bluuebunny/crossref_metadata_2025_split huggingface dataset:
Untersuchung der Bildung und des Wachstums von Rußteilchen in vorgemischten Kohlenwasserstoff – Sauerstoff Unterdruckflammen
Authors: Bockhorn H. , Fetting F. , Heddrich A. , Wannemacher G. 
Published: March 2014

AbstractParticle sizing by light scattering and electronmicrographing in sooting premixed low pressure hydrocarbon (propane, ethine, benzene) oxygen flames has been investigated. Particle size distributions resulting from electronmicrographs can be simulated by the limiting cases of self‐preserving distributions. When these distributions are used for evaluation of light scattering measurements good agreement is observed between particle sizes obtained by light scattering and by electronmicrographs. Indications to a correlation of the optical properties of soot particles with their age are obtained from particle size moments and both scattering and extinction measurements. This correlation for the refractive index can qualitatively be explained by means of the dispersion model due to structural changes of the soot particles.
Kinetics of Geminate Pair Recombination in Polyvinylcarbazole
Authors: Stolzenburg F. , Ries B. , Bässler H. 
Published: March 2014

AbstractRecombination of geminate electron hole pairs (GP) in Polyvinylcarbazole (PVK) has been investigated by (i) monitoring the decay of delayed luminescence (DF) following pulse excitation with 4.02 eV photons at temperatures between 20 K and 294 K and (ii) Monte Carlo computer simulation. It is found that the decay of the GP reservoir obeys a t−s law with s being close to unity and exhibiting small yet systematic variations depending on temperature and time domain. DF extends up to seconds even at 294 K delineating GP lifetimes accordingly long. It is concluded that recombination kinetics is controlled by both the intrinsic energetic disorder of the bulk hopping sites, i.e. the carbazole groups, and by intermediate trapping at presumably incipient carbazole dimers. The Noolandi, Hong and Street theory is found inadequate for data analysis because it ignores the energetic relaxation of carriers subject to random walk within the energy distribution of hopping sites generally present in amorphous solids.
Configurational Dynamics of Doped Low Temperature Glasses and Polymers
Authors: Köhler W. , Friedrich J. 
Published: March 2014

AbstractWe investigated configurational relaxation of doped organic glasses by monitoring the changes of spectral holes as a function of time and temperature. The configurational changes occur either by tunneling processes or by thermally activated processes. At extremely low temperatures the tunneling processes prevail leading to logarithmic features in the relaxation function. The activated processes determine the temperature dependence. It is shown that the distribution of activation barriers follows closely a 1√‐dependence, which can be measured in a most direct way. We also demonstrate that thermally induced hole filling and hole broadening arise from different microscopic processes.
Pyroelectricity of Aromatic Compounds
Authors: Weiss Alarich , Fleck Silvia 
Published: March 2014

AbstractRecent studies of pyroelectricity in crystallized aromatic compounds – benzene derivatives – are discussed and summarized. The dielectric and pyroelectric behaviour of some di‐ and trisubstituted benzenes as a function of temperature is presented and experimental results are compared with evaluations based on the INDO‐approximation including a self‐consistant electrostatic crystal field approach.
The Influence of Potassium Iodate on Hydrogen Peroxide Decomposition in Bray‐Liebhafsky Reaction
Authors: Anî S. , Kolar‐Anić Lj. 
Published: March 2014

AbstractThe influence of the potassium iodate concentration on the hydrogen peroxide decomposition in the Bray‐Liebhafsky reaction is analysed by the kinetic observations described in our previous publication [1]. The overall decomposition of hydrogen peroxide in the presence of KIO3 and H2SO4 is found to follow the first order kinetics, not only with respect to hydrogen peroxide, but also with respect to potassium iodate. The rate constant of the process is evaluated.
High Pressure NMR Study of the Molecular Dynamics of Liquid Fluoroform and Deutero‐Fluoroform
Authors: Lang E. W. , Prielmeier F. X. , Radkowitsch H. , Lüdemann H.‐D. 
Published: March 2014

