Volume 33, Issue 3

β-Nitrostyrene (βNS) was irradiated at r. t. in solutions of hexamethylphosph. triamide (HMPT) with 50 ns pulses of 15 MeV electrons. It was found that βNS reacts with solvated electrons almost encounter controlled (k(e - solv + βNS) = (9 ± 3) · 10 9 l/mol s) forming the radical anion · βNS - . The optical absorption spectrum of the latter was recorded in dilute solutions ([βNS] < 5 × 10 -3 mol/l). At higher βNS concentrations the formation of an additional optical absorption after the pulse in the wavelength range between 460 nm and 570 nm was detected, which is attributed to the reaction of βNS with · βNS- yielding the dimeric radical anion (· βNS-βNS-). The rate constant for this process is 4 × 10 7 l/mol s. At low βNS concentrations ( < 5 × 10 -3 mol/l) the transient spectrum decayed by a second order process (k 2 - (2.2 ± 0.5) · 10 9 l/mol s). This process is correlated to the neutralization of radical anions by cations formed initially. At [βNS] > 5 × 10 -3 mol/l only the band at 630 nm decays according to second order kinetics. This band is correlated to the part of the anions with the highest electron density, the nitro groups. At wavelengths below 570 nm the absorptions of various species overlap. These species decay by different rate laws.

An energy principle for the dissipative two-fluid theory in Lagrangian form is given. It represents a necessary and sufficient condition for stability allowing the use of test functions. It is exact for two-dimensional disturbances but is still correct in terms of perturbation theory for long wavelengths along the magnetic field. This may well find application in tokamak plasmas. A discussion of the general case and its relation to the stability of flows in hydrodynamics is given. This energy principle may be applied for estimating the magnitude of residual tearing modes in tokamaks.

The propagation of high-frequency axially-symmetric surface waves along a current-carrying hot plasma column in a glass tube is investigated by means of a kinetic plasma model. The wave spectrum and the wave damping rate are obtained. Our results agree with the experimental data for surface wave propagation in a gas-discharge plasma at low pressures. It is found that the wave damping is mainly due to the Landau mechanism.

Kossel patterns from Silicon and Niobium were obtained with a convergent electron beam. An intensity maximum in the direction of the zone axes [001] and [111] of Nb was interpreted as axial channeling. The intensity distribution in Kossel patterns was calculated by means of the Bloch wave picture of the dynamical theory of electron diffraction. Particularly zone axis patterns were calculated for different substance-energy combinations and they were compared with experimental observations. The intensity distribution in the calculated Kossel patterns was very sensitive to the model of absorption and it was found that a treatment of the absorption close to the model of Humphreys and Hirsch [Phil. Mag. 18, 115 (1968)] gave the best agreement with the experimental observations. Furthermore it is shown which Bloch waves are important for the intensity distribution in the Kossel patterns, how they are absorbed and how they change with energy.

Spherically shaped crystals of gold were grown by solidification of a drop of melt in UHV. Their surfaces were investigated in situ by RHEED. The superstructures (001) (5 × 20) and (110) (1 × 2) were observed again. Further superstructures were found: on (001) vicinal planes, (227) (1 × 1), (111) (23 × 1) and (551)c(1 × 1). Several of the new structures are related to structures already known.

The fractional intensities of different infrared vibration bands due to hydrogen impurities have been studied in clear natural quartz, amethyst, citrine and synthetic quartz. Integral absorptions of the different bands were found to increase linearly with total hydrogen concentration. The differences in intensity ratios for some prominent bands are distinctive for the type of quartz in some cases. The ratios of isotropic to anisotropic absorption from hydrogen impurities were found to increase with total hydrogen concentration.

