bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microcomputer controlled 4π‐zeeman split NQR spectroscopy of 35Cl in single crystal p‐chloroanilinium trichloroacetate. Crystal structure and activation energy for the bleaching out process
Authors: Markworth Axel , Weiden Norbert , Weiss Alarich 
Published: March 2014

AbstractA computer controlled 4π‐Zeeman split pulse fourier transform NQR spectrometer has been constructed. The NQR spectra for more than 200 different magnitutes and orientations of the magnetic field in the sphere can be obtained and stored under software control. This allows an almost fully automatic determination of the zero splitting cones by refining grids of field orientations in the space. — The crystal structure of p‐chloroanilinium trichloroacetate (4‐ClC6H4NH⊕3) (Cl3CCOO⊖), has been determined (C52h ‐ P21/c, z = 4, a = 942.3 pm, b = 722.8 pm, c = 1748.6 pm, β = 100.54°). — The direction cosines of the principal axes and the asymmetry parameters η of the electric field gradient tensors have been obtained together with the nuclear quadrupole coupling constants e2Qφzzh−1 of the chlorine atoms of the CCl3 group (η(1) = 0.0255, e2Qφzzh−1 (35Cl(1)) = 76.790 MHz, η(2) = 0.0355, e2Qφzzh−1 (35Cl(2)) = 76.410 MHz, η(3) = 0.0132, e2Qφzzh−1 (35Cl(3)) = 75.910 MHz and of the chlorine atom bound to the ring (η(4) = 0.0996, e2Qφzzh−1 (35Cl(3)) = 69.244 MHz) at T = 295 K. — The frequencies v(35Cl), linewidths Δv(35Cl) and the spin lattice relaxation times T1(35Cl) have been investigated as function of temperature for v1…v4 and the activation energy for the bleaching out process has been calculated from the Δv = f(T) data (Ea = 65 kJmol−1) and T1 = f(T) data (Ea = 72 kJmol−1). The results are discussed in context with the crystal structure.
Structures and phase transitions in piperazinium hexachlorometallates, (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn. A X‐ray diffraction and 35Cl NQR study
Authors: Borchers Dirk , Weiss Alarich 
Published: March 2014

AbstractCrystal structures and the nature of the chemical bond in piperazinium hexachlorometallates (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn, were studied by X‐ray diffraction and 35Cl NQR spectroscopy. Piperazinium hexachlorostannate trihydrate shows a solid‐solid phase transition at Tc = 256 K. A disorder of the piperazinium ring and of one of the three water molecules appears in the high temperature phase (space group D122h‐Pnnm, a = 1147.5 pm, b = 959.9 pm, c = 719.4 pm, Z = 2). The disorder affects the 35Cl NQR spectrum. The low temperature phase of (C4H12N2)[SnCl6] · 3H2O reveals two 35Cl NQR lines, whereas in the high temperature phase only one resonance line was observed besides the existence of two crystallographically different chlorine atoms in the unit cell. — Piperazinium hexachlorotellurate crystallizes with space group D162h‐Pnma (a = 1398.5 pm, b = 1203.1 pm, c = 822.2 pm, Z = 4). The TeCl6 octahedra is strongly distorted, with the Te‐Cl bond lenghts differing by about 15%. This distortion is reflected in the 35Cl NQR spectra; the resonance lines are spread over a wide frequency range. — The crystal structure of piperazinium hexachloroplatinate (space group C32h‐C2/m, a = 1016.0 pm, b = 1184.7 pm, c = 695.2 pm, β = 130.227°, Z = 2) shows only small distortions in the PtCl6 octahedra. The two line 35Cl NQR spectrum at lower temperature is in agreement with the crystal structure. — Piperazinium hexachloroplumbate reveals a three 35Cl NQR lines at lower temperature. At Tc = 310 K a phase transition occurs and a one line 35Cl NQR spectrum appears. A hysteresis, about 5 K wide, is connected with the transition.
Time‐resolved fluorescence of bichromophoric rotors — confermational dynamics of 1,3‐di(N‐carbazolyl)propane
Authors: Buchberger Eva M. , Mollay Bernhard , Weixelbaumer Wolf‐Dieter , Kauffmann Harald F. , Klöpffer Walter 
Published: March 2014