AbstractThe 2D‐, 1H‐ and 19F‐spin‐lattice relaxation rates R1 have been investigated in fluid fluoroform in the temperature range 150 K < T < 450 K and at pressures up to p = 200 MPa. Previous measurements of the self‐diffusion coefficient D have been supplemented to cover the same p, T‐interval. Within the rough hard sphere (RHS) approximation a temperature independent RHS diameter d and a strongly temperature dependent rotation‐translation coupling ART are obtained. Both parameters are also compared with those obtained in a series of related halomethanes. The total 2D‐, 1H‐ and 19F‐relaxation rates in CDF3 and CHF3 are decomposed into their respective quadrupole, dipolar and spin‐rotation contributions and orientational and spin‐rotational correlation times are extracted from these rates. It is shown that they are in good agreement with the predictions of the Fokker‐Planck‐Langevin model. Inertial effects influence the molecular dynamics at high temperatures and low densities. The agreement of self‐diffusion coefficients and orientational correlation times with MD‐simulation data is very satisfactory.
Nichtlineare, quantitative NMR‐Spektralanalyse in der Reaktionskinetik
Authors: Schmidt M. , Ziessow D. 
Published: March 2014

AbstractThe applicability of nonlinear spectral analysis (maximum entropy method, MEM) for quantitative NMR studies has been investigated by means of computer simulation. First, extensive calculations were performed with the Burg algorithm to validate the superposition principle and to ascertain the relation between the experimental (time length of observation; relative amplitude, phase, and decay rate of the free induction NMR signals (FID); number of coefficients in the MEM filter) and spectral parameter to be determined (frequency, line‐shape and intensity of the resonance lines). The result indicate that MEM power spectra have great potential for the accurate determination of relative NMR intensities. Second, as an example for a particularly demanding application, the FID for both reactants of a first‐order, irreversible reaction, the start of which is triggered by the r.f. excitation pulse, has been simulated with a rate constant of the order of the inverse decay time constants. The acquired FID is cut into short, interleaved slices which are subjected to nonlinear analysis. The resulting power spectra directly reflect the time dependence of the intensities of both reaction species. Exponential fit yields the rate constant which differs by less than 2% from the exact one with a correlation coefficient greater than 0.99. These findings suggest that MEM analysis provides an useful approach to the study of complex chemical reactions where time constants are of the order of the NMR relaxation times.
NMR imaging of restricted diffusion
Authors: Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Frahm Jens 
Published: March 2014

AbstractNuclear magnetic resonance (NMR) techniques using pulsed magnetic field gradients provide noninvasive access to the investigation of molecular diffusion. In this paper the applicability of the NMR approach is extended to complex physico‐chemical or biological systems where diffusion experiments generally are complicated by spatial heterogeneity of the sample and the presence of restricted diffusion. Diffusion imaging using stimulated echoes overcomes these problems in offering both spatial resolution as well sensitivity to restricted diffusion. Preliminary experimental results are presented of a 100‐MHz 1H NMR imaging study of water diffusion in plants using a 2.35T 40 cm magnet.
Hydrogen bonds in ammonium hydrogen‐DL‐malate monohydrate studied by2H‐NMR, IR, and LCAO‐MO calculations
Authors: Fleck Silvia , Böhm Michael C. , Weiden Norbert , Weiss Alarich 
Published: March 2014

AbstractSingle crystal2H‐NMR‐spectra of ammonium deutero‐DL‐malate monohydrate, ND⊕4(⊖OOCCHODCH2COOD) · D2O, were studied at room temperature. The electric field gradient tensors (EFGT) and the asymmetry parameters (η) were calculated from the angular dependence of the2H nuclear quadrupole interaction by Volkoff's formalism. The resulting EFGTs can be assigned to the different OD‐groups, the D2O‐molecule and the ND⊕4‐ion, respectively. AtT≃ 298 K the D2O‐molecule and the ND⊕4‐ion show fast reorientation. The2H‐EFGT for the “static” D2O molecule was calculated and correlated with IR‐data. — The hydrogen bonding system in the crystal has been studied by an extended LCAO‐model supplemented by Madelung type and repulsive Born‐Mayer type calculations for contributions of the lattice. An INDO‐procedure was used, which includes crystal‐field effects in a self‐consistent electrostatic field approach (SCEF). Dynamic parameters of the proton transfer are evaluated by semi‐classical techniques. The vibrational frequencies of the hydrogen bonds can be deduced and are in qualitative agreement with experimental data.
Lowest excited states of [Ru(bpy)3]X2 host material, [Os(bpy)3]2+ guest complexes, and radiationless energy transfer
Authors: Yersin H. , Braun D. , Gallhuber E. , Hensler G. 
Published: March 2014

