Initial quantum levels of captured muons in CO,CO2, and COS

The role of valence electrons for the muon capture process by molecules is experimentally investigated with the aid of cascade calculations. Low-momentum muons are introduced to gas targets of CO, CO₂, and COS below atmospheric pressure. The initial states of captured muons are determined from the measured muonic X-ray structure of the Lyman and Balmer series. We propose that the lone pair electrons in the carbon atom of CO significantly contribute to the capture of a muon with large angular momenta.

     

On the electron transfer in low-energy collisions of the fully-ionized muonic boron with helium atoms

In connection with recent experiments on the observation of the metastable 2s state of muonic boron (μB)⁴⁺ formed in helium with a small admixture of diborane (B₂H₆) we estimated the cross-section of the electron transfer from helium to the muonic ion. The collisions energy T was considered to lie between the thermal energy and 1 a. u. The muonic ion (μB)⁴⁺ was treated as a heavy beryllium isotope Be4+. It was found that the main reaction responsible for the electron transfer at the energies specified above was: Be⁴⁺ + He → Be³⁺(1s) + He²⁺ + e^-. . Its mechanism is the Auger effect in the two-electron quasi-molecule (Be-He)⁴⁺. In our estimation of its cross-section we used adiabatic quasi-molecular terms obtained by diagonalizing the electronic Hamiltonian on a basis of several diabatic states constructed from two-centre orbitals. The electronic wavefunctions built with this way were employed to calculate Auger effect rates. The outgoing electron was treated to be free. The relative motion of the nuclei was considered classically. It was found that in the region 0.001 ≤ T ≤ 0.01 (in atomic units) the cross-section was a decreasing function of T and it was small (～ 10^-2 Ų). Then it starts to increase and mounts to typical atomic values (1 Ų) at T = 1 ÷ 2. The comparison of the reaction rate constant estimated on the basis of the obtained cross-section with experimental results establishes the upper limit of the energy of muonic boron during the 2s state lifetime (≈ 40 ns). It proves to be about 25 eV. This limit is in agreement with the typical value of 1 eV resulting from the energy transfer in the muon capture by the diborane molecule and the recoil energy acquired in the cascade. However, it does not exclude the possibility of an additional acceleration of muonic boron during its formation in the molecule.     

Phase composition and texture of Sr(La)Mn hexaaluminates

Hexaaluminates synthesized by precipitation and calcined at 700–1400°C have been characterized by atomic absorption spectroscopy, thermal analysis, X-ray powder diffraction, and adsorption methods. The heat treatment of the Mn-substituted and unsubstituted materials at 1100 and 1200°C yields a hexaaluminate phase. The specific surface area of the samples calcined at 1100°C is 20–49 m²/g. The texture of the samples calcined at 1000°C is characterized by a unimodal mesoporous pore size distribution with a mean pore diameter of 290 Å.     

L X-ray production cross sections, average L shell fluorescence yield and intensity ratios in heavy elements

L X-ray fluorescence cross sections, and intensity ratios were measured for elements in the 70￡Z￡92 atomic range at the excitation energy 59.5 keV using a Si(Li) detector. Furthermore, L X-ray fluorescence cross sections and intensity ratios were calculated for elements in the same range. The average L shell fluorescence yields were derived using experimental L X-ray fluorescence cross sections and theoretical photoionization cross sections. The obtained results were compared with other experimental and theoretical values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Computation of hydration free energies using a parameterized continuum model: Study of equilibrium geometries and reactive processes in water solution

A parameterized self-consistent reaction field model allowing computation of the total free energy of hydration of organic molecules at the ab initio level is presented. The approach uses electrostatic plus polarization energies calculated with the help of a continuum model. The remaining solvation free energy terms are obtained by a simple formula based on atomic parameters and atomic accessible surface areas (ASAs), which are determined with the ASA analytical algorithm. Analytical derivatives of the atomic surfaces areas have been implemented. The atomic parameters have been obtained by a linear regression fit of the calculated and experimental free energies of solution in water for a set of 35 molecules, leading to a standard deviation of 0.75 kcal/mol. Effects of nonelectrostatic terms on solute geometries, association energies, and activation barriers are illustrated. © 1996 by John Wiley & Sons, Inc.     

Kinetics and modelling of heptane steam-cracking

The kinetics and product distribution during the cracking of heptane in the presence of steam were investigated. The experiments were performed in a flow reactor under atmospheric pressure in a temperature range of 680–760°C with a mass ratio of steam to heptane of 3: 1. The overall decomposition of heptane is represented by a first-order reaction with activation energy of 249.1 kJ mol^?1 and a frequency factor of 3.13 × 10¹³ s^?1. The reaction products were analysed using gas chromatography, the main product being ethylene. The molecular reaction scheme, which consists of a primary reaction and 24 secondary reactions between primary products, was used for modelling the experimental product yields. The yields of ethylene and hydrogen were in good agreement; however the experimental yields of propylene were higher than the predicted yields.     