AbstractTime‐Resolved Fluorescence Spectroscopy has been used to reinvestigate the conformational pathways for 1,3‐di(N‐carbazolyl)propane, 1,3‐DCP, in toluene as solvent. Excited‐state dynamics of 1,3‐DCP triggered by rotational diffusion has been probed by analyzing the transient profile of monomer and excimer fluorescence as a function of temperature. In the intermediate temperature regime, numerical reconvolution of excimer raw data yields a significant triple‐exponential fluorescence response (biexponential rise + single‐exponential decay) which degenerates to a biexponential result at higher temperatures. On the basis of a transient scheme (two monomeric conformations X1, X2 and one excimer X3, the experimental patterns have been analyzed with the help of the exact δ‐pulse solutions to the scheme, for two different boundaries. Simulation of plausible parameter sets proves useful for recovering a) the time constants and b) the signs of the amplitudes in the experimental data profile. The kinetic procedure gives insight into the time scales of serial, conformational transitions in a three‐state model, it allows a discussion of ground state distribution for X1 and X2, and, finally, it leads to a preliminary understanding of the pseudo‐Birks behavior at higher temperatures.
Photochromism of spirooxazines II. CARS‐investigation of solvent effects on the isomeric distribution
Authors: Schneider S. , Baumann F. , Klüter U. , Melzig M. 
Published: March 2014

AbstractThe isomeric distribution of metastable “photomerocyanines” produced by UV‐photolysis of spiroindolinonaphthoxazine derivatives is examined by resonance‐enhanced CARS spectroscopy. — In unpolar and polar aprotic solvents CARS spectra prove the existence of two pairwise similar isomeric species. They differ, however, in Franck‐Condon factors for excitation S0 → S1. In the protic solvent methanol an additional isomer is found for certain derivatives.
X‐ray absorption spectroscopy
Authors: Lytle Farrel W. 
Published: March 2014

AbstractThe X‐ray absorption near‐edge structure (XANES) of transition metal oxides is analyzed in terms of scattering resonances from neighboring atoms. Spectra from reference compounds of simple, known structure were used to facilitate identification of XANES peaks with scattering from specific coordination spheres. The resulting correlation between bond distance and energy of the absorption feature allows determination of bond distances in unknown materials. This is illustrated with the Cu K‐edges of YBa2Cu3O7 and Lau1.8Sr0.2CuO4. — The intensity of the L‐edge absorption resonances of the 5d elements is shown to be proportional to the number of 5d holes as determined by band structure calculations. In principle even the spin codiguration of the 5d orbitals can be determined. This is illustrated with data for a Re on A1203 catalyst.
Rotational tunnelling of methyl groups in bis(trimethyltin) sulfate dihydrate
Authors: Zhang Da , Walz Leonhard , Prager Michael , Weiss Alarich 
Published: March 2014

AbstractRotational tunnelling and librations of methyl groups in bis(trimethyltin) sulfate dideuterate, [(CH3)3Sn)]2SO4·2D2O, have been studied by inelastic neutron scattering (INS) technique. Tunnel splittings of 11. 36 μeV and 1.10 μeV and librational peaks at 9.98 meV and 14.8 meV were observed. The corresponding activation energies are calculated to be 4. 4 kJmol−1 and 2.6 kJmol−1, respectively. The INS measurements showed the existence of two types of inequivalent methyl groups of the occurrence ratio 1:2. The crystal structure of bis(trimethyltin) sulfate dihydrate was determined by single crystal X‐ray diffraction. [(CH3)3Sn)]2SO4·2H2O crystallizes orthorhombic, space group D142h‐Pbcn with 4 molecules in the unit cell. The lattice constants are a = 1124.4(2) pm, b = 1269.3(2) pm and c = 1080.9(2) pm. The sulfur atom lies on a twofold axis and therefore the two “(CH3)3Sn(H2O)” units in the molecule are crystallographically equivalent. The crystal structure analysis shows the three methyl groups bond to one tin atom to be inequivalent. This is not in agreement with the INS results. The discrepancy is discussed.
EXAFS studies of ammonia catalysts at synthesis conditions
Authors: Niemann W. , Clausen B. S. , Topsøe H. 
Published: March 2014

AbstractThe reduction of the precursors of different NH3 catalysts and the structure of the catalysts at reaction conditions are investigated by in situ X‐ray absorption spectroscopy at the K‐edge of Fe. From the XANES and EXAFS data a different reduction behaviour is found for K‐promoted and Cs‐promoted catalysts, respectively.
The role of geminate reaction in the self‐sensitized photooxygenation of helianthrene and hetianthrene‐derivatives encounter‐ and reencounter probabilities
Authors: Brauer H.‐D. , Acs A. , Schmidt R. 
Published: March 2014

