Darstellung und spektroskopische Untersuchungen von Trivinyl- und Triallyl-fluorsilan

Preparation and Spectroscopical Investigations of Trivinyl- and Triallylfluorosilane Trivinyl- and Triallylfluorosilane were prepared. The i.r. and Raman spectra have been recorded. The discussion of intra- and intermolecular interactions is based on the spectroscopic data.     

Spektroskopische Untersuchungen an Phenoxydimethylfloursilanen

Spectroscopie Investigations on R? C₆H₄O(CH₃)₂SiF Compounds The i.r. and Raman spectra of a number of R? C₆H₄O(CH₃)₂SiF compounds (R = H, CH₃, CH₃O, Cl, Br, NO₂, NH₂) have been recorded. The intramolecular and intermolecular interactions were discussed by means of ν SiF, ν Si? O? (C), ν C? O? (Si) and ν_s SiC₂ vibrations.     

Untersuchungen an Zinnverbindungen. XVII. Infrarot-, RAMAN-, Mossbauer- und massenspektroskopische Untersuchungen an Triorganozinnfluoriden

The IR, in the solid state (33 to 4000 cm^?1) and in gaseous state, the RAMAN , MÖSSBAUER and mass spectra of (CH₃)₃SnF, (C₂H₅)₃SnF, (n-C₃F₇)₃SnF, (n-C₄H₉)₃SnF and (C₆H₅)₃SnF were recorded. The frequencies of the vibrational spectra were almost completely assigned. By means of this methods the properties of the triorganyl tin fluorides, which differ considerably from the other organyl tin halides, were examined. The difference in their properties are due in all cases to strong intermolecular interactions.     

An “optical” theorem for acoustic scattering by baffled flexible surfaces

The classical optical theorem for scattering by compact obstacles is a forward scattering theorem. That is, the total cross section of the obstacle is proportional to the imaginary part of the far field directivity factor evaluated in the forward scattering direction. An analogous theorem is derived in this paper for the scattering of acoustic waves by baffled membranes and plates. In this “optical” theorem the directivity factor is evaluated in the direction of the specularly reflected wave, so that it is a reflected scattering theorem.     

Pattern formation in microwave heated ceramics: cylinders and slabs

Analyses of microwave heating of a thin ceramic cylinder and a thin ceramic slab in a single mode, highly resonant cavityare presented. Realistic assumptions regarding the effectiveelectrical conductivity, thermal parameters, and physical dimensionsare adhered to throughout. Consequently, the models developedherein incorporate most of the features of actual experiments.They incorporate both the effects of cavity detuning and alocal electric field perturbation on the heating process. The models presented take the form of one- and two-dimensionalreaction–diffusion equations which contain a functionaland an inhomogeneous source term for the cylinder and slab,respectively. The development of these equations is the product of a systematic modelling process that involves S-matrix theory,a small Biot number asymptotic analysis, and a matched asymptotic analysis of a non-standard electromagnetic scattering problem.The one-dimensional equation for the cylinder reveals boththe mathematical structure and physical mechanism for the formationof hot-spots. The two-dimensional equation supports a hot stripe pattern, due to preferential electromagnetic heating, whichbecomes unstable and evolves into an oval-like spot. Accuratenumerical methods which approximate the solutions of theseequations and their stability are presented and these agreequalitatively with experiments and predict observed trends. Received 1 June, 1999. ⁺ antoine@mip.ups-tlse.fr     

Stability of a microwave heated fluid Layer

When a time harmonic electromagnetic wave impinges on a slaba certain portion of the wave creates heat within the slab throughdipolar and ohmic heating. The electrical and thermal propertiesof the material dictate the dynamical nature of the heatingprocess, as well as the steady-state temperature profile. Thematerial considered here is a slab of fluid. We consider thecase where the fluid is bounded by thin rigid layers of transparentmaterial. The steady-state heating profile governs the typesof convective motions that can occur and also affects the stabilitycharacteristics of temperature, pressure and velocity perturbationsintroduced in the slab. The main objective here is to examinesuch stability characteristics, initially in the linear regime.Both rigid-rigid and rigid-free configurations are considered.     

