The sequence to hydrogenate coronene cations:A journey guided by magic numbers

The understanding of hydrogen attachment to carbonaceous surfaces is essential to a wide variety of research fields and technologies such as hydrogen storage for transportation, precise localization of hydrogen in electronic devices and the formation of cosmic H2. For coronene cations as prototypical Polycyclic Aromatic Hydrocarbon (PAH) molecules, the existence of magic numbers upon hydrogenation was uncovered experimentally. Quantum chemistry calculations show that hydrogenation follows a site-specific sequence leading to the appearance of cations having 5, 11, or 17 hydrogen atoms attached, exactly the magic numbers found in the experiments. For these closed-shell cations, further hydrogenation requires appreciable structural changes associated with a high transition barrier. Controlling specific hydrogenation pathways would provide the possibility to tune the location of hydrogen attachment and the stability of the system. The sequence to hydrogenate PAHs, leading to PAHs with magic numbers of H atoms attached, provides clues to understand that carbon in space is mostly aromatic and partially aliphatic in PAHs. PAH hydrogenation is fundamental to assess the contribution of PAHs to the formation of cosmic H2.</p

Low energy electron impact on gas phase 5-nitrouracil

Excitation of the first electronic states, vibrational excitation between 1 and 3 eV, and negative ion formation (0–2 eV) in gas phase 5-nitrouracil are presented. Five singlet states are clearly identified at 4.76; 5.72; 6.82; 7.82 and 9.2 eV. A band at 3.7 eV could be assigned to a triplet state. The vibrational modes observed indicate resonant states having both p* and r* character. The most intense anions (MNO2), (MH) appear at zero energy with huge cross sections (P1018 m2). Anion cross sections versus electron energy reveal structures interpreted using the anion energy thresholds found by DFT calculations. 2008 Elsevier B.V. All rights reserved

Dynamique d'états électroniques excités à la surface d'un film ultra-mince d'Ar condensé sur un métal

Ce travail de thèse porte sur l'étude de la dynamique d'états électroniques excités à la surface d'un métal recouvert d'une couche ordonnée ultra-mince de diélectrique (Ar). On s'est intéressé à la façon dont cette couche adsorbée modifie les propriétés des deux types d'états excités en surface : états délocalisés (comme états image, résonances image, résonances de puits quantique) et états localisés sur un adsorbat moléculaire (ion négatif transitoire). Pour décrire l'interaction entre l'électron excité et la couche d'Ar on a développé un modèle microscopique tridimensionnel sans paramètre ajustable, qui intègre la structure électronique et géométrique de la couche adsorbée sur métal. Les propriétés des états électroniques délocalisés (énergie, durée de vie, masse effective) sont discutées en fonction de l'épaisseur de la couche d'Ar (entre 1 et 4 mono-couches). Le caractère isolant d'une couche d'Ar très mince, même une seule mono-couche, est mis en évidence. Les résultats théoriques concernant les états image sur Cu(100) recouvert d'Ar sont comparés à des résultats expérimentaux et l'accord est très bon. Sur le même système, on a mis en évidence des résonances de puits quantique qui ont été par la suite confirmées expérimentalement. L'existence et les propriétés des résonances image sur un métal à électrons libres recouvert d'Ar sont aussi discutées.Les propriétés (énergie et largeur) de la résonance N2-(2?g) de la molécule d'azote adsorbée sur une mono-couche d'Ar déposée sur métal sont calculées et discutées en termes d'effets locaux(site d'adsorption) et globaux (réflectivité à l'interface Ar-vide).The present work concerns the dynamics of electronic excited states at the surface of a metal covered by a very thin dielectric ordered layer (Ar). We have studied how this layer modifies the properties of two types of excited states at surface: delocalised states (image states, image resonances, quantum well resonances) and localised states on molecular adsorbates at the surface. In order to describe the interaction between the excited electron and the Ar layer we have developed a parameter free microscopic model. This model takes into account the electronic and geometrical structures of the adsorbed layer on the metal. The properties of the delocalised electronic states (energy, lifetime, effective mass) as a function of the Ar layer thickness (from 1 to 4 monolayers) are discussed. We have shown that a very thin Ar layer exhibits an insulating character. The theoretical results concerning the image states on Cu(100) covered by Ar are compared to experimental results and the agreement between them is very good. We have observed quantum well resonances on the same system. These resonances have been confirmed experimentally afterwards. The existence and properties of image resonances on a free electron metal covered by an Ar layer are also discussed.The properties (energy and width) of the N2-(2?g) resonance of the nitrogen molecule adsorbed on an Ar monolayer deposited on a metal are calculated and discussed in terms of local (adsorption sites) and global (reflectivity of the Ar-vacuum interface) effects.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Hydrogenation reactions and adsorption : From CO to methanol on a graphene surface

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Industrial Resources: Lee County

Industrial Resources: Lee County, Kentucky prepared by the Kentucky Department in cooperation with the City of Beattyville, 1970. The report includes, but is not limited to, information about: population, labor market, local manufacturing, transportation, utilities, fuel, water, sewage, industrial sites, local government and services, taxes, educational and health facilities, housing, communication, recreation, natural resources, markets, and climate

A combined DFT/HREELS study of the vibrational modes of terphenylthiol SAMs

Self-assembled monolayers of p-terphenylthiol (TPT, HS-(C6H4)2-C6H5) deposited onto gold can serve as model systems for aromatic lithography resists. Such thin molecular films are suitably probed using high resolution electron energy loss spectroscopy, due to its high surface sensitivity. Extended energy loss spectra were measured at different probing energies. The TPT monolayer overlapping ν(CH) stretching modes could be modelled by a single effective anharmonic oscillator sustained by a Morse potential energy curve, thanks to the resonant excitation of the associated overtone series at 6 eV. A remarkably good agreement was obtained between the TPT monolayer energy loss spectrum and the computer-simulated infrared vibrational spectrum of the isolated TPT molecule. Density Functional Theory calculations for TPT, fully deuterated TPT and benzenethiol isolated molecules were performed with the exchange correlation functional B3LYP and a dispersion correction, using a triple ζ+ polarisation basis set. By comparing the vibrational patterns obtained for these parent systems, (re-)assignments of all the features observed in the TPT self-assembled monolayer energy loss spectrum are discussed. The obtained vibrational assignments can be confidently transposed to other related systems, such as benzenethiol and biphenyl self-assembled monolayers

The sequence to hydrogenate coronene cations: A journey guided by magic numbers

The understanding of hydrogen attachment to carbonaceous surfaces is essential to a wide variety of research fields and technologies such as hydrogen storage for transportation, precise localization of hydrogen in electronic devices and the formation of cosmic H2. For coronene cations as prototypical Polycyclic Aromatic Hydrocarbon (PAH) molecules, the existence of magic numbers upon hydrogenation was uncovered experimentally. Quantum chemistry calculations show that hydrogenation follows a site-specific sequence leading to the appearance of cations having 5, 11, or 17 hydrogen atoms attached, exactly the magic numbers found in the experiments. For these closed-shell cations, further hydrogenation requires appreciable structural changes associated with a high transition barrier. Controlling specific hydrogenation pathways would provide the possibility to tune the location of hydrogen attachment and the stability of the system. The sequence to hydrogenate PAHs, leading to PAHs with magic numbers of H atoms attached, provides clues to understand that carbon in space is mostly aromatic and partially aliphatic in PAHs. PAH hydrogenation is fundamental to assess the contribution of PAHs to the formation of cosmic H2

Reactivity of coronene with O-atoms, a possible route to ketene in the interstellar medium

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