1,721,034 research outputs found
Valence hole localization in core-valence doubly ionized states of ionic molecules and its impact on KLV Auger spectroscopy
No full textThe complete spectra of core-valence dicationic states, i.e., states with one vacancy in the core and one in
the valence shell, of the molecules BF3, AlF3 , BCl3, and AlCl3, are investigated by the Green’s-function
method. An analysis of the double-hole density in the corresponding correlated states shows that when the core
hole is on a ligand ~halogen! atom, the valence hole is also strongly localized, either on the same ligand or on
a different ligand. As a result these states can be classified as either on-core or off-core site states. We discuss
how the localization phenomena are at the origin of the chlorine KLV Auger spectra of BCl3 and AlCl3 and,
in particular, how they provide a complete and conclusive interpretation of these spectra. Due to the intraatomic
nature of the Auger process, the simulation of the chlorine and aluminum KLV Auger spectra is done
by a simple convolution of the respective on-core site component of the computed two-hole density distribution.
The ligand atom spectra contain almost no information about the molecular system, representing an
indistinct self-image of the ligand atom itself, whereas the central atom spectra render a distinct foreign image
of the molecular environment
Intermolecular Coulombic decay of molecular clusters: Identification of the decay mechanism using a new hole-population analysis
No full textSingly ionized states of molecular clusters with an inner-valence vacancy have recently been shown to undergo an efficient electronic decay. The mechanism of the decay, which is absent in the isolated molecules that build up the clusters, is proposed to be of intermolecular Coulombic nature. As explicit example to further investigate this new decay process, the valence ionization spectrum of the HF(H2O)2 cluster is computed with the ADC(3) one-particle Green's function method. In the inner-valence part of the spectrum, characteristic dense line bundles due to the ultrafast electronic decay of the corresponding cationic states are observed. A new hole-population analysis method for the very many computed cationic states is presented. This method allows for a quantitative measure and characterization of the hole localization pattern of the cationic states. The dense line bundles which mimic the continuous decay distributions in our finite basis set approach are analyzed in detail. The resulting intermolecular character of the states confirms the recently proposed intermolecular Coulombic mechanism for the electronic decay in molecular clusters. The decay leads to dicationic states with two vacancies located on neighboring monomer units
Impact of narrow-band excitation on resonant decay spectra
No full textThe influence of narrow-band excitation on the decay spectra of dissociative core-excited molecular states is investigated in detail. Surprising interference phenomena have been reported previously in the resonant Auger spectrum of HF of Pahl et al. [Phys. Rev. Lett. 80, 1865 (1998)]. Apart from a general quenching of the “atomic” contribution by detuning, pronounced interference patterns are found for small detuning above the resonance of the core-excited state. Utilizing the time resolution gained within the theory of wave-packet dynamics, the underlying interference mechanisms are analyzed thoroughly. Special attention is paid to the selection process of intermediate-state eigenfunctions accompanying narrow-band excitation. We present a method that enables the assignment of different contributions in the decay spectrum to the internuclear distances at which the corresponding transitions take place. In particular, information about the origin of the atomic transitions is obtained
Ab initio calculation of energies and lifetimes of metastable dianions: The C2— resonance
No full textMost small dianions known in the solid state and solutions cannot exist as isolated entities and decay in the gas phase by electron autodetachment. These dianions show rare-gas-like closed-shell electronic ground states and represent a new type of metastable system. Here we study the prototype closed-shell resonance C2^2− in the framework of the complex absorbing potential method. We investigate in detail a number of unsettled methodological issues. In particular, there is no “natural” choice of orbital set for closed-shell metastable states and we study several orbital sets as well as other basis set and correlation effects on resonance energy and width. Closed-shell resonances typically show several open decay channels and we compute partial widths for the three open channels of C2^2−. Finally, we study the complex potential energy curve and compare our bond lengths and vibrational frequencies with geometrical parameters which have been obtained ignoring the metastable character of C2^2−
Intermolecular coulombic decay of clusters
No full textFollowing inner-valence ionization of a cluster, the system can relax by ultrafast electron emission. In contrast to Auger decay this novel process is intermolecular. It is characterized by an efficient Coulombic energy transfer mechanism between monomers in the cluster. As an example, we present an analysis of the hydrogen fluoride trimer, based on extensive ab initio computations
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
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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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