Band 46, Heft 12

We give experimental evidence that self-organized criticality takes place during the formation of low-temperature semiconductor breakdown. Quantitative evaluation of the characteristic scaling properties together with the appropriate parameter ranges of validity further support the applicability of the model conjectured

Spontaneous oscillations developing during low-temperature impact ionization breakdown in extrinsic germanium are looked at with respect to characteristic features of type-I intermittency

Sputtered amorphous Fe-Co Tb-films with perpendicular and in-plane magnetic anisotropy were investigated by wide- and small angle neutron scattering. By combination with X-ray data the maxima in the pair correlation function could be attributed to the individual atomic pairs. Thus also partial coordination numbers and a short range order parameter could be determined. Wide angle diffraction revealed that the film with magnetic in-plane anisotropy contained 13 atomic percent hydrogen. The hydrogen incorporation causes substantial changes in the short range order, associated with enhanced formation of Tb-rich clusters, and the in-plane anisotropy. The clustering effect was confirmed by results from small angle scattering with polarized neutrons

The energetic requirement and mechanisms for CHO' loss from the molecular ions of isomeric C 7 H 8 O precursors have been reported. The heat of formation of [C 6 H 7 ] + (protonated benzene) was determined and ε* evaluated. Measurement of the kinetic energy release T B gives the energy-partitioning quotients q= TB/ε r * which range from 0.38 to 0.99. The energy available and T B are small for the strongly endothermic reaction of benzyl alcohol but increase sharply in the case of the weakly endothermic reaction of anisole. All reactions have "late" transition states, the position X 0 *of the transition state on the reaction coordinate varying from 0.64 to 0.93

This paper aims to examine if the classical tests of General Relativity (GR) can be predicted by a simpler approach based on minimal changes in the Newtonian gravity. The approach yields a precession of the perihelion of Mercury by an amount 39.4"/century which is very close to the observed Dicke-Goldenberg value (39.6"/century), but less than the popularly accepted value (43"/ century). The other tests exactly coincide with those of GR. Our analysis also displays the genesis as well as the role of geometry in the description of gravitational processes. The time dependent spherically symmetric equations, which are mathematically interesting, call for a further study. The model also allows unambiguous formulation of conservation laws. On the whole, the paper illustrates the limited extent to which a second rank tensor analogy (nonlinear) with flat background Faraday-Maxwell electrodynamics can be pushed in describing gravitation

A dyadic procedure is given for the planewave scattering response of an electrically small, bianisotropic sphere moving with a constant velocity in free space. Lorentz transformations and the polarizability dyadics of a stationary bianisotropic sphere are used in this procedure

Mean transit times in heavy-ion collisions are calculated as functions of the relativistic incident energy and the impact parameter. As a consequence of special relativity, they become constant in a central collision of O with Pb at T~0.15TeV. Together with a geometrical estimate of the maximum energy densities in the interaction region, it is argued that heavy ions in a large hadron collider may produce a quark-gluon plasma due to the plateau in the transit times at ultra-relativistic energies

Deactivation of three co-substituted acceptors in 4-dimethylamino-trans-styrenes (P(S)Ph 2 (la), P(0)Ph 2 (2a) and SO 2 CH 3 (3a)), dissolved in «-paraffins (from n = 5 to n = 16) at 293 K, was investigated. Trans-cis isomerization and intersystem crossing are the main processes responsible for radiationless deactivation of the S 1 excited state. High fluorescence anisotropy, r, observed in low-viscous «-paraffins, is due to strong fluorescence quenching resulting in the considerable shortening of the lifetime τ of these molecules. The fluorescence depolarization which occurs when lowering the viscosity, η, of the solution is caused by Brownian rotations and conformational changes due to fast adiabatic twisting of the planar trans-S 1 form around the double bond, leading to the formation of the perp.-S 1 structure with perpendicularly oriented parts of the molecule, and to the concomitant change in the transition moment direction. Linear dependence of τ 2 {r 0 /r - 1) on η - τ in the whole viscosity range was only observed for molecule 3a

