Volume 54, Issue 8-9

The results of dielectric studies of 5-n-hexyl-2-(4'-isothiocyanato)-l,3-dioxane (6DBT) in the smectic A, phase at pressures up to 150 MPa and temperatures up to 340 K are presented. The low frequen-cy relaxation time τ || (p, T) yields the activation volume Δ # V || = RT(∂ || In τ || /p)T and activation enthalpy Δ # H || = R(∂ In τ || /∂T -1 ) p . The calculated values of these parameters are compared with those ob-tained recently for n-octyl-cyanobiphenyl (8CB) forming the smectic A d phase. In the case of 6DBT both these quantities are practically constant, whereas those for 8CB decrease, when going away from the phase transitions isotropic -smectic A 1 (6DBT) or nematic -smectic A d (8CB). These differences support our earlier conclusion that increase of pressure leads to a breaking of the antiparallel associa-tions of cyanobiphenyl molecules in the smectic as well as in the nematic phases.

A dense z-pinch generated by a high voltage discharge over a corrugated helical sawtooth-shaped capillary tube with a solid DT core, is by shear flow stabilized against the m = 0 and m= 1 magnetohydrodynamic instabilities, and by rotational flow against the Rayleigh-Taylor instability. The shear-and rotational flow result from jet formation by the corrugated surface. A programmed voltage pulse can then isentropically compress the DT core to high densities, and if ignited at one end by a petawatt laser pulse, a thermonuclear detonation wave can be launched propagating along the z-pinch channel. The proposed z-pinch burn should also work without tritium as a thermonuclear detonation wave in deuterium.

Based on a universal relationship between the extinction coefficient and the fluorescence intensity in their overlapping region, local temperatures T* higher than the ambient T were determined for short-lived luminescent molecules of lifetimes from 7 ps to 77 ps. The reason for such a local temperature T*, which holds also during the emission process, is the non-establishment of statistical equilibrium over the vibrational levels of excited molecules. It is found that the intensity distribution in the fluorescence band depends slightly on the wavelength of the excitating light, which evidences the lack of thermal equilibrium with the vicinal surrounding.

A novel mathematical formulation to deal with interfacial stability problems of the Kelvin-Helmholtz type with heat and mass transfer in the presence of oblique electric fields is presented. The perturbed system is composed of two homogeneous, inviscid, incompressible, dielectric, and streaming fluids sep-arated by a horizontal interface, and bounded by two rigid planes. The effect of a phase transition on the instability is considered, and the linear dispersion relations are obtained and discussed. It is found that the electric field has a major effect and can be chosen to stabilize or destabilize the flow. For Ray-leigh-Taylor instability problems of a liquid-vapor system it is found that the effect of mass and heat transfer enhances the stability of the system when the vapor is hotter than the liquid, although the clas-sical stability criterion is still valid. For Kelvin-Helmholtz instability problems, however, the classical stability criterion is found to be substantially modified due to the effects of the electric field, mass and heat transfer. A new stability condition relating the magnitude and orientation of the electric field and the dielectric constants is obtained. Oblique electric fields are found to have stabilizing effects which are reduced by the normal components of the electric fields. The effects of orientation of the electric fields and fluid depths on the stability configuration are also discussed.

54a, Melting of aluminium and iron trichloride crystals is accompanied by a structural transition from octahedral to tetrahedral coordination of the metal ions, and a widely accepted interpretation of their liquid structure is that it mainly consists of strongly correlated dimeric units. Such Al 2 Cl 6 and Fe 2 Cl 6 molecules are stable in the vapour phase and coexist in gaseous mixtures together with AlFeCl 6 molecules. In this work we extend to Fe 2 Cl 6 and AlFeCl 6 our earlier study of the ionic interactions in Al 2 Cl 6 [Z. Akdeniz and M. P. Tosi, Z. Naturforsch. 180 (1999)], using a model which accounts for ionic deformability through (i) effective valences and (ii) electrostatic and overlap polarizabilities. The main disposable parameters of the model are adjusted to the Fe-Cl bond length in FeCl 3 monomer molecule and to the Fe-Fe bond length and a bond-stretching frequency in the Fe 2 Cl 6 molecule. The results are used to evaluate the structure of the AlFeCl 6 molecule, which has so far only been inferred from the observed Raman spectrum in mixed vapours. Extensive comparisons with data on molecular vibrational frequencies are also presented for Fe 2 Cl 6 and AlFeCl 6 .

