Band 26, Heft 11

Ausgehend von den Hartree-Gleichungen wird durch Mittelung der Potentialfelder eine einzige SCF-Gleichung hergeleitet, die als eine Näherung für die HF-Gleichung aufgefaßt werden kann. Nach Einführung der LCAO(STO) (GO)-Darstellung und der Mulliken-Approximation gelangt man zu einer sehr einfachen Form des SCF-Operators, die näher besprochen wird.

Kubo type time correlation formulae for turbulent transport coefficients in incompressible but heat conducting fluids are derived, especially for eddy viscosity, eddy heat conductivity, and pressure. The connection to the cascade method as well as its equivalence to the methods of closure of hierarchy are established. Lagrangean time integration is used. If the retarded Green’s function has exponential time behaviour the damping constant Γ q can be calculated explicitely. In this approximation in the inertial range one finds the Kolmogoroff k -5/3 spectrum including its numerical factor (C=1.53). This induces a frequency spectrum ∼ ω -2 .

The symmetry selection rules for the mixing of states by spin orbit interaction are known to cause unequal population of the three electronic levels of excited triplet states in aromatic molecules. It is shown here that the same selection rules, when combined with the hyperfine interaction, can also produce a selective population and depopulation of the nuclear sublevels. This mechanism is proposed to be responsible for the large optical nuclear polarisation (ONP) in low fields observed experimentally.

The infrared absorption and Raman spectra, evaluation of potential energy constants with various potential functions, and other spectroscopic studies have been briefly analyzed for the isotopic species of nitrogen trichloride molecule possessing a trigonal pyramidal symmetry. Among the various quantum mechanical models, the delta-function potential model based on the variational method and the delta-function electronic wave functions has been employed here to evaluate the atomic polarizabilities, the contributions by the bonding and nonbonding electrons to the bond parallel component of the polarizability, the bond perpendicular component of the polarizability, and the mean molecular polarizability of nitrogen trichloride. On the basis of group theoretical considerations, the symmetrized mean- square amplitudes, mean-square amplitudes, and root-meansqare amplitudes for both bonded and nonbonded atom pairs have been computed at the temperatures 298 °K and 500°K. On the basis of a rigid rotator and harmonic oscillator approximation, enthalpy function, free enthalpy function, entropy, and heat capacity have been computed for the temperatures from 200°K to 2000° K for both isotopic species of nitrogen trichloride. A discussion of the results follows.

Stark-effect measurements on pure rotational transitions of TlBr and Til are described. The derived electric dipole moments of the most abundant isotopic molecules on the ground vibrational state are: 205 TL 79 Br : | μ 0 | = (4.493 ± 0.050) D , 205 Tl 127 I | μ 0 | =(4.607 ± 0.070) D . The electric dipole moment of 205 Tl 19 F | μ 0 |=4.2282 (8) D was used as standard.

The NQR-spectrum of 127 I in orthoperiodic acid, Η 5 ΙΟ 6 , has been studied on powder samples in the temperature range 77 Κ ≦ Τ ≦ 398 Κ. The resonance frequencies ν 1 of the transition m(±3/2) ⇄ m (±1/2) are 45.248±0.005 MHz (77 K) and 44.976 ± 0.005 MHz (296 K). For the⇄ transition m(±5/2) ⇄ m(±3/2) the resonance frequencies v 2 are 83.478±0.005 MHz (77 K) and 83.960 ± 0.005 MHz (296 K). The corresponding quadrupole coupling constants, e 2 q Q/h, are 282.977±0.005 MHz (296 K), and 281.892±0.005 MHz (77 K). The asymmetry parameters η have been determined as 0.2372±0.0001 (296 K), and 0.2580±0.0001 (77 K). A small change of 0.4% for e 2 qQ/h is accompanied by a rather large change of 21% for η within the temperature range investigated. e 2 q Q/h=f(T) shows a maximum at ~ 313 K. No evidence of phase transition has been observed by NQR spectroscopy between 77 K and 398 K.

The present paper shows how to incorporate the correlation between successive nuclear jumps, which are well known to play a role in defect mechanisms of self-diffusion in crystals, into the calculation of the correlation functions describing the temperature dependence of the nuclear spin relaxation in solids. The treatment is based on an extension of Torrey’s theory of nuclear spin relaxation by randomly migrating nuclei. Explicit and detailed results are given for the monovacancy mechanisms of self-diffusion in an isotopically pure face-centred cubic crystal.