The rotational Zeeman effect of H 2 F 12 C 12 C 14 N was observed at fields up to 20 kG (2 Tesla). The observed vibronic ground state expectation values for the molecular ^-values, the magnetic susceptibility anisotropies and the molecular electric quadrupole moments, all referred to the molecular principal inertia axes system, are: g aa = -0.03572 (11), g bb = -0.03438 (7), g cc = -0.03988 (6). 2ξ aa - ξ bb - ξ cc = - 14.58 (10) • 10 -6 erg/(G 2 mole), 2ξ aa - ξ bb - ξ cc = 1.60 (11) • 10 -6 erg/(G2 mole), Qaa= -9.13 (6) DÅ, Q bb = 4M (7) DÅ, and Q cc = 4.96 (9) DÅ, respectively. The latter are in close agreement with the results of a restricted Hartree Fock self consistent field calculation with a basis of TZVP quality, which was carried out at the partial restructure determined earlier. Therefore the RHF/TZVP-value for the second electronic moment perpendicular to the heavy atom plane, <0|Σ c 2 c |0) RHF , was used as additional input to predict the molecular bulk susceptibility and the individual components of the magnetic susceptibility tensor

The electrical conductivities (x's) of molten LaCl 3 -NaCl, LaCl 3 -KCl, and LaCl 3 -CaCl 2 were measured at 893-1168 K, by a conventional ac technique and fitted by quadratic functions of temperature. They increase with increasing temperature and decrease with increasing mole fraction of LaCl 3 . The equivalent conductivities (A's) follow a linear relationship of In A vs. 1/T The A's of LaCl 3 -NaCl and LaCl 3 -KCl decrease drastically with increasing LaCl 3 concentration. A of molten LaCl 3 is smaller than that of molten CaCl 2 , in which the octahedral complex anion CaCl 4- 6 is known to exist. It seems reasonable to assume that complex ions or cluster species such as LaCl 3 6 - and La2Cl 3 exist in molten LaCl 3 and its mixture melts. Similar results, reported in a previous paper, were obtained for PrCl 3 -NaCl, PrCl 3 -KCl, and PrCl 3 -CaCl 2

The boron and the nitrogen hyperfine structure in the rotational spectra of two borane monoammoniate isotopomers, 11 BH 3 NH 3 and 11 BH 3 ND 3 have been investigated and the quadrupole coupling constants of boron and nitrogen have been determined. It was also possible to determine the spin rotation constants CN of boron. In the spectrum of 11 BH 3 NH 3 we observed additional splittings which are not caused by quadrupole coupling. In the spectra of the ammonia dimer, (NH3)2, to our opinion the same kind of splittings occur. As interpretation of this phenomenon it was proposed that two different vibrational states cause the splitting. They were called ■x and ß. We use the same model for 11 BH 3 NH 3 . The deuterated isotopomer 11 BH 3 ND 3 shows the normal spectrum of a symmetric top with two coupling nuclei, similar to the deuterated ammonia dimer (ND3)2. We obtained the following results: 11 BH 3 ND 3 in the x vibrational state, l/2(B + C) = 17517.21399(48) MHz, eQq aa ( 11 B) - 2.584 (10) MHz, eQ g aa ( 14 N) = -2.135 (5) MHz, C N ( 11 B) = 4.59 (87) kHz, 11 BH 3 NH 3 in the ß vibrational state, 1/2(B + C) - 17517.27706 (52) MHz, eQq aa ( 11 B) = 2.583 (8) MHz, eQq aa ( 14 N) = -2.132 (5) MHz, C N ( 11 B) = 4.76 (99) kHz, and 11 BH 3 ND 3 , 1/2 (B + C) = 15076.79992 (41) MHz, eQq aa ( 11 B) = 2.550 (7) MHz, eQq aa ( 14 N) = -2.169 (4)"MHz, C N ( 11 B) = 3.42 (67) kHz

