Band 28, Heft 1

The charge density distribution in the strongest Bloch waves for a dynamical many-beam diffraction situation was calculated for electrons and positrons. Near the [110] zone axis of MgO there exist three strong Bloch waves for electrons. One Bloch wave is concentrated at the rows of Mg-atoms, a second at the rows of O-atoms and a third one between the atoms. The positron Bloch waves are mainly concentrated between the atom rows and have only small charge density at the positions of the atoms. For an incident beam parallel to the [110] axis there exists only one strong positron Bloch wave while for electrons more than three Bloch waves are strong, explaining the channeling behaviour of positrons and electrons. Strong partial waves of different electron Bloch waves can be identified in the diffraction pattern from a MgO crystal wedge.

It is shown that the admixture of a D-state in the wave function for the relative motion of the s-particle and the deuteron in the nucleus 6 Li leads to M1 transitions. Their mixture with E2 transitions does not lead to an asymmetry of the differential cross section of the reaction 6 Li(γ, 2 H) 4 He about 90°, and they are negligibly small.

The following problem is investigated: How large must an ideal Bose-system be to allow for the approximation of the finite system free energy by the thermodynamic limit. The obvious condition that the energy separations between the single-particle states must be small compared to kT is necessary but is not sufficient near the critical concentration. Instead, for this case additional stronger conditions apply due to the singularity of the thermodynamic free energy at the critical point which is caused by contributions of the lowest-energy single-particle states. These conditions are derived and the relevancy of the results is emphasized for a generalized theory of metastability in co-operative systems.

In a single step process the H 2 O molecule is dissociated into excited atoms or ions. The radiation of these particles - H*, O I and O II - is investigated by means of VUV spectroscopy. The excitation functions of the various lines show a pronounced structure. An attempt is made to explain these structures by different excitation processes.

The pure rotational and the rotation-vibrational Raman spectrum of gaseous F 2 at a pressure of 2 atm were photoelectrical^ recorded. The vibrational transitions 0→1, 1→2 and 0→2 were observed. The analysis of the spectra yields the molecular constants ⊿G 1/2 = (893,5 ± 1,5) cm -1 , ω e x e = OM ± 1) cm -1 , B 0 = (0,8847 ± 0,0010) cm -1 , B 1 = (0,872 ± 0,002) cm -1 . D 0 = (0,49 ± 0,10) · 10 -5 cm -1 ,

The 60 MHz proton magnetic resonance spectra of 2-(3,4-dichlorophenyl)oxetane and 2-(2,4-dichlorophenyl)oxetane in 10 mole per cent CCl 4 solution have been analyzed using the sub-spectral method. The proton chemical shifts and the proton-proton couplings have been determined. Some aspects concerning the effects of the 3- and 2-chlorines in the phenyl ring on the magnetic parameters have been put foward. The proton-proton couplings 4 J 0 and 5 J m from the benzyl proton to the ortho and meta protons in-the phenyl ring, respectively, were found to be opposite in sign. Comparing the absolute values of these couplings, it was concluded that the rotation around the Ph-C bond between the phenyl and oxetane rings is more hindered in 2-(2,4-dichlorophenyl)oxetane than in 2-(3,4-dichlorophenyl)oxetane.

Contrary to the MISES' theory, the effort of materials under load is discussed in this paper on the base of the elastic potential. This leads to the elastic strain energy theory due to BELTRAMI. This theory is only true for the elastic case. For υ = 1/2 we obtain the MISES' theory, and by changing υ to υ ep it is possible to enlarge the elastic strain energy theory to the elastic-plastic deformation. υ ep is the ratio between transverse and longitudinal elastic-plastic strain, and υ is the POISSON's ratio.

The earlier observation of delayed fluorescence in mixed crystals of aromatic hydrocarbons in benzophenone is studiedby time-resolved spectroscopy using methyl-coronene, pentaphene, anthanthrene and 1.8.9-peri-naphto-xanthene besides naphthalene as guests. Host-guest triplet annihilation is identified as the mechanism of delayed fluorescence. Naphthalene as an additional guest component acts as trap for the triplet excitation of the host and further increases the delay of fluorescence emission.

The self-diffusion coefficients of the constituent cations in the systems (Ag-Na)NO 3 and (Ag-K)NO 3 have been investigated by the "diffusion-into-the capillary" method at three concentrations (x Ag NO 3 = 0.25; 0.50; 0.75) and at temperatures ranging from 250 to 400°. A temperature dependence given by the Arrhenius equation and an almost linear variation with composition were observed. The correlation existing between the ionic size of diffusing cations and the diffusion coefficients in these melts is discussed.

The possible effect of a cosmological background (such as proton - neutron preponderance) on the meaning of time"reversal violation is discussed in the context of the Dürr - Heisenberg degenerate vacuum theory of strangeness.

The dependence of the field ionization behaviour of olefines on field-induced surface reactions is demonstrated using 1-Hexene as an example. Different emitter- and field strength dependent reaction mechanisms leading to the production of (M+1) + and (M-1) + ions may be distinguished. The characteristics of define spectra taken using activated emitters are determined largely by surface induced reactions which appear at higher field strengths. These have as their starting point an ionic field adsorption of the olefine. In particular the field enhancement of the organic microneedles is strongly influenced by field adsorbed ions so that field dissociation products are also measured with increased intensity.

