Volume 251, 2024

Vibrational energy transfer in ammonia–helium collisions

Abstract

While the rotational energy transfer of ammonia by rare gas atoms and hydrogen molecules has been the focus of many studies, little is known about its vibrational relaxation, even though transitions involving the umbrella bending mode have been observed in many astrophysical environments. Here we explore the vibrational relaxation of the umbrella mode of ammonia induced by collisions with helium atoms by means of the close-coupling method on an ab initio potential energy surface. We compute cross sections up to kinetic energies of 1500 cm−1 and rate coefficients up to a temperature of 300 K for vibrational, rotational, and inversion transitions involving the lowest two vibrational states. We show that vibrational relaxation is much less efficient than rotation–inversion relaxation, although the rate coefficients for vibrational relaxation strongly increase with the temperature. We also observe important differences for vibrationally-elastic transitions within the lowest two vibrational states, i.e., for rotation–inversion transitions. These are a direct consequence of the difference in the tunnelling splitting of the lowest inversion levels.

Graphical abstract: Vibrational energy transfer in ammonia–helium collisions

Associated articles

Article information

Article type
Paper
Submitted
22 Dec 2023
Accepted
27 Feb 2024
First published
28 Feb 2024
This article is Open Access
Creative Commons BY-NC license

Faraday Discuss., 2024,251, 249-261

Vibrational energy transfer in ammonia–helium collisions

J. Loreau and A. van der Avoird, Faraday Discuss., 2024, 251, 249 DOI: 10.1039/D3FD00180F

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