G+0.693-0.027 with the Yebes 40-m, IRAM 30-m and APEX telescopes covering nearly 150 GHz of bandwidth between 31 and 275 GHz.
We report the first detection of HNCOH+ in the ISM with a column density of N = (9.9 ± 0.5)×1012 cm−2, which corresponds to a molecular abundance relative to H2 of (7.3+1.3−1.0)×10−11. With the measured H2NCO+ column density of N = (2.6 ± 0.3) ×1012 cm−2, this yields a HNCOH+/H2NCO+ ratio of 3.8+0.5−0.4.
This result is consistent with recent kinetic calculations that favour the formation of HNCOH+ over H2NCO+. The detection of HNCOH+ in the ISM broadens the inventory of molecules known to contain the isocyanate functional group and reinforces recent works showing that isomer abundances in the ISM do not necessarily correlate with thermodynamic stability.
M. Rey-Montejo (1 and 2), I. Jimenez-Serra (1), M. Sanz-Novo (3), V. Lattanzi (3), S. Thorwirth (4), V. M. Rivilla (1), S. Zeng (5), L. Colzi (1), D. San Andres (1 and 2), A. Megias (1), A. Martinez-Henares (5), M. A. Requena-Torres (6), S. Martin (7 and 8), B. Tercero (9 and 10), P. de Vicente (10) ((1) Centro de Astrobiologia (CAB), CSIC-INTA, Torrejon de Ardoz, Spain, (2) Departamento de Fisica de la Tierra y Astrofisica, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, Spain, (3) Center for Astrochemical Studies, Max-Planck-Institut fur extraterrestrische Physik, Germany, (4) I. Physikalisches Institut, Universitat zu Koln, Germany, (5) Star and Planet Formation Laboratory, RIKEN Pioneering Research Institute, Japan, (6) Department of Physics, Astronomy, and Geosciences, Towson University, USA, (7) European Southern Observatory, Alonso de Cordova, Chile, (8) Joint ALMA Observatory, Alonso de Cordova, Chile, (9) Observatorio Astronomico Nacional (OAN, IGN), Madrid, Spain, (10) Centro de Desarrollos Tecnologicos, Observatorio de Yebes (IGN), Guadalajara, Spain)
Comments: Letter, Accepted in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2610.39654 [astro-ph.GA] (or arXiv:2610.39654v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2610.39654
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Submission history
From: Marta Rey-Montejo
[v1] Thu, 29 Oct 2026 09:08:50 UTC (435 KB)
https://arxiv.org/abs/2610.39654
Astrobiology, Astrochemistry,
