Rotational excitation and de-excitation of interstellar thionylimide ( <i>cis</i> -HNSO) by helium collisions

ABSTRACT The recent identification of cis-thionylimide (cis-HNSO) in the interstellar medium (ISM) has opened new avenues for exploring nitrogen-, sulphur-, and oxygen-bearing molecules in space. To support astrophysical modelling and improve abundance estimates, we present the first comprehensive theoretical investigation of the collisional excitation and de-excitation of cis-HNSO by helium atoms. An accurate three-dimensional potential energy surface (PES) for the weakly bound cis-HNSO–He complex is first computed at the CCSD(T)-F12/aug-cc-pVTZ level, where we also consider basis set superposition error corrections. Then, an analytical form of this PES is derived, which is incorporated later for quantum close-coupling scattering calculations for cis-HNSO colliding with He, yielding state-to-state cross-sections and temperature-dependent rate coefficients across ISM-relevant conditions ($5\!-\!100 \, \mathrm{K}$). The results exhibit a strong propensity for $\Delta j= \pm 1$ transitions at low collision energies, with $\Delta j= \pm 2$ transitions becoming dominant at higher energies, reflecting the interplay between long-range and short-range anisotropies in the interaction potential. Astrophysical implications are also discussed. The collisional data provided here are essential for non-local thermodynamic equilibrium radiative transfer models and will enable more accurate interpretations of current and future astronomical observations dealing with such N-, S-, and O-containing molecules.