Discovery of thionylimide, HNSO, in space: the first N-, S- and O-bearing interstellar molecule (2404.01044v1)

Abstract: We present the first detection in space of thionylimide (HNSO) toward the Galactic Center molecular cloud G+0.693-0.027, thanks to the superb sensitivity of an ultradeep molecular line survey carried out with the Yebes 40$\,$m and IRAM 30$\,$m telescopes. This molecule is the first species detected in the interstellar medium containing, simultaneously, N, S and O. We have identified numerous $K$$a$ = 0, 1 and 2 transitions belonging to HNSO covering from $J$${\rm up}$ = 2 to $J$$_{\rm up}$ = 10, including several completely unblended features. We derive a molecular column density of $N$ = (8 $\pm$ 1)$\times$10$^{13}$ cm$^{-2}$, yielding a fractional abundance relative to H$_2$ of $\sim$6$\times$10$^{-10}$, which is about $\sim$37 and $\sim$4.8 times less abundant than SO and SO2, respectively. Although there are still many unknowns in the interstellar chemistry of NSO-bearing molecules, we propose that HNSO is likely formed through the reaction of the NSO radical and atomic H on the surface of icy grains, with alternative routes also deserving exploration. Finally, HNSO appears as a promising link between N- , S- and O- interstellar chemistry and its discovery paves the route to the detection of a new family of molecules in space.

• The paper reports the first interstellar detection of thionylimide (HNSO) containing nitrogen, sulfur, and oxygen.
• The study uses deep molecular line surveys from Yebes 40m and IRAM 30m telescopes to derive a column density of (8 ± 1) × 10^13 cm⁻² and a fractional abundance of ~6 × 10⁻¹⁰.
• These findings suggest that HNSO may serve as a key intermediary in complex astrochemical reactions, prompting extensions of theoretical and observational models.

Discovery of Thionylimide (HNSO) in the Interstellar Medium

The paper presents a pioneering detection of the molecule thionylimide (HNSO) in space, specifically within the Galactic Center molecular cloud G+0.693-0.027. Conducted using the Yebes 40m and IRAM 30m telescopes, the paper reports HNSO as the first interstellar molecule to simultaneously contain nitrogen (N), sulfur (S), and oxygen (O). Through the identification of multiple transitions of HNSO, the authors derive a molecular column density of $N = (8 \pm 1) \times 10^{13} \, \text{cm}^{-2}$ with a fractional abundance relative to $\text{H}_2$ of approximately $6 \times 10^{-10}$.

HNSO's discovery adds a new dimension to our understanding of astrochemical processes because such species may act as vital intermediaries in the complex chemistry of nitrogen-, sulfur-, and oxygen-bearing interstellar compounds. The detection method, involving deep molecular line surveys in the microwave to millimeter-wave regions, leverages the advanced sensitivity of contemporary telescopic technology.

Implications and Future Directions

Astrochemical Significance:

The identification of HNSO is significant for astrochemistry, as molecules containing N, S, and O are rare but crucial for understanding the links between different chemical pathways in space. Given that the molecule is up to 37 times less abundant than sulfur monoxide (SO) and 4.8 times less abundant than sulfur dioxide ($\text{SO}_2$), it holds a potential intermediary role between simpler and more complex interstellar molecules.

Formation Pathways:

The paper proposes potential pathways for HNSO formation, primarily suggesting surface reactions on icy grains involving radicals such as NSO and atomic hydrogen, or alternative routes through radical diffusion on surfaces. Moreover, the discussion posits that the feasibility of such surface reactions might depend on the shock-induced desorption mechanisms common in dense interstellar environments.

Theoretical and Practical Considerations:

On the theoretical side, the detection encourages the extension of existing chemical models to include NSO-bearing species and investigate unexplored reaction pathways both in the gas phase and on surfaces. Practically, this finding could lead to more targeted searches for other members of the NSO family and expand our understanding of the molecular complexity within the interstellar medium.

Further Research:

Future studies could explore high-resolution spectroscopic characterizations of other [H,N,S,O] isomers, as well as understanding the interstellar NSO radical chemistry. The discovery exemplifies how interstellar spectroscopy can illuminate the complex chemical environments of space and prompt expansions in both the observational and laboratory research of molecular astrophysics.

Summarily, this paper contributes a notable finding to the catalog of interstellar molecules and suggests implications that reach beyond its immediate chemical lineage, stimulating both theoretical advancements and experimental pursuits in the field of astrochemistry.