1,720,962 research outputs found
Isomerization around C-C and C-O bonds in 1-propanol: Collisional relaxation in supersonic jets and selective IR photo-isomerization in cryogenic matrices
No full textThe conformational equilibria and isomerization processes of 1-propanol are analyzed by vibrational spectroscopy at low temperatures. Supersonic jet experiments provide constraints on the energy sequence. All five distinguishable monomer conformers are assigned in the OH stretching region. Collisional relaxation affects the OH group conformation (gauche or trans, g/t), but the barriers to alkyl chain isomerization (G/T) prevent relaxation of the latter. Alkyl chain isomerization can be induced in rare gas and nitrogen cryogenic matrices by suitable monochromatic irradiation. Selective excitation of the OH stretch of the Gt isomer transfers the alkyl chain from G to T. In N-2 matrices, reversible OH group isomerization between Tt and Tg can also be induced by selective irradiation, whereas in solid CCl4 matrices, only Gt reversible arrow Gg OH group isomerization is observed. The competition between intramolecular and intermolecular energy transfer and the matrix-dopant interaction determines the torsional subspace dynamics of the vibrationally excited propanol molecules. (C) 2011 Elsevier B.V. All rights reserved
PROTON TUNNELING ESTIMATES FOR MALONALDEHYDE VIBRATIONS FROM SUPERSONIC JET AND MATRIX QUENCHING EXPERIMENTS
No full textAuthor Institution: Institut f. Physikalische Chemie, Universitat Gottingen, Tammannstr. 6, D-37077 Gottingen, Germany; Chemistry Departement, University of British Columbia, 6174 University Blvd., Vancouver, BC, Canada; Laboratoire Physique des Interactions Ioniques et Moleculaires, UMR 6633, Universite de Provence-CNRS, Centre St-Jerome, 13397 Marseille Cedex 20, FranceMalonaldehyde (MA) in its stable enolic form is known as a prototype molecule for fast intramolecular proton transfer processes in a double minimum potential with a relatively large ground state splitting of 21.58\,cm.} Due to its moderate size it is a popular testing case for theoretical model calculations. So far, only few examples of vibrationally excited tunneling splittings are known experimentally.}} \\ We provide several new experimental estimates for excited state tunneling splittings in MA obtained by adiabatic cooling and symmetry breaking experiments in three different molecular states (isolated, coated by Ar layers and embedded in bulk Ar matrices).} The application of a straightforward approach allows the estimate of the splittings by the joint interpretation of gas phase, supersonic jet and matrix FTIR data. Our results constitute an important step towards a complete mapping of the MA tunneling splittings as a function of vibrational excitation and thus facilitate the critical assessment of multidimensional dynamical approaches
Vibrational tuning of the Hydrogen transfer in malonaldehyde - a combined FTIR and Raman jet study
No full textTunnelling splittings in vibrationally excited malonaldehyde are derived from complementary FTIR and Raman spectra utilising jet cooling and matrix isolation. Values from 0 to 69 cm(-1) (i.e. from complete quenching of the proton tunnelling to an acceleration by a factor of 3) are firmly assigned, underscoring a strong coupling between hydrogen transfer and vibrational excitation. More tentative assignments involve even larger effects for the OO breathing vibration. The results are discussed with respect to the corresponding normal modes and compared to previous theoretical predictions
Periodic bond breaking and making in the electronic ground state on a sub-picosecond timescale: OH bending spectroscopy of malonaldehyde in the frequency domain at low temperature
No full textProton tunneling between the two equivalent structures of malonaldehyde through a substantial barrier is accelerated by more than a factor of 3 to approximate to 0.24 ps by OH-bend excitation in phase with suitable motions of the molecular backbone. This is derived from a combined FTIR and Raman spectroscopy study in supersonic jets and rare gas matrices and compared to previous theoretical predictions.DFG [Su 121/2]; Fonds der Chemischen Industri
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
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