Laboratory Detection and Rotational Spectroscopy of $trans$-HNSO: Implications for Astronomical Observations
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| Format: | Preprint |
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2025
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| _version_ | 1866918221355941888 |
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| author | Lattanzi, Valerio Sanz-Novo, Miguel Rivilla, Víctor M. Jiménez-Serra, Izaskun Caselli, Paola |
| author_facet | Lattanzi, Valerio Sanz-Novo, Miguel Rivilla, Víctor M. Jiménez-Serra, Izaskun Caselli, Paola |
| contents | 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2511_22548 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Laboratory Detection and Rotational Spectroscopy of $trans$-HNSO: Implications for Astronomical Observations Lattanzi, Valerio Sanz-Novo, Miguel Rivilla, Víctor M. Jiménez-Serra, Izaskun Caselli, Paola Astrophysics of Galaxies 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. |
| title | Laboratory Detection and Rotational Spectroscopy of $trans$-HNSO: Implications for Astronomical Observations |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2511.22548 |