1,721,007 research outputs found
Fuel production from waste CO2 using renewable energies
No full textAn experimental study aiming at reusing CO2 and implementing a validated laboratory technology based on a prototype methanation reactor (ProGeo) producing carbon neutral methane through the chemical conversion of CO2 waste flue gases using renewable energy in a circular economy scheme, is presented. ProGeo is able to produce a CH4 flux of 1 Nm3/h, using the Sabatier reaction at high pressure (1.5–3bar) and temperature (200–400°C) with a solid phase catalyst. Furthermore, the investigation of a new methanation pathway by exploring mechanisms involving a plasma generation by electrical discharges on CO2+H2 gas mixtures has been undertaken. Obtained results indicate the formation of hydrocarbons as methane, formic acid and/or dimethyl ether as well as small amounts of HCO+,H 2CO+,H 3CO+, HCO2+ ions. These ionic species together with CO+ and O+ ions, having a very high kinetic energy content, should increase the chemical reactivity of generated plasmas playing a pivotal role in the plasma-assisted CO2 conversion on CH4 fuel. Further experimental work is in progress to optimize the experimental conditions of the CO2 methanation process via alternative microscopic mechanisms, using plasma assisted catalyzed reactions that are of great importance in new emerging catalysts development in chemical engineering
Production and Characterization of Molecular Dications: Experimental and Theoretical Efforts
No full textMolecular dications are doubly charged cations of importance in flames, plasma chemistry and physics and in the chemistry of the upper atmosphere of Planets. Furthermore, they are exotic species able to store a considerable amount of energy at a molecular level. This high energy content of several eV can be easily released as translational energy of the two fragment monocations generated by their Coulomb explosion. For such a reason, they were proposed as a new kind of alternative propellant. The present topic review paper reports on an overview of the main contributions made by the authors’ research groups in the generation and characterization of simple molecular dications during the last 40 years of coupling experimental and theoretical efforts
Coulomb explosion of simple molecules by ionizing radiations in space
No full textAn experimental investigation on the fragmentation dynamics following the double photoionization of simple molecules of astrochemical interest, as carbon dioxide, propylene oxide and N-methylformamide, induced by VUV photons has been reported. Experiments used linearly polarized light in the 18-37 eV (propylene oxide), 26-45 eV (N-methylformamide) and 34-50 eV (carbon dioxide) photon energy range at the Elettra Synchrotron Facility of Trieste (Italy) [1-3]. Ion imaging and photoelectron-photoion-photoion (PEPIPICO) coincidence techniques are used with time-of-flight mass spectrometry (see Fig. 1) [4,5]. In the case of propylene oxide, six different two-body fragmentation processes has been recorded with the formation of CH2+/C2H4O+, CH3+/C2H3O+, O+/C3H6+, OH+/C3H5+, C2H3+/CH3O+, C2H4+/CH2O+ ion pairs. The double photoionization of N-methylformamide occurs producing two main fragmentation reactions, forming CH3++CH2NO+ and H++C2H4NO+, while carbon dioxide dissociates by Coulomb explosion of the intermediate (CO2)2+ dication into CO++O+ final ions. The relative cross sections and the threshold’s energy for all fragmentation channels are recorded as a function of the photon energy. In the case of the double photoionization of propylene oxide, the measure of the kinetic energy released distribution for the CH3+/C2H3O+ final ions with the their angular distributions allowed the identification of a bimodal behavior indicating the possible formation of two different stable isomers of C2H3O+: acetyl and oxiranyl cations. In the case of CO2, the production of CO+ and O+ fragments with a high kinetic energy content (2.0 and 3.8 eV, respectively) can explain the lack in the O+ expected concentration of the Mars atmosphere as measured by Viking 1 lander and Mariner 6 spacecraft [4]. This energy is large enough in the case of Mars and Titan to allow these fragments to reach sufficient velocity to escape into space. Therefore this process can in principle contribute to the continuous erosion of these planetary atmospheres
Autoionization Processes Involving Molecules of Atmospheric Interest: A Computational Test for Ne*-N2 System
