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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.
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.
Mid-infrared emission features probe the properties of ionized gas, and hot or warm molecular gas. The Orion Bar is a frequently studied photodissociation region (PDR) containing large amounts of gas under these conditions, and was observed with the MIRI IFU aboard JWST as part of the "PDRs4All" program. The resulting IR spectroscopic images of high angular resolution (0.2") reveal a rich observational inventory of mid-IR emission lines, and spatially resolve the substructure of the PDR, with a mosaic cutting perpendicularly across the ionization front and three dissociation fronts. We extracted five spectra that represent the ionized, atomic, and molecular gas layers, and measured the most prominent gas emission lines. An initial analysis summarizes the physical conditions of the gas and the potential of these data. We identified around 100 lines, report an additional 18 lines that remain unidentified, and measured the line intensities and central wavelengths. The H I recombination lines originating from the ionized gas layer bordering the PDR, have intensity ratios that are well matched by emissivity coefficients from H recombination theory, but deviate up to 10% due contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni, and show how certain line ratios vary between the five regions. We observe the pure-rotational H$_2$ lines in the vibrational ground state from 0-0 S(1) to 0-0 S(8), and in the first vibrationally excited state from 1-1 S(5) to 1-1 S(9). We derive H$_2$ excitation diagrams, and approximate the excitation with one thermal (~700 K) component representative of an average gas temperature, and one non-thermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model for the Orion Bar PDR and highlight the differences with the observations.
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.
Sujets
Alanine dipeptide
QSAR
Clustering
Agrégats protonés uracile-eau
Abundances -ISM
Charge resonance
Astrochimie
Database
1
Modélisation
DFTB
Dynamique moléculaire
Excited states
Car-Parrinello molecular dynamics
Molecular dynamics
Infrared spectroscopy
Dynamique électronique
Density functional theory
Configuration interaction
Water clusters
Density functional based tight binding DFTB
Dftb
Carbon clusters
Benzene
Infrared spectra
Approche mixte quantique/classique
Argon
Dusty plasma
Charged system and open shell
Probability flows
Barium
22 pole cryogenic ion trap
Amorphous
ADFT
DFTB-CI
Atrazine
Disconnectivity Tree
Au147
Charge transfer state
Molecular processes
Agrégats
Corannulene
Agrégats aqueux d'ammonium/ammoniac
DFT
Carbon cluster
Anharmonic Infrared Spectroscopy
Clay mineral
PAH
Nanoparticles
White dwarfs
Dissociation
Dynamique Moléculaire Car-Parrinello
Biodegradation
Density Functional Theory
Agrégats protonés
Argile
Astrochemistry
DUST
Molecular data
Collision Induced Dissociation
Agrégats d'eau
Cryogenic ion trap
Catalysis
Atomic data
Polycyclic aromatic hydrocarbon PAH
Chimie quantique
Ammonium/ammonia water clusters
CONFIGURATION-INTERACTION
CAH
Atomic scattering from surfaces
CID
Carbonaceous grains
Disconnectivity tree
Dynamics
Benzene dimers
Quantum chemistry
Dissipation
Optical spectra
Chemical shift
Polycyclic Aromatic Hydrocarbons
HAP
Line profiles
Brown dwarfs
Agrégats moléculaires
Molecular clusters
BOMD
SCC-DFTB
ISM molecules
Auxiliary density functional theory
Modelling
Catalyse
Agrégats aqueux
2
Champ de forces
Methods laboratory molecular
Threshold algorithm
Density functional tight binding
Clusters
CONSTANTS