Time filter

Source Type

Talyzin A.V.,Umea University | Luzan S.M.,Umea University | Leifer K.,Uppsala University | Akhtar S.,Uppsala University | And 6 more authors.
Journal of Physical Chemistry C | Year: 2011

The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500-700°C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530-550°C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550-600°C by oligomerization into larger molecules. Above 600°C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes. © 2011 American Chemical Society. Source

Antichi J.,Istituto Nazionale di Astrofisica Osservatorio Astrofisico di Arcetri | Munari M.,Istituto Nazionale di Astrofisica Osservatorio Astrofisico di Catania | Magrin D.,Istituto Nazionale di Astrofisica Osservatorio Astronomico di Padua | Riccardi A.,Istituto Nazionale di Astrofisica Osservatorio Astrofisico di Arcetri
Journal of Astronomical Telescopes, Instruments, and Systems | Year: 2016

Following the unprecedented results in terms of performances delivered by the first light adaptive optics system at the Large Binocular Telescope, there has been a wide-spread and increasing interest on the pyramid wavefront sensor (PWFS), which is the key component, together with the adaptive secondary mirror, of the adaptive optics (AO) module. Currently, there is no straightforward way to model a PWFS in standard sequential ray-tracing software. Common modeling strategies tend to be user-specific and, in general, are unsatisfactory for general applications. To address this problem, we have developed an approach to PWFS modeling based on user-defined surface (UDS), whose properties reside in a specific code written in C language, for the ray-tracing software ZEMAX™. With our approach, the pyramid optical component is implemented as a standard surface in ZEMAX™, exploiting its dynamic link library (DLL) conversion then greatly simplifying ray tracing and analysis. We have utilized the pyramid UDS DLL surface - referred to as pyramidal acronyms may be too risky (PAM2R) - in order to design the current PWFS-based AO system for the Giant Magellan Telescope, evaluating tolerances, with particular attention to the angular sensitivities, by means of sequential ray-tracing tools only, thus verifying PAM2R reliability and robustness. This work indicates that PAM2R makes the design of PWFS as simple as that of other optical standard components. This is particularly suitable with the advent of the extremely large telescopes era for which complexity is definitely one of the main challenges. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE). Source

Dubernet M.L.,University Pierre and Marie Curie | Dubernet M.L.,University of Paris Descartes | Boudon V.,University of Burgundy | Culhane J.L.,University College London | And 31 more authors.
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2010

The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu) is a European Union funded collaboration between groups involved in the generation, evaluation, and use of atomic and molecular data. VAMDC aims to build a secure, documented, flexible and interoperable e-science environment-based interface to existing atomic and molecular data. The project will cover establishing the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing atomic and molecular databases. It will also provide a forum for training potential users and dissemination of expertise worldwide. This review describes the scope of the VAMDC project; it provides a survey of the atomic and molecular data sets that will be included plus a discussion of how they will be integrated. Some applications of these data are also discussed. © 2010 Elsevier Ltd. Source

Garcia-Hernandez D.A.,Institute of Astrophysics of Canarias | Garcia-Hernandez D.A.,University of La Laguna | Villaver E.,Autonomous University of Madrid | Garcia-Lario P.,European Space Agency | And 8 more authors.
Astrophysical Journal | Year: 2012

We present a study of 16 planetary nebulae (PNe) where fullerenes have been detected in their Spitzer Space Telescope spectra. This large sample of objects offers a unique opportunity to test conditions of fullerene formation and survival under different metallicity environments because we are analyzing five sources in our own Galaxy, four in the Large Magellanic Cloud (LMC), and seven in the Small Magellanic Cloud (SMC). Among the 16 PNe studied, we present the first detection of C60 (and possibly also C70) fullerenes in the PN M 1-60 as well as of the unusual ∼6.6, 9.8, and 20 μm features (attributed to possible planar C24) in the PN K 3-54. Although selection effects in the original samples of PNe observed with Spitzer may play a potentially significant role in the statistics, we find that the detection rate of fullerenes in C-rich PNe increases with decreasing metallicity (∼5% in the Galaxy, ∼20% in the LMC, and ∼44% in the SMC) and we interpret this as a possible consequence of the limited dust processing occurring in Magellanic Cloud (MC) PNe. CLOUDY photoionization modeling matches the observed IR fluxes with central stars that display a rather narrow range in effective temperature (∼30,000-45,000K), suggesting a common evolutionary status of the objects and similar fullerene formation conditions. Furthermore, the data suggest that fullerene PNe likely evolve from low-mass progenitors and are usually of low excitation. We do not find a metallicity dependence on the estimated fullerene abundances. The observed C60 intensity ratios in the Galactic sources confirm our previous finding in the MCs that the fullerene emission is not excited by the UV radiation from the central star. CLOUDY models also show that line- and wind-blanketed model atmospheres can explain many of the observed [Ne III]/[Ne II] ratios using photoionization, suggesting that possibly the UV radiation from the central star, and not shocks, is triggering the decomposition of the circumstellar dust grains. With the data at hand, we suggest that the most likely explanation for the formation of fullerenes and graphene precursors in PNe is that these molecular species are built from the photochemical processing of a carbonaceous compound with a mixture of aromatic and aliphatic structures similar to that of hydrogenated amorphous carbon dust. © 2012. The American Astronomical Society. All rights reserved. Source

Cataldo F.,Istituto Nazionale di Astrofisica Osservatorio Astrofisico di Catania | Cataldo F.,Actinium Chemical Research | Angelini G.,CNR Methodological Chemistry Institute | Anibal Garcia-Hernandez D.,Institute of Astrophysics of Canarias | And 3 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

A series of 33 different polycyclic aromatic hydrocarbons (PAHs) were studied by far infrared spectroscopy (terahertz spectroscopy) in the spectral range comprised between 600 and 50 cm-1. In addition to common PAHs like naphthalene, anthracene, phenanthrene, fluoranthene, picene, pyrene, benzo[α]pyrene, and perylene, also quite unusual PAHs were studied like tetracene, pentacene, acenaphtene, acenaphtylene, triphenylene, and decacyclene. A series of alkylated naphthalenes and anthracenes were studied as well as methypyrene. Partially or totally hydrogenated PAHs were also object of the present investigation, ranging from tetrahydronaphthalene (tetralin) to decahydronaphthalene (decalin), 9,10-dihydroanthracene, 9,10- dihydrophenanthrene, hexahydropyrene, and dodecahydrotriphenylene. Finally, the large and quite rare PAHs coronene, quaterrylene, hexabenzocoronene, and dicoronylene were studied by far infrared spectroscopy. The resulting reference spectra were used in the interpretation of the chemical structure of asphaltenes (as extracted from a heavy petroleum fraction and from bitumen), the chemical structures of other petroleum fractions known as DAE (distillate aromatic extract) and RAE (residual aromatic extract), and a possible interpretation of components of the chemical structure of anthracite coal. Asphaltenes, heavy petroleum fractions, and coal were proposed as model compounds for the interpretation of the emission spectra of certain proto-planetary nebulae (PPNe) with a good matching in the mid infrared between the band pattern of the PPNe emission spectra and the spectra of these oil fractions or coal. Although this study was finalized in an astrochemical context, it may find application also in the petroleum and coal chemistry. © 2013 Elsevier B.V. All rights reserved. Source

Discover hidden collaborations