bluuebunny/crossref_metadata_2025_split huggingface dataset:
K‐Conservation in the dissociation of singlet ketene
Authors: Mellinger Axel , Hall Melonie A. , Wade Elisabeth A. , Moore C. Bradley 
Published: July 2012

AbstractThe effect of K‐conservation on the photodissociation of ketene has been investigated. Rate constants and photo‐fragment excitation (PHOFEX) spectra have been calculated using phase space theory (PST) in a helicity basis. While the effect of K‐conservation on rate constants is relatively subtle, PHOFEX spectra with state‐selected reactant molecules appear to provide a feasible way to experimentally resolve the question of K‐conservation.
Ultrafast photochemical pericyclic reactions and isomerizations of small polyenes
Authors: Fuß Werner , Hering Peter , Kompa Karl L. , Lochbrunner Stefan , Schikarski Thomas , Schmid Wolfram E. , Trushin Sergei A. 
Published: July 2012

AbstractPotential energy surfaces for pericyclic reactions can easily be predicted by means of correlation diagrams. Whereas the initially excited state (called 1 B in this paper) may vary from molecule to molecule, its population is collected by a lower, dark state (2A) of always the same nature, which corresponds to a two‐electron excitation. From there, the system leaves to the ground states of educt and product(s) via a conical intersection (CI). Using transient absorption and transient ionization spectroscopy, we measured the lifetimes t1B and t2A of these states after initiating electrocyclic ring opening of 1,3‐cyclohexadiene and some of its derivatives (α‐terpinene, α‐phellandrene and 7‐dehydrocholesterol). t2A can be considered the reaction time constant. Whereas t2A = 5.2 ps for dehydrocholesterol. it is 80–100 fs for the other three molecules. We suggest that the former system needs some time to find the exit (the CI) from the 2A surface, whereas in the latter cases the CI is located right in the line of the steepest descent. We apply the same scheme to, and compile the time constants for, some other fast processes: the [1.3] sigmatropic reactions of norbornene and norbornadiene (t2A = 220 and 210 fs) and the fast internal conversions of cycloheptatriene (80 fs) and several UV stabilizers. The latter two processes are suggested to take the same pathway as the pericyclic hydrogen shifts in these molecules. We also point out the similarity of the pericyclic potential surfaces to those of cis‐trans isomerizations and give evidence that cis‐stilbene (t2A < 300 fs), too, is accelerated directly in the direction of the CI. For cis‐trans isomerization of longer polyenes there are however several 2A minima and conical intersections. We also give examples where additional branchings and competing reactions play a role.
A state‐to‐state statistical‐dynamical theory for large molecule collisional energy transfer
Authors: Barker John R. 
Published: July 2012

AbstractA statistical‐dynamical theory of large molecule energy transfer based on state‐to‐state transition probabilities is derived and a demonstration calculation is presented for cyclopropane deactivation by helium. For demonstration purposes, the SSH(T) theory is used for calculating state‐to‐state transition probabilities, and thus the present calculations are expected to provide only general trends. Various tests for convergence of the calculations are described. The calculations are shown to be practical even for energies where the vibrational state densities exceed 1010 states cm−1. The results predict that energy transfer propensities persist even at very high vibrational energies. The predicted collision step size distributions resemble the exponential model, but with strong fluctuations about the mean. The predicted average energy transferred in deactivation collisions (<ΔE>down) depends on vibrational energy, due to the changing fraction of inelastic collisions; the shape of the distribution function remains nearly unchanged. In future calculations, the SSH(T) theory will be replaced by other theories in order to obtain more accurate predictions.
Collisional deactivation of vibrationally highly excited azulene in supercritical xenon/ethane mixtures
Authors: Schwarzer D. , Troe J. , Votsmeier M. , Zerezke M. 
Published: July 2012

AbstractThe collisional deactivation of vibrationally highly excited azulene was studied in equimolar supercritical mixtures of xenon and ethane at 385 K from gas to liquid phase densities. Azulene with an energy of 18000 cm−1 was generated by laser excitation into the St‐ and subsequent internal conversion to the S*σground state. The loss of vibrational energy was monitored by transient absorption at the red edge of the S3←S0 absorption band at 290 nm. Transient signals were converted into energy‐time profiles using hot band absorption coefficients from shock wave experiments for calibration and accounting for solvent shifts of the spectra. Under all conditions, the decays were monoexponential. At densities below 10−3mol/cm3, the observed collisional deactivation rate constants kc of the mixture were equal to the sum of the individual contributions of ethane and xenon collisions as expected from simple gas kinetics. At mixture densities above 2×10−3 mol/cm3, kc is smaller than the deactivation rate constant found in neat ethane at half the density. This behavior can be rationalized by a model employing an effective collision frequency which is related to the finite lifetime of collision complexes; the required parameters follow from experiments in neat xenon and ethane.
Equilibrium glass transition in a polymer‐solvent system
Authors: Frank W. , Schwarz J. 
Published: July 2012