The 79-81 Br NQR spectra of tribromocadmates with the cations K ⊕ , NH 4 ⊕ , Rb ⊕ , Cs ⊕ , CH 3 NH 3 ⊕ , (CH 3 ) 2 NH 2 ⊕ , (CH 3 ) 4 N ⊕ , H 2 NNH 3 ⊕ , and C(NH 2 ) 3 ⊕ were studied as functions of temperature from 77 K on up to T>300 K. CsCdBr 3 shows a singlet 81 Br NQR spectrum over the whole temperature range studied. [CH 3 NH 3 ]CdBr 3 , with one 81 Br NQR line spectrum at room temperature, experiences a phase transition at 167 K; below this temperature an 18-line spectrum is observed. In [(CH 3 ) 4 N]CdBr 3 (phase II), at 290 K, a singlet 81 Br NQR is present as is in the high temperature phase III (T II.1 , = 390 K); the low temperature phase III (T II,m , = 160 K has a triplet 81 Br NQR spectrum. KCdBr 3 shows an 81 Br NQR doublet spectrum, as do RbCdBr 3 , [H 2 NNH 3 ]CdBr 3 , and [C(NH 2 ) 3 ]CdBr 3 . 81 Br NQR triplets are observed for [(CH 3 ) 2 NH 2 ]CdBr 3 and NH 4 CdBr 3 . Several crystal structures were determined (at room temperature). [(CH 3 ) 4 N]CdBr 3 : P6 3 /m, Z = 2, a - 940 pm, c = 700 pm, disordered cation, single chain Perovskite with face connected [CdBr 6 ]- octahedra (nearly CsNiCl 3 -type). [(CH 3 ) 2 NH 2 ]CdBr 3 : P2 1 /c, Z = 4, a = 898 pm, 6 = 1377 pm, c = 698 pm, ß = 91.2°, face connected [CdBr 3 -octahedra single chain Perovskite. NH 4 CdBr 3 : Pnma, Z = 4, a = 950 pm, b = 417 pm, c= 1557 pm, with a double chain of condensed [CdBr 6 ]-octahedra, NH 4 CdCl 3 -type. [N 2 H 5 ]CdBr 3 : P 2 ,/c, Z = 4, a = 395 pm, 6 = 1749 pm,c = 997 pm,ß = 94.2°, double chain polyanion similar to NH 4 CdBr 3 . [C(NH 2 ) 3 ]CdBr 3 : C 2 /c, Z = 4, a = 778 pm, 6 = 1598 pm, c = 746 pm, ß = 110.2°, a single chain Perovskite with a chain of condensed trigonal bipyramids [CdBr5]. Three types of anion chains of CdBr 3 have been observed: Single octahedral chains, face connected; double octahedral chains, edge connected; a trigonal-bipyramidal chain, edge connected. The relation between the crystal structure and the Br NQR is discussed

Molecular dynamics simulations of concentrated aqueous Csl solutions have been performed for Csl: H 2 O = 1:20 (2.78 molal) at 298 K and 341 K and 1:10 (5.56 molal) at 349 K. Effects of temperature and concentration on the structures of the hydrated ions, the ion pairs, and ionic aggregates are discussed by comparing the results with X-ray diffraction data obtained under similar conditions [1]

The various evaluation procedures of IR reflection spectra, viz. Kramer-Kronig analyses (KKA), 3 parameter (coTO, g, y) (3 PM), and 4 parameter (ω ro , ω LO y ro y LO ) oscillator-model calculations (4 PM), are compared. For the zone-centre phonon energies, the oscillator parameters ω ro and ω LO of 4 PM as well as the frequencies of the dielectric functions ε" and - Im(l/ε), respectively (KKA, 3 PM), are recommended. The pole frequencies of the |ε| functions yield too large TO/LO splittings, especially in the case of large damping of the phonons. In the case of asymmetric reststrahlen bands, the use of 4 PM with different damping constants y for the TO and LO phonons is recommended. Computer simulations of the influence of the various oscillator parameters on the reflection spectra as well as the phonon frequencies of spinel-type MnCr 2 O 4 are included