No full textThis paper provides basic aspects of the stereodynamics of autoionization reactions, triggered by collisions of N2 molecules with metastable neon atoms, Ne*(3P2,0), that are of great relevance for the balance of phenomena occurring in atmospheric environments under various conditions. A computational analysis based on the long-range intermolecular forces involved, some of chemical and other of physical origin, allows a first attempt in order to reproduce experimental data from our and other laboratories. This is a good test of the reliability of our recently proposed semiclassical model for atom-atom self-ionization processes and here extended to a simple atom-molecule system
Molecular beam scattering experiments probing the interaction of Cl2 with simple molecules (D2, O2, D2O, ND3)
No full textMolecular beam experiments for the scattering of D2, O2, D2O, and ND3 by Cl2 have been carried out to probe the involved intermolecular interaction and the quantum “glory” interference effect has been observed for all the systems. Simple and reliable interaction potentials, defined as a combination of an anisotropic van der Waals, polar flattening, charge transfer and electrostatic terms have been obtained
Editorial: Reaction Dynamics Involving Ions, Radicals, Neutral and Excited Species
No full textThe aim of this Research Topic is to provide relevant contributions relating to the study of the reactivity of ionic and excited species with atoms, molecules, and radicals of interest in atomic and molecular physics as well as in chemical reaction dynamics
Stereo-Dynamics of Autoionization Reactions Induced by Ne*(3P0,2) Metastable Atoms with HCl and HBr Molecules: Experimental and Theoretical Study of the Reactivity Through Selective Collisional Angular Cones
No full textIn this paper are presented mass spectrometric determinations as a function of the collision energy in the 0.03–0.50 eV range as recorded in a crossed molecular beam experiments involving autoionization reactions between Ne*(3P2,0) metastable atoms and HCl and HBr molecules. The total and partial ionization cross sections for both investigated systems are presented and discussed in a comparative way. The comparison of the recorded data allows to point out similarities and differences on the collisional stereodynamics of Ne*(3P0,2)-HCl and Ne*(3P0,2)-HBr systems. In particular, an accurate characterization of the interaction potentials, which is mandatory for a comprehensive description of Ne*-HX (X = Cl and Br) reactive collisions, has been outlined. Such a theoretical analysis suggests that the formation of the proton transfer, NeH+, ions as well as of other possible product ions (i.e. HX+ and NeHX+, parent and associate ions, respectively) comes from reactivity that is selectively open along angular cones showing different orientation and acceptance. In particular, the performed analysis highlights that the proton transfer rearrangement reaction, which is open in both Ne*-HX autoionizing collision, is much more efficient for Ne*+HCl respect to Ne*+HBr autoionization. The present investigation points out that such an efficiency variation is related to the following crucial points: (i) the different charge distribution on HX+ ionic products, (ii) the balance between two distinct microscopic mechanisms that are operative in such processes (a pure physical-photoionization-indirect mechanism and a chemical-oxidation-direct mechanism), which are reactions of interest in combustion chemistry, plasma physics and chemistry, as well as in astrochemistry and for the chemistry of planetary ionospheres
Pseudomonas aeruginosa nitrite reductase (or cytochrome oxidase): an overview.
No full textThe biochemistry and molecular biology of nitrite reductase, a key enzyme in the dissimilatory denitrification pathway of Ps aeruginosa which reduces nitrite to NO, is reviewed in this paper. The enzyme is a non-covalent homodimer, each subunit containing one heme c and one heme d(1). The reaction mechanisms of nitrite and oxygen reduction are discussed in detail, as well as the interaction of the enzyme with its macromolecular substrates, azurin and cytochrome c(551). Special attention is paid to new structural information, such as the chemistry of the d(1) prosthetic group and the primary sequence of the gene and the protein. Finally, results on the expression both in Ps aeruginosa and in heterologous systems are presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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