Volume 43, Issue 7

The rotational spectrum of gas phase HSSSH has been recorded for the first time in absorption with the Cologne free-space-cell millimeterwave spectrometer. In the frequency region between 80 and 300 GHz a prominent series of Q-branches has been observed and assigned. The hitherto identified rotational lines unambigously arise from a perpendicular-type spectrum. In addition, successive J lines of the compact Q-branches show no indication of the easily detectable intensity alternation which arises when the molecule possesses an axis of symmetry due to nuclear spin statistical weights. Therefore the geometrical structure of the molecule does not have a C 2 axis of symmetry. The present data are not complete enough for a unique structure determination. However on the basis of the present data we can definitely rule out conformations with C 2 or C 2v symmetry to be responsible for the strongest observed transitions of the spectrum. The molecule is not floppy as predicted from semi empirical MO calculations. On the contrary the conformation observed is rather rigidly locked into one position with no sign of possible internal rotation. We consider a sulfur triangle with the two hydrogen atoms sticking out symmetrically to the same side of the SSS-plane to be the most likely structure.

The CNDO/2 CI method was used for the examination of 1,4-dioxane and 1,4-dioxane-water complexes (2:1), taking into account various conformations of the dioxane molecule. The energies of the molecules in the ground and excited states, the energies of hydrogen bond formation, the dipole moments, the transition moments, and the oscillator strengths for both the complexed and isolated 1,4-dioxane molecules were evaluated. The results of these studies are used to reveal the influence of water on the features of energy transfer from excited, by y-radiation, 1,4-dioxane or dioxane-water complexes to the luminophor.

The article deals with the influence of reversible excitation energy transfer on the fluorescence decay in systems with random distribution of molecules. On the basis of a hopping model, we have obtained an expression for the Laplace transform of the decay function and an expression for the average decay time. The case of dipole-dipole interaction is discussed in detail.

ESR experiments aiming at clarifying the structure of radicals present in X-irradiated crystals of ethylene glycol and other diols are reported. By comparison with data for the corresponding glasses it is concluded that a major source of free radicals is the decomposition of trapped electrons. The radical structure is identified.

For molten (Li, Na, K)Cl of the eutectic composition (53.5-8.6-37.9 mol%), in the temperature range from 773 K to 973 K the relative differences in the internal cation mobilities have been measured by the Klemm method, and the conductivity by a direct current method. From these data and the molar volumes, evaluated from those of the pure salts on the assumption of additivity, internal mobilities of the cations, b Li , b Na and b K , have been calculated. Below ca. 873 Kt b Li < b K < b Na , and above bu b Li < b Na < b K . These orders are interpreted in terms of the potential profiles for cations located between two Cl - ions. b Li and b K in the present ternary system can be fairly well expressed by function of the number density of Cl - ions presented previously for the binary system (Li, K)Cl.

The electric field gradient (EFG) at the chlorine site is calculated for cubic compounds of the K 2 PtCl 6 -type (space group Fm3m), M 2 I M IV Cl 6 , where M 1 is an alkali metal and Me IV a tetravalent element. In the calculations the total EFG is subdivided into the contribution of the complex [M IV Cl 6 ] 2- , EFG complex , and the contribution of the ions outside the complex, EFG lattice . EFG complex is calculated by the local electron density formalism using the MS-Xα-method, and EFG lattice is determined by the point charge model. It is found that EFG complex is positive whereas EFG lattice is negative. Including antishielding effects, the magnitude of EFG lattice is about one fourth of EFG complex . The trends in the EFG for the various compounds found theoretically are the same as the trends in the experimental nuclear quadrupole coupling constants e 2 Q q/h. However, the absolute values of EFG theo are smaller than the values EFG exp deduced from e 2 Q q/h. For a fixed central atom M IV the (positive) EFG exp is increasing with increasing radii of the cations (and increasing lattice constant). This increase can be understood by an increase of EFG lattice . On the other hand, for fixed cations and different tetravalent metal atoms, the EFG is increasing with increasing electronegativity of the central atom. This can be understood by an increase of EFG complex . For distorted octahedra it is found that the change in the EFG due to the distortion is also due to a change in EFG complex .

