Isomerism Effects in the Collisional Excitation of Cyanoacetylene by Molecular Hydrogen

Author

Cheikh T. Bop
Fidel A. Batista-Romero
Alexandre Faure
Ernesto Quintas-Sánchez, Missouri University of Science and TechnologyFollow
Richard Dawes, Missouri University of Science and TechnologyFollow
Francois Lique

Abstract

Rotational excitation of the interstellar HC₂NC and HNC₃ molecules, two isomers of HC₃N, induced by collisions with H₂ is investigated at low collision energy using a quantum time-independent approach. The scattering calculations are based on new high-level ab initio four-dimensional (4D) potential energy surfaces (PESs) computed at the explicitly correlated coupled cluster with single, double, and perturbative triple excitations [CCSD(T)-F12b] level of theory. The method of interpolating moving least squares (IMLS) was used to construct 4D analytical PESs. Rotationally inelastic cross sections among the low-lying rotational levels of HC₂NC and HNC₃ were obtained using a pure quantum close-coupling approach for total energies up to 100 cm^-1. The corresponding thermal rate coefficients were computed for temperatures ranging from 1 to 20 K. Propensity rules in favor of even Δj1 transitions were found for both HC₂NC and HNC₃ in collisions with para-H₂(j₂ = 0), with j1 being the rotational level of HC₂NC and HNC₃ molecules. The new rate coefficients were compared to previously published HC₃N-para-H₂(j₂ = 0) rate coefficients. As expected, differences were found, especially for the rate coefficients corresponding to Δj1 = 1 transitions. Such a comparison confirms the importance of having specific collisional data for the different isomers of a molecule. The new rate coefficients will be crucial to improve the estimation of the HC₃N/HC₂NC/HNC₃ abundance ratio in the interstellar medium.

Recommended Citation

C. T. Bop et al., "Isomerism Effects in the Collisional Excitation of Cyanoacetylene by Molecular Hydrogen," ACS Earth and Space Chemistry, vol. 3, no. 7, pp. 1151 - 1157, American Chemical Society (ACS), Mar 2019.

The definitive version is available at https://doi.org/10.1021/acsearthspacechem.9b00049

Department(s)

Chemistry

Research Center/Lab(s)

Center for High Performance Computing Research

Comments

Richard Dawes and Ernesto Quintas-Sánchez are supported by the U.S. National Science Foundation (CHE-1566246).

Keywords and Phrases

Astrochemistry; Energy Transfer; Molecular Processes; Quantum Scattering; Van Der Waals Complexes

International Standard Serial Number (ISSN)

2472-3452

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2019 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Mar 2019