The rates of dipolar and Zeeman energy creation under detuned irradiation are measured as function of the distance to resonance in isolated spin systems and in systems with known coupling to the lattice. The experimental results are compared with the Provotorov theory and, with some restrictions for the long correlation time region, the agreement with theory is found to be excellent.

Th 1 H-NMR-spectra of benzene and benzene-1- 13 C in the isotropic phase (CCl 4 solution) as well as in the nematic phase of a liquid crystal are analysed and the resulting direct and indirect couplings presented. The comparison of observed direct couplings with values calculated from known Raman structural data shows deviations of up to 9% relative to the HH (orto) -coupling. This corresponds to an apparent increase of the carbon-proton distance of 0.03 A. Possible reasons are discussed such as anisotropy of the indirect couplings, solvent effects on indirect couplings and intramolecular vibrations. The conclusion is reached that the consideration of intramolecular vibrational motion perfectly explains the discrepancies.

Two complementary radicals in fluorene and carbazole single crystals, irradiated by UV-, γ- or X-rays, have been identified by investigation of the hyperfine structure of ESR-spectra. Species I is formed by dissociation of a hydrogen atom from position 9, whereas species II results from addition of a hydrogen atom to one of the benzene rings. In carbazole there is evidence of a third radical. The annealing kinetics of all these radicals have been proved to be of second order, requiring activation energies between 1 and 2.1 eV.

The rotational structures of the ν 1 and 2 ν 1 infrared bands of monofluoroacetylene were investigated. The values B 0 =0.32374±0.00005 cm -1 and 0.32372±0.00010 cm -1 , respectively, were obtained. In addition, the analysis of the fundamental gave α 1 = (6.85±0.15) × 10 -4 cm -1 and D 0 = (15±3) × 10 -8 cm -1 . Theoretically, the centrifugal disortion constant was computed to be 13 × 10 -8 cm -1 . The hot bands accompanying the fundamental were also studied.

The integrated intensity of the absorption band of carbon disulfide at about 316 nm has been measured in the gas phase and in sixteen solvents. It is found that the absorption intensity rises steeply with the refractive index of the solvent, whereas the wavenumbers of the absorption maxima exhibit a small red shift. Both results are explained, according to Liptay’s theory of solvatochromism, as due to dispersion interactions.

Für die Emissionsanisotropie der Photolumineszenz als Funktion der Konzentration wird ein Ausdruck angegeben, der sowohl die Depolarisation als auch die bei hohen Konzentrationen auftretende Repolarisation beschreibt. Remigration und Konzentrationslöschung sind dabei berücksichtigt. Ein Vergleich mit experimentellen Messungen der Konzentrationsdepolarisation am Rhodamin 6G in Wasser-Glyzerin-Lösungen ergibt eine gute Übereinstimmung im ganzen Konzentrationsbereich.

The dark conductivity of annealed silver bromide single crystals, containing trace amounts of silver sulfide, has been measured as a function of dopant concentration. At 21 °C the conductivity exhibited a more rapid than linear increase with silver sulfide concentration at levels below 8 ppm. At 4 ppm, the lowest level achieved, a limiting dependence of the conductivity upon the fourth pwoer of the dopant concentration was observed. The room temeprature conductivity of the annealed samples became constant at dopant levels above 10 ppm. The dark conductivity of these samples, measured at 21°C after exposure to light at room temperature, dropped by more than an order of magnitude to constant levels typical of undoped silver bromide in the extrinsic range. This negative photoeffect could be largely reversed upon subsequent annealing. These results imply the formation of electrically active complexes incorporating several (~ 4) sulphur ions. The observed negative photoeffect is attributed to the photoreduction of interstitial silver ions to free silver. The relevance of the results to the photographic process is discussed.

