Calculation of the electronic structure of ethylene by the SCF-Xα scattered wave method

The electronic structure of ethylene is investigated by the implementation of the Xα scattered wave method and a comparison is made with SCF LCAO results. Calculations are also carried out for different geometrical configurations of the molecule, in which one HCH plane is rotated through different angles relative to the other.     

Mesures des densites locales d'atomes metastables dans un arc stabilise par parois

We have measured by two different methods, the local densities of the 3p⁵4s levels of argon in a wall-stabilized arc at atmospheric pressure. Comparison between experimental results and calculated values obtained on the assumption of LTE shows that the hypothesis is not valid near the walls (i.e. r/R > 0·5 for an axiall temperature of 11,000°K).     

Etude par RMN de la structure dynamique de l'alanate Na3AlH6

A low temperature wide-line NMR study has allowed a determination of the AI-H bond lengths in cryolite-type Na₃AlH₆. It was found from the thermal behavior of the proton lines that the |AIH₆|^3? octahedra reorient around a C₄ axis. Starting below 170 K, this rotation can be hindered by lattice defects. Above room temperature it becomes isotropic, and a quick protonic exchange appears.The thermal narrowing of the linewidth and the T₁ and T_1ρ relaxation times lead to activation energies of about 0.38 eV for axial rotation and 0.51 eV for protonic exchange. The minimum in T₁ is in good agreement with the exchange model. Absorption phenomena, as well as partial decomposition of Na₃AlH₆ during the heat treatments, explain the presence of small amounts of mobil hydrogen.     

Some graphs with chromatic number three

A question of P. Erdös is solved by showing that certain graphs have chromatic number at most three. The proof proceeds by showing a conjecture of Erdös and Bollobás holds, namely, that under certain circumstances, a graph which contains an odd circuit must contain an odd circuit with diagonal.     

Equations fonctionnelles et systèmes induits en théorie ergodique

Sans résuméEquipe de Recherche n 1 «Processus stochastiques et applications», associèe au C.N.R.S.