Ro-vibrational excitation of AlCl induced by H2 collisions: The missing piece for accurate modeling of AlCl emission spectra from circumstellar gas
4 affiliations
- 1Faculty of Sciences, Tunis El-Manar University LSAMA, Department of Physics, , 1060 Tunis ,
- 2School of Science, University of Newcastle , University Drive, Callaghan 2308, New South Wales ,
- 3Anton Pannekoek Institute for Astronomy, University of Amsterdam , P.O. Box 94249, 1090 GE Amsterdam ,
- 4Univ Rennes, CNRS , IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes ,
Abstract
Ro-vibrational transitions of metal-bearing molecules such as AlCl are key probes of warm and dense astrophysical environments such as circumstellar envelopes. Reliable non-local thermodynamic equilibrium (non-LTE) modeling of these regions requires accurate collisional data for both rotational and ro-vibrational excitation. This work presents the first comprehensive study of the ro-vibrational excitation of AlCl(X1Σ+) induced by collisions with H2. A new AlCl–H2 potential energy surface, which accounts for the vibrational motion of AlCl, has been calculated. Quantum scattering calculations were performed using the coupled states (CS) and vibrational close-coupling rotational infinite order sudden (VCC-IOS) approaches. These calculations yielded state-to-state cross sections for total energies up to 6000 cm−1, as well as rate coefficients for temperatures up to 1000 K for ro-vibrational transitions between rotational levels belonging to the v = 0 - 2 vibrational levels. The VCC-IOS approximation is shown to be accurate for pure rotational transitions and for vibrational excitations with Δv = 1 at high kinetic temperatures above ~300 K. In such regimes, it offers a computationally efficient alternative to the CS approach, which remains essential for capturing low temperature regime accurately. To evaluate the impact of these new rate coefficients on the interpretation of AlCl observational spectra, we perform radiative transfer calculations. We found that non-LTE excitation occurs for physical conditions representative of circumstellar gas. Finally, we reinterpret AlCl emission spectra from the W Aquilae circumstellar enveloppe using the new collisional data. Our results show that actual AlCl-H2 collisional data are needed for correctly modeling AlCl observations.
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BibTeX
@article{mhamdi2026rovibrational,
title = {{Ro-vibrational excitation of AlCl induced by H2 collisions: The missing piece for accurate modeling of AlCl emission spectra from circumstellar gas}},
author = {M M’hamdi and A Ben Houria and T Danilovich and C T Bop and K Hammami and F Lique},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = nov,
doi = {10.1093/mnras/stag2116},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2116/9012724},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Ro-vibrational excitation of AlCl induced by H2 collisions: The missing piece for accurate modeling of AlCl emission spectra from circumstellar gas
AU - M M’hamdi
AU - A Ben Houria
AU - T Danilovich
AU - C T Bop
AU - K Hammami
AU - F Lique
PY - 2026
DA - 2026/11/04
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag2116
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2116/9012724
AB - Ro-vibrational transitions of metal-bearing molecules such as AlCl are key probes of warm and dense astrophysical environments such as circumstellar envelopes. Reliable non-local thermodynamic equilibrium (non-LTE) modeling of these regions requires accurate collisional data for both rotational and ro-vibrational excitation. This work presents the first comprehensive study of the ro-vibrational excitation of AlCl(X1Σ+) induced by collisions with H2. A new AlCl–H2 potential energy surface, which accounts for the vibrational motion of AlCl, has been calculated. Quantum scattering calculations were performed using the coupled states (CS) and vibrational close-coupling rotational infinite order sudden (VCC-IOS) approaches. These calculations yielded state-to-state cross sections for total energies up to 6000 cm−1, as well as rate coefficients for temperatures up to 1000 K for ro-vibrational transitions between rotational levels belonging to the v = 0 - 2 vibrational levels. The VCC-IOS approximation is shown to be accurate for pure rotational transitions and for vibrational excitations with Δv = 1 at high kinetic temperatures above ~300 K. In such regimes, it offers a computationally efficient alternative to the CS approach, which remains essential for capturing low temperature regime accurately. To evaluate the impact of these new rate coefficients on the interpretation of AlCl observational spectra, we perform radiative transfer calculations. We found that non-LTE excitation occurs for physical conditions representative of circumstellar gas. Finally, we reinterpret AlCl emission spectra from the W Aquilae circumstellar enveloppe using the new collisional data. Our results show that actual AlCl-H2 collisional data are needed for correctly modeling AlCl observations.
SN - 0035-8711
SN - 1365-2966
ER -