AbstractFrom the results of long time measurements on the dependence of the mole fraction on temperature and solvent activity in the system atactic polystyrene‐cyclohexane we see evidence for an equilibrium glass transition range, which begins closely below the kinetically caused glass transition at a cooling rate of about 1 K min−1. The thermodynamic background is discussed, starting from the so called Kauzmann paradox and the extension of the Ehrenfest equations on mixed phases with the additional variable mole fraction. The results of Rehage from swelling curves in the glass transition range are reinterpreted.
On the sequence of events in H2S oxidation reactions
Authors: Melsheimer J. , Schlögl R. 
Published: July 2012

AbstractIn‐situ reflectance UV‐VIS spectroscopy and on‐line GC were performed on pressed and powdered wafers made from industrial aluminas in different microreactor cells at 400 K. At a steady state conversion of 60–70% a very strong absorption band formed initially at 290 nm. A broadening of this peak with time on stream was observed during the modified Claus reaction (2H2S + SO2  (3/x)Sx + 2H2O) in these cells.A conversion of < 10% was measured for the Claus reaction (2H2S + O2  (2/x)Sx + 2H2O) during which the response was similar to that recorded in the reaction given above.The results of reference spectra obtained on sulfur‐containing compounds showed that an attribution of the observed absorption bands to various sulfur species is possible. A deconvolution of the reflectance data and an analysis of peak areas indicated that the species S2O2−2 and S2O2−2 affect the steady state for the modified Claus reaction and the species S2O2−3 for the Claus reaction. Reaction sequences are suggested for these H2S oxidation reactions.
Comments on time‐resolved charge transfer with hot electrons at the silver/electrolyte interface
Authors: Kulmala S. , Ala‐Kleme T. 
Published: July 2012

AbstractAdditional information is presented to that previously published by Diesing et al. in this journal considering metal/insulator/metal tunnel junctions in contact with aqueous solution. Hot electron injection into aqueous electrolyte solutions from metal/insulator/metal/electrolyte and metal/insulator/electrolyte tunnel junctions is considered and the thermodynamic basis of probable electrochemical generation of hydrated electrons is discussed.
Thermodynamics of the amalgam cell: {MexHg1‐x|MeCl(m)| AgCl| Ag} (with Me = K, Rb) in (methanol+water) solvent mixtures
Authors: Basili Alessandro , Mussini Patrizia R. , Mussini Torquato , Rondinini Sandra , Vertova Alberto 
Published: July 2012

AbstractThe electromotive force E of the amalgam cell {MexHg1‐x|MeCl(m)|AgCl|Ag}, where Me = K or Rb, has been measured at the temperature 298.15 K as a function of the molality m of MeCl in (methanol + water) mixed solvents up to 0.8 mass fraction of methanol, with relative permittivities ϵ>40, and as a function of the mole fraction x of Me in amalgam. The respective standard electromotive forces E0m have been determined, together with the mean molal activity coefficients y ± of the relevant MeCl as a function of its molality. For interpolation purposes the E0m values can be expressed as a function of the methanol mass fraction wM by the following polynomials, valid for 0≤wM≤0.8:

These results for standard e.m.f.s, interpreted in terms of primary medium effects, lead to primary hydration numbers nhydr = 6.6 for KCl, and = 6.7 for RbCl, in good agreement with previous results using different methods.
Matrix‐theoretical calculation of diffusion parameters for composite membranes with periodic structure
Authors: Chen Jenn‐Shing , Shi Way‐Chia 
Published: July 2012

