Detection of HNCOH+ in the interstellar medium
Abstract
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.
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BibTeX
@misc{reymontejo2026detection,
title = {{Detection of HNCOH+ in the interstellar medium}},
author = {M. Rey-Montejo and I. Jimenez-Serra and M. Sanz-Novo and V. Lattanzi and S. Thorwirth and V. M. Rivilla and S. Zeng and L. Colzi and D. San Andres and A. Megias and A. Martinez-Henares and M. A. Requena-Torres and S. Martin and B. Tercero and P. de Vicente},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39654},
eprint = {2610.39654},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39654},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Detection of HNCOH+ in the interstellar medium
AU - M. Rey-Montejo
AU - I. Jimenez-Serra
AU - M. Sanz-Novo
AU - V. Lattanzi
AU - S. Thorwirth
AU - V. M. Rivilla
AU - S. Zeng
AU - L. Colzi
AU - D. San Andres
AU - A. Megias
AU - A. Martinez-Henares
AU - M. A. Requena-Torres
AU - S. Martin
AU - B. Tercero
AU - P. de Vicente
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.39654
UR - https://arxiv.org/abs/2610.39654
AB - 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 H_2NCO^+. 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 H_2NCO^+ 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)×10^12 cm^−2, which corresponds to a molecular abundance relative to H_2 of (7.3^+1.3 _−1.0)×10^−11. With the measured H_2NCO^+ column density of N = (2.6 ± 0.3) × 10^12 cm^−2, this yields a HNCOH^+/H_2NCO^+ ratio of 3.8^+0.5 _−0.4. This result is consistent with recent kinetic calculations that favour the formation of HNCOH^+ over H_2NCO^+. 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.
ER -