Infrared band intensities of cyanobutadiyne (HC5N) between 400 and 4000 cm

We report the first infrared spectra of pure gaseous cyanobutadiyne between 400 and 4000 cm⁻¹. A great care has been taken to obtain a pure sample so that, for the first time, intensities could be determined for all the main bands in the studied domain. The results are compared with available theoretical works. A sample containing a mixture of HC₅N and DC₅N was also studied in the same wavenumber range. The data obtained in this study should be very useful to identify those compounds by IR spectroscopy and will allow the quantification of cyanobutadyine in various environments.     

Oxidized silicon surfaces studied by high resolution Si 2p core-level photoelectron spectroscopy using synchrotron radiation

The Si 2p soft X-ray photoemission study of various oxidized surfaces (thermal oxidation and room temperature (RT) oxidation) shows the benefit derived from the use of high-energy resolution (70 meV). Interesting structural information can be retrieved from an analysis of the line widths of the oxides, suboxides, and elemental Si peaks. In particular the binding energy (BE) of elemental silicon layers adjacent to the oxidized layer can be distinguished from that of deeper silicon layers (the two prominent ‘interfacial' elemental Si lines are shifted by about +0.2 and −0.2 eV). These new data show a possible effect of oxygen second neighbors on elemental Si 2p binding energies. Moreover, changes in the oxide/suboxide line widths – as seen in a comparative study of the Si(1 1 1)-7×7 surface thermally oxidized in O₂ and exposed at RT to O₂ or H₂O – may be attributed to static disorder, i.e., variations in Si–O bond lengths.     

Preserving dissipation in approximate inertial forms for the Kuramoto-Sivashinsky equation

It has been observed, in earlier computations of bifurcation diagrams for dissipative partial differential equations, that the use of certain explicit approximate inertial forms can give rise to numerical artifacts such as spurious turning points and inaccurate solution branches. These shortcomings were attributed to a lack of dissipation in the forms used. We show analytically and verify numerically that with an appropriate adjustment we can eliminate these numerical artifacts. The motivation for this adjustment is to enforce dissipation, while maintaining the same order of approximation. We demonstrate with computations that the most natural remedy, namely, preparation of the equation, can be highly sensitive to assumptions on the size of the absorbing ball. In addition, we show that certain implicit forms are dissipative without any adjustment. As an illustrative example we use here the Kuramoto-Sivashinsky equation.     

Synthèse de nouvelles amidines bicycliques . Dérivés de la pyrimidine,de la quinazoline et de la diazépine-1,3

The synthesis of pyrrolo[1,2-α] pyrimidines is described. Several homologous compounds contain pyridine or azepine instead of pyrrole ring. They are obtained by cyclization of iminolactams with β-ketoesters, αβ-unsaturated esters, aldehydes or ketones, or diketene. The possibility of obtaining isomers is discussed.