Untersuchungen an Zinnverbindungen. XVIII. Schwingungsspektren und Normalkoordinatenanalyse von n-Propylzinntrichlorid – ein Beitrag zur Rotationsisomerie in Organozinnverbindungen

Studies on tin compounds. XVIII. Vibrational spectra and normal co-ordinate analysis of n-propyltintrichloride – a contribution to rotational isomerism of organotin compounds The infrared and RAMAN spectra of liquid and solid n-propyltintrichloride have been recorded. By normal coordinate treatment the vibrations are assigned to the gauche- and trans-isomers. The Sn–C stretching vibrations are calculated for the gauche-form at 523^?1, and for the trans-form at 599 cm^?1. In the liquid state both isomers are present, in the solid state only the gauche isomer is existing.     

Electromagnetic propagation in periodic porous structures

A variational technique is employed to compute approximate propagation constants for electromagnetic waves in a dielectric structure which is periodic in the X−Y plane and translationally invariant in the Z-direction. The fundamental cell, in the periodic structure, is composed of a pore and the surrounding host media. The pore is a circle of radius R₀ filled with a dielectric ε₁ and the host dielectric characterized by ε₂. The size of the cell is characterized by the length A which is R₀.

Two limiting cases are considered. In the first, the pore size is assumed to be much smaller than the wavelength; this limit is motivated by microwave heating of porous material. The approximate propagation constants are explicitly computed for this case and are shown to depend upon the two dielectric constants, the relative areas of the two regions in the cell, and on a modal number. They are not given by a simple mixture formula.

In the second limit, the pore size is taken to be of the same order as the wavelength; this limit is motivated by the propagation of light in a holey fiber. In this case our argument directly yields the dispersion relationship recently derived by Ferrando et al. [Opt. Lett. 24 (1999) 276], using intuitive and physical reasoning. Thus, our method puts theirs into a mathematical framework from which other approximations might be deduced.     

NMR study of orgnasilicon compounds : X. The transmission of substituent effects in phenoxysilanes as studied by 29Si and 13C NMR

²⁹Si and ¹³C NMR chemical shifts for a series of meta and para substituted phenoxytrimethylsilanes are given and compared with those in phenyltrimethylsilanes using the formal single and dual substituent parameter analysis of substituent effects.The silicon chemical shift is found to be about twice as sensitive to substituent effects in phenoxytrimethylsilanes as in phenyltrimethylsilanes. The chemical shift sensitivity to substituent effects, ?, is considered to be a product of two factors, ?^el and ?^shield, which describe the sensitivity of the electron density to substituent effects and the sensitivity of the shielding to the electron density, respectively.Using ¹³C chemical shifts and CNDO/2 net atomic charges, it is shown that the substituent effects propagate within XC₆H₄ fragment of phenoxysilanes no better than in phenylsilanes. The ¹³C chemical shifts of the terminal methyl groups are affected by the substituents in the former series of compounds much less than in the latter. An increase in the relative basicity of oxygen is accompanied by an increase in silicon shielding in phenoxytrimethylsilanes.According to CNDO/2 calculations, the substituents cause larger changes in net atomic charges on the silicon atom if it is bonded directly to the benzen ring rather than via the oxygen bridge. In spite of the fact that the possibility of a dative O·→Si interaction, not reflected by the CNDO/2 calculations, cannot be completely excluded, the results that the increased silicon shift sensitivity to substituent effects in phenoxysilanes is due to higher sensitivity of silicon shielding (?^shield) to electron density in these compounds rather than to a bettr transmission of electronic effects (?^el). The existing theory of silicon shielding must be improved or refined if it has to accomodate the increased sensitivity in the phenoxysilanes.