arXiv subjects

Louan de Bentzmann

Publications and source records attributed to Louan de Bentzmann.

3 recordsLinked to original sources

arXiv2026

CosmicPAH-IRDB: A Web Application for Including Anharmonicity in Simulated PAH Spectra for Astrophysics

Advances in infrared observations with the James Webb Space Telescope (JWST) call for new tools to exploit the information associated with the Aromatic Infrared Bands (AIBs), now observed in both distant galaxies and the embryos of planetary systems. The AIBs contain information about their carriers as well as the excitation conditions, making them powerful probes of the chemical and physical conditions of their environments - if their spectral information can be decoded. While large datasets of theoretical infrared spectra are becoming available, efforts have primarily focused on the contribution of chemical diversity to the AIBs. However, the results remain limited by the impact of the excitation process on the band profiles. The AIB carriers, thought to be polycyclic aromatic hydrocarbons (PAHs), are hot molecules, which affects their spectral characteristics. We report here our approach to quantify these effects empirically by collecting IR spectra - both experimental and theoretical - and studying the evolution of band positions and widths with temperature. We present our methodology, including the development of the CosmicPAH-IRDB web application and spectral database, along with the associated cosmicPAHmfit multi-component spectral fitting tool. Our philosophy emphasizes open sharing, user-friendly access, and machine readability. The web application, tool and their update are accessible via the Cosmic PAH portal (https://cosmic-pah.irap.omp.eu/)

astro-ph.IM↗

arXiv2026

Infrared spectroscopy of gas-phase hydrogenated and methylated pyrenes: from laboratory spectra to the simulated 3.4 $μ$m emission band

Observations of the aromatic infrared emission band at 3.3 $μ$m often reveal satellite emission features in the 3.4 - 3.6 $μ$m range. While the 3.3 $μ$m band is attributed to the CH stretching vibration of polycylic aromatic hydrocarbons (PAHs), the satellite bands - particularly its prominent 3.4 $μ$m component - is assigned to aliphatic CH stretching vibrations in hydrogenated and methylated PAH-like species. Our aim is to derive state-of-the-art infrared emission spectra for aliphatic-containing pyrene derivatives and compare them with astronomical observations. This will help refine our understanding of the contribution of these species to the 3.4 $μ$m emission band. Mid-infrared spectra (1.4-25 $μ$m) of gas-phase dihydropyrene, tehtrahydropyrene, hexahydropyrene methylated pyrene, and pyrene were recorded at temperatures ranging from 373 to 673 K, depending on the species. The band profiles were analyzed using a multi-component fitting tool, and empirical anharmonicity laws were derived to quantify the evolution of the band positions and widths with temperature. The obtained spectral data was combined with the results of a Monte Carlo emission model to simulate the emission spectra following UV-photon absorption, up to the dissociation limit ($\lesssim$6 eV). The resulting synthetic spectra were compared with James Webb Space Telescope observations of the Orion Bar region (PDRs4All program). Based on these state-of-the-art simulated spectra, we propose 1,2,3,6,7,8-hexahydropyrene as the carrier of the red component of the 3.4 $μ$m band observed at 3.403 $μ$m. While 1-methylpyrene may also contribute to the underlying emission plateau, its lack of a strong infrared band complicates detection in observed spectra, unlike hexahydropyrene. All experimental spectra and their temperature-dependent analyses are available in the new cosmicPAH-IRDB database.

astro-ph.GA↗

arXiv2024

The Emergence of the Hexagonal Lattice in Two-Dimensional Wigner Fragments

At very low density, the electrons in a uniform electron gas spontaneously break symmetry and form a crystalline lattice called a Wigner crystal. But which type of crystal will the electrons form? We report a numerical study of the density profiles of fragments of Wigner crystals from first principles. To simulate Wigner fragments we use Clifford periodic boundary conditions and a renormalized distance in the Coulomb potential. Moreover, we show that high-spin restricted open-shell Hartree-Fock theory becomes exact in the low-density limit. We are thus able to accurately capture the localisation in two-dimensional Wigner fragments with many electrons. No assumptions about the positions where the electrons will localise are made. The density profiles we obtain emerge naturally when we minimise the total energy of the system. We clearly observe the emergence of the hexagonal crystal structure which has been predicted to be ground-state structure of the two-dimensional Wigner crystal.

quant-ph↗