According to Erters identity and Ertel's vorticity theorem some aspects on general relativistic vortex dynamics and relationships are discussed in detail.

A quantity has been introduced, whose dependence on the composition along the branches of the solubility isotherms of ternary systems consisting of two salts with a common ion and water exhibits breaks, which can be explained by the introduction of a previously unobserved configuration of the ternary saturated solution. In the respective region, a saturated solution in a ternary system may undergo second-order phase transitions to achieve specific configurations that are not derived from the structure of the binary saturated solution of the particular solute. It is assumed that further study of this phenomenon could contribute to a better understanding of the processes occurring in concentrated electrolyte solutions.

NMR second moment and spin-lattice relaxation times in the laboratory (60 and 25 MHz) and in the rotating frame (B 1 = 2.1 mT) were studied for polycrystalline tetraphenyltin Sn(C 6 H 5 ) 4 in a wide temperature range. Two kinds of motions were detected: isotropic rotation of whole molecules and reorientations/ oscillations of phenyl rings. A dependence of the potential energy of the molecule in the crystal on the angle of the phenyl ring rotation about the Sn-C bond was obtained on the basis of atom-atom calculations. The amplitude of the ring-oscillations at 133 K was estimated as ± 7°. Below room temperature the magnetisation recovery is significantly non-exponential, which may be interpreted as due to the correlated motion of phenyl rings.

Steady-state and time-resolved spectroscopic studies of benzanilide (I) and jV-methylbenzanilide (II) were performed at 298 and 77 K in various solvents. The results indicate that benzanilide fluorescence in non-polar solvents at room temperature involves three independent modes of emission: F 1 (LE) normal fluorescence from the initially excited state S 1 (LE) with λ max = 320 nm, F 2 ´(PT) fluorescence from the proton transfer tautomer with λ max = 468 nm, F 2 ″CT) fluorescence from the species where intramolecular charge transfer appears, with λ max = 510 nm. At 77 K in MCH a new fluorescence band, F ag , appears at λ max =415 nm instead of the F 2 (PT) and F 2 ″CT) fluorescence. This new emission originates from benzanilide dipolar aggregates or cis-imidol dimers. The decay times of these emission modes are different. N-methylbenzanilide, dissolved in nonpopular and weakly polar solvents at room temperature and at 77 K, shows only two fluorescence modes, i.e., the normal and the charge-transfer emissions at 320 nm and 520 nm, respectively. The fluorescence is deactivated with two decay times, 30 ps and 2.05 ns, in MCH solution.

The Conformational stability and barriers of interconversion between the eis and gauche conformers of vinyldichlorosilane, CH 2 CHSiHCl 2 , have been studied using ab initio calculations employing the RHF/3-21G* and RHF/6-31G* basis sets. The eis conformer was found to be more stable than the gauche one by 45 cm -1 (539 J/mol) and 140 cm -1 (1.68 kJ/mol) from the RHF/3-21G* and RHF/6-31G* basis sets, respectively. Additionally, the structural parameters of both rotamers have been calculated. These results are compared with results of related molecules.

Short-lived phosphenous fluoride, 0=PF, has been made by flash pyrolysis of F 2 POPF 2 in Ar at 1200°C and detected by gas phase IR spectroscopy. The υ 1 band, υ 0 = 1297.5372 cm -1 , has been studied with a resolution of 8 x 10 -3 cm -1 , and about 1500 transitions have been assigned. These were fitted using a Watson-type Hamiltonian, σ = 1.5 x 10 -3 cm -1 , to excited state parameters up to quartic centrifugal distortion constants. The υ 2 band was located at 819.58 cm -1 . An extended set of ground state parameters was obtained by combining recently measured microwave transitions with ground state combination differences formed from υ 1 transitions. The experimental results are in perfect agreement with the matrix IR spectra, mw measurements and ab initio calculations but disagree with a recently claimed low resolution detection of OPF in the gas phase.

