Actualités du Laboratoire

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Ref Arxiv: 2211.04765
DOI: 10.1093/mnras/stac3302
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DOI: 10.1117/12.2628689
Résumé:

The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs (UBV, RIZ, YJH) providing a spectral resolution of similar to 100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 mu m with the goal of extending it to 0.35-2.4 mu m with the addition of a K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Its modularity will ensure that ANDES can be placed entirely on the ELT Nasmyth platform, if enough mass and volume is available, or partly in the Coude room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature's fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of more than 200 scientists and engineers which represent the majority of the scientific and technical expertise in the field among ESO member states.

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Résumé:

Gas hydrates are nanoporous crystalline solids composed of hydrogen-bonded water molecules forming cages within which gaseous molecules are encapsulated. Since their initial discovery, interest in gas hydrates has grown exponentially from being of mere scientific curiosity to offering a potential new energy solution to the imminent energy crisis [1]. Gas hydrates are considered to be pivotal terrestrial and extraterrestrial ingredients, as they make up a great part of the Earth's seafloor sediments and play a role in extraterrestrial planetary formation scenari [2]. For example, clathrate hydrates of methane are extensively studied in astrophysics because they are suspected to be present on several planets, satellites and comets of the Solar System [3]. However, the description of such encapsulated molecular systems is often far from complete. Indeed, in such nanoscale confinement, the translational center-of-mass motions of the caged molecules are quantized and strongly coupled to the molecular rotations, which are quantized too. To interpret experimental data (like inelastic neutron scattering), theoretical tools are useful but we need to go beyond the simple harmonic approximation as the guest molecule presents very large amplitude motions (translation and rotation) and its interaction with the nanoscale cavity can be far from harmonic. A rigorous quantum treatment of the intricate coupled translation-rotation and/or vibration-translation-rotation (considering the molecular hydrogen stretching mode) dynamics of the caged diatomic molecules is far from a routine task. In this contribution, I will present a review on our recent progress in the development of efficient/accurate computational methods for the rigorous quantum treatment of the intricate coupled translation-rotation dynamics of the molecular hydrogen in water clathrates [4-7]. In particular, the efficiency of the computational method will highlight the impact of the condensed-phase environment on the spectroscopy of the confined molecule. Moreover, the efficiency of our computational scheme allows us to directly probe the quality of the considered intermolecular potentials (ranging from semiempirical to the most sophisticated ab initio potentials). Bibliography: [1] C. I. Ratcliffe, Energy fuels, 36 (2022) [2] B.K. Chastain et al., Planetary and Space Science, 55 (2009) [3] O. Mousis et al., Astrobiology, 15, 4 (2015) [4] A. Chen et al., J. Chem. Theory Comput., 18, 7 (2022) [5] D. Lauvergnat et al., J. Chem. Phys., 150 (2019) [6] D. Benoit et al., Faraday Discuss., 212, 533 (2018) [7] A. Powers et al., J. Chem. Phys., 148 (2018)