bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solvatochromism in Alcohol‐Water Mixtures: Effects of the Molecular Structure of the Probe
Authors: Novaki Luzia P. , El Seoud Omar A. 
Published: July 2012

AbstractSolvatochromic behavior of 2,6‐diphenyl‐4‐(2,4,6‐triphenyl‐1‐pyridinio)‐1‐phenolate (RB), 1‐methyl‐8‐oxyquinolinium betaine (QB), sodium 1‐methyl‐8‐oxyquinolinium betaine‐5‐sulphonate (QBS), and 1‐methyl‐3‐oxypyridinium betaine (PB) was studied UV/Vis spectrophotometrically in binary mixtures of water with methanol, ethanol, 1‐propanol, 2‐methyl‐2‐propanol, ethane‐1,2‐diol, 2‐methoxyethanol, and 2‐n‐butoxyethanoI. The solvent polarity parameter, ET (in kcal/mole), was calculated from the position of the longest‐wavelength absorption band of the solvatochromic probe, and was then correlated with χw, the mole fraction of water in the mixture. Except for PB in aqueous methanol, aqueous ethanol and aqueous 1‐propanol, plots of ET versus χw are not linear because of preferential solvation of the probe by one component of the mixed solvent and, when applicable, because of solvent microheterogeneity. In the same aqueous alcohol mixtures, deviation from linearity in the ET versus χw plots increases as a function of the increasing hydrophobic character of the probe. For the same solvatochromic probe in different aqueous mixtures, the above mentioned deviation increases as a function of increasing the chain length of the alcohol. Preferential solvation of the probe is described in terms of the so called “solvent fractionation factor, ϕs”, whose value indicates the relationship between composition of the solvation shell of the probe, and composition of the bulk solvent. In the absence of solvent microheterogeneity, all values of ϕs are less than unity, which indicates preferential solvation of the probe molecule by the alcohol. An attempt to evaluate contributions from preferential solvation and solvent microheterogeneity to solvatochromism in aqueous methanol, and aqueous THF showed that the approach used by Park et al. [J. Phys. Org. Chem. 7, 757 (1994)] is not applicable.
Density Measurements for Expanded Fluid Selenium up to the Liquid‐vapour Supercritical Region by the X‐Ray Absorption Method
Authors: Hosokawa Shinya , Kuboi Takeshi , Tamura Kozaburo 
Published: July 2012

AbstractDensity of expanded fluid selenium was measured in the temperature and pressure ranges up to 1650°C and 700 bar including the liquid‐vapour critical point by the x‐ray absorption method. For the measurements, a new type of cell made of polycrystalline sapphire and a high‐pressure vessel of authors' own design were developed. The critical temperature, pressure and density of 1615 ± 5°C, 385 ± 5bar, 1.85 ± 0.03g cm−3, respectively, were obtained. We found that isochores bend in the semiconductor‐metal transition region. The shape of the isochore seems an elongated inverse‐S letter. The diameter of the liquid‐vapour coexistence curve is deviated from the law of the rectilinear diameter to the liquid side slightly around the SC‐M transition region and strongly near the critical point. A distinct crossover was also found in the critical exponent β; the value of β drastically changes from 0.30 to 0.10 when the critical point is approached.
The nature of valence band holes in pure and Fe‐doped NiO: An ab initio Hartree‐Fock study
Authors: Mackrodt W. C. 
Published: July 2012

AbstractFirst principles periodic Hartree‐Fock calculations of the first ionised state of Fe0.125Ni0.875 are reported from which the Mulliken populations, charge and spin distributions and atom projected densities of valence band states provide direct evidence of Fe(3d) holes in complete agreement with recent conductivity measurements on materials with approximately the same composition. This is in marked contrast to the self‐trapped hole in NiO, also reported here, and the bound hole in Li‐doped NiO where both experiment and a recently reported calculation find holes of predominantly O(2p) character.
Defect structure and solubility range of gallium‐doped cobalt oxide)
Authors: Schönfeld D. , Laqua W. 
Published: July 2012

