Rotational rate coefficients of MgC3N+(<i>X</i>1Σ+) by collision with He(1<i>S</i>)

ABSTRACT Rotational (de-)excitation of the interstellar species MgC$_{3}$N$^{+}$($X^{1}\Sigma ^{+}$) with He is investigated. A two-dimensional potential energy surface (2D-PES) for the MgC$_{3}$N$^{+}$–He system is calculated at an internuclear MgC$_{3}$N$^{+}$ distances frozen at its equilibrium minimum energy. This 2D-PES, derived with the RCCSD(T)-F12 method using the aug-cc-pVTZ basis sets for all atoms, presents two minima with well depths of $-1127.7$ cm$^{-1}$ and $-59.1$ cm$^{-1}$. Close coupling calculations of the collisional (de-)excitation cross-sections between the first 21 rotational levels of MgC$_{3}$N$^{+}$ by collisions with He are calculated at low energies (≤170 cm$^{-1}$). These cross-sections yield, after Boltzmann thermal average, rate coefficients up to $30\:\mathrm{K}$. A non-local thermodynamical equilibrium radiative transfer calculation is performed using the new collisional rate coefficients to model the MgC$_{3}$N$^{+}$ excitation in the interstellar medium.