Composition and Formation Kinetics of Erosion Products of the Metallic Charge in an Electric-Discharge Reactor

The composition and formation kinetics of erosion products of the metallic charge (aluminum, iron) in an electric-discharge reactor operating at an open-circuit voltage of 500–1000 V, peak pulse current of 250 A, and pulse energy of 0.5–1 J were studied. Dispersion products of the charge were subjected to electron-microscopic and X-ray phase analyses. The energy yield of erosion products was determined by chemical analysis to be hundreds of times the calculated yields of electrolysis. The erosion kinetics was studied and the mechanism of erosion was considered.     

High-sensitive amperometric hydrazine sensor based on chemically synthesized zinc nitroprusside nanoparticle-supported carbon ceramic electrode

Zinc nitroprusside (ZnNP) nanoparticles were fabricated at the surface of zinc powder-doped carbon ceramic electrode (CCE) by a chemical derivatization process. This modified electrode was characterized by scanning electron microscopy, atomic force microscopy and cyclic voltammetry techniques. The charge transfer rate constant (k _s) and charge transfer coefficient (α) were calculated for the electron exchange reaction of the ZnNP thin film. The ZnNP nanoparticle-modified CCE (ZnNP|CCE) showed good electrocatalytic activity toward hydrazine oxidation. The limit of detection (S/N = 3) and sensitivity were found to be 0.16 µM and 0.21 µA/µM, respectively. The mechanism of hydrazine electrooxidation at the electrode surface was studied. Finally, the ZnNP|CCE was successfully used for the determination of trace amount of hydrazine in different spiked and real samples.     

Selected ion flow tube study of the ion-molecule reactions of monochloroethene, trichloroethene, and tetrachloroethene

Data for the rate coefficients and product cations of the reactions of a large number of atomic and small molecular cations with monochloroethene, trichloroethene, and tetrachloroethene in a selected ion flow tube at 298 K are reported. The recombination energy of the ions range from 6.27 (H3O(+)) through to 21.56 (Ne(+)) eV. Collisional rate coefficients are calculated by modified average dipole orientation theory and compared with experimental values. Thermochemistry and mass balance predict the most feasible neutral products. Together with previously reported results for the three isomers of dichloroethene ( Mikhailov, V. A. ; Parkes, M. A. ; Tuckett, R. P. ; Mayhew, C. A. J. Phys. Chem. A 2006, 110, 5760 ), the fragment ion branching ratios have been compared with those from threshold photoelectron photoion coincidence spectroscopy over the photon energy range of 9-22 eV to determine the importance or otherwise of long-range charge transfer. For ions with recombination energy in excess of the ionization energy of the chloroethene, charge transfer is energetically allowed. The similarity of the branching ratios from the two experiments suggest that long-range charge transfer is dominant. For ions with recombination energy less than the ionization energy, charge transfer is not allowed; chemical reaction can only occur following formation of an ion-molecule complex, where steric effects are more significant. The products that are now formed and their percentage yields are a complex interplay between the number and position of the chlorine atoms with respect to the C=C bond, where inductive and conjugation effects can be important.     

Muon transfer from mesic hydrogen to lithium and the atomic intershell correlations

The rates of the molecular muon transfer from mesic hydrogen to lithium are calculated. The obtained rates are of the order of magnitude 10⁶ s^?1. It is shown, that taking into account the intershell correlations results in a considerable change in the reaction rates for some isotope mixtures. The experimental study of the muon transfer can yield an information about the contribution of the intershell correlations to the rate of the process.     

Muon transfer from the excited mesic hydrogen in the metastable 2s-state to helium nuclei

The rate of the molecular charge exchange of the excited muonic hydrogen in the 2s-state on helium nuclei is calculated. Resonance muon transfer is shown to occur with the formation of the intermediate excited complex ([(H μ)*He²⁺]2e)*. The resulting rates prove that the muon transfer from the 2s-state alone can not account for the experimental data on the muon transfer frompμ-atoms to⁴He nuclei.     