AbstractThe electrical conductivity σ of polycrystalline cobalt oxide doped with gallium oxide, Co1‐xGa2x/3O, was measured as a function of temperature (800– 1400°), oxygen activity (10−4–0.21) and composition x (0–0.125). The phase boundary of the solid solution as a function of temperature and oxygen activity was ascertained by a well‐defined change of the slope in the σ‐T‐Arrhenius plot. As a function of Ga2O3‐content, the electrical conductivity runs through more or less distinct minima at all temperatures and oxygen activities. To explain these dependencies, a defect model was developed, which contains different defect associates and a 4:1‐cluster. It emerges from a model in which associated holes contribute to the total conductivity as well as free holes. Due to this fact different mobilities result for the respective holes.
Influence of the preparation conditions on the properties of electropolymerised polyaniline
Authors: Brandl Volker , Holze Rudolf 
Published: July 2012

AbstractPolymerisation conditions have a remarkable effect on the electrochemical properties of polyaniline. Care has to be taken to ensure identical conditions for electrochemical experiments when films electropolymerised differently are examined in comparison, especially when films are prepared potentiodynamically. UV‐vis spectra of PANI films show a hypsochromic shift with increasing potential, and a theory of this phenomenon is presented. It is based on the assumption of a distribution of chain segments of different effective conjugation length.
Conformational fluctuation and ion permeation of lipid bilayers doped with azobenzene derivative: Infrared spectroscopic study
Authors: Tanaka Motomu , Kohno Yoshiumi , Yonezawa Yoshiro , Shimidzu Takeo 
Published: July 2012

AbstractWe have fabricated the liposome dispersions of L‐α‐dimyristoylphosphatidylcholine (DMPC) doped with an amphiphilic azobenzene derivative, 4‐octyl‐4'‐(5‐carboxypentamethyleneoxy)azobenzene (8A5). The conformation of the DMPC liposome membrane was changed reversibly according as photoisomerization of 8A5. Fourier transform infrared spectroscopy (FTIR) was applied to study interactions between dopants and host lipids. Dependence of FTIR spectra of the CH2 stretching bands on the molar ratio of 8A5 and on temperature indicates that 8A5 molecules induce a large fluctuation on the molecular packing of the membrane around the phase transition temperature. We have carried out K+ ion permeation measurements across the liposome membrane in varying molar ratios at T = 283–303 K. A large overshoot and the following relaxation of the ion permeability were observed with UV irradiation at T = 293 K. We have proposed that the specific photoresponse is operated by two factors: the expansion of pores (‘quasi‐channels’) due to trans‐ti‐cis isomerization of 8A5 and the increase of the boundaries between gel phase and liquid‐crystalline phase around the phase transition temperature. FTIR spectroscopy yields useful information about the conformational fluctuations of the DMPC bilayer induced by photoisomerization of 8A5.
Competitive counterion binding to poly(alkylene phosphate)s related to natural teichoic acids. The Poisson‐Boltzmann approach
Authors: Ostrowska‐Czubenko Jadwiga , Czubenko Marek 
Published: July 2012

AbstractThe problem of competitive metal ion binding to poly(alkylene phosphate)s, considered as synthetic models of natural teichoic acids, was analysed theoretically applying the Poisson‐Boltzmann (PB) equation to a cylindrical cell model. There were calculated the radial distribution functions as well as the degree of ion binding of mono‐and divalent metal ions to polyphosphate ions in solutions of different concentrations ranging from 10−5 M to 10−2 M and containing different amounts of M⊕ and M2+ counterions. For comparison, analogous calculations were performed also for poly(styrenesulfonate)s. The results indicate the preferential binding of divalent metal ions to polyphosphate ions over monovalent ones. The selectivity for M2+ ions is concentration dependent and increases with decreasing the polymer solution concentration. It results from PB calculations, that condensation of divalent metal ions at the surface of polyion chains seems to be responsible for preferential binding of biologically important metal ions, for example magnesium, to natural teichoic acids and their synthetic analogues.
State‐to‐state studies of intramolecular dynamics and unimolecular reactions
Authors: Kuhn B. , Boyarkin O. V. , Rizzo T. R. 
Published: July 2012

