1,721,004 research outputs found
Studies of molecular photoionization of simple systems by advanced photon sources
Full text linkThis doctorate thesis reports on a variety of experimental investigations aiming to advance the understanding of fundamental processes in molecules and clusters by exploiting the properties of Synchrotron and FEL radiation: photoionization dynamics, double ionization, dissociation and molecular recognition were subject of investigation. The emphasis of the thesis lies on the application of advanced light sources in the study of photoionization processes in simple gas-phase molecules, with particular
attention on chiro-optical properties of chiral systems. The valence photoionization dynamics of a chiral molecule, namely the
epichlorohydrin molecule, was studied for the first time and a peculiar electron correlation effect was observed. The experimental data were supported by state-of-the-art theoretical calculations. VUV direct double ionization was studied for the methyl oxirane chiral molecule by the use of Photoelectron-Photoion-Photoion Coincidence spectroscopy using synchrotron radiation.
The chiral recognition mechanism of 1-methoxy-2-propanol oligomers was studied by FEL based IRMPD-VUV vibrational spectroscopy, a technique that exploits the nature of the photoionization process in order to apply the IRMPD spectroscopy to systems of arbitrary structure. The collaboration between the Sapienza University of Rome, the CNRIOM institute, and the Elettra Instrumentation and Detector Laboratory, has resulted in the development of a position sensitive cross delay line electron detector integrated in an experimental apparatus with the flexibility to perform synchrotron radiation (SR) photoemission experiments on gasphase systems. The improvement of the apparatus detection system has stimulated the collaboration with the Theoretical Chemistry group of the University of Trieste, in a joint experimental and theoretical long-term research activity, whose first part was the study of the photoionization dynamics of the Osmium tetroxide molecule, a highly reactive tetraoxo complex
Thermally Activated on‐Surface Self‐Metalation of Pd‐Phthalocyanines
No full textPhthalocyanines (Pcs) are essential organic molecules with wide-ranging applications in fields such as catalysis and optoelectronics, owing to their stable aromatic structure and exceptional thermal stability. Equally important is their versatility, which can be achieved by modifying the central metal atom. In this context, metalation—the process by which a central metal atom is incorporated into the macrocycle—plays a critical role in tailoring both the electronic and structural properties of Pcs. In this work, we investigate the thermally activated on-surface synthesis of palladium phthalocyanine (PdPc) by depositing metal-free phthalocyanine ((Formula presented.)) onto a Pd(001) surface in ultra-high vacuum (UHV) conditions. Using temperature-dependent X-ray photoemission spectroscopy (XPS), we analyze the evolution of the N (Formula presented.) core level signal, confirming the successful formation of PdPc. The appearance of a secondary peak in the Pd (Formula presented.) core level, attributed to Pd atoms coordinated within the phthalocyanine molecule after metalation, provides further evidence for the PdPc synthesis. Additionally, near-edge X-ray absorption fine structure (NEXAFS) reveals that no desorption or chemical degradation occurs during the process. We believe this study represents a significant step forward in the scalable synthesis of PdPc, which, like other Pd-containing organic molecules, holds great potential for applications in catalysis and cancer therapy
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
Single-photon hot-electron ionization of C70
No full textGas phase C70 molecules have been ionized with single photons of energies between 16 and 70 eV, and the electron spectra measured with velocity map imaging in coincidence with the ions. The doubly ionized and unfragmented species was present at photon energies of 22 eV and up, and triply charged ions were present from 55 eV. The low-kinetic-energy parts of the spectra are explained with thermal emission of transient hot electrons.
We propose a generally applicable mechanism, named resonance ionization shadowing, for the creation of hot electrons by absorption of above-threshold energy photons
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
Stabilization versus competing de-metalation, trans-metalation and (cyclo)-dehydrogenation of Pd porphyrins at a copper surface
Full text linkMetal-porphyrins are studied intensively due their potential applications, deriving from the variety of electronic and chemical properties, tunable by selecting metal centers and functional groups. Metalation, de- and trans-metalation processes are fundamental in this sense to investigate both the synthesis and the stability of these molecular building blocks. More specifically, Pd coordination in tetrapyrroles revealed to be potentially interesting in the fields of cancer therapy, drug delivery and light harvesting. Thus, we focused on the stability of palladium tetraphenyl porphyrins (PdTPPs) on a copper surface by means of combined spectroscopy and microscopy approaches. We find that PdTPPs undergo coverage-dependent trans-metalation accompanied by steric rearrangements already at room temperature, and fully trans-metalate to CuTPPs upon mild annealing. Side reactions such as (cyclo)-dehydrogenation and structural reorganization affect the molecular layer, with Pd-Cu alloying and segregation occurring at higher temperature. Instead, oxygen passivation of the Cu support prevents the metal-involving reactions, thus preserving the layer and increasing the chemical and temperature stability of the Pd porphyrins.LN
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
- …
