bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the Dissociation Energy of the Cr2 Molecule
Authors: Hilpert K. , Ruthardt R.
Published: March 2014

A Knudsen cell — mass spectrometer system has been developed allowing for the determination of extremely small partial pressures. This instrument and a second different Knudsen cell — mass spectrometer system were used to study the thermochemistry of the vapour over chromium. The results obtained by the two instruments agreed excellently. The partial pressure of Cr2(g) was determined in the temperature range between 1542 and 1819 K to be magnified image The enthalpies of sublimation and dissociation for Cr2(g) essentially resulted from eight independent runs according to a second‐law evaluation as ΔsubH = 612 ± 4 kJ mol−1, ΔsubH = 653 ± 4 kj mol−1, and ΔsubH = 652 ± 4 kJ mol−1 as well as ΔsubH = 150 ± 5 kJ mol−1, ΔsubH = 142 ± 5 kj mol−1, and ΔsubH = 139 ± 5 kj mol−1. The binding energy for Cr2(g), De = 142 ± 5 kJ mol−1, was determined. An evaluation of the enthalpy cf dissociation for Cr2(g) according to the third‐law method shows indirectly the existence of low‐lying electronic states for this dimer. The binding energy of Cr2(g) obtained here is compared with those predicted by numerous theoretical computations using different methods. The ionization potential of Cr2+ was determined by ionization efficiency measurements to be 6.4 ± 0.2 V.
The Influence of Dissolved Electrolytes on the Miscibility of Binary Liquid Systems with Closed Miscibility Gaps
Authors: Erol M. , Kocak M. , Richter P. , Steiger A. , Becker F.
Published: March 2014

The dependence of the upper and lower critical solution temperatures Tc of the systems (1) oxolane + water, and (2) 2‐butoxyethanol + water on the mole fraction XEl of dissolved 1‐1, 2‐1, and 3‐1 electrolytes has been investigated. The material stability of the homogeneous state of both systems is extremely sensitive to small electrolyte concentrations so that the observed shift of Tc may be interpreted as the result of a perturbation of the mutual solvation of both non‐electrolytes by ion solvation. Cations destabilize homogeneity in the order Me+ < Me2+ Me3+. The nature of the anions, however, for which the order Cl− > Br− > I− > NO−3 > ClO4− is established, determines whether the closed miscibility gap expands, shrinks, or is shifted to higher temperatures with increasing xEL. The importance of the anions is evident from a comparison of MgCl2 and Mg(ClO4)2, for which the lower critical solution temperatures of oxolane + water at XEl = 0.003 differ by about 70 K.
Impurity Diffusion in a Chemical Potential Gradient (II): Iron Tracer Diffusion in Cobalt Oxide in an Oxygen Potential Gradient
Authors: Martin M. , Dorris S.
Published: March 2014

Impurity tracer diffusion coefficients for 59Fe in CoO have been measured as a function of the oxygen activity at a temperature of 1200°C. The results can be described by a weak impurity‐vacancy binding at high oxygen potential and a strong binding (Δgv = −0.7 eV) at low oxygen potential. Impurity tracer diffusion has also been measured for 59Fe in CoO which has been exposed to an oxygen potential gradient. In addition to the normal Brownian motion the impurity cations are seen to drift in the crystal as a result of the cation vacancy wind. These results confirm the picture of weak binding at high oxygen potential and strong binding at low oxygen potential. From both experiments it is possible to calculate frequency ratios or directly the frequencies of vacancy jumps.
Studies on the Interaction of Anthraquinone Triplet and α‐Phenylethyl Hydroperoxide in Benzene and Chlorobenzene
Authors: Móger G. , Paál‐Lukács J. , Gál D.
Published: March 2014