AbstractDouble‐resonance vibrational overtone excitation spectra of small molecules, in combination with laser‐induced fluorescence product detection, provide information on both their energetics and intramolecular energy redistribution dynamics. Application of this approach to measure OH stretch overtone spectra of HOOH and NH2OH near their dissociation threshold provides estimates of the O‐O and N‐O bond energies of 17051.8±4 cm−1 and 21620±20 cm−1 respectively.In symmetrical molecules, such as HOOH, the double‐resonance excitation technique allows us to prepare molecules in either pure OH stretch overtone levels or combination levels in which the excitation energy is divided between two identical OH stretch oscillators. Comparison of the resulting vibrational overtone linewidths indicates no clear difference between the pure OH stretch and the local‐local combination levels. However, comparison of the energy transfer rates from pure OH stretch vibrations and those in which one quantum of energy is put in a low frequency mode reveals faster rates from the latter. This observation clearly indicates that coupling strengths depend markedly on the vibrational character of the coupling partner and not simply on the total energy.Comparison of the OH stretch overtone spectra of the structurally similar molecules HOOH, NH2OH, and CH3OH reveal similar rates of vibrational energy redistribution, despite the difference in the density of states in these molecules. This observation reinforces the notion that energy flow between the OH stretch and dark background states is not statistical but rather is controlled by coupling to a small subset of background states.
Intramolecular energy transfer from isotope selective overtone spectroscopy by vibrationally assisted dissociation and photofragment ionization
Authors: Hippler Michael , Quack Martin 
Published: July 2012

AbstractOvertone spectroscopy by vibrationally assisted dissociation and photofragment ionization (OSVADPI) has been coupled with the detection of fragments in a mass spectrometer allowing isotope selective overtone spectroscopy (ISOS) on naturally occurring isotopomer mixtures. The room temperature CH‐chromophore spectra of CF2HCl (polyad component Nj = 41 near 11430 cm−1) and of chloroform (Nj = 21 near 5942 cm−1 and Nj = 31 near 8726 cm−1) have been investigated in this way and discussed in relation to intramolecular energy transfer. The features of the central Q‐branch regions are assigned with resolution of the Cl‐isotopomers, and Q‐branch maxima and Cl‐isotopomer shifts are determined. The effect of the strong Fermi resonance, mixing CH‐stretching and bending modes, on the position of vibrational hot band transitions is demonstrated. We describe in detail the extension of our technique into the near and mid infrared range with a high resolution optical parametric oscillator system which has a wide range of potential applications as a general infrared spectroscopy with isotope and mass selection (IRSIMS).
The influence of hindered rotations on recombination/dissociation kinetics
Authors: Wagner Albert F. , Harding Lawrence B. , Robertson Struan H. , Wardlaw David M. 
Published: July 2012

AbstractThe variational canonical flexible transition state theory expressions for the thermal reaction rate constant are reviewed and then applied to the barrier‐less recombination reactions H + CCH, H + CF3, and CH + H2. The rate constant expressions can classically accommodate any description of the hindering potential governing relative orientation changes between the reactants at a given distance. The distance held fixed during the relative orientation changes can be fully optimized. The three applications display comparable and large variations between the harmonic oscillator and free rotor limits of the hindering potential. The actual hindering potentials are all derived from similar ab initio electronic structure calculations. With these potentials, the rate constant for H + CF3 is somewhat free‐rotor like, the rate constant for CH + H2 is mostly harmonic‐oscillator like, and the rate constant for H+CCH is largely in between these two limits.
The calculation of vibrational eigenstates by MINRES filter diagonalization
Authors: Yu Hua‐Gen , Smith Sean C. 
Published: July 2012

AbstractA spectral filtering method reported recently [Faraday Disc. 102, 17 (1996)], which utilizes the optimal expansion of the Green operator in a finite Lanczos subspace, is used to construct a new scheme for the calculation of bound vibrational states by filter diagonalization. The method requires storage of only two real vectors in the primary representation, i.e., those required to generate the Lanczos subspace. Calculations for the HO2 molecule show that the new scheme efficiently generates converged eigenvalues within a nominated energy window which maybe scanned through the bound spectrum, and utilizes just a single Lanczos subspace (generated once only). It not only is more efficient than the regular Lanczos algorithm for computing high‐lying eigenstates, but also has the interesting property of eliminating duplicated and ghost eigenvalues, which can cause problems in interpretation of the regular Lanczos spectrum.
Rigidity factors in unimolecular reactions
Authors: Troe Jürgen 
Published: July 2012

