Issue |
A&A
Volume 693, January 2025
|
|
---|---|---|
Article Number | A181 | |
Number of page(s) | 9 | |
Section | Atomic, molecular, and nuclear data | |
DOI | https://doi.org/10.1051/0004-6361/202452977 | |
Published online | 15 January 2025 |
Inelastic H + H3+ collision rates and their impact on the determination of the excitation temperature of H3+
1
Unidad Asociada UAM-IFF-CSIC, Departamento de Química Física Aplicada, Facultad de Ciencias M-14, Universidad Autónoma de Madrid,
28049
Madrid,
Spain
2
Instituto de Física Fundamental (IFF-CSIC), C.S.I.C.,
Serrano 123,
28006
Madrid,
Spain
3
Sorbonne Université, Observatoire de Paris, Université PSL, CNRS, LERMA,
92190
Meudon,
France
4
Université Paris-Cité,
Paris,
France
★ Corresponding author; octavio.roncero@csic.es
Received:
13
November
2024
Accepted:
6
December
2024
Context. In diffuse interstellar clouds, the excitation temperature derived from the lowest levels of H3+ is systematically lower than that derived from H2. The differences may be attributed to the lack of state-specific formation and destruction rates of H3+, which are needed to thermalize the two species.
Aims. In this work, we aim to investigate the possible influence of rotational excitation collisions of H3+ with atomic hydrogen on its excitation temperature.
Methods. We used a time-independent close-coupling method to calculate the state-to-state rate coefficients, incorporating a very accurate and full-dimensional potential energy surface recently developed for H4+. We take a symmetric top approach to describe a frozen H3+ as an equilateral triangle.
Results. We derive rotational excitation collision rate coefficients of H3+ with atomic hydrogen in a temperature range corresponding to diffuse interstellar conditions up to (J, K, ±) = (7, 6, +) and (J, K, ±) = (6, 4, +) for its ortho and para forms. This allows us to obtain a consistent set of collisional excitation rate coefficients and to improve on a previous study that included speculations regarding these contributions.
Conclusions. The new state-specific inelastic H3+ + H rate coefficients yield differences of up to 20% in the excitation temperature, and their impact increases with decreasing molecular fraction. We also confirm the impact of chemical state-to-state destruction reactions on the excitation balance of H3+, and that reactive H + H3+ collisions are also needed to account for possible further ortho to para transitions.
Key words: astrochemistry / molecular processes / radiative transfer / scattering
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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