AbstractThe properties of the lowest excited electronic states under variation of temperature and magnetic field are discussed for single‐crystal [Ru(bpy)3](PF6)2 and for [Os(bpy)3]2+ guests, doped into the [Ru(bpy)3]X2 host material, mainly focusing to the emission properties. Especially, the spectra of the [Os(bpy)3]2+ guests are highly structured and it is possible to identify the three lowest zero‐phonon lines (in the host matrix with the counter ion X = ClO4) and a large number of vibronic components. This structure depends on the counter ion of the host material. Further, a radiationless energy transfer, occurring from the [Ru(bpy)3]2+ hosts to the [Os(bpy)3]2+ guests, is governed by a donor‐donor transfer and a direct donor‐acceptor transfer process. An investigation of the emission decay properties for various acceptor concentrations allows to conclude on a relatively ineffective donor‐donor transport mechanism.
Photophysics of single crystal [Pt(o‐phen) (CN)2]: Optical properties at external magnetic fields and at high pressures
Authors: Schwarz R. , Lindner M. , Gliemann G. 
Published: March 2014

AbstractProperties of the polarized emission (energy, intensity, lifetime) of single crystal [Pt(o‐phen) (CN)2] as functions of temperature (1.9 K ≤ T ≤ 295 K), of homogeneous magnetic fields (0 ≤ H ≤ 6 T), and of hydrostatic pressures (1 bar ≤ p ≤ 30 kbar) are reported, and the temperature dependence of the polarized absorption is described. Between T = 1.9 K and room temperature the E⟂a polarized emission (E: electric field vector; a: crystallographic a axis) and the E⟂a polarized absorption are blue shifted by ∼ 2000 cm−1 and 1400 cm−1, respectively. Application of a homogeneous magnetic field H⟂a with field strength H = 6 T shifts the low temperature E⟂a emission by ∼ 190 cm−1 to higher energies, shortens the lifetime by two orders of magnitude, and increases the emission intensity by a factor of ∼ 18. Increasing hydrostatic pressure between p = 1 bar and 30 kbar reduces the emission energy by −70 cm−1/kbar. The experimental results can be interpreted by a system of coupled complexes of C'2v, symmetry.
Excited state dynamics of triphenylmethane‐dyes used for investigation of microviscosity effects
Authors: Vogel Martin , Rettig Wolfgang 
Published: March 2014

AbstractThe nonexponential fluorescence decay behaviour of triphenylmethane‐(TPM)‐dyes can be understood as barrierless relaxation, i.e. intramolecular rotational relaxation of dialkylanilino groups under the influence of a driving force. The observed viscosity dependent rotational relaxation rates of TPM‐dyes with large and small, rigid and flexible rotor groups do not obey the Debye‐Stokes‐Einstein relationship but can be fitted within the microviscosity theory of Gierer and Wirtz and show that free volume effects are important. The relative size of free volume effects in n‐alcohols, diols and glycerol can be determined by comparing the rates of different TPM‐dyes.
Neutron scattering and dynamics of small molecules in cryogenic matrices
Authors: Langel W. , Kollhoff H. , Knözinger E. , Prager M. 
Published: March 2014

AbstractNeutron inelastic scattering spectra of HC1, CH3Cl, CH3CN, and CH3I isolated in matrices of solid argon and sulphur hexafluoride at energy transfers of 0–300 cm−1 are reported. Only HCl shows rotation, whereas the spectra of the other compounds are due to liberational modes of the methyl group about the figure axis. In argon, all modes are strongly damped by the phonons of the matrix.
FTIR‐spectroscopy of molecular clusters in liquid solutions and cryogenic solids
Authors: Schrems O. , Huth M. , Kollhoff H. , Wittenbeck R. , Knözinger E. 
Published: March 2014

AbstractSmall hydrogen bonded molecular clusters of HCN have been investigated in CCl4 solutions and in solid Ar, N2, and CCl4 matrices by means of FTIR spectroscopy in the spectral range 4000 ‐ 10 cm−1. In Ar and N2 matrices aggregated species up to tetramers can readily be identified. HCN dimers have been formed selectively in these matrices by photofragmentation of s‐tetrazine. Both the intra‐ and intermolecular modes observed are consistent with a linear dimer structure. Photolysis of s‐triazine generated selectively HCN trimers, obviously with a cyclic structure stabilized by the matrix cage. On the other hand, linear trimers and tetramers were detected in Ar and N2 matrices after time and temperature controlled diffusion of isolated monomers and dimers, respectively. Linear configurations are also typical for the HCN aggregation in CCI4. In liquid solutions no HCN clusters larger than dimers were observed. In the plastic crystalline phase of CCl4, on the other hand, dimers and trimers are present. Only in the crystalline CCl4 phase larger HCN chains of unspecified length may be formed.
High temperature ligand field spectra in spinels: Cation disorder and cation kinetics in NiAl2O4
Authors: Becker K. D. , Rau F. 
Published: March 2014