The quantum yields of the formation of products as well as their temperature dependence during the photochemical decomposition of α‐phenylethyl hydroperoxide (HROOH) have been measured in the presence of triplet anthraquinone (TQ) in air‐saturated benzene and chlorobenzene at 301–373 K. The photochemical and thermal decomposition of HROOH have been compared. Experimental results and their mathematical simulation indicate that in the reaction of TQ with HROOH peroxy radicals, HRO2, are generated. According to the measurements magnified image at T = 30 K, and the energy of activation of the reaction magnified image is about 5.9 kJ mol−1.
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

Particle 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

Recombination 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

We 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

Recent 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

The 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

The 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

The 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

Nuclear 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

Single 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

The 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

Properties 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

The 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

Neutron 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

Small 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

Results 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

The 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

DTA 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

Nine 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

The 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

Twenty 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

The 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

A 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

Anthracene 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.
Intramolecular Dynamics and Unimolecular Reactions
Authors: Marcus R. A.
Published: March 2014

In this article we describe recent research of our group on the rate constants and the distribution of quantum states of the reaction products of unimolecular dissociations and on methods to treat intramolecular dynamics. Connections among various transition state type theories are also discussed.
The Conservation of the Correlation Length of Quantum and Classical Chaotic States
Authors: Shapiro Moshe , Ronkin Jacob , Brumer Paul
Published: March 2014

A 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.
Statistical Properties of Energy Levels in Non‐Born‐Oppenheimer Systems
Authors: Zimmermann Th. , Cederbaum L. S. , KÖppel H.
Published: March 2014

Basic ideas and methods of the statistical analysis of energy spectra are reviewed. Complex nuclear, atomic and molecular spectra show typical fluctuation patterns which can be modeled with the aid of random matrices. Calculations on model systems and theoretical results show the existence of two universality classes of spectral fluctuations which depend on whether there are strong or only weak couplings between the various degrees of freedom. This correspondence also provides a link between quantum spectral statistics and classical dynamics. We illustrate statistical methods by analyzing model spectra obtained from a Hamiltonian which describes non‐Born‐Oppenheimer coupling of nuclear and electronic motion in molecules.
Quantal Fluctuations in Unimolecular Rate Constants
Authors: Levine R. D.
Published: March 2014

Rate constants for molecules excited to well defined states can vary, in an erratic fashion, over even narrow energy intervals. The theory of such fluctuations is discussed with special reference to the transition from regular to chaotic motion. It is argued that the distribution of the fluctuations with respect to the local average rate constant k(E) is that known as “chi square with v degrees of freedom”. In particular, the width of the fluctuations is (2/v)1/2 k (E). In the statistical limit the parameter v equals the number of channels (≡ number of decay modes) accessible to an energy rich molecule in a given state. In this limit the distribution of fluctuations is universal and is independent of the dynamics. In general, v < number of channels, with v decreasing (i.e., the fluctuations are increasing), the more restricted is the intramolecular vibrational energy exchange.
How Robust are Bottlenecks to Unimolecular Fragmentation?
Authors: Tersigni Samuel H. , Rice Stuart A.
Published: March 2014

Some properties of classical mechanical phase space resonances that serve as bottlenecks to the redistribution of internal molecular energy are investigated. Resonances of a two degree of freedom model van der Waals (vdW) molecule are subjected to a linear harmonic perturbation from an additional degree of freedom. The resulting effects on the phase portrait of the subsystem appear to be independent of the frequency of the third oscillator but relatively small coupling critically affects most quasi‐periodic resonances. The approximate separatrix in the vdW degree of freedom is used as a dividing surface in an analysis of the vdW molecule fragmentation rate. The influence on the separatrix of coupling to a third oscillator supports the validity of the two degree of freedom model for systems with small to moderate coupling. The golden mean resonance remains the most robust resonance of the two degree of freedom phase portrait even when the third oscillator coupling is nonzero, an observation which supports the recognition of golden mean resonances as the main intramolecular bottlenecks.
A Tour of Vibrational Predissociation from Seven Levels in the S1 p‐Difluorobenzene‐Ar van der Waals Complex
Authors: Hye‐Keun O. , Parmenter Charles S. , Su Meng C.
Published: March 2014

