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Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photodissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, which affects planet formation within the disks. We report James Webb Space Telescope and Atacama Large Millimeter Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modeling their kinematics and excitation allowed us to constrain the physical conditions within the gas. We quantified the mass-loss rate induced by the FUV irradiation and found that it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk.
Atrazine is one of the most widely used herbicide molecules in the triazine family. Despite its interdiction in the European Union in 2004, atrazine and its main degradation products remain among the most frequently found molecules in freshwater reservoirs in many European Union countries. Our study aims in obtaining insight into the desorption process of atrazine from the main soil absorbent material: clay. Constrained Molecular Dynamics simulations within the Density Functional Theory framework allow us to obtain a free energy desorption profile of atrazine from a Ca2+-montmorillonite surface. The results are interpreted in terms of atrazine inclination to the clay surface and moreover, in terms of hydration states of the cations present in the clay interlayer as well as the hydration state of the atrazine. The desorption mechanism is driven by atrazine alkyl groups and their sizes because of dispersion stabilizing effects. The highest barrier corresponds to the loss of the isopropyl interaction with the surface.
Fullerene C 60 is one of the most iconic forms of carbon found in the interstellar medium (ISM). The interstellar chemistry of carbon-rich components, including fullerenes, is driven by a variety of energetic processes including UV and X-ray irradiation, cosmic-ray (CR) bombardment, electron impact, and shock waves. These violent events strongly alter the particle phase and lead to the release of new molecular species in the gas phase. Only a few experimental studies on the shock processing of cosmic analogs have been conducted so far. We explored in the laboratory the destruction of buckminsterfullerene C 60 using a pressure-driven shock tube coupled with optical diagnostics. Our efforts were first devoted to probing in situ the shock-induced processing of C 60 at high temperatures (≤ 4500 K) by optical emission spectroscopy. The analysis of the spectra points to the massive production of C 2 units. A broad underlying continuum was observed as well and was attributed to the collective visible emission of carbon clusters, generated similarly in large amounts. This proposed assignment was performed with the help of calculated emission spectra of various carbon clusters. The competition between dissociation and radiative relaxation, determined by statistical analysis, alludes to a predominance of clusters with less than 40 carbon atoms. Our laboratory experiments, supported by molecular dynamics simulations performed in the canonical ensemble, suggest that C 60 is very stable, and that high-energy input is required to process it under interstellar low-density conditions and to produce C 2 units and an abundance of intermediate-sized carbon clusters. These results provide some insights into the life cycle of carbon in space. Our findings hint that only J-type shocks with velocities above ~100 km s −1 or C-type shocks with velocities above 9 km s −1 can lead to the destruction of fullerenes. Observational tracers of this process remain elusive, however. Our work confirms the potential of shock tubes for laboratory astrophysics.
Possible transformations of canonical neutral glycine in interstellar water clusters and ices.
Sujets
Argile
CONFIGURATION-INTERACTION
Clustering
Argon
Modélisation
Infrared spectroscopy
DFTB
Benzene dimers
Cryogenic ion trap
DFT
White dwarfs
DFTB-CI
Chimie quantique
QSAR
Agrégats aqueux d'ammonium/ammoniac
Catalyse
Methods laboratory molecular
Auxiliary density functional theory
Approche mixte quantique/classique
Au147
Anharmonic Infrared Spectroscopy
Benzene
Carbon clusters
CONSTANTS
Density functional based tight binding DFTB
Agrégats moléculaires
Charged system and open shell
Nanoparticles
Collision Induced Dissociation
ISM molecules
2
Carbonaceous grains
Agrégats d'eau
Polycyclic aromatic hydrocarbon PAH
Atrazine
Dynamique moléculaire
Polycyclic Aromatic Hydrocarbons
PAH
Optical spectra
Agrégats
Atomic scattering from surfaces
Density functional theory
Dftb
CID
Water clusters
Threshold algorithm
Agrégats aqueux
Molecular data
Quantum chemistry
Brown dwarfs
Car-Parrinello molecular dynamics
CAH
Abundances -ISM
Astrochemistry
Amorphous
HAP
Agrégats protonés uracile-eau
Modelling
Clay mineral
Dissipation
Catalysis
Infrared spectra
Disconnectivity tree
Dynamics
Excited states
Molecular clusters
Champ de forces
Disconnectivity Tree
SCC-DFTB
Density Functional Theory
Dusty plasma
Database
1
ADFT
Biodegradation
Astrochimie
Charge transfer state
Probability flows
BOMD
Density functional tight binding
Chemical shift
Atomic data
Molecular processes
Barium
Ammonium/ammonia water clusters
Line profiles
Dynamique Moléculaire Car-Parrinello
Corannulene
Clusters
Alanine dipeptide
Dissociation
Agrégats protonés
22 pole cryogenic ion trap
Configuration interaction
DUST
Charge resonance
Carbon cluster
Dynamique électronique
Molecular dynamics