1,720,981 research outputs found
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
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
Theoretical and Computational Analysis at a Quantum State Level of Autoionization Processes in Astrochemistry
No full textChanges in atomic-molecular alignment and/or in molecular orientation, can affect strongly the fate of basic collision events. However, a deep knowledge of these phenomena is still today not fully understood, although it is of general relevance for the control of the stereo-dynamics of elementary chemical-physical processes, occurring under a variety of conditions, both in gas phase and at surface. In particular, understanding the mode-specificity in reaction dynamics of open-shell atoms, free radicals, molecules, atomic and molecular ions, under hyper-thermal, thermal and sub-thermal conditions is of fundamental importance for catalysis, plasmas, photo-dynamics as well as interstellar and low-temperature chemistry. In this paper recent results on the role of atomic alignment effects on the stereo-dynamics of autoionization reactions are presented and discussed
New insights on the stereodynamics of ethylene adsorption on an oxygen precovered silver surface
No full textThe control of spatial orientation of molecules has a great influence on the stereodynamics of elementary processes occurring both in homogeneous and heterogeneous phases. Nonpolar molecules have so far escaped direct experimental investigations because of their poor sensitivity to several external constraints. Recently, it has been shown that the collisional alignment produced in supersonic expansions coupled with molecular-beam velocity selection can help solve such problems. Here we show that the sticking probability of ethylene, a nonpolar molecule prototypical of unsaturated hydrocarbons, on an O-2-precovered Ag(001) surface is larger for molecules approaching in a helicopterlike motion than for those cartwheeling. A mechanism involving a weakly bound precursor state is suggested, with helicopter molecules having a lower chance of being scattered back into the gas phase than cartwheels when colliding with preadsorbed ethylene
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
A simple and compact mechanical velocity selector of use to analyze/select molecular alignment in supersonic seeded beams
No full textA light and compact mechanical velocity selector, of novel design, for applications in supersonic molecular-beam studies has been developed. It represents a simplified version of the traditional, 50 year old, slotted disks velocity selector. Taking advantage of new materials and improved machining techniques, the new version has been realized with only two rotating slotted disks, driven by an electrical motor with adjustable frequency of rotation, and thus has a much smaller weight and size with respect to the original design, which may allow easier implementation in most of the available molecular-beam apparatuses. This new type of selector, which maintains a sufficiently high velocity resolution, has been developed for sampling molecules with different degrees of rotational alignment, like those emerging from a seeded supersonic expansion. This sampling is the crucial step to realize new molecular-beam experiments to study the effect of molecular alignment in collisional processes
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Heterolitic photolysis of O2 on Ag(001)
No full textIt is shown that at high O-2(-) coverage on Ag(100) photo dissociation by soft X-rays generates oxygen atoms of covalent and of oxidic nature. The former species is obtained also by thermal dissociation and is the only observed product when irradiating at low O-2(-) coverage. The latter one is produced only photochemically and assigned to an Ag oxide. Them fragments produced in the photochemical process end up eventually in identical or in different sites, depending on the presence of other O-2(-) molecules in the immediate neighbourhood
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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