The absorption and fluorescence characteristics of p‐difluorobenzene‐Ar van der Waals complexes prove ideally suited for experimental study of vibrational predissociation (VP). The process has been observed from seven S1 complex levels that contain a total of six different ring modes. The levels have vibrational energies ranging between 240 and 900 cm−1. VP lifetimes are in the range of 2 – 12 ns for six of the levels. The other has a 200 ns lifetime, possibly because of relatively poor coupling of its hydrogenic bending motion with the dissociation coordinate. VP almost always occurs with only one or two major channels. The only exception is a level using three important channels. Remarkably, the final states of the VP are always the same, either 00 or 61 of the monomer. A strong Δv = 1 or 2 propensity rule for ring mode changes governs these VPs. The VP channels cannot be modelled well with the full collision state‐to‐state propensity rules known for Ar collisions. Difficulties are also encountered in modelling with a Golden Rule momentum gap formulation that has been successful in other systems.
Some Mechanisms in the Photodissociation of Polyatomic Molecules
Authors: Dixon R. N.
Published: March 2014

The various mechanisms promoting predissociation in polyatomic molecules are reviewed, and illustrated by the spectroscopy of various electronic states of HNO, DNO, NH3 and ND3. The quantum number dependences of the predissociation rates are used to discuss the particular mechanism(s) operating in each case. Recent observations using H‐atom time‐of‐flight spectroscopy of the energy disposal in the photodissociation of NH, through its Ã state show that a conical intersection in the exit channel has a massive influence on the dissociation dynamics.
Vibronic Level Density of Excited NO2‐States and its Statistical Analysis
Authors: Persch G. , Mehdizadeh E. , Demtröder W. , Zimmermann Th. , KÖppel H. , Cederbaum L. S.
Published: March 2014

Measurements of vibronic term values in excited electronic states of NO2 have been performed with cw dye lasers over the whole spectral range from 12117 cm−1 to 24563 cm−1. The low rotational temperatures, achieved by adiabatic cooling of NO2 seeded in a supersonic argon beam, allow the separation of closely lying bands as well as a distinction between transitions to the 2B1 state and the vibronically coupled 2B2 – 2A1 states. The statistical analysis of the distribution P(S), where S is the energy separation between adjacent vibronic levels and of the intensity distribution of all measured bands, suggests that a short range correlation exists between the excited levels. Whether also a long range correlation exists is still under investigation. A definite answer requires an unambiguous determination of all bands even with low intensities and a safe assignment of all hot bands. These points are discussed in detail.
Rotationally Resolved Intramolecular Processes in Benzene
Authors: Neusser H. J. , Schubert U. , Riedle E. , Kiermeier A. , Kühlewind H. , Schlag E. W.
Published: March 2014

The influence of the molecular rotation on intramolecular processes is investigated for both a non‐reactive and a reactive large polyatomic system. The non‐reactive system chosen is the S1 state of benzene, C6H6. Doppler‐frec spectra of the 1401 band show isolated rotational perturbations due to a highly selective coupling of the “light” zero‐order states to “dark” rovibrational states within the S1 state. These perturbations are caused by J, K dependent Coriolis coupling, which will induce energy randomization in the excited molecule. The reactive process investigated is the unimolecular dissociation of rotationally selected excited benzene cations. It is found that energy is completely randomized and the benzene cations behave like a statistical system. Dissociation rates are found to decrease with rotational quantum number, J. It is concluded that rotational selection has to be included in precise experiments and theoretical models of intramolecular processes.
Local versus Hyperspherical Modes of Formaldehyde I. Model Hamiltonian and Decay of the CH2‐Fragment
Authors: Joseph T. , Manz J. , Mohan V. , Schreier H.‐J.
Published: March 2014