AbstractResults are reported of optical transmission experiments on the spinel NiAl2O4 that have been made at temperatures up to 1400°C. The spectra are discussed, and analyzed in relation to the temperature dependence of the distribution of cations on the two cation sublattices. The kinetics of cation sublattice exchange is studied by means of temperature jump experiments performed under in‐situ conditions in the temperature range between 600°C and 700°C.
Local order in liquid bromobenzene ‐ EXAFS measurement and its combination with X‐ray and neutron diffraction results
Authors: Bertagnolli H. , Engelhardt T. , Lengeler B. 
Published: March 2014

AbstractThe local order in liquid bromobenzene is studied by measurement of the extended X‐ray absorption fine structure (EXAFS) of bromine. Following standard procedures for data reduction and data interpretation the deduced intramolecular distances are in very good agreement with other spectroscopic methods. From the remaining intermolecular distances a configuration of maximum occurrence probability can be constructed, which is caused by strongly attractive interaction of the bromine atom with other bromine atoms as well as with the aromatic system. The combination of these results with X‐ray and neutron diffraction data gives a detailed picture of the local order, consistent with the three different techniques applied in this work.
X‐ray investigations of the thulium‐iron crystallization process
Authors: Beuthien H. , Torkler A. , Gunßer W. , Niemann W. 
Published: March 2014

AbstractDTA results of amorphous co‐precipitated thulium‐iron hydroxides, with the cation stoichiometry of crystalline thulium‐iron garnet (TmIG) indicate two well separated exothermic phase transitions in a narrow transition region (770–860°C). Extended X‐ray absorption‐fine structure (EXAFS) spectroscopy at the Tm LIII‐ and the Fe K‐absorption edge was used for determining the short‐range order structural parameters. ‐ In the transition region the EXAFS analysis shows an increase of Tm‐O bond lengths and coordination numbers with increasing annealing temperature, and decreasing Fe‐O distances. The Fe‐O coordination numbers do not change significantly. X‐ray near edge structures (XANES) were used to prove changes of the iron coordination.
A dielectric relaxation study of self and heteroassociation in binary liquid mixtures of three pyrrolidinones with alcoholes and water
Authors: Dachwitz E. , Stockhausen M. 
Published: March 2014

AbstractNine binary mixture systems AB are considered, where A = 2‐pyrrolidinone, N‐methyl‐2‐pyrrolidinone or N‐cyclohexyl‐2‐pyrrolidinone and B = water, methanol or ethanediol. Their complex permittivity, as measured in the 20 MHz to 36 GHz range at 20°C, is interpreted by a model supported analysis. It applies in particular an empirical correlation between relaxation time and viscosity as established for the case of rigid molecules, relaxing by rotational tumbling. From this, constraints are obtained for those spectral components which are due to species of that category. The procedure yields, among others, for any system a spectral component which can be ascribed to heteroassociates of probably definite AB or AB2 composition. Again with any system, self association of B type molecules is observed, which is strongly affected by addition of A. Special relaxation features of some substances are also considered.
Optical Absorption Spectra of the Homocyclic Sulfur Molecules Sn (n = 6, 7, 8, 9, 10, 12, 15, 20) in Solution [1]
Authors: Steudel Ralf , Jensen Detlef , Göbel Petra , Hugo Peter 
Published: March 2014

AbstractThe optical absorption spectra of the sulfur homocycles Sn (n = 6–10,12, 15, 20) in methanol or methylcyclohexane solution have been recorded in the region 200–360 nm using a conventional spectrophotometer as well as a diode‐array spectrophotometer. Each compound shows a characteristic absorption curve. The extinction coefficients at 254 nm increase with increasing ring size, and the lowest‐energy absorption maximum shifts to the red with increasing number of atoms in the molecule. The data are used to re‐interprete the published absorption spectra of liquid and irradiated sulfur.
Potentiometrie Investigations of the Liquid Al + Ga + Sb Alloy Between 623 K and 1300 K
Authors: Girard C. , Miane J. M. , Riou J. , Baret R. , Bros J. P. 
Published: March 2014

