2018MNRAS.480.4259T

Neutral and ionic nitrogen sulfide, NS, are closely connected with the chemistry of the larger nitrogen-containing molecular species. NS⁺ cation was recently detected in some regions of the interstellar medium, where a small abundance is estimated. In order to help for the identification of this cation in other sources, we present the collision rates for the rotational (de-)excitation of NS⁺ by He. They are obtained using quantum scattering calculations for collision energies between 1.26 and 1400 cm^–1, followed by averaging of the cross-sections over a Maxwell-Boltzmann distribution. These quantum nuclear motion treatments are performed on a new 3D potential energy surface (PES) for the NS⁺(X¹Σ⁺) - He weakly bound complex. This PES is generated in Jacobi coordinates and using the explicitly correlated coupled cluster method (CCSD(T)-F12) in conjunction with the aug-cc-pVTZ basis set. Afterwards, rate constants for rotational levels of NS⁺ up to 10 and temperatures in the range of 2-300K are deduced. Particularly, the 3-2 transition, recently observed in the surveys, is found to be predominant at very low temperatures, whereas the 5-4 transition is predicted to dominate at higher temperatures, which may be used for the identification of this cation in hot media. The use of the rates of CS colliding with He are viewed to be a good approximation for the estimation of NS⁺ abundances.