AbstractThe probabilities pexpRQ of the geminate reaction between singlet oxygen (1Δ) and helianthrene (H), mesodiphenylhelianthrene (MDH) and mesodiphenylbenzhelianthrene (MDBH) were determined in several solvents of different viscosity. pexpRQ strongly depends on the viscosity of the solvent. For H pexpRQ increases from 0.17 (n‐pentane) over 0.44 (benzyl alcohol) to 0.97 (m‐cresol). For the first time experimental results clearly demonstrate that the reaction already takes place in the initial encounter, which is formed in the energy transfer from the T1‐states of the hydrocarbons to molecular oxygen. The solvent dependence of pexpRQ is only caused by the solvent dependence of the total reencounter probability, po. The results permit calculation of the probabilities per encounter (αR) and rate, k01, for an equilibrium distribution of 1Δ and the hydrocarbons.
Viscosity of Potassium Nitrate + Silver Nitrate Melt Mixtures
Authors: Schardey A. , Richter J. , Øye H. A. 
Published: March 2014

AbstractThe viscosity of KNO3 +AgNO3 melt mixtures has been determined in the range 0.25 ≤ χ ≤ 1.460 K. to 610 K. The viscosity of pure KNO3 was measured over the temperature span 620 K to 720 K. An oscillating‐cylinder viscosimeter was used. This method is absolute and requires no calibration against reference liquids. The viscosities in units of mPa s conform to the expanded Arrhenius type equation

with 0.04 to 0.31% standard deviations in the fit.
Das Dampf‐Flüssigkeitsgleichgewicht des ternären Systems Ammoniak‐Kohlendioxid‐Wasser bei hohen Wassergehalten im Bereich zwischen 373 und 473 Kelvin
Authors: Müller G. , Bender E. , Maurer G. 
Published: March 2014

AbstractExperimental results for the vapor‐liquid equilibrium in the ternary system ammonia‐carbon dioxide‐water are reported for six temperatures between 373 and 473 Kelvin at total liquid concentrations from 4 to 30 mole percent of ammonia and up to 14 mole percent of carbon dioxide as well as for the binary gaseous electrolyte‐water mixtures at the same temperatures and liquid phase concentrations of up to one mole percent (CO2) and 30 mole percent (NH3) respectively. The newly measured data agree well with the very limited literature data for the binary as well as for the ternary systems. Caused by the low solubility of carbon dioxide in water, the experimental results for that binary are described applying Henry's law. For correlating the results for the ammonia‐water system. Henry's law has to be corrected by introducing activity coefficients. The model of Edwards et al. with recently published new parameters is used to compare the experimental results for the ternary with existing correlations. Deviations between predicted and measured total and partial pressures amount up to 60 percent, thus indicating that the model needs further improvement.
Uni molecular Reaction Dynamics on Ab Initio Potential Energy Surfaces
Authors: Troe J. 
Published: March 2014

AbstractOne‐parameter fit versions of unimolecular rate theory for complex elimination and simple bond fission reactions are compared with detailed experiments. The agreement generally is so good that no further extension of this operational version of the theory is required. However, the relation between the fit parameter and properties of the potential surface not always is transparent. The article discusses the implementation of ab initio calculations of the potential by constructing adiabatic channel potential curves. Explicit results for charge‐dipole interactions are presented. SACM‐modified PST applies for selected conditions. Strategies for handling more complex potentials are outlined. The treatment closes the gap between operational fit parameters and potential properties.
The Optical Spectrum of NO2: Is it or Isn't it Chaotic?
Authors: Lehmann Kevin K. , Coy Stephen L. 
Published: March 2014

AbstractWe have used the technique of microwave detected, microwave‐optical double resonance to study the optical absorption spectrum of NO2 in the region near 17000 cm−1 above the ground state [1 – 3]. Spectra were recorded from ten lower states, ranging in rotational excitation from the 20.2 through the 101.9 states. Each lower state was scanned between 150 and 300 cm−1, and between 54 and 510 lines were observed in each spectrum. The method of double resonance uniquely identified the lower state of the observed transitions. Because the optical spectrum is dominated by a parallel transition and all of the observed lower states are K = 0 or 1, most of the observed transitions belong to either a qR or qP branch. For two pairs of lower states, states differing in J by two were studied, which allowed at least a partial assignment of transitions between P and R branches. Also, by studying spectra that have the same value for J and overall symmetry, but different values for N (the rotational angular momentum of the molecular frame), the extent of the breakdown of N selection rules could be quantified.
IVR Viewed Through State‐Selected Dispersed Fluorescence Spectroscopy of Jet‐Cooled Polyatomics
Authors: Knight Alan E. W. 
Published: March 2014