The 14 N quadrupole coupling tensor in CH 2 FCN and CD 2 FCN was determined from the hyperfine splittings of low J rotational transitions to give indirect structural information on the geometry of the CCN chain. The CCN chain turns out to be slightly bent (2° away from F), in excellent agreement with the result of an earlier ab initio calculation.

We redetermined the rotational and the chlorine-35 and nitrogen-14 nuclear quadrupole coupling constants of 3-chloropyridine. The values are A = 5839.5330(12) MHz, B = 1604.1875(6) MHz, and C = 1258.3121 (5) MHz for the rotational constants, and χ aa (Cl) = - 72.255(19) MHz, χ bb (Cl) = + 38.500(13) MHz, χ cc (Cl) = + 33.755(23) MHz and χ aa (N) = - 0.009(13) MHz, χ bb (N) = - 3.473(10) MHz, χ CC (N) = + 3.482(16) MHz for the chlorine-35 and nitrogen-14 nuclear quadrupole coupling constants, respectively. Application of double resonance modulation technique is shown to greatly simplify the assign­ment of hyperfine structure components even of weak rotational transitions.

General expressions are derived for the anisotropy of the viscosity and for the Leslie coefficients governing the flow alignment subject to the assumption that the equipotential surfaces for the interaction of oriented nonspherical molecules in the nematic or nematic discotic phase of a liquid crystal are related to a spherical interaction potential by an affine transformation. In particular, for uniaxial particles, the seven independent viscosity coefficients of a nematic are given in terms of the two viscosity coefficients of a reference fluid of spherical particles and the axes ratio of the nonsphe­rical molecules. The theory is compared with results from nonequilibrium molecular dynamics computer simulations and with experimental data.

We present an explicit construction of minimal deterministic automata which accept the languages of L-R symbolic sequences of unimodal maps resp. arbitrarily close approximations thereof. They are used to study a recently introduced complexity measure of this language which we conjecture to be a new invariant under diffeomorphisms. On each graph corresponding to such an automaton, the evolution is a topological Markov chain which does not seem to correspond to a partition of the interval into a countable number of intervals.

The Julia set of Ramanujan's iterated exponential map, F r+1 (z) = exp {F r (z)} -1, is investigated for positive integral r. Connection with Devaney's work on the map z r+1 = λ exp[z r ] is also made.

A set of fully symmetric maxwellian equations is proposed, with a quantum mechanical coupling term between matter and fields. Its relativistic transformation properties and conservation laws are presented. Dual, monopole-like solutions are described, which have properties consistent with those of the Dirac electron and magnetic monopole. The spatial extent of the monopole fields is proposed to be bound within two extreme radial limits r p and R 0 such that α In (R 0 /r p ) ≡ 1, where α ≃ 1/137 is the electromagnetic fine structure constant, yielding for the ratio R 0 /r p a very large number in the order of the ratio of the so-called universe radius to the Planck length.

Self-diffusion in the isotropic and twisted nematic phases of mesogenic substances has been studied by means of 1 H- and 13 C-NMR. From the line shape analysis of the recorded 13 C-NMR spectra we obtained the diffussion coefficient D ⊥ along the helical pitch. Various concentrations of a chiral additive changed the pitch P 0 of a nematic mixture of phenyl-benzoates from 4.7 μm to 7.8 μm. The measured values of D ⊥ were in the range from 2.4 · 10 -12 m 2 s -1 to 1.9 · 10 -11 m 2 s -1 We found an Arrhenius behaviour with an activation energy of about 55 kJ/mole nearly independent of the pitch. The obtained data for D ⊥ seem to have a lower than quadratic dependence on P 0 .

The previous report on enumeration and classification of benzenoids and coronoids is supplemented. Perhaps the most significant contribution is the enumeration of benzenoids with 12 hexagons.

The Maxwell theory is related to the Dirac theory by two heuristic arguments based on electromagnetic spinors. First, given the condition to have spinors, if the free field Maxwell's equations are satisfied, then the spinors satisfy the Weyl equations. Second, a sufficient condition for electromagnetic spinors directly gives the Weyl equations with the usual substitutions for momentum and energy. It is proposed that the heuristic nature of the first argument is related to the idea of a point having a more general symmetry than a sphere.