A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk.

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.

UV photoreaction pathways of acetylacetaldehyde trapped in cryogenic matrices.

The broadband UV photochemistry kinetics of acetylacetaldehyde, the hybrid form between malonaldehyde and acetylacetone (the two other most simple molecules exhibiting an intramolecular proton transfer), trapped in four cryogenic matrices, neon, nitrogen, argon, and xenon, has been followed by FTIR and UV spectroscopy. After deposition, only the two chelated forms are observed while they isomerize upon UV irradiation toward nonchelated species. From previous UV irradiation effects, we have already identified several nonchelated isomers, capable, in turn, of isomerizing and fragmenting; even fragmentation seems to be most unlikely due to cryogenic cages confinement.

Insights into the Photodecomposition of Azidomethyl Methyl Sulfide: A S/S Conical Intersection on Nitrene Potential Energy Surfaces Leading to the Formation of -Methyl--sulfenylmethanimine.

UV photodecomposition of azidomethyl methyl sulfide (AMMS) yields a transient -methylthiaziridine which rapidly evolves to -methyl--sulfenylmethanimine at 10 K. This species was detected by infrared matrix isolation spectroscopy. The mechanism of the photoreaction of AMMS has been investigated by a combined approach, using low-temperature matrix isolation FTIR spectroscopy in conjunction with two theoretical methods, namely, complete active space self-consistent field and multiconfigurational second-order perturbation.

Theoretical determination of adsorption and ionisation energies of polycyclic aromatic hydrocarbons on water ice.

In dense interstellar environments, Polycyclic Aromatic Hydrocarbons (PAHs) are likely to condense onto or integrate into water ice mantles covering dust grains. Understanding the role of ice in the photo-induced processes involving adsorbed PAHs is therefore a key issue in astrochemistry. This requires (i) the knowledge of PAH-ice interactions, i.

Correction: Adsorption of PAHs on interstellar ice viewed by classical molecular dynamics.

Correction for 'Adsorption of PAHs on interstellar ice viewed by classical molecular dynamics' by Eric Michoulier et al., Phys. Chem.

Adsorption of PAHs on interstellar ice viewed by classical molecular dynamics.

Polycyclic Aromatic Hydrocarbons (PAHs) are a family of molecules which represent the best candidates to explain the observation of one set of features in the Interstellar Medium (ISM): the Aromatic Interstellar Bands (AIBs). They could also contribute to the Diffuse Interstellar Bands (DIBs). In dense molecular clouds, PAHs may condense onto interstellar grains, contributing to the complex chemistry occurring in their icy mantles, composed essentially of water.

Photochemistry of Fe:HO Adducts in Argon Matrixes: A Combined Experimental and Theoretical Study in the Mid-IR and UV-Visible Regions.

The photochemistry of Fe:HO adducts is of interest in fields as diverse as catalysis and astrochemistry. Industrially, iron can be used as a catalyst to convert HO to H, whereas in the interstellar medium it may be an important component of dust grains, influencing the chemistry on their icy surfaces. This study consisted of the deposition and spectral characterization of binary systems of atomic iron with HO in cryogenic argon matrixes.

Electronic Spectroscopy of Protonated 1-Aminopyrene in a Cold Ion Trap.

In aromatic systems that contain an amino group, there is competition between protonation on a carbon atom of the skeleton and protonation on the amino group. Herein, we studied the photofragmentation of protonated 1-aminopyrene in a cold ion trap and mainly observed the protonated amino tautomer, which led to fragmentation pathways through the loss of H or NH groups. Several excited states were assigned, among which the fourth excited state showed broadened bands, thus indicating a fast decay that was attributed to the presence of a πσ* charge-transfer state by comparison of the experimental results with ab initio calculations.

Formation of coronene:water complexes: FTIR study in argon matrices and theoretical characterisation.

In this paper, we report a combined theoretical and experimental study of coronene:water interactions in low temperature argon matrices. The theoretical calculations were performed using the mixed density functional-based tight binding/force field approach. The results are discussed in the light of experimental matrix isolation FTIR spectroscopic data.

Water clusters in an argon matrix: infrared spectra from molecular dynamics simulations with a self-consistent charge density functional-based tight binding/force-field potential.

The present theoretical study aims at investigating the effects of an argon matrix on the structures, energetics, dynamics, and infrared (IR) spectra of small water clusters (H2O)n (n = 1-6). The potential energy surface is obtained from a hybrid self-consistent charge density functional-based tight binding/force-field approach (SCC-DFTB/FF) in which the water clusters are treated at the SCC-DFTB level and the matrix is modeled at the FF level by a cluster consisting of ∼340 Ar atoms with a face centered cubic (fcc) structure, namely (H2O)n/Ar. With respect to a pure FF scheme, this allows a quantum description of the molecular system embedded in the matrix, along with all-atom geometry optimization and molecular dynamics (MD) simulations of the (H2O)n/Ar system.