AbstractState selected dispersed fluorescence spectroscopy provides a means of unscrambling the identity of emitting states in polyatomic manifolds that are extensively mixed relative to the basis set pertinent to lower parts of the manifold. A view is presented of the methodology that may be used to unravel complex electronic spectra when information from dispersed fluorescence is available. The dispersed fluorescence spectrum serves as a means of projecting the excited state electronic wave function onto the ground state potential surface, thereby allowing the vibrational composition of the (mixed) excited state eigenvector to be evaluated in terms of a ground state vibrational basis. Examples are drawn from experimental data relating to the spectroscopy of benzene and azulene. In the case of benzene‐d6, Fermi resonances between the levels comprising the progressions 61 1n and 61 1021n‐1 lead to an interesting pedagogical example of how dispersed fluorescence spectroscopy may be used to chart IVR as it progresses from isolated mixing of a few states to more widespread scrambling of vibrational identity among many states. Azulene serves as an example of the more extreme case of widespread state mixing that in large polyatomics has its onset in relatively low regions of the excited state vibrational manifold. It is demonstrated that vibrational state mixing in azulene is still amenable to a detailed analysis that yields the composition of mixed eigenvectors.
The Dynamics of Polar Solvation
Authors: Castner E. W. , Bagchi B. , Maroncelli M. , Webb S. P. , Ruggiero A. J. , Fleming G. R. 
Published: March 2014

AbstractFluorescence upconversion experiments with subpicosecond resolution are described. The time dependent fluorescence spectra of several probe molecules in polar solvents are measured and used to construct the Stokes shift correlation function C(t). The correlation functions decay nonexponentially in contrast to the predictions of simple Debye/Onsager continuum theory. At high values of the static dielectric constants the solvation times are much slower than predicted from standard continuum theory. Generalizations of continuum theory to include non‐spherical shapes, non‐Debye dielectric response and saturation effects are discussed. The experimental data are qualitatively in accord with predictions based on a frequency and position dependent dielectric response.
Time Dependent Absorption of Fragments During Dissociation
Authors: Bersohn R. , Zewail A. H. 
Published: March 2014

AbstractThe development of methods of generation of very short pulses of light with widths about or below 100 fs has enabled the measurement of the rate of direct photodissociation of a bond. The experiment measures absorption as a function of both time and the degree to which the probing light is off resonance with one of the fragments. A classical model with an exponential repulsion is used to relate experimental observables to the dissociation time and properties of the potential surface. The delicateness of the probe will improve as the photon energy approaches the threshold energy for dissociation.
Dynamics of Vibrational Predissociation of (C2H4)2 and of IR‐Multiphoton Excitation of SF6
Authors: Liedenbaum C. , Heijmen B. , Dam N. , Stolte S. , Reuss J. 
Published: March 2014

AbstractHigh resolution measurements are discussed which indicate two decay channels for IR‐excited (C2H4)2; for cold dimers, from observed linewidths a 45 ns lifetime is derived after which the products are in their vibrational ground state. For hot dimers a many orders of magnitude shorter lifetime is indicated after which one of the product monomers is found in an excited v10 level. For highly excited SF6 (〈n〉 = 4 ÷ 5) narrow spectral features are observed attributed to rapid adiabatic passage processes. The IVR lifetime of the excited state is found to be longer than about 1 ms.
Understanding Unimolecular Dissociations with Loose Transition States: Photofragmentation Dynamics of Ketene at the Singlet Threshold
Authors: Green William H. , Chen I‐Chia , Moore C. Bradley 
Published: March 2014