Chlorine NQR spin-lattice relaxation times T 1Q were determined for [Co(H 2 O)6][PtCl 6 ] at 4.2 400 K. Above ca. 350 K, T 1Q decreased rapidly showing the onset of a reorientation of [PtCl 6 ] 2 -. The activation energy Ea of this reorientation was determined as 125 ± 15 kJ mol -1 . With decreasing temperature, T 1Q showed a maximum at ca. 250 K. Below ca. 200 K, T 1Q . is governed by the magnetic dipolar interaction between chlorines and paramagnetic Co 2+ ions and is inversely proportional to the electron spin correlation time τe of CO 2+ . τe is shown to be determined by the electron spin-lattice relaxation time T 1e and the temperature independent correlation time rs for the spin-exchange between neighbouring ions above and below ca. 50 K, respectively. The temperature dependence of T 1e is explained by assuming the Orbach process with an energy gap A/k of 530 + 20 K as T 1e = 5 x 10 -14 exp(530/T)s. τ s was estimated to be 0.9 x 10 -10 s. The temperature dependence of the ESR linewidth of Mn 2+ impurities in single crystal was also measured, intending to study Co 2+ spin dynamics. The limit of the ESR method is discussed by comparing the obtained results with those of the NQR method

The redox potential of the couple Eu 3+ /Eu 2+ in aqueous NaCl, NaClO 4 and Na 2 SO 4 solutions of different ionic strength and various pH values has been determined by means of cyclic voltammetry up to 458 K and 1 kbar. In all cases reversible voltammograms were obtained. Compared to the redox potential in C1O 4 - solutions of pH 2, no significant shift was observed in Cl-solutions of the same pH, whereas a drastic shift to more negative potentials in solutions of SO 2- 4 and in Cl- solutions of higher pH (pH 3-5) was obtained. This indicates a negligible complexation of Eu3* by means of CP but a strong one by means of OH and SO 2- 4 . An isothermal pressure increase up to 1 kbar led to a shift of only few mV more negative, indicating a small pressure dependence of the change of the partial molar volume (ΔV e1 ) accompanying the redox reaction, which results in this case only due to the different degrees of electrostriction. A more drastic shift of the redox potential (in the positive direction) results with increasing temperature. The isobaric temperature dependence of the redox potential is described by a two parameter equation which remains valid up to the saturation pressure at 458 K, due to the small pressure effect. ΔS and ΔH of the redox reaction has been determined

In this contribution, the Generalized Thermodynamic Formalism is applied to a nonhyperbolic dynamical system. The associated generalized entropy function is discussed. The model considered is equipped with a generating partition of two symbols; in contrast to analogous hyperbolic models, the support of the generalized entropy function is two-dimensional. Furthermore, the phase-transition- like behavior caused by the nonhyperbolicity of the measure is shown to lead to the manifestation of a critical line in the surface described by the generalized entropy function. It is discussed how the different combinations of phase-transitions in the more specific entropy spectra fx), S G (ε) and ϕ(λ) are determined by the form of the generalized entropy function

Proton spin lattice relaxation rates have been measured at 15 and 30 MHz and down to 5 K for the partially deuterated molecular crystals 4-F-toluene, 4-Cl-toluene, and 2,6-Cl 2 -toluene. The behaviour of these materials is governed by methyl group tunnelling. As compared with the undeuterated compounds, the low temperature relaxation is enhanced and the details depend on the removal of the symmetry coupling between rotator and spin states. The hindering barriers remain unchanged, the A to E conversion rates are faster, and relaxation is dominated by spectral density contributions J(2ω o ) and J(2ω 0 ). In one case an additional influence of level-crossing energy transfer on relaxation is observed. Field-cycling spectroscopy reveals steps rather than peaks if the proton spin Zeeman and tunnelling splittings match

Symbolic-dynamical encoding of chaotic dynamics yields a precise quantitative characterization of the temporal scaling behavior at crisis points. A complete analysis in the heteroclinic tangency case is presented for an NMR-laser

The 18 O / 16 O ratio under the m- and r-faces of smoky quartz has been measured; the ratio of the growth velocities was V m /V r = 1/3. The obtained separation factor 1.00020 is compared with that obtained previously for amethyst (1.00043), where the ratio V m /V r was unity