In continuation of earlier works (temperature range 400 - 77 K) the temperature and frequency dependencies of the longitudinal relaxation time T 1 in different methyl naphthalene crystals were measured down to 4,2 K at 22 and 56 MHz. The observation of two minima in some cases below 50 K could be attributed quantitatively to the weakly hindered β-CH 3 groups (E A <0,8 kcal/mole) by comparison of the results of similar methyl naphthalenes. The low relaxation rate in the minima is due to tunneling effects of the methyl groups. The splitting of the lowest torsional niveau could be roughly determined.

The microwave investigation of propargyl mercaptan has been continued to study the internal rotation of the SH group in the molecule. A Hamiltonian is proposed to describe the over-all rotation and the torsion of the top. The analysis leads to the result that the potential function is a double minimum potential with a lower barrier of 470 ± 10 cm -1 at the eis position and a higher barrier of 2000 ± 500 cm -1 at the trans position.

The dielectric absorption of dilute solutions of chlorocyclohexane, cyclohexylamine, dicyclohexylamine, diphenylamine, N-methyldiphenylamine, and triphenylamine in various solvents has been measured between 0.3 and 135 GHz. The measurements have been carried out at 20 °C and for some solutions also at -30 and 60 °C. The previous measurements made for the compounds have been extended to higher frequencies and improved by a greater number of frequencies. The loss curves have been resolved into multiple absorption regions. A rather much contributing far infrared (FIR) term was necessary to be involved in each analysis. The intramolecular dipole reorientation process in cyclohexylamine is considerably slower than in aniline because of the lack of the mesomeric interaction. In dicyclohexylamine only the overall relaxation was observed at microwave frequencies. Two large regions were resolved for N-methyldiphenylamine at microwave frequencies whilst in diphenylamine the second region likely contributes to the very large FIR region. Evidences for weak association between diphenylamine and the aromatic solvents were obtained.

Polarized absorption spectra of technetium(IV) and rhenium(IV) in trigonal single crystals of (C 2 H 5 NH 3 ) 2 [SnCl 6 ] and (C 2 H 5 NH 3 ) 2 [SnBr 6 ] have been measured in the range of 8000 to 2800 Å at 298 and 77 °K. The crystal point group is D 3d and the metal ions occupy sites of D 3d -symmetry too. The observed excited levels arise from both π 24 d 3 and π 23 d 4 configurations; the different temperature and polarisation dependence of d → d intra-shell and π → d metal reduction transitions is discussed. Experimental values of the parameters Dq (cubic) and υ (trigonal) are reported. The nephelauxetic ratio β 55 is evaluated from the 4 A 2g → 2 T 2g intrasubshell transitions. The electron transfer spectra suggest the optical electronegativity x opt = 2.3 for Tc(IV) and x opt = 2.1 for Re(IV).

A description of the apparatus for a new dynamic polarization effect by variation of temperature, and the experimental results obtained, are presented. As described earlier a temperature jump produces a very large enhancement of the dipolar signal (about 10.000) in solid y-picolene due to the dipolar couplings between the protons of the CH 3 -group and the modes of the CH 3 -rotator with the crystal phonons. A simple phenomenological model for the interpretation of the experimental data is introduced. Within the experimental errors agreement between model and data is obtained. From the shape of the measured polarization curves a dipolar polarization time T p and the dipolar relaxation time T d is determined. From the maxima of the polarization at different temperature jumps a curve dependent only on the temperature is constructed, which together with T p and T d characterizes completely the dynamic polarization behaviour. A comparison of the Zeeman- and dipolar relaxation with earlier measurements on similar molecules containing CH 3 -groups shows that the CH 3 -rotation in solid y-picolene is almost unhindered and that the "relaxation efficiency" is very low. These last conditions are important for a large enhancement of the dipolar polarization.

For shock waves produced by special wire explosions the short time energy input condition of the theories of Lin, Sakurai and Vlases-Jones is fairly good fulfilled. In these cases the shock wave energies can be easily determined from the expansion velocity of the waves. Variation of the parameters of the discharge circuit show, how these parameters should be chosen in order to get a maximum transfer of energy either to the shock waves or to the wire material.

On concentrating liquid solutions of pyrene-3-aldehyde a fluorescence of long wave length appears with increasing intensity. It reminds of the excimer fluorescence of pyrene but behaves differently in some respects. It shows a distinct dependence on solvent and excitation wave length: Whereas it may be observed with high intensity in an unpolar solvent such as n-heptane, it is completely suppressed in the strongly polar acetic acid. When it is excited in the weak long wave length part of the first absorption band, the quantum yield is higher than with excitation at shorter wave lengths. In hydrogen free liquid solvents the fluorescence also could be detected as a delayed emission. It is assumed that weakly bound dimers are present already in the ground state of the aldehyde, these being directly excited to the excimer state.

The diffusivities of 42 K in Na and of 24 Na in K have been measured between 100 ° and 285 °C, utilizing an „infinite capillary" technique. The results are adequately described by the Arrhenius relations (in cm 2 /s) D K in Na = 0.46 · 10 -3 exp (-1.82/RT) and D Na in K = 0.93 · 10 -3 exp (-2.11/RT). The differences ΔQ in effective activation energies between impurity diffusion and self-diffusion are about -0.4 kcal/mole for Na and +0.1 kcal/mole for K. This can be satisfactorily explained by electrostatic screening arguments. The impurity diffuses slower than the host atoms in Na, faster in K.

With a multi-nuclei Fourier transform NMR spectrometer the ratio of the Larmorfrequencies of 95 Mo and 97 Mo in a solution of K 2 MoO 4 in H 2 O has been measured with high accuracy. Using hyperfine interaction constants from literature, we have calculated the hyperfine structure anomaly 95 ⊿ 97 = -0.0102(14)% of molybdenum in the atomic ground state 4 d 5 5s 7 S 3 .