Spectroscopie de photoélectron : déterminations expérimentale et théorique des potentiels d'ionisation

L'identification de la nature des états ioniques générés lors d'une photoionisation par un rayonnement U.V. est rarement possible sur la base seule d'arguments expérimentaux. L'attribution nécessite généralement un modèle théorique plus rigoureux. Si l'approximation de Koopmans est très largement utilisée, il est indispensable d'étre en mesure d'estimer lors d'une interprétation les corrections éventuelles.La confrontation d'un spectre expérimental et de calculs théoriques compte tenu des limites d'applicabilité de Koopmans permet généralement de déduire de façon non ambiguë la structure d'une molécule en phase vapeur. L'analyse du spectre SPE du tétrazolo [1,5-a] pyridine illustre ces possibilités

Detection in the gas phase of unstable ketenimines. Photoelectronic spectrum of N-methylketenimine

International audienceThe gas-phase generation of the unstable ketenimine (1) and N-methyl-ketenimine (2) has been studied by u.v. photoelectron spectroscopy. Even in short-path pyrolytic conditions, ketenimine isomerizes too quickly to acetonitrile to be detected. On the other hand, the spectrum of N-methyl-ketenimine could be recorded: the first three bands are observed at 8.95, 11.25 and 12.10 eV, respectively, attributed according to MNDO calculations to an A′ ionic state [ejection of an electron from the antisymmetric combination of the π(C=C) bond with the nitrogen lone pair], an A″ ionic state [π(C=N) bond] and the A′ ionic state arising from the symmetric combination of the π(CC) bond with the nitrogen lone pair. The energetic difference between the first and third bands indicates a weaker interaction between the double C=C bond and the nitrogen lone pair than for etheneamine

UHV-STM images on intercalated metal disulfide Ni1/4TiS2 and Ni1/3TiS2: Influence of sulfur chemical surrounding

International audienceThe specific crystallographic features of Ni1/3TiS2 and Ni1/4TiS2 led us to carry out ultrahigh vacuum-scanning tunneling microscopy (UHV-STM) studies, in order to bring to light the different atom chemical environments of the structure and the host-guest interactions. These compounds present specific structural reorganizations that involve, in particular, different chemical surroundings for chalcogen atoms (the outer layer of the compounds). We imaged the top sulfur planes (001) for both compounds and propose an explanation of the two well-differentiated contrasts observed

Étude de la structure électronique du benzothiazole et de ses homologues azoté, oxygéné et sélénié par spectroscopie photoélectronique (HeI, HeII)

Les structures électroniques comparées du benzothiazole, du benzimidazole, du benzoxazole et du benzosélénazole sont analysées à l'aide de la spectroscopie photoélectronique et des méthodes de calculs de chimie quantique STO-3 G et EHT. Les conclusions tirées de ces dernières méthodes sont confirmées par une étude comparative des intensités de bandes dans les spectres enregistrés avec les radiations Hel et Hell

Electronic structure (XPS and ab-initio band structure calculation) and scanning probe microscopy images of α-tin sulfide

International audienceThe bulk and surface electronic structure of α-SnS is investigated by X-ray photoelectron spectroscopy and band structure calculations, using ab-initio Hartree-Fock program CRYSTAL. Calculated band structure and density of states are consistent with recent calculations using other methods. Scanning tunnelling microscopy (STM) and Atomic Force microscopy (AFM) images were examined by calculating the partial electron density ρ(r, Ef) and total electron density ρ(r) of a slab which consists of height (100) α-SnS layers. It was found that bright spots in experimental STM images correspond to sulphur and tin atoms in positive bias voltage and to the outermost layer (tin atoms only) in negative bias voltage. However, the simulated image related to filled states cannot explain the new periodicity of the experimental pattern in low negative polarisation, which suggests the appearance of a surface charge density wave. The performed AFM image show a periodicity which can be simply explained by the atomic corrugation at the surface

Étude par XPS et calculs ab initio de couches minces de nitrure de bore

Des couches minces de nitrure de bore déposées par CVD sur des substrats de carbure de silicium sont étudiées par spectroscopie photoélectronique à rayonnement X (XPS ou ESCA) et calculs quantiques ab initio (base STO-3G). Les analyses XPS des couches électroniques de coeur montre la présence, de façon homogène, d'oxygène. Celui- ci n'est pas simplement adsorbé mais substitue une partie des azotes ([B] = [N] + [O]). Les spectres XPS haute résolution montre en outre l'existence des environnements NB3, BN3 et BNxOy. Ces résultats permettent d'établir un modèle de la structure turbostratique de ces couches. Ce modèle est utilisé pour le calcul ab initio de la structure électronique et la structure de bande de ces nitrures de bore oxydés, analysées par référence à celles du nitrure de bore hexagonal pur. Les spectres de valence calculés de ces composés sont en bon accord avec les spectres XPS expérimentaux

Electronic structure of intercalated metal disulfide (Fe1/4TiS2) studied by XPS and theoretical calculations

International audienceThe specific crystallographic features of Fe1/4TiS2 have led us to carry out an experimental (X-ray photoelectron spectroscopy) and theoretical (augmented spherical wave method) study to shed light on the different chemical environments of atoms in the structure and their host-guest interaction. The chemical shifts or/and broadening of the core-level peaks have been correlated with initial and final states, the former based on the charge transfer between the iron intercalant and the host titanium atoms. The valence band is modified by the intercalant, primarily towards low binding energies. The electronic structure calculations are in good agreement with the observed spectra. © 1997 Elsevier Science B.V

Photoelectron spectrum of chlorophosphaethyne

International audienceThe photoelectron spectrum of Chlorophosphaethyne, generated in the gas phase by dehydrochlorination of trichloromethylphosphine on a solid base, is reported; the spectrum is quite consistent with the spectra of the related cyanogen halides or haloacetylenes and indicates a large interaction between the degenerate P≡C triple bond and the chlorine lone pair

Probing Organization and Structural Characteristics of Alkanethiols Adsorbed on Gold and of Model Alkane Compounds through their Valence Electronic Structure: an Ultraviolet Photoelectron Spectroscopy Study

In this paper we report an ultraviolet photoelectron spectroscopy (UPS) study of saturated alkane chains in various configurations and conformations. The dependence of the valence spectra on molecular structure characteristics has been assessed by comparing the results obtained from n-alkanethiol, R,ö-alkanedithiol, and R-cycloalkyl-ö-alkanethiol monolayers adsorbed on gold, and from gas-phase model alkane compounds. The differences between the spectra reflect directly the structural changes induced in the electronic structure of the alkane chains. We have determined the type of folding sequences adopted in a 1,12-dodecanedithiol monolayer. Angular dependent measurements and investigations on the photoelectron attenuation length have evidenced very fine structural differences between films obtained on deposited gold films, annealed gold films, and gold single crystal