Wavelength-dependent photochemistry in Cr(CNPh)6: a study of photosubstitution and photoinduced electron transfer using time-resolved spectroscopy

The wavelength dependence of photosubstitution, photoinduced electron transfer, and the time-resolved spectra of Cr(CNPh)6, a compound having low-lying MLCT states, were investigated. Photosubstitution quantum yields increase with increasing excitation energy while photoinduced electron transfer quantum yields decrease with increasing excitation energy. At the lowest excitation energy used (532 nm, or 18,800 cm(-1)), the quantum yields for both electron transfer and photosubstitution reach the same maximum value, 0.29. Picosecond time-resolved absorption spectra at 355 and 532 nm excitation wavelengths show two features: a bleach signal centered at 400 nm and an excited state absorption (ESA) in the 600 nm region. The ESA signal is much weaker for 532 nm excitations than for 355 nm excitations. Following a 355 nm flash, the bleach and ESA decay exponentially with the same lifetime of 23 micros. This implies a simple ligand dissociation followed by recombination. Bleach recovery kinetics after a 532 nm flash are more complicated: two or three exponential components are required to fit the data. Cr(CNPh)6 exhibits two photochemical mechanisms: at high excitation energy, a simple charge neutral dissociation occurs; at low energy, it is proposed that a phenylisocyanide radical anion dissociates, forming a radical pair that is responsible for the observed substitution and electron transfer reactivity, and the complicated nanosecond kinetics. The primary processes for both reactions occur in less than 20 ps.     

Electronic energy transfer between metastable argon atoms and ground-state oxygen atoms

The transfer of electronic energy between metastable argon and ground-state oxygen atoms has been studied in a discharge-flow apparatus. The excitation energy of the argon metastables is transferred to the 3p ³P state of atomic oxygen with a cross section of 3 A². The energy transfer is discussed in terms of an ionic-intermediate, curve-crossing mechanism for which the calculated cross section is 13 A².     

Preparation and Exploration on the Electrochemical Behavior of Nickel Oxide Nanoparticles Coated Bacterial Nanowires

The controlled synthesis of nickel oxide nanoparticle (NiO NPs) were synthesized by homogeneous precipitation method and have been characterized using UV–visible spectrophotometer, fourier transform-infrared spectroscopy, X-ray diffraction, atomic force microscope, scanning electron microscope and high resolution-transmission electron microscope. The synthesized NiO NPs was spherical in shape with an average size ranged between 3 and 5 nm. Subsequently, synthesis of NiO NPs coated on a bacterial nanowires (BNWs) film pre-cast on a glassy carbon electrode surface and the morphology and nature of the prepared composite was characterized using HR-TEM. The electro-chemical behavior of NiO NPs coated bacterial nanowires (NiO NPs-BNWs) was observed using cyclic voltammetry, linear sweep voltammetry and electrochemical impedance spectroscopy analysis. Highly comparable electrochemical conductivity of NiO NPs-BNWs was observed in this study. The BNWs sample exhibited a polarization resistance (Rp) to be 4457 Ω and the NiO NPs-BNWs sample exhibited polarization resistance (Rp) about 2270.4 Ω. The BNWs exhibited a CPE-T value to be 6.26 µF cm^?2 and the NiO NPs-BNWs sample exhibited CPE-T to be 9.32 µF cm^?2. The enhancement of peak currents is ascribed to the short heterogeneous electron transfer among the NiO NPs-BNWs. The defined nanolayer provides a novel platform for the next generation electrochemical applications.     

Electron photodetachment from aqueous anions. 3. Dynamics of Geminate pairs derived from photoexcitation of mono- vs polyatomic anions

Photostimulated electron detachment from aqueous inorganic anions is the simplest example of solvent-mediated electron transfer reaction. As such, this photoreaction became the subject of many ultrafast studies. Most of these studied focused on the behavior of halide anions, in particular, iodide, that is readily accessible in the UV. In this study, we contrast the behavior of these halide anions with that of small polyatomic anions, such as pseudohalide anions (e.g., HS(-)) and common polyvalent anions (e.g., SO(3)(2-)). Geminate recombination dynamics of hydrated electrons generated by 200 nm photoexcitation of aqueous anions (I(-), Br(-), OH(-), HS(-), CNS(-), CO(3)(2-), SO(3)(2-), and Fe(CN)(6)(4-)) have been studied. Prompt quantum yields for the formation of solvated, thermalized electrons and quantum yields for free electrons were determined. Pump-probe kinetics for 200 nm photoexcitation were compared with kinetics obtained at lower photoexcitation energy (225 or 242 nm) for the same anions, where possible. Free diffusion and mean force potential models of geminate recombination dynamics were used to analyze these kinetics. These analyses suggest that for polyatomic anions (including all polyvalent anions studied) the initial electron distribution has a broad component, even at relatively low photoexcitation energy. There seems to be no well-defined threshold energy below which the broadening of this electron distribution does not occur, as is the case for halide anions. The constancy of (near-unity) prompt quantum yields vs the excitation energy as the latter is scanned across the lowest charge-transfer-to-solvent band of the anion is observed for halide anions but not for other anions: the prompt quantum yields are considerably less than unity and depend strongly on the excitation energy. Our study suggests that halide anions are in the class of their own; electron photodetachment from polyatomic, especially polyvalent, anions exhibits qualitatively different behavior.     

