Collisional excitation of propargylimine by helium: new ab initio 3D-potential energy surfaces and scattering calculations.

Abstract

We present quantum coupled-state calculations for the rotational excitation of interstellar propargylimine due to collisions with helium. The calculations are based on new high-accurate three-dimensional potential energy surfaces (3D-PESs) adapted for rigid-rotor scattering computations. The two PESs (Z/E-PGIM-He) were determined using the explicitly correlated coupled-cluster approach with single, double and perturbative triple excitation [CCSCD(T)-F12] and the standard aug-cc-pVTZ basis set. These PESs present many minima with a global minimum of -47.61 cm-1 for Z-PGIM-He and -54.16 cm-1 for E-PGIM-He. While the PESs for both complexes are qualitatively similar, that of E-PGIM-He is more anisotropic. The state-to-state collisional cross-section calculations are performed for all rotational levels J ≤ 12 with energies below Erot = 30 cm-1 and for total energies up to 500 cm-1. The corresponding collisional rate coefficients are derived for kinetic temperatures up to 120 K. A propensity rule is seen, for rotational excitation cross sections and de-excitation rate coefficients, that favors even ΔJ transitions but with different orders of magnitude. We expect that the retrieved results will contribute to improving atmospheric and astrophysics models.