bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical Properties of Energy Levels in Non‐Born‐Oppenheimer Systems
Authors: Zimmermann Th. , Cederbaum L. S. , KÖppel H. 
Published: March 2014

AbstractBasic 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

AbstractRate 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

AbstractSome 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

AbstractThe 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

AbstractThe 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

AbstractMeasurements 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

AbstractThe 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

AbstractHighly 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.
Selective Intracluster Ion‐Chemistry Studied by Resonant Two‐Photon Ionization Spectroscopy
Authors: Brutschy B. , Janes C. , Eggert J. 
Published: March 2014

AbstractAfter 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

AbstractSpecific 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

AbstractThe 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

AbstractThe 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

AbstractAdsorption 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

AbstractThe 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

AbstractDensities 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

AbstractWe 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

AbstractThe 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

AbstractThe 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

AbstractNickel‐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.
Light Scattering and Lateral Resolved Reflection Spectroscopy on Electrochemically Reacting Electrodes
Authors: Oelkrug D. , Reich S. , Specht M. , Stauch H. 
Published: March 2014

AbstractThe electrochemical formation and reduction of oxide films on rough and polished electrodes of iron, low‐carbon steel and copper is investigated by in situ reflection spectroscopy in the UV/VIS‐range with simultaneous detection of polarized specular reflection and depolarized scattering. The reflectivity of the electrodes can be scanned with a lateral resolution of < 10 μm, and a rapid diode array reflectometer allows the registration of a series of complete spectra in the millisecond range which help to analyze the kinetics of electrode processes. The conversion of homogeneous films into light‐scattering porous layers can be detected in the region of a few monolayers and the voltages and pH‐values at which these conversions take place are determined. The experimental change of reflectivity with film thickness is compared with model calculations. Lateral resolved measurements on copper prove that the cupric oxide film is reduced to the metal not uniformly but first on the front of the electrode and then on the rear beginning at the edges and ending in the centre.
Eine neue Methode zur Untersuchung der Elektrosorption reaktiver Verbindungen
Authors: Holze Rudolf , Schneider Jürgen , Hamann Carl Heinz 
Published: March 2014

AbstractThe determination of thermodynamic and kinetic data of reactive chemisorption of organic molecules on electrodes with a new procedure is described. It substitutes a rapid electrolyte exchange with potential control of the working electrode for an electrode transfer. A new measurement and evaluation procedure allows determination of degree of coverage, rate of adsorption and interaction between adsorbate molecules from cyclic voltamograms recorded after adsorption and electrolyte exchange. As an example the adsorption of aliphatic alcohols (C1 to C4) on a platinum electrode in contact with an acidic electrolyte solution is studied. The results show the power of the method as compared with other ones, in particular with respect to kinetic data on the process not accessible by other methods. The adsorption rate constant increases from C1 to C3 by an order of magnitude with every C‐atom; the actual rate of adsorption changes much less, since with increasing chain length repulsive interaction between adsorbate molecules increases. Sec‐propanol shows a greatly diminished rate of adsorption, t‐butanol is adsorbed only slightly.
A Molecular Dynamics Study on the Water/Metal Interfacial Potential
Authors: Spohr E. , Heinzinger K. 
Published: March 2014

AbstractSeveral Molecular Dynamics simulations of water on the (100) plane of a platinum single crystal have been performed for different degrees of surface coverage. The orientation of the water molecules is mainly determined by the water‐water interactions which is even true at low coverage as the water molecules are not distributed uniformly on the surface. The calculated work function change is in good agreement with experimental results.
Studies of the Differential Double Layer Capacitance of the Copper (111) Face in Aqueous Solutions
Authors: Weidenauer Markus , Weil Konrad G. 
Published: March 2014

AbstractThe double layer capacitance of electropolished copper (111) faces was measured in aqueous solutions in the presence of inert supporting electrolyte and in the presence of chloride ions. In the absence of chloride, we find a capacitance maximum at the anodic scan. The corresponding maximum during the cathodic scan is shifted to more negative potentials. There remains a shift even when the scan rate is extrapolated to zero. The positions of the maxima vary with ≈ 30 mV/pH. In the presence of chloride ions, the same maxima are observed. Now they are nearly two times higher, but their position also varies with the pH and not with the concentration of Cl−‐ions. This indicates a correlation between oxide layer formation and reduction with the adsorption and desorption of chloride ions. – From the time dependence of the double layer capacitance after cathodic steps, we conclude that the reduction of the oxide layer is accompanied by a phase transition.