Molekülinterne Dipolorientierung und dielektrische Absorption in verdünnter Lösung bei Mikro-und Submillimeterwellen. IV.Chlormethyl-Verbindungen

The dielectric loss of eight molecules with the polar group in aromatic bonds and three in aliphatic bonds has been measured in very dilute solutions of cyclohexane at 20 °C. The measurements have been made at microwave frequencies in the range 2 to 130 GHz and at five wave numbers in the range 8 to 85 cm-1 (generated by a pumped molecular laser). These measurements are supplemented using a Fourier transform spectrometre up to 300 cm-1. The dielectric loss spectra ε″(γ̄) have been separated into a number of absorption regions (three or four in the microwave area) using the two variable Mori formalism. The power absorption spectra α(γ̄) are fitted to the Lorentzian shapes in order to determine the FIR resonances.The dielectric dispersion step determined from loss measurements contains the contributions from all orientational processes of the permanent molecular dipole moment. The distribution of relaxation times indicates that the polar group reorientates by a fast intramolecular rotational process in five of the eight aromatic molecules investigated. Furthermore these five substances show character­istic broad resonance centred at approximately 39 cm-1. In order to determine the influence of the other substituted groups, the components of the dipole moment parallel and perpendicular to the internal axis of rotation are calculated from the dispersion steps. The perpendicular component does contribute as well to the Debye relaxation according to the Budo model as to the Poley and FIR absorptions. The relative magnitudes of these contributions are rather similar in the five molecules. In two other molecules, the intramolecular orientational process plays a relatively minor role due to the steric hindrance by a neighbouring group. However in dichloro-o-xylene, the two neighbour­ing groups do not prevent the fast process except that the net dipole moment is significantly reduced. Again, due to sterichindrance, the aliphatic bonded group molecules do not exhibit the fast dipolar orientational process or the characteristic resonance at 39 cm-1.

Electromagnetic-wave propagation over a rotating dielectric cylinder

The problem of guided electromagnetic-wave propagation over a rotating dielectric cylinder is solved by a boundary-value method assuming that the speed of rotation is much smaller than the velocity of light. From a numerical solution of the complex characteristic equation, the variation of the attenuation and the phase constants and their dependence on the speed of rotation are studied. The rotational process appears to divide the radial propagation constant inside a stationary cylinder into two waves with different propagation constants. The modes with positive and negative indices in the circumferential direction cease to be degenerate in the case of a rotating dielectric cylinder, and there appears to be a decrease in the attenuation with an increased speed of rotation for the dominant mode.

Dynamik und Struktur Phosphit-substituierter Olefinwolfram-Komplexe / Dynamics and Structure of Phosphite Substituted Olefintungsten Complexes

The barriers of rotation of olefin ligands in (OC)3 LL′W(olefin) complexes, L - P(OMe)3 , L′ = P(OMe)3 or P(OEt)3 , olefin = ethylene, methylmaleate, methylfumarate, methylacrylate (1-4) have been determined from D-NMR measurements. The preferred olefin orientation has been deduced from an X-ray analysis of the tricarbonyl-triethylphosphite-trimethylphosphite-methyl-maleatetungsten compound 2. The influence of steric and electronic factors on the rotational process has been discussed by use of EHT-calculations.

Dielectric Absorption and ESR Results on the Relaxation of some Manganese Complexes in Organic Solvents

The limiting models - rotational or fluctuational process - for electron spin relaxation of Mn2+ in solution are discussed by comparison with dielectric correlation times. Free (solvated) ions presumably relax by the fluctuational, ionic complexes with static zfs by the rotational process. The latter conclusion requires the spectral density function to be more flat than the Debye function.