Deexcitation rate coefficients of C₃ by collision with H₂ at low temperatures^★

¹ Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago 837.0415, Chile
² Instituto de Ciencias Químicas Aplicadas, Facultad de Ingeniería, Universidad Autónoma de Chile, Av. Pedro de Valdivia 425, 7500912 Providencia, Santiago, Chile
e-mail: otoniel.denis@uautonoma.cl
³ Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago 7800024, Santiago, Chile
⁴ Centro para el Desarrollo de la Nanociencia y la Nanotecnología (CEDENNA), Avda. Ecuador 3493, Santiago 9170124, Chile
e-mail: cardena@uchile.cl

Received: 14 October 2021
Accepted: 10 November 2021

Abstract

Context. An accurate analysis of the physical-chemical conditions in the regions of the interstellar medium in which C₃ is observed requires knowing the collisional rate coefficients of this molecule with He, H₂, electrons, and H.

Aims. The main goals of this study are to present the first potential energy surface for the C₃ +H₂ complex, to study the dynamics of the system, and to report a set of rate coefficients at low temperature for the lower rotational states of C₃ with para- and ortho-H₂.

Methods. A large grid of ab initio energies was computed at the explicitly correlated coupled-cluster with single-, double-, and perturbative triple-excitation level of theory, together with the augmented correlation-consistent quadruple zeta basis set (CCSD(T)-F12a/aug-cc-pVQZ). This grid of energies was fit to an analytical function. The potential energy surface was employed in close-coupling calculations at low collisional energies.

Results. We present a high-level four-dimensional potential energy surface (PES) for studying the collision of C₃ with H₂. The global minimum of the surface is found in the linear HH-CCC configuration. Rotational deexcitation state-to-state cross sections of C₃ by collision with para- and ortho-H₂ are computed. Furthermore, a reduced two-dimensional surface is developed by averaging the surface over the orientation of H₂. The cross sections for the collision with para-H₂ using this approximation and those from the four-dimensional PES agree excellently. Finally, a set of rotational rate coefficients for the collision of C₃ with para- and ortho-H₂ at low temperatures are reported.