648 research outputs found
Stereodynamics in the Collisional Autoionization of Water, Ammonia, and Hydrogen Sulfide with Metastable Rare Gas Atoms: Competition Between Intermolecular Halogen and Hydrogen Bonds
No full textRecent experiments on the title subject, performed with a high-resolution crossed-beam apparatus, have provided the total ionization crosssections as a function of the collision energy between noble gas atoms, electronically excited in their metastable states (Ng*), and H2O,
H2S, and NH3 reagents, as well as the emitted electron energy spectra. This paper presents a rationalization of all the experimental findings in a unifying picture to cast light on the basic chemical properties of Ng* under conditions of great relevance both from a fundamental and from an applied point of view. The importance of this investigation is that it isolates the selective role of the intermolecular halogen and hydrogen bonds, to assess their anisotropic effects on the stereodynamics of the promoted ionization reactions, and to model energy transfer and reactivity in systems of applied interest, such as planetary atmospheres, plasmas, lasers, and flames
Intermolecular potential energy surfaces for the interaction between H2X (X = O, S) and metastable Ne*(3P2,0) atom
No full textPotential energy surfaces for the interaction of a Ne*(3P2,0) atom with H2O and H2S molecules are obtained on the basis of a semi empirical method that has been previously used for some specific orientations in Ne*(3P2,0)–H2O system. The method is now suitable for all orientations and also for Ne*(3P2,0)–H2S system. Interesting features emerge by comparing the two systems and appear related to different characteristics of the two molecular partners. The potential energy surface for Ne*(3P2,0)–H2S has been also successfully tested for reproducing recent experimental Penning ionization electron spectroscopy data, sensible to some specific orientations of the two colliding partners
How the reactivity depends on the angular approach between reagents: stereo-dynamics of Penning ionization involving hydrogenated molecules
No full textGas phase chemiionization processes of water, hydrogen sulfide, and ammonia molecules, induced by excited metastable noble gas atoms (Ng*), known as Penning ionizations, play an important role in several phenomena occurring in low energy ionized plasmas, electric discharges, planetary atmospheres, and interstellar environments [1,2]. In the present contribution we report on ammonia molecules ionized by collisions with neon and helium metastable atoms. The investigation has been carried out by analyzing the total ionization cross section as a function of the collision energy for different approaching angles between Ng* and NH3 reagents, as well as the energy of emitted electron spectra. For such advanced analysis we have exploited a semiclassical treatment of the collision dynamics together with potential energy surfaces whose formulation, given in terms of fundamental physical properties of the involved partners, is provided in an analytical form, useful to represent the system in the whole space of configurations. Therefore, such a potential formulation appears suitable for quantitative molecular dynamics calculations that allow to control the angle of approach between the reagent particles, and therefore to perform a detailed stereo-dynamical study of Penning ionization reactions. The final results obtained from this investigation show the evidence that ionization process is controlled by the competition between the formation of a hydrogen bond like complex, when the rare gas excited atom approaches the molecules towards the hydrogen atom side, and the formation of a
halogen bond like complex, when the approach occurs towards the lone pair side. In the latter configuration the ionization is stimulated by a pronounced electron exchange probability between a filled orbital of the molecule and the inner shell hole of the ionic core of Ng* atom
The selective role of halogen and hydrogen bond interactions in ionization processes occurring in planetary atmospheres and induced by excited species
No full textGas phase chemiionization processes of water, hydrogen sulfide, and ammonia molecules, induced by excited metastable noble gas atoms, known as Penning ionizations, play an important role in several phenomena occurring in low energy ionized plasmas, electric discharges, planetary atmospheres, and interstellar environments. These reactions, in particular the ionization of H2O, H2S and NH3 molecules by collision with metastable neon and helium atoms, have been studied in crossed beam experiments by mass spectrometry and by energy analysis of the electrons emitted during the ionization processes. The experimental data have been analyzed by exploiting a formulation of the potential energy surface for atom-molecule interactions, proper for the investigation of the reaction dynamics by semi-classical methods. The combined analysis of the experimental data has indicated that a strong steric effect is present in microscopic mechanism of these reactions. This effect arises from the competition of several interaction components. Specifically, the floppy nature of the excited more external electron of the metastable rare gas atom and its ionic core play a crucial role. When such atom is approaching the molecule along the lone pair
direction, the floppy excited orbital is repelled backward establishing a rather strong attraction between the permanent dipole of the molecule and the ionic core of the excited atom (halogen bond like interaction). On the other side, when the excited atom is approaching the molecule along the direction of one of the bonds with one of the hydrogen atoms a weaker interaction is established (hydrogen bond like interaction). The competition between the various interaction components, together with the charge distributed on the molecules, that vary differently with the orientation, determines a strong anisotropic behavior of the reactivity
