Laboratory Detection and Rotational Spectroscopy of trans-HNSO: Implications for Astronomical Observations
Sulfur-bearing molecules are central to interstellar chemistry, yet their observed abundances in the gas phase remain far below cosmic expectations in dense interstellar regions. Mixed N-S-O species such as thionylimide (HNSO) are particularly relevant, as they incorporate three key biogenic elements.
The cis conformer of HNSO has recently been detected in the Galactic Center cloud G+0.693-0.027, but no high-resolution data for the higher energy conformer (trans-HNSO) had been available until now.
We report the first laboratory detection and rotational spectroscopic characterization of trans-HNSO. Spectra were recorded with the Center for Astrochemical Studies Absorption Cell (CASAC) free-space spectrometer employing a hollow-cathode discharge source, yielding 104 assigned transitions between 200 and 530 GHz.
A Watson S-reduced Hamiltonian fit reproduced the data with an rms of 40 kHz, providing accurate rotational and centrifugal distortion constants in excellent agreement with CCSD(T) predictions.
Although trans-HNSO lies only a few kcal/mol above the cis form, it has larger dipole components, making its lines particularly intense (more than 5 times brighter, assuming equal abundances) and a very promising candidate for future astronomical detection. The new measurements enable reliable frequency predictions for astronomical searches and will be added to public databases.
Combined with recent evidence for tunneling-driven trans-to-cis isomerization at cryogenic temperatures, these results open the way to test directly whether quantum tunneling governs the interstellar distribution of HNSO isomers.
Valerio Lattanzi, Miguel Sanz-Novo, Víctor M. Rivilla, Izaskun Jiménez-Serra, Paola Caselli
Comments: 15 pages, 3 figures, 2 tables. Accepted for publication in Frontiers in Astronomy and Space Sciences – Astrochemistry
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2511.22548 [astro-ph.GA] (or arXiv:2511.22548v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2511.22548
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Submission history
From: Valerio Lattanzi
[v1] Thu, 27 Nov 2025 15:29:53 UTC (482 KB)
https://arxiv.org/abs/2511.22548
Astrobiology