Auf Grund der verschiedensten Eigenschaften wird eine Klassifizierung von einer Auswahl einatomiger Flüssigkeiten vorgenommen. Es werden die Alkalimetalle, die Edelgase und die Stoffe Cu, Ag, Au, Pb, Ni und Co zu je einer Gruppe zusammengefaßt. Magnesium wird als einziger Vertreter einer vierten Gruppe zugeordnet. Mit Hilfe der Theorie des Parakristalles konnten die radialen Atomverteilungskurven mit dieser Auswahl von Flüssigkeiten kurz oberhalb ihres Schmelzpunktes berechnet werden. Der Gittertyp, der für diese Berechnung benötigt wird, ist für die Alkalimetalle das kubisch raumzentrierte Gitter, für Magnesium die hexagonal dichteste Packung mit Stapelfehlern und für die anderen Stoffe die kubisch dichteste Packung mit Stapelfehlern.

The method of tantalum-tungsten shadowing has been applied to investigate the initial stages of nucleation and growth of evaporated gold films on sodium chloride cleavage planes. It was found that the observed density of particles at “saturation” (N 3 ) is proportional to exp (+α/T) where the constant α has two different values for the temperature ranges below and above about 298°K. Two possible interpretations of the occurrence of two activation energies are discussed: the effect of point defects on the surface and the influence of re-evaporation.

Concentration Dependence of the Thermal Transport of Nitrogen in Tantalum In a temperature gradient nitrogen atoms migrate to the hot region. The heat of transport is negativ and depends on the concentration. If the concentration of the dissolved atoms is higher than 1 at.-%, its value is about -1 kcal/mol, however it increases to -7 kcal/mol for an infinitely dilute solution. This value seems to be more convenient for a comparison with data of other systems and theoretical considerations.

Within the scope of a moment method collision integrals of the Boltzmann type are formulated and evaluated for the different excited particle states of a stationary monatomic plasma macroscopically at rest. All collision and radiative processes except the three body recombination are considered. The calculations are performed within Grad’s 8-moment approximation of the momentum distribution functions of the material particle components. Assuming axial symmetry of the differential collision cross sections the evaluation leads to linear functions of generalized Chapman-Cowling integrals for binary inelastic particle interactions and to Einstein and photoionization coefficients for the radiative processes. Simplifications are given in special and limiting cases.

Emission having a large time constant has been measured recently in the decay period of plasmas produced in nitrogen and helium-nitrogen mixtures. Whereas the fast decaying emission during the early afterglow originates from the plasma volume, it was suspected that emission responsible for the large time constant (10 to 15 ms) was not due to emission processes involving nitrogen. The present studies relate to detailed measurements of this phenomenon in a decaying helium plasma produced in a Kovarglass built discharge tube. It will be shown that this slow decaying emission is due to phosphorescence of the walls of the glass tube.

The non-thermal plasma in a helium hollow cathode discharge is analysed by means of experiments and theory. The population densities of excited levels are calculated by a system of equations, including the different processes which occur in the plasma. A detailed examination of the mechanism of exitation and deexcitation follows. From this, a refined method is developed for the determination of the electron temperature by the intensity of a helium line.

Nonlinear interaction of longitudinal plasma waves in two-fluid plasma exciting the solar type II burst emission is investigated. The interaction of ion and electron waves yields radiation at the fundamental plasma frequency, while emission at twice the plasma frequency is caused by self-interaction of the electron waves. Equal flux intensity results in both the radiation bands if the variation of electron density associated with the two wave modes is of the same order of magnitude.

Measurements by an ultrasonic resonance method in the frequency range from 0.8 to 26 MHz are reported. The resonators consist of an X-cut quartz with disc shaped samples from polycrystalline nickel, cemented on both sides of the quartz. The resonance spectrum of a quartz is analysed first. From the resonances of the composite system different sound velocities are derived allowing for the interpretation of the vibrations.

The magnetic Senftleben-Beenakker effect of the viscosity is mainly determined by two collision integrals of the linearized quantum mechanical Waldmann-Snider collision term, viz. by the relaxation coefficient of the tensor polarization of the molecular rotational angular momenta and by the coefficient which couples the friction pressure tensor and the tensor polarization. Starting from a simple nonspherical potential for HD, the scattering amplitude is evaluated analytically in first order distorted wave Born approximation and the two collision integrals are calculated for room temperature. A fairly good agreement with experimental values is found.

We have produced the new nuclide 35 P by the reaction 37 Cl (y,2p) 35 P and have measured a half-life of 45±2 s and a y-ray with an energy of 1571.8±0.2 keV.

Some properties of the positive column in a low-pressure discharge in nitrogen were investigated. A form of constricted column at low pressure was observed without the presence of negative ions.