AbstractBased on the Siegel's theory, the diffusion parameters of steady‐state permeability (P), downstream time Lag (tL), forward and backward mean first passage time \documentclass{article}\pagestyle{empty}\begin{document}$ (\bar t_ + {{\rm and}}\;\bar t_\_ ) $\end{document} for absorptive unidirectional permeation for a membrane with n‐periodic structure have been calculated from the transmission matrix in the Laplace domain with the help of the Caley‐Hamilton theory. The results of calculation give that \documentclass{article}\pagestyle{empty}\begin{document}$ P = P^{(i)} /n,\;t_L = t_L^{(i)} + \frac{1}{6}(n^2 - 1)(\bar t_ + ^{(i)} + \bar t_ - ^{(i)} ,\;\bar t_ + = n\bar t_ + ^{(i)} + \frac{{n^2 - n}}{2}(\bar t_ + ^{(i)} + \bar t_ - ^{(i)} ),\;\bar t_ - = n\bar t^{(i)} + \frac{{n^2 - n}}{2}(\bar t_ + ^{(i)} + \bar t_ - ^{(i)} ) $\end{document}, where the diffusion parameter with a superscript (i) denotes its corresponding entity for a single unit period. The consistency with the previous results obtained by repeated integration is also discussed.
On the mechanism of the reaction of CF3 radicals with C6F5Cl in the temperature range 318–473 K
Authors: Nieto J. D. , Lane S. I. , Oexler E. V. 
Published: July 2012

AbstractThe gas‐phase reaction of CF3 radicals, generated by photolysis of perfluoroacetic anhydride, with C6F5Cl was studied in the temperature range 318–473 K and total pressures between 23 and 41 Torr. CF3 radicals react with C6F5Cl according to the following mechanism:magnified imageIt was found that the addition reaction becomes reversible above 390 K. The addition rate parameters can be summarized in the following equation:

where θ = 2.303 R T kJ mol−1 and kc is the recombination constant of CF3 radicals. A correlation between log [(kadd/k1/2c) and the ionization potentials for 15 aromatic compounds was found.
Chiotti integration of Gibbs‐Duhem relation and unequivocal determination of limiting partial thermodynamic quantities at infinite dilution of binary solution system
Authors: Cho Seung‐Am , Ochoa José Luis 
Published: July 2012

AbstractChiotti has made a breakthrough in the thermodynamic theory of solution after nearly a century of frustration. Activity α,i, activity coefficient γi, Darken function αi = In γi/(l‐xi)2 and other partial thermodynamic quantities \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta \bar Q_i^{{\rm{xs}}} \;{\rm{and}}\;\Delta \bar Q_i $\end{document}, where i = Bi and Sn, of binary liquid Bi‐Sn alloy solution system are critically assessed by means of the authentic Chiotti integration, as all those quantities oscillate along composition which made their procurement through classical routes, Gibbs‐Duhem and Darken integrations, impossible. The unambiguous partial quantities at their infinite dilution are obtained from the genuine Chiotti slopes. Interrelations among partial quantities in terms of composition and temperature are presented in detail. We reveal that the apparent Raoultian and Henrian α, vs. Xi behaviors are false and then demonstrate neither Bi nor Sn complies with the Raoult's law and Henry's law. The molten Bi‐Sn system is the athermal type but the behavior of the solution is rather complex and it is definitely neither subregular nor regular solution. In this context the subregular and various symmetrical solutions are systematically developed in relation to function αi and discussed in great detail. A new method of classification of complex solution systems beyond subregular and regular in terms of the difference quantities \documentclass{article}\pagestyle{empty}\begin{document}$ (\Delta \bar Q_B^{{\rm{xs}}} {\rm{-}}\Delta \bar Q_A^{xs} ) $\end{document} is proposed.
Influence of the crystallization process on the photoelectrochemical behaviour of anodic TiO2 films
Authors: Piazza S. , Calá L. , Sunseri C. , Di Quarto F. 
Published: July 2012

AbstractOn the basis of kinetic and photoelectrochemical studies we show that the formation of amorphous or strongly disordered TiO2 films on electropolished titanium rods can occur upon anodization in 0.5 M H2SO4 solution in a range of thickness which depends on the anodization rate. This finding is confirmed both by the changes in the shape of the photocurrent vs. potential curves with the energy of the incident photons, and by the impedance behaviour of the junction.Our data indicate that TiO2 films having different degree of disorder are formed depending on the anodization rate and oxide thickness. Crystalline films are formed at very low growth rates since very low thicknesses. Amorphous or strongly disordered films can be grown at high oxidation rates (≥ 100 mV/s) before the onset of a crystallization process. At higher thicknesses a gradual crystallization process takes place, as revealed both by the decrease of the anodizing current during the tensiodynamic growth and by the changes in the shape of the photocurrent vs. potential curves. The onset of the crystallization process of the film occurs at higher thicknesses with increasing the growth rate.
Spectroscopic and chromatographic investigations of sulfur ammonia solutions
Authors: Schindewolf U. , Herrguth J. , Zhou D. 
Published: July 2012

