Kinetic model of a DC oxygen glow discharge

A simple kinetic model predicting the concentration of oxygen atoms, metastable singlet molecules O₂(a ¹) and negative ions O — in the positive column of a DC glow discharge is developed. The calculated O and O₂(a ¹) concentrations are compared to previously reported measurements for pressuresp=0.2–2 Torr and discharge currentsI=10–80 mA. The electron density calculated from the continuity equationj=n _e e v _d agrees well with experiment. The rate coefficients for electron impact processes used in the balance equations of O, O₂(a ¹), and O^– were taken from the literature as a function of the reduced electric fieldE/N forE/N=40–80 Td. A reasonable agreement is obtained between the model and the experiment with a set of 10 reactions for the production and destruction of the above-mentioned species     

Nouvelle methode de detection des resonances optiques par deviation magnetique d'un jet atomique

We propose a method to be used in the investigation of the hyperfine structure and isotope shift of ²⁵Na. This method has been tested with a ²³Na beam and the limit of the signal-to-noise ratio expected with this method is discussed.     

Radiometric measurements on a plasma induced by a proton beam

The plasma radiation temperature of a neon plasma created by a dc proton beam has been measured. Variations of this temperature versus gas pressure and beam intensity are presented and related to the theoretical variation of the electronic distribution function.     

Préparation de thiocétones acycliques α-insaturées. dimérisation régiosélective en 4h-dithiine-1,3

α-Unsaturated acyclic thioketones 6 a–d were prepared by a retro-Diels-Alder reaction using flash thermolysis technique. They were detected at low temperature (blue coloured pyrolysate) but dimerize in solution as soon as the temperature rose to ?60° (case 6 a–c) and ?20° (case 6 d). The structure of 6 d was established by UV and NMR spectra taken at ?60°. Dimeric products were proved to be 4H - 1,3 dithiin by spectral data and by univocal synthesis of 7 c and 7 d from the corresponding monomeric ketone. 1–3 Dithiin 7 d was isomerized at 190° into the thermodynamic isomer (8). This observed orientation of dimerisation agrees with theorical results obtained from molecular frontier orbital calculations.     

Influence of the ion-pseudopotential on the electronic shell structure and the dipole strength distribution in metal clusters

Using the pseudo-Hamiltonian technique we investigate, through complete self-consistent ground-state calculations, nonlocal ion-pseudopotential effects on the dipole strength distribution and the electronic shell structure of alkali clusters. The results obtained for sodium clusters are compared to the predictions of the standard jellium model (JM) and to experiments. Some wrong JM-predictions — shift of some low magic sizes, insufficient redshift of the surface plasmon frequency relative to the Mie frequency — are corrected, but a noticeable discrepancy remains with regard to the supershell structure. In the second part of this paper we restore the reliability of the pseudo-Hamiltonian approximation, on which some doubts have been recently cast, because of incorrect predictions concerning the bulk properties of lithium. From a careful analysis of the nonlocal effects in a smoothed ionic background, we show that a specific pseudo-Hamiltonian parametrization has to be systematically selected for ensuring maximum accuracy. We successfully test the suitability of this parametrization in the case of lithium clusters, through a comparison with recently published results obtained using accurate norm-conserving nonlocal pseudopotentials.