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

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 $Jᵤₚ = 2 to Jᵤₚ$ = 10, including several completely unblended features. We derive a molecular column density of $N$ = (8 $±$ 1)$×$10$¹³$ cm$⁻²$, yielding a fractional abundance relative to H$_2$ of $~$6$×$10$⁻¹⁰$, which is about $~$37 and $~$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.