AbstractElemental sulfur dissolves in liquid ammonia to form an anionic adduct S5NH−2 (sulfur in zero oxidation state) which by redox reactions leads to the anionic species S3N− and S4N− (positive oxidation state), and S3− as well as its dimer S62‐ (negative oxidation state). By anion exchange chromatography under HPLC conditions the species of a sulfur ammonia solution (SAS) are separated and (using radioactive sulfur) their absolute concentrations and absorption spectra are obtained. With these the absorption spectra of SAS taken in wide concentration and temperature ranges are analysed without separation to get quantitative data of the concentrations of all species and thus of the equilibrium constants, the reaction enthalpies and entropies of the two reactions in which the species are involved. The variations of the spectra due to shifts of the equilibria by changes of the pH of the solutions or by changes of their redox potential are simulated. Finally the time dependence of the spectra during the slow dissolution process of sulfur in ammonia gives information on the solubilization process.
Surface tension of a binary liquid mixture in the vicinity of its critical point
Authors: Mainzer‐Althof T. , Woermann D. 
Published: July 2012

AbstractResults of measurement of the temperature and composition dependence of the surface tension σα,βγ of 2,6‐dimethylpyridine (abbreviated 2,6‐dp)/water mixtures are reported. The index α refers to the vapor phase and the index βγ to the homogeneous 2,6‐dp/water mixture. The experiments are carried out at constant temperatures T below and at the critical temperature Tc (= 33.87°C) in the entire composition range (0≤x≤ 1; x, mole fraction of 2,6‐dp). For mixtures with compositions in the range −0.04<(x‐xc)<0.10 (xc = 0.640) the experimental σα,βγ (x, Tc) data can be represented by the theoretically established equations σα,βγ = σc + C(xc‐x)μ*/β* for x<xc and σα,βγ = σc + D(x‐xc)μ*/β* for x>xc (Nagarajan, Webb, Widom, J. Chem. Phys. 77, 5771 (1982)). The constants C and D have different values of opposite signs. The value of the exponent (μ*/β*) obtained from experimental data with compositions x<xc is consistent with the theoretically predicted value (μ*/β*) = 3.88.
Presumed versus real artifacts of the Ewald summation technique: The importance of dielectric boundary conditions
Authors: Boresch Stefan , Steinhauser Othmar 
Published: July 2012

AbstractDespite its widespread use the Ewald summation method has been criticized for introducing spatial periodicity in the simulation system. The question whether this leads to artifacts is rigorously addressed by comparing the electric field obtained with the Ewald method to that of an unmodified Coulomb potential. It is demonstrated that the Ewald potential ϕEW is a solution of the Poisson equation under toroidal (periodic) boundary conditions; however, ϕEW gives also rise to an implicit contribution analogous to a reaction field. This additional term is connected to the dielectric boundary conditions employed in the simulation, and we show how to adjust these in a physically meaningful manner by adding an explicit reaction field term. To verify the theoretical considerations and to study the effects which modifying the dielectric boundary conditions has on the properties of the simulated system, we calculate the static dielectric constant, the distance‐dependent G‐factor, and the relaxation time of the net dipole moment of SPC water. The commonly used tin‐foil boundary conditions (characterized by a formal dielectric constant \documentclass{article}\pagestyle{empty}\begin{document}$ \varepsilon _{{\rm{EW}}}^{{\rm{eff}}} $\end{document} = ∞) are found to overstabilize the correlation between dipoles at larger distances; therefore, we recommend to adjust the dielectric boundary conditions so that \documentclass{article}\pagestyle{empty}\begin{document}$ \varepsilon _{{\rm{EW}}}^{{\rm{eff}}} = \varepsilon _0 $\end{document}, where ϵ0 is the intrinsic static dielectric constant of the simulated system.
Radicals occurring during the electroreduction of acrylic acid at mercury cathodes detected by electrochemical in situ EPR spectroscopy
Authors: Fahr T. , Petr A. , Dunsch L. 
Published: July 2012

