1,720,968 research outputs found
Matrix isolation and computational studies of the CF2I radical
No full textWe report experimental and computational studies of the spectroscopy and photochemistry of the CF2I radical, which was generated using pulsed discharge or photolytic techniques and trapped in Ar or Ne matrices held at ∼5 K. Ground state calculations were performed using UM062X and UB3LYP density functionals and the UMP2, UCCSD, and CASPT2 ab initio methods, all with high-quality basis sets. The photochemical reaction path from the lowest-lying electronically excited state was mapped using the CASPT2//CASSCF methodology. A conical intersection was found to drive the excited state species to the photoproduct/reactant wells on the ground state potential energy surface. © 2010 Elsevier B.V. All rights reserved
Reactive Pathways In The Chlorobenzene-ammonia Dimer Cation Radical: New Insights From Experiment And Theory
Get PDFPreviously, we have studied non-covalent interactions in mono-halogenated benzene clusters using mass selected resonant 2-photon ionization methods. We have extended our studies by investigating the interaction between these mono-halobenzenes with a prototypical N atom donor (\chem{NH_3}). Thus, we have obtained electronic spectra of PhX(\chem{NH_3})n ( X=F, Cl, Br and n=1,2….) complexes in the region of the PhX monomer \chem{S_0}-\chem{S_1} (*) transition. Here we are mainly focusing on PhCl\chem{NH_3} dimer. We found that upon ionization of the dimer, three reactive pathways of the [PhCl\chem{NH_3}] have been evidenced. The primary pathway is the Cl atom elimination, previously evidenced. The second and third pathways, HCl elimination and H atom elimination are identified for the first time in the R2PI studies of the dimer. Electronic spectra obtained for the three pathways shows that they originate from a common precursor. The reactive pathways in this system were extensively characterized computationally. We used DFT and post-Hartree Fock electronic structure calculations, Frank-Condon analysis to support our experimental findings. The results were consistent with previous direct ab initio molecular dynamics calculations, we found two nearly iso-energetic Wheland intermediates which lie significantly lower in energy than the initially formed dimer cation radical [PhCl\chem{NH_3}].Made available in DSpace on 2014-09-17T16:55:35Z (GMT). No. of bitstreams: 3
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
341.pdf: 18912 bytes, checksum: ead76f6835bfaf235f376b766b4442a4 (MD5)
abstract.txt: 1736 bytes, checksum: 84d65877f49b754a2e93887946130bb3 (MD5)
Previous issue date: 2014-06-19Made available in DSpace on 2015-04-14T18:38:24Z (GMT). No. of bitstreams: 4
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
RB06_Presentation.pptx: 1364666 bytes, checksum: 0c67c2335a1dd35949c37a2cc59c0a98 (MD5)
RB06_Abstract.pdf: 18912 bytes, checksum: ead76f6835bfaf235f376b766b4442a4 (MD5)
RB06_Abstract.txt: 1736 bytes, checksum: 84d65877f49b754a2e93887946130bb3 (MD5)
Previous issue date: 2014-06-1
MATRIX-ISOLATION AND COMPUTATIONAL STUDIES OF TRANSIENT POLYHALOGENATED INTERMEDIATES AND WEAKLY-BOUND COMPLEXES.
Get PDFAs time goes by and new innovations are brought up to improve living conditions, the human impact on the environment becomes more significant. It has been shown that man-made halogenated compounds play a key role in many real-world chemical processes. For example, in combustion, these compounds are used as fire retardant agents, and in atmospheric chemistry, they initiate ozone depletion reactions.
However little is known about the mechanisms governing these processes and many intermediates involved in these processes have been elusive to researchers for diverse reasons such as short lifetime and difficulty in distinguishing products from parents molecules. The studies compiled in this work are focused on exploring the photochemical behavior of various intermediates derived from polyhalogenated compounds. These intermediates are trapped in inert rigid matrix and characterized by using IR, UV/Vis spectroscopy supported by computational methods. The photochemistry is explored using selected wavelength appropriate to each species. In this work, the photolysis products of CF2I2, CF2Br2, CXBr3 (X=H, D, F), C2H4Br2, C2F4Br2 have been generated and trapped in Argon or Neon matrices and most of them were characterized for the first time. We have also studied weakly bound complexes (C2H4***Br2, C2H4***I2), formed in matrix by co-deposition of monomers or by trapping fragments resulting from high voltage discharge (H2CXBr***Br; X=H, Cl, Br). We hope that our results will contribute to better understand the photochemical behavior of polyhalogenated species, and to some extent help to understand mechanism in different phenomena involving these species
SPECTROSCOPY OF AND PHOTOINDUCED ELECTRON TRANSFER IN THE COMPLEXES OF CH WITH I AND I
No full textAuthor Institution: Department of Chemistry, Marquette University, Milwaukee, WI 53233The charge-transfer complex of ethylene and iodine was isolated in a neon matrix and characterized by infrared and electronic spectroscopy, supported by and Density Functional Theory (DFT) calculations which predict the spectra, structure, and binding energy of the complex. The intense charge transfer band of the complex was observed at 247 nm, in good agreement with Time Dependent DFT predictions. Photoinduced electron transfer initiated by laser irradiation at 240 nm gave rise to an intense band at 373 nm which is assigned to bridged ethylene-I atom radical complex. It is postulated that, following excitation of the charge transfer band, rapid back electron transfer leaves the neutral I fragment on an excited repulsive potential surface, which leads to rapid cleavage of the I-I bond. This is consistent with previous gas-phase studies of arene-I complexes. The photolysis of the radical complex, initiated by laser irradiation at 355 nm, led to the reappearance of absorptions due to the ethylene-I complex and the appearance of both the and conformers of the electrophilic addition product, 1,2-diiodoethane, indicating the importance of a radical addition mechanism
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
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
