Hydrogenation of CO on interstellar dust: what is the role of water molecules?

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An FTIR study on the catalytic effect of water molecules on the reaction of CO successive hydrogenation at 3K

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Reactivity Between Non-Energetic Hydroxyl (OH) Radicals and Methane (CH 4 )

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The Evolution of the Surface of the Mineral Schreibersite in Prebiotic Chemistry

We present a study of the reactions of the meteoritic mineral schreibersite (Fe,Ni)3P, focusing primarily on surface chemistry and prebiotic phosphorylation. In this work, a synthetic analogue of the mineral was synthesized by mixing stoichiometric proportions of elemental iron, nickel and phosphorus and heating in a tube furnace at 820 °C for approximately 235 hours under argon or under vacuum, a modification of the method of Skála and Drábek (2002). Once synthesized, the schreibersite was characterized to confirm the identity of the product as well as to elucidate the oxidation processes affecting the surface. In addition to characterization of the solid product, this schreibersite was reacted with water or with organic solutes in a choline chloride–urea deep eutectic mixture, to constrain potential prebiotic products. Major inorganic solutes produced by reaction of water include orthophosphate, phosphite, pyrophosphate and hypophosphate consistent with prior work on Fe3P corrosion. Additionally, schreibersite corrodes in water and dries down to form a deep eutectic solution, generating phosphorylated products, in this case phosphocholine, using this synthesized schreibersite

Radiation Processing of Formamide and Formamide:Water Ices on Silicate Grain Analogue

Lyman-α (121.6 nm) photon and 1 keV electron-beam irradiation of pure HCONH₂ (FA) ice and H₂O:HCONH₂ ice mixtures on high-surface-area SiO₂ nanoparticles have been investigated with FT-IR spectroscopy and temperature programmed desorption (TPD). Lyman-α photolysis of pure amorphous FA ice grown at 70 K and crystalline FA ice produced by annealing to 165 K gives spectral signatures between 2120 and 2195 cm^–1 that we assign primarily to OCN^– and CO. The OCN^– and CO yields are ∼25% less abundant for crystalline FA ice. Photon and electron processing also produces H₂ that is released from the ice between ∼90 and 140 K. A decrease in the H₂ TPD peak is seen for irradiated crystalline HCONH₂ ice. Lyman-α photolysis of H₂O:HCONH₂ mixed ices increases OCN^– and CO production, suggesting a catalytic role of H₂O. Also, for pure FA, 1 keV electron irradiation slightly increases the yield of OCN^–, while CO decarboxylation is selectively prevented. CO is also not produced in H₂O:HCONH₂ ices upon electron irradiation. Dissociative ionization, direct dissociative excitation, and dissociative electron attachment (DEA) channels are accessible in the Lyman-α (121.6 nm) photon and 1 keV electron-beam energy range. DEA energetically favors OCN^– and H^– formation, with the latter leading to H₂ formation. The FA fragment product identities, yields, and branching ratios are considerably different relative to the gas phase and depend upon the radiation type, ice structure, and the presence of SiO₂ nanoparticles. The latter may increase ion–electron recombination and radical recombination rates. The main products observed suggest very different condensed-phase dissociation channels from those reported for gas-phase dissociation. Formation of ions/products from FA is not negligible upon Lyman-α photolysis or electron irradiation, both of which could process ices in interstellar regions as well as in Titan’s atmosphere

Experimental characterization of the chemical composition and structure of molecular soot precursors and soot particles in a laminar diffusion flame by coupling ToF-SIMS and Raman spectroscopy

International audienceThe transformation process in sooting flames leading to the formation of nanoparticles in the condensed phase from molecular precursors in the gas phase (soot nucleation) is not yet fully understood [1]. Information on the physical chemical properties of the nascent particles is difficult to accessexperimentally but also essential for the validation of the hypotheses on soot nucleation currently being examined by the scientific community. In this work, we characterize the molecular precursors and the soot particles formed in a laminar diffusion methane flame by combining several in situ and ex situ diagnostics (fluorescence, incandescence, secondary ion mass spectrometry and Raman spectroscopy) with the goal of inferring the chemical composition and the structure of the nascent particles. The presented work highlights that several of the investigated physical chemical properties suddenly change within a narrow flame region that acquires the character of a discontinuity point correlated to the soot nucleation process. Notably, the obtained data shows evidences of the transition from flat to curved molecular structures, and the progressive apparition of finite size, sandwiched graphene like layers. Furthermore, the fraction of atomic hydrogen features a local maximum immediately upstream the detection of nascent soot particles consistent with the increasing in flame rate of C-C covalent bonds formation postulated by the major hypotheses explaining the nucleation of soot particles.References[1] J.W. Martin, M. Salamanca, M. Kraft, Soot inception: Carbonaceous nanoparticle formation in flames, Progress in Energy and Combustion Science. 88 (2022) 100956.https://doi.org/10.1016/j.pecs.2021.100956