Highly vibrationally exited, near degenerate stretches of the CH2‐fragment of formaldehyde yield rapid local versus slow hyperspherical decay. The dissociations are simulated using Fast‐Fourier‐Transform (FFT) time propagations of resonance wave packets on three model potentials. The time evolution allows to select an instructive model Hamiltonian for H2CO which describes normal modes as well as highly excited H2C stretches coupled to cold CO bonds.
Photophysics of Internal Twisting II. Fluorescence Spectroscopic Studies of Horizontal Transitions
Authors: Lippert Ernst
Published: March 2014

Molecular motions are investigated by experimental and theoretical studies on subnanosecond photoproduction of twisted biradicaloid excited states of aromatic compounds in liquid solutions.
Selective Intracluster Ion‐Chemistry Studied by Resonant Two‐Photon Ionization Spectroscopy
Authors: Brutschy B. , Janes C. , Eggert J.
Published: March 2014

After resonant two‐photon ionization of mixed clusters of substituted aromatics with polar and unpolar solvents we observed very selective intracluster relaxation reactions. They are assumed to take place in the cationic complexes. The selectivity of a nucleophilic substitution reaction of halogenated benzenenes with nucleophiles is rationalized by different isomeric structures of the neutral aggregates. Proton transfer from ionized methylated benzenes to polar solvents is found to be governed by the solvent's proton solvation energetics. Electron transfer, at present studied only for ether compounds as solvent, takes place, if the ionization potential of the solute is larger than of the solvent.
Measurements of Specific Rate Constants for Dissociation of Substituted Aromatic Hydrocarbons. A Direct Acces to Thermal Dissociation Rate Constants
Authors: Hippler H. , Lindemann L. , Troe J.
Published: March 2014

Specific rate constants for unimolecular bond fission reactions of substituted aromatic hydrocarbons were measured directly using excimer laser excitation at 193 nm followed by internal conversion. For methyl substituted benzenes C —H bond cleavage is the dominant process while C —C bond fission in the side chain is most important for α‐methyl substituted toluenes. Calibration of statistial adiabatic channel modell (SACM) calculation with these experimental results allows for prediction of thermal decomposition rate constants which are difficult to measure directly.
1H NMR Study of Solid Ethylammonium and Propylammonium Nitrates. Cation Motions in the Stable and Metastable Phases
Authors: Ishida Hiroyuki , Weiss Alarich
Published: March 2014

The 1H‐NMR spin lattice relaxation times, T1, were observed for ethylammonium nitrate, (CH3CH2NH3)NO3, and propylammoniumnitrate, (CH3CH2CH2NH3)NO3, and for their partially deuterated analogs, (CH3CH2ND3)NO3, and CH3(CH2)2ND3NO3, respectively. For each salt two solid phases were found, one of them being metastable and existing below ca. 200 K and ca. 210 K for the ethylammonium nitrate and propylammonium nitrate, respectively. The results of the T1 measurements are consistent with the assumption that CH3 and NH3 group reorientations about their C–C and C–N bond axes take place in the stable and in the metastable phase of both salts. The motional parameters of the cations in each phase were determined. The asymmetry in the curves T1 = f(T) observed in the metastable phases of (CH3(CH2)2NH3)NO3 and (CH3(CH2)2ND3)NO3 suggests a distribution of correlation times in the cationic motions within these phases.
A Proton Magnetic Resonance and Gravimetric Study of Water and Isopropanol Adsorption on Microcrystalline Rutile. III. Adsorption of Isopropanol
Authors: Boddenberg B. , Horstmann W.
Published: March 2014