AbstractTwenty three alloys Al + Ga + Sb have been studied by the Emf method between 623 and 1300 K using concentration cells of the type:

Partial molar functions of aluminium and some equilibrium temperatures were determined; they are in satisfactory agreement with the calculation of Kaufman et al. — The comparison of the experimental ternary ΔmixGAl values and the corresponding ones calculated using several empirical equations shows that the best agreement is obtained by Colinet's equation.
Polymorphism in Dialkylammonium Chlorides. An Adiabatic Calorimetry Study
Authors: van Oort Michiel J. M. , White Mary Anne 
Published: March 2014

AbstractThe heat capacities of four di‐n‐alkylammonium chlorides (di‐n‐pentylammonium chloride, di‐n‐hexylammonium chloride, di‐n‐octylammonium chloride, and di‐n‐decylammonium chloride) were measured from T = 25 K to 350 K using adiabatic calorimetry. All of the compounds investigated were observed to undergo solid‐solid phase transitions in the temperature region examined. The thermodynamic properties obtained for these compounds were compared with those of the layered perovskites (alkylammonium metal halides) and the mono‐n‐alkylammonium chlorides. The high entropies of the solid‐solid phase transitions suggest that there is a significant amount of conformational disorder in the high‐temperature phase, most likely due to solid‐state alkyl‐chain melting, analogous to the layered perovskites and the monoalkylammonium chlorides. The contribution of a CH2 unit to the heat capacity of these complexes was calculated and compared to the n‐alkanes and the layered perovskites.
Microprobe Photocurrent Investigations and Laser Induced Radiation Effects on TiO2‐Films
Authors: Leitner K. , Schultze J. W. 
Published: March 2014

AbstractA scanning laser system has been set up, which allows microprobe photocurrent measurements and the generation and investigation of localized radiation effects. The laser beam was focused on a spot size of less than 10 μm and the sample could be scanned with a digitally controlled x — y stage in steps of 1 μm. Local photocurrent fluctuations on anodically formed TiO2‐films are quantitatively correlated to the microscopically observed grain structure of the underlying metal. — Moreover, laser irradiation was found to change the colour, the crystallinity and the photoresponse of the oxide film. This is explained by light induced changes of the electric field within the passive film and the Helmholtz layer, which supports an epitaxial oxide formation on top of the already existing film. The influence of light intensity, illumination time and electrode potential is investigated in detail.
Time Resolved Electron Paramagnetic Resonance Spectroscopy of Anthracene in Frozen Aqueous Micellar Solutions: Triplet Yields and Lifetimes
Authors: Meling H. , Wolff T. , von Bünau G. 
Published: March 2014

AbstractAnthracene in frozen aqueous micellar solutions of n‐alkyltrimethylammonium halides, CnTAX (n = 10, 12, 14, 16, 18; X = I, Br, Cl), was subjected to laser pulse excitation in the cavity of an EPR‐spectrometer. Decaying triplet signals were recorded with a signal processing unit designed for time resolution in the ms‐range. Measured triplet lifetimes τT at 80 K were lowest in C16TAI‐solutions, highest in CnTACl‐solutions, and varied with n; relative triplet quantum yields ΦT were lowest in C16TAI and highest in CnTACl‐solutions. Relative fluorescence quantum yields ΦF were also higher in CnTACl‐ than in CnTABr‐solutions. Both τT and ΦT decreased with increasing temperature. At 270 K triplet quantum yields ΦT were higher in CnTACl‐solutions while the contrary holds for ΦF‐values. It follows that both intersystem crossing and internal conversion processes may be influenced by heavy atoms.
The Conservation of the Correlation Length of Quantum and Classical Chaotic States
Authors: Shapiro Moshe , Ronkin Jacob , Brumer Paul 
Published: March 2014

AbstractA spatial correlation function has been previously proposed as a means of quantifying chaotic characteristics of quantum wavefunctions. In this paper we show that the classical analogue of the spatial correlation of a quantum wavefunction is identical (over short ranges) to its quantum counterpart, for the majority of high lying eigenstates of the classically chaotic stadium billiard problem. This behaviour is identified with quantum ergodicity. Furthermore the classical correlation function is used to derive an energy‐scaling law for the correlation lengths. The spatial correlation approach is then generalized by considering cross‐correlation functions and the time evolution of the correlation lengths for non‐stationary quantum states. This quantity is shown to be a near constant of the motion for wavepackets comprised of chaotic states and may relate to mixing properties of the dynamics.