Protonated molecules have been increasingly detected in the interstellar medium (ISM), and usually astrochemical models fail at reproducing the abundances derived from observational spectra. Rigorous interpretation of the detected interstellar emission lines requires prior calculations of collisional rate coefficients with H2 and He, i.e., the most abundant species in the ISM. In this work, we focus on the excitation of HCNH+ induced by collision with H2 and He. Therefore, we first calculate ab initio potential energy surfaces (PESs) using the explicitly correlated and standard coupled cluster method with single, double, and non-iterative triple excitation in conjunction with the augmented-correlation consistent-polarized valence triple zeta basis set. Both the HCNH+–H2 and HCNH+–He potentials are characterized by deep global minima of 1426.60 and 271.72 cm−1, respectively, and large anisotropies. From these PESs, we derive state-to-state inelastic cross sections for the 16 low-lying rotational energy levels of HCNH+ using the quantum mechanical close-coupling approach. The differences between cross sections due to ortho- and para-H2 impacts turn out to be minor. Using a thermal average of these data, we retrieve downward rate coefficients for kinetic temperatures of up to 100 K. As it could be anticipated, differences of up to two orders of magnitude exist between the rate coefficients induced by H2 and He collisions. We expect that our new collision data will help to improve the disagreement between abundances retrieved from observational spectra and astrochemical models.
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21 February 2023
Research Article|
February 21 2023
Collisional excitation of HCNH+ by He and H2: New potential energy surfaces and inelastic rate coefficients
C. T. Bop
;
C. T. Bop
a)
(Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Writing – original draft)
Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251
, F-35000 Rennes, France
a)Author to whom correspondence should be addressed: cheikhtidiane.bop@ucad.edu.sn
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F. Lique
F. Lique
(Funding acquisition, Resources, Writing – review & editing)
Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251
, F-35000 Rennes, France
Search for other works by this author on:
a)Author to whom correspondence should be addressed: cheikhtidiane.bop@ucad.edu.sn
J. Chem. Phys. 158, 074304 (2023)
Article history
Received:
January 09 2023
Accepted:
February 02 2023
Citation
C. T. Bop, F. Lique; Collisional excitation of HCNH+ by He and H2: New potential energy surfaces and inelastic rate coefficients. J. Chem. Phys. 21 February 2023; 158 (7): 074304. https://doi.org/10.1063/5.0141851
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