Band 43, Heft 10

A continuum-mechanical formalism is presented for the phenomenological description of moving, curvilinear, material surfaces in electric fields in interaction with volume-phases. In addition to conventional equations (balance and constitutive laws) the explicit use of relations for the surface geometry is introduced. A method to establish nonlinear constitutive equations by tensorial and thermodynamical considerations is proved to be applicable to two-dimensional continua. The resulting equations for boundaries interacting with adjacent volumes are of practical importance for the selfconsistent calculation of boundary values. The physical meaning of the different relations is discussed.

We have computed the concentration fluctuations, S cc (0), in a binary mixture of hard spheres on the basis of the Percus-Yevick compressibility (PYC), Percus-Yevick virial (PYV) and Mansoori- Carnahan-Starling (MCS) equations of state. We have also used the Flory-Huggins (FH) model for an athermal solution as a first approximation to the hard sphere description. At fluid packing fraction values, the PYC and MCS theories give similar S cc (0) results, whereas the differences between these and those derived from the PYV equation are more significant. The FH model appears to give rather bad results, which is consistent with the studies of other authors on the entropy of mixing of a binary mixture of hard spheres. The impossibility of a fluid-fluid phase transition in this kind of system is clearly shown by the behaviour of S cc (0) in any of the theories studied.

The electronic structure of mixed methylene dihalides CH 2 XY (X, Y = F, Cl, Br. I) has been studied using extended Fenske-Hall LCAO MO method. The comparison with available photoelec­tron spectra confirmes previous assignments of all bands with binding energies <100 eV. The electronic structure changes occurring upon varying the halogen substituents are discussed.

Mossbauer spectroscopy results on bulk iron pentacarbonyl Fe(CO) 5 and as adsorbate on (0001) graphite display a sharp transition at ~ 110K. related to intramolecular hindered rotations of CO-ligands, with no associated structural changes. The hysteresis in the temperature dependence of the quadrupole splitting and the abrupt change in the spectral intensity suggest a cooperative first-order phase transition.

The Lorentz transformations between the space-time coordinates of a point in two inertial frames with arbitrary relative velocity, are reformulated as Galilei transformations with length and time contractions, by introducing the ether rest frame (in which light signals propagate isotropically with the vacuum speed of light). The generalized Galilei transformations for the (longitudinal) space coordinates (x 1 , 2 ) and the time variables (t 1,2 ) of a point in two inertial frames ∑ 1,2 are not only of analogous structure, but have remarkable symmetry properties, too. The appearing length and time contractions are absolute effects in the sense of Lorentz-Fitzgerald, i.e., a rod has its largest length and a clock its fastest rate when at rest in the ether frame ∑ 0 . Thus, an analytical reformulation and a physical interpretation of the Lorentz transformations within Galilean relativity physics is achieved.

If we assume that the integrity of an elastic solid is governed by exchanges of real and virtual photons, the solid becomes a seat of innumerable interconnected microscopic Kennedy-Thorndike experiments. The null result of that experiment leads to a deformation criterion having the Lorentz- Fitzgerald contraction as a special case. For a spinning disc the criterion, combined with an equation of compatibility, gives radial and tangential deformations which resolve the Ehrenfest paradox.

The 35 Cl NQR spectra of 2,4,4,6-tetrachloro-3,5-dimethyl-cyclohexadiene-2,5-one-l and 2,4,4,6- tetrachloro-cyclohexadiene-2,5-one-l were studied from 77 K up to the decomposition temperature, their crystal structure having been determined by single crystal X-ray diffraction. The first com­pound crystallizes in the monoclinic space group C 2 2h -P2 1 /m with two molecules in the unit cell. The lattice constants are a = 887.2 (3) pm, b = 704.8 (3) pm, c = 824.0 (3) pm, β = 96.10(1)°. The sec­ond compound crystallizes orthorhombic, space group D 18 2h - Cmca, with 8 molecules in the unit cell which has the dimensions a = 711.2(2) pm, b = 1388.4(3) pm, c = 1729.8(4) pm. The structures deter­mined belong to the stable phases of the title compounds as seen from the NQR spectra as a function of temperature which show no sign for a phase transition between the melting point and 77 K. In both title compounds the molecules are planar. Their symmetry is compared with other chloro- cyclohexadiene-2,5-ones-1 and chloro-cyclohexadiene-2,5-diones-1.4. The intramolecular distances d (C-Cl) of the sp 2 carbon atoms and the 35 Cl NQR frequencies assigned to the corresponding Cl atoms correlate quite well according to the theory: ν( 35 Cl) ~ (d (c-cl) ) -3 The relation is ν( 35 Cl)/MHz = 2 + 174 · 10 6 -(d/pm) -3 .

X-ray measurements on disubstituted biphenylcyclohexanc BCH 52 show a crystalline smectic B phase with an ABCA layer stacking in bulk samples when cooled from the nematic to the smectic phase. No temperature dependence of this stacking can be seen. When cooling freely suspended thin films (below 20 μm) from the nematic to the smectic B phase, the obtained X-ray reflexes indicate an arrangement of the molecules in an orthorhombic F like stacking.

Benzenoid systems and their ⊿ values are studied. Here ⊿ is the absolute magnitude of the difference between the numbers of black and white vertices. The systems with maximum ⊿ at a given h (number of hexagons) are treated in particular. TP benzenoids are defined as consisting of fused triangulenes and phenalenes only. All benzenoids with ⊿ = ⊿ max = 1,2,3,... for h = 3,6,9,..., re­spectively, are TP benzenoids. By means of a computer program all benzenoid systems with ⊿ = h/3 up to h = 15 are generated. In conclusion, a number of supplementary data to the enumerations of benzenoids are reported.

2 H-NMR powder spectra of tunneling ammonium-d 4 ions are computed. A representation of the tunneling Hamiltonian is worked out in the basis of simple product spin wavefunctions. Secular parts of quadrupole and dipole Hamiltonians are taken into account. Examples of spectra are given for tunneling about one C 2 or C 3 axis, as well as for overall rotations in potentials of higher symmetry. Ranges of tunneling frequencies measurable from the spectra are given for each case. Characteristic shapes of the spectra allow recognition of various ground torsional level structures. Possible further applications and available data are discussed.