AbstractWe performed electrochemical reduction investigations of acrylic acid and methylacrylate in aqueous solutions at a mercury cathode. Tetraalkylammoniumhalides were used as supporting electrolytes and the pH was adjusted in the range of pH = 3–12. Electrolyses in 1 M solutions of acrylic acid have yielded oligomers with a degree of polymerization depending on the pH value. At pH>pKs + 1 the acrylate anion is reduced and forms oligomers, if alkali ions are absent. Polarographic techniques are used to characterize the electrochemical behaviour of the acid and the ester, especially the coupling of two monomeric units, that was found as a radical‐substrate coupling reaction for the acrylate anion and an ion‐substrate coupling for the ester. The radical species were detected and characterized by electrochemical in situ EPR spectroscopy. The EPR spectrum is attributed to a propagating chain radical of the acrylate anion. In the case of methylacrylate no EPR spectrum could be recorded during the electroreduction. Finally, a reaction scheme for the electrochemical reduction of acrylate anions in aqueous media containing tetraalkylammonium cations is presented.
Nanoclusters of semiconductors and metals: Colloidal nano‐particles of semiconductors and metals: Electronic structure and processes
Authors: Henglein Arnim 
Published: July 2012

AbstractThe electronics of colloidal nano‐particles of semiconductors and metals has been one of the fastest growing research fields in physical chemistry for the past 10 years. The historical development is briefly reviewed and a number of fundamental effects and processes are described. They include the transition from the compact material to the atom, heterogeneous photo‐catalysis, and various aspects of nano‐electrochemistry, such as the storage of excess electrons and metal deposition on nano‐particles. Preparative aspects, such as the synthesis of composite metal and semiconductor particles and of nano‐crystals of semiconductors are also discussed.
Scaling law for structural metastability in semiconductor nanocrystals
Authors: Alivisatos A. P. 
Published: July 2012

AbstractIn contrast to extended solids, nanometer size crystals convert from one structure to another by single nucleation events, and the transformation obey simple kinetics. Barrier heights are observed to increase in nanocrystals of larger size, but also depend on the nature of the nanocrystal surface. These results are analogous to magnetic phase transitions in nanocrystals and suggest some general rules which may be of use in the discovery of new metastable phases.
Cadmium nanoclusters with phenylselenolato‐ and phenyltellurolato ligands synthesis and structural characterization of [Cd17Se4(SePh)24(PPh3)4][Cd8Se(SePh)12Cl4], [Cd(DMF)6][Cd8Se(SePh)12Cl4], [Cd8Se(SePh)14(PPh3)2], [Cd8Se(SePh)14(DMF)3] and [Cd8Te(TePh)14(PEt3)3]
Authors: Behrens Silke , Fenske Dieter 
Published: July 2012

AbstractA method of synthesis for cadmium selenide and cadmium telluride clusters is proposed. PhSeSiMe3 reacts with [CdCl2(PPh3)2] to yield a series of cadmium selenide clusters depending on the kind of solvent used. The reaction of PhTeSiMe3 with CdCl2 and PEt3 yields a cadmium telluride cluster. Crystalline products suitable for single‐crystal X‐ray analysis could be obtained. We describe the molecular structures of [Cd17Se4(SePh)24(PPh3)4][Cd8Se(SePh)12Cl4] (1), [Cd(DMF)6][Cd8Se(SePh)12Cl4] (2), [Cd8Se(SePh)14(PPh3)2] (3), [Cd8Se(SePh)14(DMF)3] (4) and [Cd8Te(TePh)14(PEt3)3] (5).
Mie resonances: Sensors for physical and chemical cluster interface properties
Authors: Kreibig U. , Gartz M. , Hilger A. 
Published: July 2012

AbstractMetal clusters exhibit unique optical properties due to the excitation of Mie plasmon resonances. It is well known since decades that measured resonances of clusters, surrounded by some adsorbate, or some solid or liquid embedding material (as e.g., in colloidal systems), are often not described quantitatively by Mie's theory. Only recently, these discrepancies were traced back to complex physical and chemical influences of the cluster‐matrix interlayer onto the optical response. They prove often to be more important than cluster size effects.These findings opened a new field of surface/interface research where deviations of measured Mie resonances from the predictions of Mie's theory are used as sensitive sensors for physical and chemical interface properties and processes in cluster‐matter.By combining optical spectroscopy experiments on free clusters in UHV and on the same clusters after embedding, this method was calibrated to separate, quantitatively, the cluster‐matrix interface effects from other cluster effects like shape and structure effects, nonlocal dielectric effects and cluster size effects.Among all metals, silver exhibits the most pronounced Mie resonances, so silver clusters were used as model systems and were embedded in a broad variety of solid and liquid embedding media, in course of the investigations reported in the present Progress Report.A theoretical description of the obtained data, based upon static and dynamic charge transfer processes of the cluster electrons into/out of adsorbate states is, however, only at its beginning. It allows to ascribe the extremely short decay times of the resonances of the order of 1 to 10 fs to phase relaxation processes; the decay times are in good correspondence with results of direct femtosecond‐experiments.