1,721,173 research outputs found
Spiers Memorial Lecture: New directions in molecular scattering
No full textMolecular scattering is reviewed as it pertains to gas–gas as well as gas–surface reaction dynamics. We emphasize the collaboration of experiment and theory, from which new directions of research are being pursued on increasingly complex problems.The field of molecular scattering is reviewed as it pertains to gas–gas as well as gas–surface chemical reaction dynamics. We emphasize the importance of collaboration of experiment and theory, from which new directions of research are being pursued on increasingly complex problems. We review both experimental and theoretical advances that provide the modern toolbox available to molecular-scattering studies. We distinguish between two classes of work. The first involves simple systems and uses experiment to validate theory so that from the validated theory, one may learn far more than could ever be measured in the laboratory. The second class involves problems of great complexity that would be difficult or impossible to understand without a partnership of experiment and theory. Key topics covered in this review include crossed-beams reactive scattering and scattering at extremely low energies, where quantum effects dominate. They also include scattering from surfaces, reactive scattering and kinetics at surfaces, and scattering work done at liquid surfaces. The review closes with thoughts on future promising directions of research.Funder:
Office of Naval Research Global
https://doi.org/10.13039/10000729
Product angular anisotropy in CO2 photodissociation at 157 nm
No full textThe Photodissociation dynamics of CO2 has been reinvestigated using the photofragment translational spectroscopic technique based on direct vacuum ultraviolet (VUV) ionization using synchrotron radiation. The product translational energy spectrum as well as the product angular anisotropy have been measured for both the CO & O products. The experimental results indicate that the O(3P)+CO channel has an anisotropy parameter of 1.25, while that for the O(1D)+CO channel depends on the translational energy dependent
Photodissociation dynamics of CH3Cl at 157.6 nm: Evidence for CH2((X)over-tilde(3)B(1)/(a)over-tilde(1)A(1))+HCl product channels
No full textPhotodissociation of methyl chloride at 157.6 nm has been investigated using a molecular beam apparatus with a universal detector, which is based on VUV photoionization by synchrotron radiation. Three dissociation channels have been observed: Cl þ CH3, H þ CH2Cl & HCl þ CH2. Product translational energy distributions were determined for all observed dissociation channels. An intriguing HCl elimination channel was observed, which consists of two distinctive micro channels: one is CH2ð~XX3B1Þ þ HCl, the other is CH2ð~a1A1Þ þ HCl. The fraction of the available energy released as product translational energy was determined to be 0.75 for CH2ð~XX3B1Þ þ HCl & 0.38 for CH2ð~a1A1Þ þ HCl. Other product channels such as H2 þ CHCl were not found
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
Orienting polar molecules without hexapoles: Optical state selection with adiabatic orientation
Full text linkA pedagogic review of technology used to orient polar molecules is presented to place in context the report of a new approach to this problem. Laboratory frame orientation of polar molecules is achieved by state-specific optical pumping in a region free of electric fields followed by adiabatic transport into a static electric field. This approach overcomes some of the limitations of the more common hexapole focusing method. In particular the method is nearly insensitive to the kinetic energy of the sample. We demonstrate production of oriented samples of NO (mu(el) = 0.15 D) with translational energies above 1 eV in both high-and low-field seeking states. The method can be extended to many other classes of molecules, including near symmetric tops and ions. (C) 2012 Elsevier B. V. All rights reserved
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
Surface photochemistry probed by two-photon photoemission spectroscopy
Full text linkTwo-photon photoemission (2PPE) has been widely used in the study of electronic structure and dynamics of unoccupied electronic states on different types of surfaces and interfaces. Since 2PPE probes electronically excited states, it should be sensitive to surface excited electronic structure changes that accompany surface chemical reactions. Therefore, this method could potentially be used to study the kinetics and dynamics of surface chemical reactions as well as surface photocatalysis. In this article, we briefly review recent progress made in the study of surface photochemistry and photocatalysis using the time-dependent 2PPE (TD-2PPE) method. A few examples are given to demonstrate the application of this method in probing surface photochemistry and photocatalysis, particularly photocatalysis of methanol on TiO2 surfaces. Since many problems associated with surface photochemistry and surface photocatalysis are related to energy and environmental issues, the 2PPE technique could have important applications in the study of the fundamental problems in energy and environmental sciences
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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