A series of Fe 2 O 3 -SiO 2 nanocomposites (9 -33 wt% of Fe 2 O 3 ) has been prepared by a sol-gel method and submitted to thermal treatments at 300 -900 °C. The samples were characterized by X-ray diffraction and Mössbauer Spectroscopy measurements. Superparamagnetic behavior is exhibited by all the samples, indicating that the size of iron oxide grains is in the nanometer range (4-6 nm). Increase of iron content and temperature treatment give rise to a small particle growth, while the spread of sizes around the average value increases with the iron concentration. The Mössbauer spectra, at all the explored compositions, show a very steep increase of the peak width by treatment temperature at 900 °C, indicating the formation of the ferrimagnetic γ-Fe 2 O 3 phase from the antiferromagnetic amorphous Fe 2 O 3 phase, which dominates in the samples treated at lower temperatures. The samples at 28.5% and 33.2%, treated at 900 °C, also show a component of γ-Fe 2 O 3 in the blocked state at room temperature. Moreover, the growth of the particles favours the formation of other oxide phases (α and ε phase) along with the γ phase.

The temperature dependences of 7 Li and 15 N NMR spin-lattice relaxation times and spectra in LiNO 2 were measured in the range 120 K -473 K (m.p.). The 180°-flip motion of NO 2-- ions along or perpendicular to the molecular C 2 -axis and the self-diffusion of Li + ions (activation energies of 42 -44 and 100 kJ mol -1 , respectively) were observed in this range. From the comparison of the observed activation parameters with those reported for plastic phases of alkali metal nitrites, a new characteristic of the plastic crystal was obtained.

We report the assignment and analysis of all stable monosubstituted isotopomers of trifluoroacetic acid. The 13 C and 18 O isotopomers were observed in natural abundance. The rotational constants and quartic centrifugal constants are presented. The rotational constants are used to derive a partial substitution structure and a complete ro structure for future comparison with the corresponding values in hydrogen bridged bimolecules containing trifluoroacetic acid as a subunit. The deuterium nuclear quadrupole coupling constants are derived from the hfs-splittings of low-J rotational transitions of the CF 3 COOD isotopomer. The results of ab initio quantum chemical calculations are presented, which were carried out to assist in the assignment of the rotational spectra of the isotopomers and for comparison with the experimental molecular parameters.

The symmetry and disorder of the Eu 3+ site was investigated in some phosphate and borate glasses by means of 151 Eu Mössbauer spectroscopy. The quadrupole interaction parameter, which is due to the distortion of the Eu site compared to a cubic symmetry, has been measured together with the asymmetry parameter, which points out the absence of a threefold or fourfold axis of symmetry at the rare earth site. The correlation of the isomer shift with the optical basicity of the glass indicates a covalent component with 6s character in the Eu-O bond. The axial component of the electric field gradient at the Eu site is also correlated with the optical basicity.

The dielectric relaxation of 7CP5BOC (2-chloro-4-heptylphenly 4-pentylbicyclo-[2,2,2]octan-l-car-boxylate) in its isotropic and nematic phase has been studied. The substance has a negative dielectric anisotropy. The complex dielectric permittivity was measured in the frequency range 10 kHz -3 GHz with the aid of an impedance analyzer and a time domain spectroscopy (TDS) method. The relaxation time, activation enthalpy and dielectric increments, characterizing the rotation of the molecules about the principal inertia axes, were obtained. It was found that the relaxation process connected with rota-tions about the long axis can be split into two independent motions of molecular moieties around the

We show that the application of the truncated Painlevé expansion and symbolic computation leads to a new class of analytical solitary-wave solutions to the general fifth-order nonlinear evolution equations which include Lax, Sawada-Kotera (SK), Kaup-Kupershmidt (KK), and Ito equations. Some explicit solitary-wave solutions are presented.

This paper presents a new approach to localize molecular vi-brations. By analyzing YX 2 type molecules we show that lo-calized vibrations can be created if we stimulate a set of the molecule's Raman-active normal modes properly by lasers.

Electron paramagnetic resonance of [(CH 3 ) 4 N] 2 MnCl 4 and [(CH 3 ) 4 N] 2 FeCl 4 single crystals was studied between 20 and 400 K. The peak-to-peak derivative linewidths of these crystals seem not to change in this temperature interval and approximately 100 mT for [(CH 3 ) 4 N] 2 MnCl 4 and ~20 mT for [(CH 3 ) 4 N] 2 FeCl 4 .The spectra were found to be isotropic, with g = 2.0039 for [(CH 3 ) 4 N] 2 MnCl 4 and g = 2.0042 for [(CH 3 ) 4 N] 2 FeCl 4 .This temperature independence is attributed to isotropic strong ex-change interactions of Mn 2- and Fe 2+ nuclei, and it seems that hindered rotation of the MnCl 4 2- and FeCl 4 2- tetrahedra does not occur in this temperature interval.