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Context. The James Webb Space Telescope (JWST) has captured the most detailed and sharpest infrared (IR) images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR).Aims. We investigate the fundamental interaction of far-ultraviolet (FUV) photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments.Methods. We utilized NIRCam and MIRI to obtain sub-arcsecond images over ~150″ and 42″ in key gas phase lines (e.g., Pa α, Br α, [FeII] 1.64 µm, H2 1−0 S(1) 2.12 µm, 0–0 S(9) 4.69 µm), aromatic and aliphatic infrared bands (aromatic infrared bands at 3.3–3.4 µm, 7.7, and 11.3 µm), dust emission, and scattered light. Their emission are powerful tracers of the IF and DF, FUV radiation field and density distribution. Using NIRSpec observations the fractional contributions of lines, AIBs, and continuum emission to our NIRCam images were estimated. A very good agreement is found for the distribution and intensity of lines and AIBs between the NIRCam and NIRSpec observations.Results. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of ~0.1–1″ (~0.0002–0.002 pc or ~40–400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. The spatial distribution of the AIBs reveals that the PDR edge is steep and is followed by an extensive warm atomic layer up to the DF with multiple ridges. A complex, structured, and folded H0/H2 DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar as our observations show that a 3D “terraced” geometry is required to explain the JWST observations. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate.Conclusions. This study offers an unprecedented dataset to benchmark and transform PDR physico-chemical and dynamical models for the JWST era. A fundamental step forward in our understanding of the interaction of FUV photons with molecular clouds and the role of FUV irradiation along the star formation sequence is provided.
We present the first theoretical line profile calculations of the ultraviolet spectral lines of carbon perturbed by helium using a semiclassical collision approach and high-quality ab initio potentials and electronic transition dipole moments. The temperature range is from 5000 to 8000 K. These results are important for astrophysical modelling of spectra in atmospheres of white dwarf stars showing atomic carbon in an helium atmosphere. Beyond the conventional symmetrical Lorentzian core at low He density, these lines exhibit a blue asymmetric behaviour. This blue asymmetry is a consequence of low maxima in the corresponding C–He potential energy difference curves at short internuclear distances. The collisional profiles are carefully examined and their perturber density dependence allow to understand the various line shapes of the observed carbon spectral lines in helium-rich white dwarf photosphere where the He perturber densities reach several 1021 cm−3.
For many years, the recombination of excited ions of argon, Ar+(P1/22), has been assumed negligible under ambient conditions as compared to the recombination of ground-state ions, Ar+(P3/22). This opinion was confronted with detailed experimental results that seem to clearly support it. Here, we propose a new interpretation in light of our recent calculations, which shows that the recombination efficiency is comparable for both fine-structure states. Noteworthily, in our model leading to a picture consistent with the experiment, residual dimer ions emerge from Ar+(P1/22) due to non-adiabatic dynamics effects and interplay in measured data.
A general scheme for calculating ternary recombination rate constants of atomic species based on a hybrid quantum–classical nonadiabatic dynamics approach is presented and applied to the specific case of the ternary recombination of atomic ions of argon in cold argon plasmas. Rate constants are reported for both fine-structure states of the ion, and , T = 300 K, and for selected values of the reduced electric field. A thorough comparison with the literature data available for T = 300 K and a couple of close temperatures is performed with a favorable agreement achieved. It is shown that the excited ions may contribute to the formation of dimer ions, , as efficiently as the ground-state ions, , due to fast internal conversion of the electronic energy, which takes place in ternary collision complexes, .
Formation, distribution and behaviour of Complex Organic Molecules (COM's) in space is an important subject of research to the better understanding of the initial condition for the appearance of life on Earth. Furthermore, the study of high energy chemical processes in the interstellar medium (cosmic radiation's effect) and in solar system (solar wind's effect), is been of high interest. The aim of this work is to study astrophysical molecules trapped in interstellar ice systems under the effect of high energy radiation. These ices are characterised by being large systems, with large number of atoms. QM/MM hybrid method has become a very popular tool for molecular systems' simulations with a large number of atoms, appearing as a good compromise between accuracy and computational costs. We report the implementation of QM/MM hybrid method in the deMonNano software, using the Density Functional based Tight Binding (DFTB), an approximated DFT scheme, combined with Molecular Mechanic (MM) approach, namely Force Fields (FF) of class 1, such as OPLS-AA and AMBER-families of FFs. A complete implementation was performed using the QM/MM additive coupling scheme. In addition, the investigation of high energy chemical processes requires the explicit simulation of the electronic dynamics beyond the Born Oppenheimer approximation. As first step towards such dynamics, we will report the implementation of Real Time TD-DFTB in deMonNano, consisting in solving the Time-Dependent Schrödinger equation within the DFTB, where the electronic density matrix is propagated along time. We report a detailed introduction to new DFTB/MM and RT-TD-DFTB implementations as well as the complete study on glycine prebiotic molecule trapped in an interstellar ice. PAH interstellar systems will be also a matter of study.
Sujets
Polycyclic aromatic hydrocarbon PAH
Density Functional Theory
White dwarfs
Abundances -ISM
Nanoparticles
Cryogenic ion trap
Dftb
Atomic scattering from surfaces
Molecular clusters
Methods laboratory molecular
BOMD
QSAR
1
Charge transfer state
Corannulene
Charged system and open shell
HAP
Infrared spectra
Probability flows
Molecular processes
Atomic data
Anharmonic Infrared Spectroscopy
Biodegradation
Density functional based tight binding DFTB
Molecular data
Catalyse
Catalysis
Configuration interaction
PAH
Argile
SCC-DFTB
Car-Parrinello molecular dynamics
Collision Induced Dissociation
Threshold algorithm
CAH
Modélisation
Benzene
Disconnectivity tree
Agrégats protonés
Polycyclic Aromatic Hydrocarbons
Au147
Agrégats aqueux d'ammonium/ammoniac
Dissipation
ISM molecules
Agrégats
Carbon clusters
Agrégats aqueux
Atrazine
Ammonium/ammonia water clusters
Astrochimie
Charge resonance
Benzene dimers
CONSTANTS
Photon-dominated region PDR
DFT
Clustering
Dissociation
Dynamique moléculaire
Optical spectra
Auxiliary density functional theory
DUST
Disconnectivity Tree
Chemical shift
Agrégats d'eau
22 pole cryogenic ion trap
Brown dwarfs
Modelling
Carbon cluster
Argon
Water clusters
Density functional theory
Astrochemistry
Database
Agrégats protonés uracile-eau
Dusty plasma
Infrared spectroscopy
CID
2
Amorphous
Chimie quantique
ADFT
Approche mixte quantique/classique
Barium
Quantum chemistry
Molecular dynamics
DFTB-CI
Density functional tight binding
Alanine dipeptide
Clay mineral
DFTB
Dynamique électronique
Infrared ISM
Carbonaceous grains
Clusters
Champ de forces
Excited states
Line profiles
CONFIGURATION-INTERACTION
Agrégats moléculaires