The concept of long range coherence in biological systems of Fröhlich and its physical basis as well as his general theoretical considerations leading to the brain wave model are reviewed. The importance of these ideas is stressed both, as a possible explanation of the increasing experimental results and as a starting point to allow a theoretical description of biological events. The brain wave model is studied in detail. All possible bifurcations and the stability of the steady states is considered. The existence, stability and direction of bifurcation of a stable limit cycle is proven. The system may exhibit different types of phase transitions when it is externally disturbed. Phase plane diagrams, arguments of catastrophe theory and approximations to the model equations give a qualitative description of the system's time behaviour. Correspondence between this limit cycle model and nerve impulse generating models is established.

The out-of-plane fluctuations of fluid membranes are sterically hindered in multilayer systems. The repulsive interaction associated with the steric or excluded-volume effect is studied theoretically by two methods. The interaction energy per unit area of membrane is derived as a function of temperature, membrane curvature elasticity and mean membrane spacing; it is inversely proportional to the square of the latter. Steric repulsion is estimated for lecithin bilayers in water. There and in other cases, it may compete with van der Waals attraction.

In practice a standard specimen used for the elimination of instrumental broadening, by deconvolution, is never ideal. The instrumental line profile always contains some additional broadening due to finite particle size and distortion present in the standard specimen. Further it is sometimes unavoidable to use a standard specimen of a material different from the material to be analyzed, leading to reflections at incorrect sin θ-values (different spectral broadening). Firstly the effect of these deficiencies on the Fourier coefficients of the pure line profile is analyzed. Secondly the consequences for size-strain analysis are considered. A correction [Eq. (3.4) ] for the difference in spectral broadening between the exact and the approximate instrumental line profile is given. To avoid serious errors, this correction should be performed before particle size and strain are determined according to the so-called Warren- Averbach analysis. Accurate relative determinations of size and strain are possible even in the case that the line profile under investigation and the line profile of the reference specimen are at different sin θ-values. It is suggested that standard specimens which cause noticeable structural broadening can be used profitably.

The surface topography developed on copper-based and ferrous alloys after being sputtered in a glow discharge lamp and in an ion microprobe was studied by means of a scanning electron microscope and an ion microprobe mass analyser. The observed surface topography, though obtained under completely different conditions, was found to be similar to that predicted by the theory of Stewart and Thompson.

The structure of monoatomic liquids in the static approximation is described by a soft sphere model and the corresponding equation of state is derived. This geometrical model is then extended to binary liquid or amorphous substitution alloys where both components have the same size. The structure of these alloys is shown to be determined by the first neighbour order parameter which is positive, negative or zero for segregated, ordered or disordered alloys respectively. The variations of the partial structure factors with concentration are presented for these three cases. Size effects are then studied by varying the ratio of atomic diameters. Many experimental results are shown to fit this simple framework.

The electrical resistivity of the tetracyanoquinodimethane salts of ten alkali and transition metal cations has been investigated at temperatures from 300 to 470 K. The measurements indicate a phase transition, the activation energy of conductance being smaller in the high temperature region. The nature of this phase transition is discussed.

Ar, Ar/N 2 , Ar/Xe, Kr and Kr/Xe were tested in a spherical gas scintillation counter. The examinations led to the conclusion that only the four lowest lying states 3 P 2 , 3 P 1 , 3 P 0 , 1 P 1 of the noble gas atoms in the luminescence process are involved. From a practical point of view, the best energy resolution could be reached by Xe. We got a full width at half maximum of 83 eV for boron X-rays (183 eV).

In applying the theory of the thermal diffusion separation column with containers at both ends to quantitative isotope enrichment, the volume of the column has not yet been exactly accounted for. A formula is derived which describes the effective volume as a function of the characteristic values of the enrichment apparatus. An iteration method for calculation of the effective volume is presented. The theoretical values are compared with experimental results in the case of time dependent enrichment of two isotopes ( 13 CH 4 , 14 CH 4 ) and three different ways of enrichment. Agreement within the experimental limits of error of ± 6% was found.

Closed-shell diamond clusters and saturated hydrocarbons are investigated with PCILO and ab-initio Hartree-Fock using very small basis sets. The ab-initio distances for the C-C bonds differ by 5% or less, the PCILO distances by 2 to 2.5% from experimental data. The dependence of bond lengths and force constants on the cluster construction is studied. For selected molecules the effect of intermolecular rotations on the total energy is considered.