AbstractPhotofragment excitation (PHOFEX) spectra of ketene (CH2CO) were taken by probing rovibronic transitions of the singlet methylene fragment while scanning the photolysis laser frequency. CH2(ã1A1) was detected by laser‐induced fluorescence in a supersonic free jet. The dissociation threshold of the reaction, CH2CO → 1CH2 + CO was determined to be 30116.2 ± 0.4 cm1. The nuclear spin is conserved during the dissociation. Sharp rises in the 1CH2 PHOFEX spectra are observed whenever a new CO rotational state becomes energetically accessible. Phase Space Theory (PST) is in excellent agreement with the experimental data. The Statistical Adiabatic Channel Model (SACM) and the related SACM‐PST theory fail to fit the experimental PHOFEX curves except in the limit where they become indistinguishable from PST (i.e. α/β > 0.7). The data show that there are no barriers to dissociation and that essentially every accessible product quantum state is equally likely to be formed. The implications of these findings for the theory of unimolecular dissociation are discussed.
Vibrational Relaxation of HBr (υ = 1) in Hydrogen Gaseous Mixtures at Low Temperature
Authors: Losert O. , Schwarz H.‐V. , Schramm B. 
Published: March 2014

AbstractMeasurements of vibrational relaxation rates of HBr (v = 1) in collisions with n‐H2, para‐enriched H2, HD and D2 are presented for temperatures ranging from room temperature down to 140 K. In all cases strong deviations of the V‐R, T rate from Landau‐Teller behaviour are observed. Neither the temperature dependence nor the mass dependence of the data can be explained by Landau‐Teller or Schwartz‐Slawsky‐Herzfeld theory.
An Investigation of Electrochemical Oxidation/Reduction Processes on Gold with the Kelvin Probe and Cyclic Voltammetry
Authors: Piller Gerd W. , Schumacher Rolf 
Published: March 2014

AbstractThe oxidation and reduction of gold electrodes contacted to acid and alkaline media were investigated with the Kelvin probe and cyclic voltammetry. The used set‐up allows a simultaneous operation of both methods. Surface processes to passivate and to repassivate gold electrodes were followed with these methods as function of the externally applied potential and time. The measurements provided kinetic data, which allows the identification of potential regions, in which either solid oxidic overlayers or adsorbed adlayers were formed at gold electrodes. The presented data are consistent with a recent XPS study, an investigation with the microbalance and data, obtained with classical electrochemical techniques.
Water Motion in Harmotome – Studied by Incoherent Inelastic and Quasielastic Neutron Scattering
Authors: Stuckenschmidt E. , Fuess H. , Stockmeyer R. 
Published: March 2014

AbstractThe mobility of the water molecules in the natural zeolite harmotome Ba2[(AlO2)4(SiO2)12] · 12H2O has been studied by incoherent neutron scattering on powder samples in several dehydration states and at different temperatures. – The external vibrational modes of the water molecules were determined from the inelastic part of the spectra (energy transfers 5 < ΔE < 100 meV) and were assigned to translational and rotational vibrations. The diffusive motion of water was evaluated from the quasielastic scattering and values of the residence time τ0 = 2.9 – 5.5 · 10−12 s, diffusion constant D = 5.0–25·10−5 cm2/s and mean jump length 〈I〉 = 0.41–0.66 nm were derived. – The results from the neutron scattering experiments were interpreted based on a redetermination of the crystal structure.
Systematic Investigations of the Dipolar Interaction in Aromatic Liquids. A Neutron Diffraction Experiment I. Structure Factors and Intramolecular Structure
Authors: Bertagnolli H. , Hummel I. , Chieux P. 
Published: March 2014

AbstractThe present work represents the experimental basis for the determination of short range order in some aromatic liquids as a function of the magnitude of the permanent dipole moment and the temperature. Neutron diffraction experiments were performed on liquid toluene, bromobenzene and nitrobenzene at various temperatures near the corresponding freezing points. These systems were chosen, as the sizes of the substituents are very similar, but the dipole moments are significantly different. After data reduction and evaluation the calculated intramolecular contributions of the investigated molecules were fitted to the corresponding total corrected differential cross section and the intramolecular geometries in the liquid phase were determined. As the temperature variation produced no significant change in the intramolecular structure, the determination of the molecular parameters for the various temperatures was based on an averaged molecular structure.
Elastic and Rheological Properties of Hydrocarbon Gels
Authors: Ebert G. , Platz G. , Rehage H. 
Published: March 2014

AbstractWe have investigated high elastic gels which can be formed from biphasic systems of hydrocarbon, water and surfactant. These new phases contain up to 99% hydrocarbon, but there exists a well defined upper limit for the incorporation of excess oil. – The hydrocarbon gels exhibit strong elastic properties which can be described by a frequency independent static shear modulus. The influence of the surfactant concentration, the surfactant chainlength and the volume fraction of hydrocarbon on the modulus was systematically investigated. The experimental data are in fairly good agreement with theoretical models which have been derived for such hydrocarbon rich gels.