A novel laser-based method to measure the adsorption energy on carbonaceous surfaces

International audienceThe reactivity of carbonaceous surfaces bears a fundamental role in various fields, from atmospheric chemistry and catalysis to graphene and nanoparticles. This reactivity is mainly driven by the surface chemical composition and by the strength of the interaction between the adsorbates and the surface (physi-/chemisorption). While the surface composition of complex natural samples can be well characterized, adsorption energies (ergo, adsorption processes) of the corresponding adsorbate/adsorbent systems are often overlooked. We propose a novel laser-based method for measuring the adsorption energy of chemical species on various carbonaceous surfaces. The proof of concept of this original method has first been demonstrated by deriving adsorption energies of various systems consisting of polycyclic aromatic hydrocarbons and activated carbon. The great potential of this fast, spatially resolved, and surface-sensitive method, which can also act as a defect density probe at the mesoscale, has been further demonstrated through the study of systems of increasing complexity

Ice Nucleation Activities of Carbon-Bearing Materials in Deposition Mode: From Graphite to Airplane Soot Surrogates

International audienceSoot particles emitted by aircraft engines may act as ice nuclei within the atmosphere, subsequently triggering the formation of condensation trails. Such contrails might further evolve as cirrus clouds and thus greatly influence the Earth’s radiative budget and impact the amount of precipitation. In order to monitor in situ deliquescence, efflorescence, and nucleation processes followed by ice growth in the laboratory, we developed the ice and droplet nucleation experimental setup, which combines optical imaging and micro-Raman measurements to follow nucleation events in a pressure-, temperature-, and humidity-controlled optical chamber. We first compare against the literature data and later confirm the deliquescence relative humidities of micrometer-sized sodium chloride salt crystals in the −5 to −35 °C temperature range. Then, we investigate the ice nucleation activity of graphite and aircraft soot analogues, in the −15 to −45 °C temperature range, when exposed to humid nitrogen (N2/H2O gas flow). Soot samples exhibiting various surface chemistries, morphologies, and sizes are thoroughly examined via mass spectrometry and spectroscopic and optical techniques. All carbon-bearing samples are found to be active at nucleating ice at low ice saturation ratios (Sice determined when the first crystal is detected). When normalizing Sice to the total surface area of a sample, one can derive the ice-active surface site density (ns). This parameter provides a means to compare the ice nucleating behavior of various particle types with distinct surface areas. As all samples studied in our work feature large surface areas, we provide ice nucleation data (Sice and ns) for a range of surface areas that remained largely unexplored to date. We find that the interplay between surface composition and morphology (micro, meso, and macro pores, surface roughness) influences the ice onset relative humidity

Evidence on the formation of dimers of polycyclic aromatic hydrocarbons in a laminar diffusion flame

International audienceThe role of polycyclic aromatic hydrocarbons (PAHs) in the formation of nascent soot particles in flames is well established and yet the detailed mechanisms are still not fully understood. Here we provide experimental evidence of the occurrence of dimerization of PAHs in the gas phase before soot formation in a laminar diffusion methane flame, supporting the hypothesis of stabilization of dimers through the formation of covalent bonds. The main findings of this work derive from the comparative chemical analysis of samples extracted from the gas to soot transition region of a laminar diffusion methane flame, and highlight two different groups of hydrocarbons that coexist in the same mass range, but show distinctly different behavior when processed with statistical analysis. In particular, the identified hydrocarbons are small-to-moderate size PAHs (first group) and their homo-and heterodimers stabilized by the formation of covalent bonds (second group)

Chemical differentiation of the solid and gas-phase fractions in combustion exhausts using a two-filter collection system and mass spectrometry techniques

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