CNDO/2-type calculations have been carried out on 1,1-dihaloethylenes, 1,2-dihaloethylenes and 1,2-dihaloethanes treating all four halogens. The energy was minimized with respect to the coordinates by use of the FORCE method. The results are consistent with experimental isomer and conformer stabilities and it is shown, by means of a cis-trans correlation diagram and calculated intramolecular atomic interaction energies, that previous explanations of the apparent halogen-halogen attraction are inconsistent with our results.

The homologous series of Alcohols from Butanol to Tetradecanol was investigated with para-and diamagnetic shift-reagents with regard to their influences on the 1 H relaxation-times. For the protons of the OH-, the CH 2 -O-, and the (CH 2 ) n -groups, with increasing distance from the shiftmolecule, a decreasing influence on the T 1 -relaxation times could be verified. The Methylgroups of the long-chained Alcohols show an inverse tendency which can be explained by paramagnetic and Dipole-Dipole-Interactions with neighbour-complexes. The purely paramagnetic influence on the T 1 -relaxation times of the different protons may be obtained by subtracting the diamagnetic influence from the total.

The 4 T 1g (t 4 2g e 1 g ) → 6 A 1g (t 3 2g e 2 g ) phosphorescence spectrum of manganese (II) in single crystals of [Mn(CO(NH 2 ) 2 ) 6 ] (ClO 4 ) 2 has been recorded in the temperature range of 4.2 to 298 K. With decreasing temperature the emission maximum is shifted from 17138 cm -1 (298 K) to 16809 cm -1 (4.2 K). This red shift points to a linear thermal expansion coefficient of α = 24 · 10 -6 K -1 . Crystal field parameters of Dq = 748 cm -1 and B = 827cm -1 have been calculated from the room temperature absorption and excitation spectra.

By Fourier transform high resolution NMR spectroscopy the 31 P signals of the phosphate species 31 P 16 O 4-n 18 O n 3- (n = 0, 1, 2, 3, 4) have been resolved in aqueous solutions of potassium phosphate. An isotope effect on the Larmor frequency of δ( 31 P) = (0.019 ± 0.002) to lower frequency was found for the substitution of a 18 O atom for a 16 O atom in the phosphate ion.

Using our VTPES technique cyclopentadienone is generated in the gas phase at 500-600 °C from the three different precursors cyclobutene-3,4-dicarboxylic acid anhydride, o-phenylene sulfite and o-benzoquinone and its PE spectrum is recorded. The PE spectrum and also the PE spectra of the various precursors as well as of the cyclopentadienone dimer are interpreted on the basis of our recently developed PERTCI method (i. e. performing large scale perturbation configuration interaction calculations in connection with selection procedures). The agreement between measured and calculated ionization potentials is good.

The investigation on phase relationships and pertinent heat effects in branched alkali alkanoates was extended to lithium, sodium and potassium 2,2-dimethylpropanoates, 2-ethylbutanoates and 3,3-dimethylbutanoates. The results allow to discuss some aspects of the thermal behaviour of these salts, among which only the potassium ones can still exist as mesomorphic liquids.

The earlier reported dielectric properties of solid 1,4-Butanediol are critically examined in terms of conventional dipolar orientational theory. An explanation of the low frequency dielectric dispersion that involves molecular orientational effects associated with lattice deformations appears to require a value of the order 0.53 to 0.58 for the so-called Kirkwood dipole moment reduction factor. A model involving the hopping of charge carriers between localized energy states is offered as an alternative mechanism for the dielectric dispersion.

A competition technique has been employed to study the kinetics of the rapid reaction Cl 2 +2Br - → Br 2 + 2Cl - in aqueous solution. The specific rate at 25 °C and the energy of activation for the reaction are found to be 88.8 M -1 s -1 and 71.1 kj mole -1 , respectively.