Rotational inelastic excitation of MgC4H( <i>X</i> 2Σ+) by collision with He(1 <i>S</i> ): new scattering calculations

ABSTRACT In this study, we report the rate coefficients calculation of MgC4H($X^{2}\Sigma ^{+}$) induced by collision with He. This calculation is based on a new two-dimensional potential energy surface (PES), obtained from the explicitly correlated restricted open-shell coupled cluster approach with single, double, and perturbative triple excitation (rccsd(t)-f12) and the augmented-correlation consistent-polarized valence triple zeta (aug-cc-pVTZ) Gaussian basis set. The PES presents two minima with well depths of $-46.6$ and $-25.5$ cm−1. This PES is used to calculate the (de)-excitation cross-sections, for total energies up to 500 cm−1 and nuclear rotational angular momentum $N\le 40$, using the close-coupling quantum time-independent formalism. By integrating these cross-sections on a Maxwell–Boltzmann distribution of kinetic energies, we derive the collisional (de)-excitation rate coefficients for thermal temperatures below $50 \, \mathrm{K}$. These MgC4H–He rate coefficients present a propensity rule given by $k(\Delta N = \Delta j = -2) &amp;gt; k(\Delta N = \Delta j = -1) &amp;gt; k(\Delta N = -1,\,\, \Delta j = 0)$ with j being the total molecular angular momentum. This collisional data can be useful for the estimation of MgC4H abundance in the investigated interstellar medium.