AbstractUnimolecular reactions with loose activated complexes, i.e. simple bond fission and the reverse bond formation processes, are conveniently characterized by phase space theory (PSD, which accounts for the maximum attraction potential between the fragments, and by additional rigidity factors which are the result of the anisotropy of the potential. This article summarizes recent calculations of specific rigidity factors frigid (E, J) and of thermal rigidity factors frigid (T) for a series of different potentials such as, e.g., ion‐dipole, dipole‐dipole, or standard valence potentials. The calculations have been made by rigorous statistical adiabatic channel (SACM) in combination with classical trajectory (CT) calculations.
Quantum and classical calculations of adiabatic and nonadiabatic capture rates for anisotropic interactions
Authors: Nikitin E. E. , Troe J. 
Published: July 2012

AbstractA uniform and systematic approach to the calculation of the capture rate constant is presented in the case of most typical long‐range intermolecular interactions. We consider ion‐linear dipole rotor, ion‐axially symmetric quadrupole rotor and two dipole linear rotors with additional isotropic ion‐induced dipole and induced dipole‐induced dipole interactions. The results for the capture rate constants are given in analytical form for nonadiabatic and adiabatic capture of classical as well as quantum rotors in very wide range of dynamic and kinematic parameters of the capture events.
Measurement of the rate constant k(E) of the unimolecular H2 elimination from ethane radical cations in a reflectron mass spectrometer
Authors: Güthe Felix , Weitzel Karl‐Michael 
Published: July 2012

AbstractA brief review of the literature concerning the H2 loss reaction from ethane radical cations is given. The reaction most likely proceeds by tunneling of H atoms through a transfer barrier. In this contribution a new experimental approach is presented, which combines the high energy resolution of a zero kinetic energy (ZEKE) electron spectrometer with the high kinetic resolution of a reflecting ion time of flight spectrometer in a coincidence experiment. With this technique it is possible to measure the rate constant k(E) of the title reaction an ion energy resolution of 10 meV directly over three orders of magnitude. The implementation of this technique will ultimately enable the study of D2 loss from isotopically labeled ethane‐d6 cations.
Unimolecular decomposition of large organic radicals with low reaction thresholds: Decomposition and reversible isomerization of n‐pentyl radicals
Authors: Tsang Wing , Bedanov Vladimir , Zachariah Michael R. 
Published: July 2012

AbstractThe decomposition kinetics of n‐pentyl radicals in the high temperature regime where steady state distributions are not achieved and reversible isomerization to decomposing 2‐pentyl radicals is of importance has been analyzed through the solution of the time‐dependent master equation. The reactions are characterized by low activation thresholds and lead to large rate constants that vary with time. Particular attention is paid to branching ratios for direct decomposition of the n‐pentyl radical and the decomposition that follows reversible isomerization to the 2‐pentyl species. The behavior of the system under a variety of conditions is described and the use of branching ratios as a possible means of characterizing the reactions in a manner that is compatible with present methods for employing kinetic data for simulating complex chemical phenomenon is considered. At higher temperatures, rate constants and branching ratios collapse to limiting values. The combination of limiting and the onset of steady state behavior complicates the situation at lower temperatures. The overall behavior of such systems is highly dependent on the magnitude of the barrier to isomerization. The extent of departures from the high pressure‐branching ratios are defined.
Kinetics and energy partitioning in complex‐forming reactions between neutral species
Authors: Smith Ian W. M. 
Published: July 2012

AbstractA short survey is presented of some recent experiments on the kinetics and dynamics of complex‐forming reactions. Differences and similarities between bimolecular reactions in which a pair of products are formed and collisionally assisted association reactions are considered. Some emphasis is placed on those reactions whose rates are determined by ‘capture’ on the long‐ and medium‐range attractive potential acting between the reagents. Such processes are discussed in relation to specific reactions, such as those of CN with O2 and C2H2, OH with butenes, and CH with O2, C2H2, N2, CO and H2, for which rate constants have been determined over most of the temperature range from 10 to 1000 K. The CH + H2 system is considered in some detail as it serves as a prototype of complex‐forming reactions in which there is competition between collisionally assisted association (to CH3 radicals) and bimolecular reaction (to CH2 + H).
Collisional energy transfer probabilities in the deactivation of highly vibrationally excited aromatics
Authors: Hold U. , Lenzer T. , Luther K. , Reihs K. , Symonds A. 
Published: July 2012