On the chemical reactions of carbon dioxide isoelectronic molecules CS2 and OCS with 1-butyl-3-methylimidazolium acetate.

Raman and NMR spectroscopies show that CS2 and OCS react spontaneously with 1-butyl-3-methylimidazolium acetate [C4mim] [Ac] in the liquid phase. The formation of [C4mim] CO2, [C4mim] COS, CH3COS(-) and gaseous CO2 and OCS in both systems demonstrates that the anion plays an unexpected role not observed in the CO2-[C4mim] [Ac] reaction.

CO2 in 1-butyl-3-methylimidazolium acetate. 2. NMR investigation of chemical reactions.

The solvation of CO(2) in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been investigated by (1)H, (13)C, and (15)N NMR spectroscopy at low CO(2) molar fraction (mf) (x(CO(2)) ca. 0.27) corresponding to the reactive regime described in part 1 of this study.

Vibrational spectroscopy and molecular dynamics of water monomers and dimers adsorbed on polycyclic aromatic hydrocarbons.

This paper reports structures, energetics, dynamics and spectroscopy of H2O and (H2O)2 systems adsorbed on coronene (C24H12), a compact polycyclic aromatic hydrocarbon (PAH). On-the-fly Born-Oppenheimer molecular dynamics simulations are performed for temperatures T varying from 10 to 300 K, on a potential energy surface obtained within the self-consistent-charge density-functional based tight-binding (SCC-DFTB) approach. Anharmonic infrared (IR) spectra are extracted from these simulations.

Photochemistry of coronene with water at 10 K: first tentative identification by infrared spectroscopy of oxygen containing coronene products.

UV photochemistry of a polycyclic aromatic hydrocarbon model, coronene (C(24)H(12)), has been investigated when it is in interaction with water in argon cryogenic matrices, adsorbed on amorphous water ice films, and embedded in solid water. Photoprocessing, carried out at 10 K and λ > 235 nm by means of a high-pressure Hg arc lamp, results in the oxidation and reduction of coronene. These species have been tentatively identified as being the 1,10-dihydroxycoronene and the 1,10-coroquinone by FTIR spectroscopy with the support of isotopic experiments and DFT calculations.

Photochemistry of pyrene with water at low temperature: study of atmospherical and astrochemical interest.

Photochemistry of a polyaromatic hydrocarbon, pyrene C(16)H(10), with water has been investigated at cryogenic temperatures. Photoprocessing of this species, performed at λ > 235 nm, in argon matrices, adsorbed onto amorphous water surfaces, and trapped in solid water, led to the formation of ketonic isomers, C(16)H(10)O, and possibly quinones. These species have been identified for the first time by infrared spectroscopy with the support of isotopic substitution experiments and DFT calculations.

Organization of beta-cyclodextrin under pure cholesterol, DMPC, or DMPG and mixed cholesterol/phospholipid monolayers.

The complexation of beta-cyclodextrin with monolayers of cholesterol, DMPC, DMPG, and mixtures of those lipids has been studied using Brewster microscopy, PMIRRAS, and ab initio calculations. An oriented channel-like structure of beta-cyclodextrin, perpendicular to the air/water interface, was observed when some cholesterol molecules were present at the interface. This channel structure formation is the first step in the cholesterol dissolution in the subphase.

Theoretical investigation of the reactivity of copper atoms with OCS: comparison with CS2 and CO2.

The reaction mechanism of the Cu atom with OCS and CO2 has been studied by means of density functional method (B3LYP). The overall energetics has been refined at the CCSD(T) level. In the case of the Cu + OCS reaction, the CS insertion route is found much more favorable than the CO insertion one.

The photodimerisation of trans-cinnamic acid and its derivatives: a study by vibrational microspectroscopy.

Infrared and Raman spectroscopies have been used to monitor the [2 + 2] photodimerisation reactions of alpha-trans-cinnamic acid and of a number of its derivatives. The principal changes observed in the spectra upon dimerisation are decay of a band around 1637 cm(-1), which is assigned to v(C=C) of the ethene bond of the monomer, and growth of bands just above 3000 cm(-1), which result from v(C-H) of saturated carbon atoms of the dimer. The use of microscope attachments has allowed us to follow the reactions of single crystals and we conclude that the reactions are topotactic in nature.

Mechanism of Formation of Peroxocarbonates RhOOC(O)O(Cl)(P)(3) and Their Reactivity as Oxygen Transfer Agents Mimicking Monooxygenases. The First Evidence of CO(2) Insertion into the O-O Bond of Rh(eta(2)-O(2)) Complexes.

Extended labeling experiments have shown that formation of rhodium peroxocarbonate from CO(2) and [RhCl(eta(2)-O(2))(P)(3)] (P is PEt(2)Ph or PEtPh(2)) proceeds through O-O bond cleavage and CO(2) insertion. O-transfer to ancillary phosphine ligand to give R(3)P=O selectively (>85%) involves the Rh-linked O atom of the peroxo group of RhCl(CO(4))(P)(3).