The Pottesman Collection in the British Museum. Early Dynastic and Sargonic administrative texts. With an Appendix on a Palmyrene Inscription
No full textEdizione, trascrizione, traduzione e commento di un frammento di iscrizione palmirena inedita presente nella collezione Pottesman del British Museum (Appendice Agostini).The British Museum houses a small collection of six cuneiform tablets and a Palmyrene dedicatory inscription purchased in 1987 from the private collection of Solomon Pottesman. The aim of the present contribution is to provide a catalog of this lot and an edition of the so far unpublished cuneiform texts. In the appendix, Alessio Agostini added the edition of the Palmyrene inscription, which would have otherwise gone beyond the capabilities of the present author
Complex: Molecular Beam Scattering Experiments and Ab-Inito Calculations
No full textNew molecular beam scattering experiments are reported for the H2S−H2 system recording, under high angular and velocity resolution conditions, the “glory” quantum interference in the velocity dependence of the total cross section. The analysis of the experimental data permits the determination, for the first time,
of a spherically averaged intermolecular potential for this system. An evaluation of significant cuts of the potential energy surface, obtained by accurate ab initio CCSD(T) calculations using large basis sets, combined with the analysis of the electronic charge displacement accompanying the formation of H2S−H2, has been also performed in order to rationalize the experimental findings. A direct comparison with the analogous water−hydrogen complex (Belpassi, L. et al. J. Am. Chem. Soc. 2010, 132, 13046), investigated with the same experimental conditions and theoretical methodology, brings to light detailed differences in the intermolecular interaction affecting the observables. In particular, it shows the important fact that the charge transfer (CT) component of the interaction plays a minor role in H2S−H2, whereas it was found to be a crucial stabilization component of the interaction in water−H2, determining the potential energy surface anisotropy and the precise location of the energy minima
Recensione di Cecilia Falchini (2023). Ruperto di deutz - Un’intima familiarità. Antologia, Edizioni Qiqajon (Comunità di Bose), Magnano (Bi), 281 pp.
No full textReview of Cecilia Falchini (2023). Ruperto di deutz - Un’intima familiarità. Antologia, Edizioni Qiqajon (Comunità di Bose), Magnano (Bi), 281 pp.
Author: Alessio MagogaRecensione di Cecilia Falchini (2023). Ruperto di deutz - Un’intima familiarità. Antologia, Edizioni Qiqajon (Comunità di Bose), Magnano (Bi), 281 pp.
Autor: Alessio Magog
Handheld-Impedance-Measurement System with seven-decade capability and potentiostatic function
No full textThis paper describes design and test of a new impedance-measurement system for nonlinear devices that exhibits a seven-decade range and works down to a frequency of 0.01 Hz. The system is specifically designed for electrochemical measurements, but the proposed architecture can be employed in many other fields where flexible signal generation and analysis are required. The system employs an unconventional signal generator based on two pulsewidth modulation (PWM) oscillators and an autocalibration system that allows uncertainties of less than 3% to be obtained over a range of 1 kΩ to 100 GΩ. A synchronous demodulation processing allows the noise superimposed to the low-amplitude input signals to be made negligibl
An experimental and kinetic modeling study of glycerol pyrolysis
No full textPyrolysis of glycerol, a by-product of the biodiesel industry, is an important potential source of hydrogen. The obtained high calorific value gas can be used either as a fuel for combined heat and power (CHP) generation or as a transportation fuel (for example hydrogen to be used in fuel cells). Optimal process conditions can improve glycerol pyrolysis by increasing gas yield and hydrogen concentration. A detailed kinetic mechanism of glycerol pyrolysis, which involves 137 species and more than 4500 reactions, was drastically simplified and reduced to a new skeletal kinetic scheme of 44 species, involved in 452 reactions. An experimental campaign with a batch pyrolysis reactor was properly designed to further validate the original and the skeletal mechanisms. The comparisons between model predictions and experimental data strongly suggest the presence of a catalytic process promoting steam reforming of methane. High pyrolysis temperatures (750–800 °C) improve process performances and non-condensable gas yields of 70%w can be achieved. Hydrogen mole fraction in pyrolysis gas is about 44–48%v. The skeletal mechanism developed can be easily used in Computational Fluid Dynamic software, reducing the simulation time
Shielding coating based on graphene-loaded nanomaterials
No full textIn this paper a novel Radar Absorbing Material (RAM) structure with enhanced reflecting and absorbing properties in the 2-18 GHz band is presented. Shielding properties are improved with nano-graphene particles deposited on the surface of composite materials. The nanomaterial allows an ad hoc optimization of the electrical properties of the bulk material in order to obtain a substantial improvement of its shielding performances. Moreover, nano-graphene-based materials can be exploited for improving performances in various applications such as antennas, lenses, and metamaterial-based radomes
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