AbstractFull sets of experimentally determined “collisional energy transfer probability distributions”, P(E', E), have become available first time for the deactivation of highly vibrationally excited large molecules. These data from KCSI measurements (kinetically controlled selective ionization) on the vibrational relaxation of toluene (<E0> = 50000 cm−1) and azulene (<E0> = 30000 and 20000 cm−1) are discussed with emphasis on systematic aspects. Under proper conditions the KCSI measurements become self‐calibrating. This provides i.a. very high quality results on <ΔE>, free from possible calibration errors. Detailed second moments are given and consequences on energy distributions during relaxation are discussed. The P(E', E) distributions show extended wings of finite probabilities for transfer of large ΔE. Their relative role is characterized. A double‐exponential representation of P(E' E) is useful, mainly for atomic and shall molecular collider gases. However, a more universal and better analytical representation of P(E', E), using one parameter less, is recommended. The fraction of “super‐collisions” (independent from details of definition) is very small.
Progress on the modeling of the collisional energy transfer mechanism in unimolecular reactions
Authors: Nordholm Sture , Börjesson L. E. B. , Ming Liu , Svedung Harald 
Published: July 2012

AbstractThe RRKM theory of unimolecular reaction rates is a statistical mechanical theory based on an assumption of microcanonical equilibrium in the reactant phase space. The energy transfer in reactant medium collisions was originally described by a canonical strong collision assumption, i.e., an assumption of full thermal equilibration in each collision. In our work we first introduce a microcanonical strong collision assumption which gives the RRKM theory a consistent form. We then introduce parameterizations of the degree of weakness (nonergodicity) of the collisions. A concept of collision efficiency is defined. The weakness of the collision is expressed in terms of reduced subsets of active reactant and medium degrees of freedom. The corresponding partially ergodic collision theory (PECT) yields physical functional forms of the collisional energy transfer kernelP(E', E). In order to resolve the energy and temperature dependence and the dependence on interaction strength a multiple encounter theory is introduced (PEMET). Initially each encounter may be described by a semiempirical PECT model. Eventually the encounters may be resolved by quantum dynamical calculations of the semiclassical or CAQE (classical approach/quantum encounter) type. Simple statistical collision models only distinguish between “hits and misses”. In reality the energy transfer efficiency exhibits characteristic fall off with increasing impact parameterb.Thisb‐dependence can be explicitly accounted for in the master equation for the reaction rate coefficient.
Photodissociation and size analysis of (HBr)n clusters
Authors: Baumfalk R. , Buck U. , Frischkorn C. , Gandhi S. R. , Lauenstein C. 
Published: July 2012

AbstractHydrogen bromide clusters that are generated in an adiabatic expansion with Ar are size‐selected by scattering from a He or a Ne beam and a subsequent separation by a velocity selector. The complete fragmentation pattern for electron impact ionization of clusters n = 3,5,7,10, and 15 is obtained for electron energies of 70 eV. Up to cluster sizes of n = 15 strong fragmentation is observed. Based on these results the cluster sizes are measured as a function of different source conditions. For the same experimental conditions the (HBr)n clusters are photoionized at 243.1 nm. A time‐of‐flight mass spectrometer with low extraction fields is used to obtain the translational energy distributions of hydrogen atoms. Several distinct features are observed which sensitively depend on the cluster size. At small cluster sizes a tail appears towards lower energies in the fast hydrogen kinetic energy distribution which is caused by few collisions with the cluster molecules. Peaks at higher energies are attributed to internally excited HBr molecules which gain their energy in collisions with photofragmented H atoms. Small clusters exhibit pure rotational excitation with averaged J = 7, while the larger ones show vibrational excitations to v = 1 with J = 8 and v = 2. Finally, we observe a narrow H component peaking near zero velocity and exhibiting an isotropic angular distribution. This effect appears only at larger cluster sizes and is attributed to a complete caging of the photofragments.