N-bromosuccinimide-fluorescein system for the determination of protein by flow injection chemiluminescence

A method for flow injection with chemiluminescence (CL) detection has been developed for the determination of proteins. It is based on the luminescence of the N-bromosuccinimide-fluorescein-protein system, where fluorescein is used as an energy transfer reagent in alkaline medium. The CL of the system is strongly enhanced by hexadecyl trimethyl ammonium bromide. Optimum conditions and possible mechanisms have been investigated. Under optimum experimental conditions, the linear range is from 0.4 to 40 µg·mL^?1 for egg albumin, 0.2 to 20 µg·mL^?1 for bovine serum albumin, and from 1 to 100 µg·mL^?1 for bovine hemoglobin. The detection limits are 37, 62, and 240 ng·mL^?1, respectively.     

Charge transfer in S2++H collisions at intermediate energy

Partial cross-sections for the charge transfer process of S²⁺ ions in collision with atomic hydrogen at impact energies up to 8 keV have been calculated by means of a semi-classical method using ab initio potential energy curves and couplings. The results are in relatively good agreement with experiment and improve significantly previous Landau-Zener calculations.     

A simulation model for long-chain branching in vinyl acetate polymerization: 1. Batch polymerization

A new simulation model for the kinetics of long-chain branching formed via chain transfer to polymer and terminal double-bond polymerization is proposed. This model is based on the branching density distribution of the primary polymer molecules. The theory of branching density distribution is that each primary polymer molecule experiences a different history of branching and provides information on how each primary polymer molecule is connected with other chains that are formed at different conversions, therefore making possible a detailed analysis on the kinetics of the branched structure formation. This model is solved by applying the Monte Carlo method and a computer-generated simulated algorithm is proposed. The present model is applied to a batch polymerization of vinyl acetate, and various interesting structural changes occurring during polymerization (i.e., molecular weight distribution, distribution of branch points, and branching density of the largest polymer molecule) are calculated. The present method gives a direct solution for the Bethe lattice formed under nonequilibrium conditions; therefore, it can be used to examine earlier theories of the branched structure formation. It was found that the method of moments that has been applied successfully to predict various average properties would be considered a good approximation at least for the calculation of not greater than the second-order moment in a batch polymerization. © 1994 John Wiley & Sons, Inc.     

Spectrophotometric,Thermodynamic and Density Functional Studies of Charge Transfer Complex Between Benzhydryl Piperazine and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone

The charge transfer complex of benzhydryl piperazine as donor with the π-acceptor 2,3-dichloro-5,6-dicyano-p-benzoquinone has been studied spectrophotometrically in acetonitrile medium at different temperatures. On mixing the donor with acceptor, a reddish brown colored charge transfer complex is formed. Electronic absorption spectra of the complex show charge transfer bands at 587, 546 and 457 nm. The molecular composition of the complex was studied by applying Job’s continuous variation and spectrophotometric titration methods. These results support the formation of the complex in a 1:2 ratio. The Benesi–Hildebrand equation has been applied to compute the formation constant and molecular extinction coefficient. Thermodynamic parameters of the charge transfer complexation reaction (standard entropy, standard enthalpy and standard Gibbs free energy) have been calculated. The results of the spectrophotometric study demonstrated that the charge transfer complex formation is endothermic. The computational studies of the charge transfer complex were performed by using the Gaussian 09 W package of programs. The bond lengths, bond angles, dihedral angles, Mulliken atomic charges, molecular electrostatic potential maps and characterization of the highest occupied molecular orbital and lowest unoccupied molecular orbital surfaces of charge transfer complex were computed.     

Collisional energy transfer in highly vibrationally excited molecules: A very low-pressure pyrolysis study of acetyl chloride

The average downward energy transfer (〈Δ E_down〉) is obtained for highly vibrationally excited acetyl chloride with Ne and C₂H₄ bath gases at ca. 870 K. Data are obtained by the technique of very low-pressure pyrolysis (VLPP). Fitting these data by solution of the appropriate reaction-diffusion integrodifferential master equation yields the gas/gas collisional energy transfer parameters: 〈Δ E_down〉 values are 220 ± 10 cm^?1 (Ne bath gas) and 330 ± 20 cm^?1 (C₂H₄). These energy transfer quantities are much less than those predicted by statistical theories, or those observed for similar sized molecules such as CH₃CH₂Cl. These results are explained by the qualitative predictions of the biased random walk model wherein the fundamental mechanism of energy transfer is the multiple interactions between the bath gas and the individual atoms of the reactant molecule, during the course of the collision event. The charge distribution of acetyl chloride decreases the number of such interactions, thereby reducing the amount of energy transferred per collision.