1,721,034 research outputs found
Dataset for Mapping the complete reaction coordinate of a complex chemical reaction
No full textData associated with paper:
Mapping the complete reaction path of a complex photochemical reaction. / Smith, Adam D.; Warne, Emily M.; Bellshaw, Darren; Horke, Daniel; Tudorovskya, Maria; Springate, Emma; Jones, Alfred; Cacho, Cephise; Chapman, Richard T.; Kirrander, Adam; Minns, Russell S.
In: Physical Review Letters, 120(18), 1-6. [183003].
DOI: 10.1103/PhysRevLett.120.183003</span
Resonant multiphoton ionisation probe of the photodissociation dynamics of ammonia
No full textThe dissociation dynamics of the ?-state of ammonia have been studied using a resonant multiphoton ionisation probe in a photoelectron spectroscopy experiment. The use of a resonant intermediate in the multiphoton ionisation process changes the ionisation propensity, allowing access to different ion states when compared with equivalent single photon ionisation experiments. Ionisation through the E? 1A?1 Rydberg intermediate increases the observation window allowing us to monitor the excited state population for several hundred femtoseconds. The vibrational states in the photoelectron spectrum show two distinct timescales, 200 fs and 320 fs, that we assign to the non-adiabatic and adiabatic dissociation processes respectively. The different timescales derive from differences in the wavepacket trajectories for the two dissociation pathways that resonantly excite different vibrational states in the intermediate Rydberg state. The timescales are similar to those obtained from time resolved ion yield measurements, suggesting we can measure the different trajectories taken out to the region of conical intersectio
Fermiology, 3D to 2D dimensionality crossover and electron-phonon coupling in the electronic structure of transition metal dichalcogenides
No full textThe dosing of layered materials with alkali metals has become a commonly usedstrategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we performed a systematic study of 1T-HfTe2, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of Potassium (K) deposition. From the kz maps, we observed the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wavefunction confinement at the topmost layer. In our highest-dosing cases, a monolayer-like electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below EF, we could directly measure a band overlap of ∼ 0.2 eV. However, 3D bulk-like states still contribute to the spectra even after considerable dosing. Our work on HfTe2 provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES. In our second work, we investigated the electronic band structure of the two polytypes of NbS2, namely 2H-NbS2 and 3R-Nb1+xS2 combining ARPES and DFT calculations again. The measured Fermi surfaces show a remarkable difference in size, reflecting a significantly increased band filling in 3R-Nb1+xS2 due to the presence of additional Nb interstitials. Thus we found that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the 2H phase shows strong kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands withNb 4dx2-y2,xy character than for the Nb 4d3z2-r2. Our results provide an experimental framework for interpreting the two-gap superconductivity and latent CDW in 2H-NbS2Le dosage des matériaux en couches avec les métaux alcalins est devenue une stratégie commune dans la technique de photoémission résolue en angle ARPES (angle-resolved photoemission spectroscopy), mais exactement ce qui se passe structurellement et électroniquement est resté débâté. Ici, on réalise une étude de 1T-HfTe2, un semimetal prototypique de la famille des métaux de transition dichalcogénides TMDs (transition metal dichalcogenides). En utilisant ARPES en dépendance de l’énergie de photons, nous avons examiné la structure électronique de ce matériau en fonction de dosage avec le potassium K. D’après nos spectres de kz, on a observé l’apparence de 2D états électronique après le dosage, avec une amélioration remarquable de la qualité des data mesurées, en accord avec le confinement de la fonction d’onde à la plus haute monocouche. A notre niveau de dosage le plus élevé, la structure électronique mesurée est similaire à celle d’une monocouche, attestant l’intercalation des atomes alcaline dans le gap de van der Waals. En ramenant le top de la bande de valence en dessous du niveau de Fermi, nous avons directement mesuré le gap négatif d’une valeur de 0.2 eV. Toutefois, des états électroniques de volumes contribuent toujours au spectre même après une quantité considérable du dosage. Enfin, la bande de valence de HfTe2 contient un point de Dirac et un gap inversé, en analogie avec tous les TMDs du même groupe de symétrie. Dans notre deuxième projet, nous avons étudié les deux polytypes de NbS2, notamment 2H-NbS2 et 3R-Nb(1+x)S2 en utilisant ARPES et les calculs DFT (density functional theory). Les deux surfaces de Fermi mesurées montrent une grande différence en taille, indiquant un remplissage de bande plus import dans le 3R phase en raison d’atomes interstitielles de Nb. Donc nous avons trouvé que c’est plutôt la stoichiométrie est le facteur le plus important dans la différence des propriétés électronique et physiques des deux phases, et pas l’empilement de couche. Nos data avec la meilleure résolution de 2H-NbS2 montrent de forts ‘kinks’ dans la fonction spectrale, témoignant l’électron-phonon couplage dans ce système. Nous avons trouvé que ce couplage est plus fort dans les sections de bandes dérivées de Nb 4dx2−y2 ,xy orbitales que celles de Nb 4d3z2−r2 orbitales. Nos résultats présentent un cadre expérimental pour l’interprétation des deux gaps supraconducteurs et l’absence de l’onde de densité de charge dans 2H-NbS2
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
Time resolved detection of the S(<sup>1</sup>D) product of the UV induced dissociation of CS2
No full textThe products formed following the photodissociation of UV (200 nm) excited CS2 are monitored in a time resolved photoelectron spectroscopy experiment using femtosecond XUV (21.5 eV) photons. By spectrally resolving the electrons, we identify separate photoelectron bands related to the CS2 + hν → S(1D) + CS and CS2 + hν → S(3P) + CS dissociation channels, which show different appearance and rise times. The measurements show that there is no delay in the appearance of the S(1D) product contrary to the results of Horio et al. [J. Chem. Phys. 147, 013932 (2017)]. Analysis of the photoelectron yield associated with the atomic products allows us to obtain a S(3P)/S(1D) branching ratio and the rate constants associated with dissociation and intersystem crossing rather than the effective lifetime observed through the measurement of excited state populations alone.</p
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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