SFG experiment and ab initio study of the chemisorption of CN on low-index platinum surfaces

A dual analysis is proposed in order to have a better understanding of the adsorption of the cyanide ions on a platinum electrode. The SFG (Sum Frequency Generation) spectroscopy allows the in situ vibrational study and the SFG spectra of the CN⁻ species adsorbed on single crystal Pt electrode allow a systematic study of the low-index platinum surfaces. This experimental work is supported by ab initio calculations using density functional theory and cluster models. For each surface orientation and each geometry, a cluster model of 20-30 Pt atoms has been built in order to interpret the chemisorption of the CN⁻ ions through four kinds of adsorption geometry: on-top or bridge site, bonding via C or N atoms. Geometries have been optimized and adsorption energies, electronic properties and vibrational frequencies have been computed. From the electronic properties, we can propose an analysis of the bonding mechanism for each studied kind of adsorption.The SFG spectra of the CN⁻/Pt(1 1 1) system present an unique resonance owing to the top C adsorption. It is mainly the same for the CN⁻/Pt(1 0 0) system. It is also the case for the SFG spectra of the CN⁻/Pt(1 1 0) system recorded at negative electrochemical voltage; at more positive voltage, a second resonance appears at a lower frequency, owing to the top N adsorption.Experimental and theoretical values of the C-N stretching frequencies are in excellent agreement.     

$Ab~initio$ and experimental study of the K-shell spectra of s-triazine

The carbon and nitrogen K-shell spectra of gaseous s-triazine have been studied using inner-shell electron energy loss spectroscopy (ISEELS) method. Ab initio Configuration Interaction calculations have been carried out in order to assign the observed bands. As in many similar molecules, both spectra are dominated by an intense π^* peak, followed by lower intensity features. At the C1s edge, the calculations show that some previous assignments made using an underestimated core ionisation energy of about 2.5 eV have to be revisited. At the nitrogen edge, the calculations predict a high intensity π^* doubly excited state lying below the ionisation threshold, which could be responsible for one the most intense observable bands at 405.32 eV.     

Hypergraphes arbores

Un hypergraphe arboré est l'hypergraphe d'une familie de sous-arbres d'un arbre. Un hypergraphe est arboré si, et seulement si, il a la propriété de Helly et sa représentation triangulée; cette derniére propriété est ensuite remplacée par une condition sur les cycles de l'hypergraphe.     

Recherches sur les arǒmes. 16e communication [1]. Sur l'arǒme du cacao III

The isolation and analysis of a cocoa concentrate is described: 62 constituents have been identified, 42 of which for the first time. Most identifications are based upon mass spectrometry combined in many cases with IR. spectrometry, and comparison with reference compounds. A number of minor constituents could not be identified.     

Spin-orbit configuration interaction study of the electronic structure of the 5f (2) manifold of U(4+) and the 5f manifold of U(5+)

The energy levels of the 5f configuration of U(5+) and 5f(2) configuration of U(4+) have been calculated in a dressed effective Hamiltonian relativistic spin-orbit configuration interaction framework. Electron correlation is treated in the scalar relativistic scheme with either the multistate multireference second-order multiconfigurational perturbation theory (MS-CASPT2) or with the multireference single and double configuration interaction (MRCI) and its size-extensive Davidson corrected variant. The CASPT2 method yields relative energies which are lower than those obtained with the MRCI method, the differences being the largest for the highest state (1)S(0) of the 5f(2) manifold. Both valence correlation effects and spin-orbit polarization of the outer-core orbitals are shown to be important. The satisfactory agreement of the results with experiments and four-component correlated calculations illustrates the relevance of dressed spin-orbit configuration interaction methods for spectroscopy studies of heavy elements.