SIMBAD references

Nitriles have been identified in space. Accurately modelling their abundance requires calculations of collisional rate coefficients. These data are obtained by first computing potential energy surfaces (PES) and cross-sections using high accurate quantum methods. In this paper, we report the first interaction potential of the HNCCN⁺-He collisional system along with downward rate coefficients among the 11 lowest rotational levels of HNCCN⁺. The PES was calculated using the explicitly correlated coupled cluster approach with simple, second, and non-iterative triple excitation (CCSD(T)-F12) in conjunction with the augmented-correlation consistent-polarized valence triple zeta Gaussian basis set. It presents two local minima of ∼283 and ∼136 cm^–1, the deeper one is located at R = 9 a₀ towards the H end (He\cdotsHNCCN⁺). Using the so-computed PES, we calculated rotational cross-sections of HNCCN⁺ induced by collision with He for energies ranging up to 500 cm^–1 with the exact quantum mechanical close coupling method. Downward rate coefficients were then worked out by thermally averaging the cross-sections at low temperature (T <= 100 K). The discussion on propensity rules showed that the odd Δj transitions were favoured. The results obtained in this work may be crucially needed to accurately model the abundance of cyanogen and its protonated form in space.