The proton spin‐lattice (T1) and spin‐spin (T2) relaxation times of isopropanol (CH3)2CDOD chemisorbed on two types of preconditioned rutile surfaces (free of water and covered with chemisorbed D2O) were measured as function of temperature (100 to 300 K) and resonance frequency (20 to 90 MHz). The spin‐lattice relaxation rates were found to be separable according to 1/T1 = 1/T1D + 1/T1S. The proton dipolar term 1/T1D as well as T2 turned out to be essentially independent on the preloading with water indicating the same surface sites to be involved in alcohol chemisorption for both types of preconditioned surfaces. The temperature independent term 1/T1S was found to be proportional to the inverse of the square root of the resonance frequency signifying proton relaxation via spin diffusion at paramagnetic centers to be operative. – From T1D the methyl group reorientation rate was evaluated as 1/τ = 2·1011 exp(– 1100/T K−1) s−1. The absolute values of T1D could not be accounted for quantitatively on the basis of known models of dipolar spin relaxation of protons contained in rotating methyl groups.
Halogen Adsorption on n‐MoSe2 (0001) van der Waals Faces: Simulation of Electrochemical Junctions in UHV
Authors: Jaegermann W.
Published: March 2014

Adsorption of halogens (Cl2, Br2, I2) on semiconducting n‐MoSe2 surfaces and changes due to the adsorption are investigated and related to photoelectrochemical results. Clean (0001) faces are prepared by cleaving the crystals in UHV and are characterized by UPS, XPS and LEED. At low doses the photoelectron spectra indicate adsorption of halogens via charge transfer. Changes of the energy correlation at the interface due to the adsorbates are observed in the He I photoelectron energy distribution curves. For this n‐type semiconductor a depletion layer (band bending) as well as increased electron affinities are obtained. The induced band bending can partly be reversed by white light illumination creating a surface photovoltage, which was found to be dependent on the surface ideality. The values determined for the work function, electron affinity and band bending (approximately equivalent to the observed photopotential) are very similar to values obtained in electrochemical junctions of nonreacting organic electrolytes. Evidently the electronic conditions of the semiconductor/adsorbate junction in UHV is comparable to the semiconductor/electrolyte junction containing the respective X2/X− (X = Cl, Br, I) redox couple. The results indicate the possibility to model semiconductor/electrolyte junctions in UHV in such adsorption experiments which allow the spectroscopic identification of surface species and in addition the investigation of their electronic influence.
Volume Profile of the Reversible Dimerization Reaction of 2‐Methyl‐2‐nitrosopropane: Validity of the Hard Sphere Fluid Model and the Transition State Theory
Authors: Yoshimura Y. , Kimura Y. , Nakahara M.
Published: March 2014

The volume profile of the reversible dimerization reaction of 2‐methyl‐2‐nitrosopropane in carbon tetrachloride was determined at 25.0°C on the basis of the study of the pressure effect and the measurement of the solution density at 0.1 MPa. For the dissociation process, the configurational reaction volume was +30.3 ± 0.8 cm3 mol−1 and the apparent activation volume was +7.7 ± 0.3 cm3 mol−1 at 25.0°C and 61.3 MPa. The configurational reaction volume at 0.1 MPa was estimated as +36 cm3 mol−1 from the high pressure study in agreement with the result of the density measurement. The experimental values of the reaction and activation volumes were successfully reproduced by using the hard sphere fluid model. The agreement of experiment and theory indicates that the hard sphere fluid model is valid for describing the volume change for the molecular reaction, and implies that the transition state theory (TST) is valid for interpreting the pressure dependence of the rate constant. A simple illustration of the validity of TST is presented; the energy relaxation process plays a key role in determining the validity.
Partial Molal Volume of Some Alkali Halides in Water‐Urea Mixtures at 298.15 K
Authors: Woldan Marian
Published: March 2014

Densities of solutions of NaCl, Nal, KCl, KBr and CsCl in three mixtures containing 10 wt% (3.22 mol%), 20 wt% (6.98 mol%) and 30 wt% (11.39 mol%) urea in water have been measured at 298.15 K using the magnetic float densitometer. The apparent molal · volumes of the electrolytes calculated from the experimental data were extrapolated to infinite dilution by means of the Masson equation. The ionic partial molal volumes of alkali‐metal and halide ions have been estimated. The disordered and electrostriction partial molal volumes of investigated ions were calculated and the effect of urea on these functions is discussed.
PVTXMeasurements and Thermodynamic Equation of State of Fluid KxKCl1−x(0 ≦x≦ 1)
Authors: Garbade K. , Freyland W.
Published: March 2014

We have measured for the first time thePVTx‐behaviour of a metal‐molten salt solution, KxKCl1_x, over the whole composition range from pure metal to pure salt at temperatures up to 900°C and pressures up to 1600 bar. Simultaneously the pressure dependence of the phase diagram has been studied and we find that the miscibility gap of fluid KxKCl1_xis reduced with increasing pressure. Within experimental error of ∼ 1 % the molar volume of mixing exhibits ideal behaviour in salt and metal rich solutions. However, we observe a clear positive excess volume of ∼1.3 cm3mol−1for compositions near the critical point. The partial molar volume of K shows a pronounced maximum at compositions near the metal‐nonmetal transition region. It is demonstrated in detail that these characteristics of the volume properties are completely consistent with the observed pressure changes of the phase diagram. The thermodynamic equation of state is derived from the measured thermal pressure coefficient and is discussed in comparison with a simple model calculation using linear screening of the ionic potentials.
Semiconductor Particles and Arrays for the Photoelectrochemical Utilization of Solar Energy
Authors: Bard Allen J.
Published: March 2014

The principles of the design of integrated chemical systems based on semiconductor materials for the photoelectrochemical utilization of solar energy to drive useful chemical reactions are described. The use of different support materials, such as Nafion and silica, to prepare particulate systems is discussed. Systems with very small (“Q‐”) particles are described. Charging of these particles is proposed as an important factor in the determination of particle energetics (optical band gap and potentials of photogenerated electrons and holes). Semiconductor arrays, with a number of junctions in series to provide higher driving potentials, are discussed, and two systems for the photosplitting of water to hydrogen and oxygen are described.
Electrochemical Impedance Spectroscopy on 3‐D Inhomogeneous Surfaces Corrosion Inhibition of Carbon Steel in Weakly Acidic NaCl Solutions
Authors: Mitzlaff M. , Hoffmann H. N. , Jüttner K. , Lorenz W. J.
Published: March 2014

The corrosion behavior of carbon steel in weakly acidic NaCl solutions which were aerated or deaerated by H2 or CO2 has been studied in the temperature range 298 K ≥ T ≥ 343 K depending on the rotation frequency of RDE and the exposure time using conventional corrosion test methods and electrochemical impedance spectroscopy (EIS). Based on different theoretical transfer functions, the EIS data were analyzed with nonlinear fit procedures. It is shown that this method can be succesfully applied for an efficient and rapid screening of about 150 organic inhibitors for oil and gas production.
Anodic Dissolution of Thin Nickel‐Phosphorus Films
Authors: Benje Michael , Hofmann Udo , Pittermann Udo , Weil Konrad G.
Published: March 2014

Nickel‐Phosphorus‐films Ni100−xPx (8 ≥ x ≥30) were galvanically deposited onto one face of a gold plated quartz crystal. The latter was used as an in‐situ microbalance. The thickness of the films was 60 nm. By the use of an anodic ramp, they could be dissolved anodically. The oxidation current was monitored simultaneously with the mass change. From the mass to charge ratio, the composition of the films could be determined. During the anodic sweep, two current maxima are observed. The ratio of the areas under the maxima changes with the nominal phosphorus content. From the mass to charge ratios it follows, that during the first part of the sweep, an alloy is dissolved with a phosphorus content below the nominal one, while during the second maximum a phosphorus‐rich phase is oxidized. From the metastable phase diagram of the Ni/P‐system one concludes, that the phase which is less noble must be supersaturated fcc nickel, while the more noble is amorphous NiP‐glass. This interpretation is corroborated by electron diffraction experiments.