Conductivity of C60 fullerene crystals under dynamic compression up to 200 kbar

The conductivity σ of C₆₀ fullerene crystals is measured under quasi-isentropic loading by a spread shock wave to a pressure of 200 kbar at the initial temperatures 293 and 77 K. A sharp increase in σ by seven to eight orders of magnitude is detected: from 10^?6?10^?7 Ω^?1 cm^?1 at normal conditions to 5 Ω^?1 cm^?1 under pressure from 100 to 200 kbar. The conductivity of samples under pressure decreases with decreasing temperature, which is characteristic of semiconductors. On pressure release, σ regains its initial value.     

The gas phase oxidation of HCOOH by Cl and NH2 radicals. Proton coupled electron transfer versus hydrogen atom transfer*

ABSTRACT

The reaction of formic acid (HCOOH) with chlorine atom and amidogen radical (NH₂) have been investigated using high level theoretical methods such BH&HLYP, MP2, QCISD, and CCSD(T) with the 6–311?+?G(2df,2p), aug-cc-pVTZ, aug-cc-pVQZ and extrapolation to CBS basis sets. The abstraction of the acidic and formyl hydrogen atoms of the acid by the two radicals has been considered, and the different reactions proceed either by a proton coupled electron transfer (pcet) and hydrogen atom transfer (hat) mechanisms. Our calculated rate constant at 298?K for the reaction with Cl is 1.14?×?10^?13?cm³?molecule^?1?s^?1 in good agreement with the experimental value 1.8?±?0.12/2.0?×?10^?13?cm³?molecule^?1?s^?1 and the reaction proceeds exclusively by abstraction of the formyl hydrogen atom, via hat mechanism, producing HOCO+ClH. The calculated rate constant, at 298?K, for the reaction with NH₂ is 1.71?×?10^?15?cm³?molecule^?1?s^?1, and the reaction goes through the abstraction of the acidic hydrogen atom, via a pcet mechanism, leading to the formation of HCOO+NH₃.     

Study of the δ− → π +π−π− Decay Mode

No enhancement in δ^? → π ⁺π^?π^? decay mode appeared at mass 962 MeV or at 996 MeV produced in π^?p → δ^?p interaction near its production threshold in a missing mass counter experiment. This finding fully supports the fact that the δ^? → π ⁺π^?π^? decay mode is not allowed by the conservations of the angular momentum and the parity.     

Dihydroxylation of styrene by sodium chlorite with scandium triflate

Dihydroxylation of styrene by chlorite (ClO₂^?) with scandium triflate [Sc(OTf)₃] occurs efficiently to produce 1‐phenylethane‐1,2‐diol under the ambient conditions. Scandium triflate acting as a strong Lewis acid is found to accelerate the disproportionation of ClO₂^? to produce ClO^? and ClO₃^?. A scandium‐chlorine dioxide complex (Sc³⁺ClO₂^?) is generated by the reaction of ClO^? with ClO₂^? in the presence of Sc³⁺. The binding of Sc³⁺ to ClO₂^? was detected by the electron paramagnetic resonance measurements, enhancing the reactivity and selectivity of styrene hydroxylation.     

Uncommon temperature dependence of the rotational motion of OH− centers in NaCl

Abstract

The correlation time τ_D of the rotational motion of OH^? centers in NaCl was studied for two different OH^?-concentrations (44 ppm and 220 ppm) between 0.5 K and 16 K by ²³Na nuclear spin relaxation measurements. The correlation time in the sample containing 44 ppm OH^? is given by phonon-assisted tunneling of isolated defects, whereas the OH^?-motion in the sample containing 220 ppm can be described by a coupled ensemble of quantum mechanical hindered rotators below a critical temperature which is determined by the strength of the interaction between the OH^? dipoles.     

Familon emissivity of dense e − e + plasma in an external magnetic field

Emission of a familon due to the processes e ^? → e ^?+φ and e ^? → μ ^?+φ by dense magnetized plasma is analyzed as a possible mechanism of energy and momentum losses by astrophysical objects. The field-induced effective familon-photon coupling in the familon-emission process is taken into account. The contribution of these processes to the familon emissivity of a magnetized plasma in a supernova explosion is calculated. It is shown that there is asymmetry of familon emission in the process e ^? → μ ^?+φ.     

Luminescence quenching of cyclometalated Pt(II) complexes by halogenide ions

The luminescence quenching of [Pt(CΛN)En]ClO₄ complexes ((CΛN)^? = ppy^?, tpy^?, and bt^? are deprotonated forms of 2-phenylpyridine, 2(2′-thienyl(pyridine), and 2-phenylbenzothiazole, respectively; En is ethylenediamine) by halogenide ions (Hal^? = Cl^?, Br^?, I^?) in ethanol solutions is studied. It is shown that the quenching has a dynamic character and its bimolecular rate constants are consistent with the enhancement of nonradiative deactivation of the excited state of {[Pt(CΛN)En]*...Hal} collision complexes with increasing spin-orbit interaction constant of the halogen.     

Anomalous enhancement of negative sputtered ion emission by oxygen

Enhancement of negative sputtered ion yields by oxygen (either O⁺₂ bombardment or O₂ gas with Ar⁺ bombardment) is demonstrated for Si^?, As^?, P^?, Ga^?, Cu^? and Au^?, sputtered from a variety of matrices. Because oxygen also enhances positive ion yields of the same species, this effect cannot be simply explained on the basis of existing sputtered ion emission models. To rationalize these phenomena, a surface polarization model is developed which invokes localized electron emissive or electron retentive sites associated with differently oriented surface dipoles in the oxygenated surface. Such sites are considered to dominate the emission of negative and positive ions respectively. The model is shown to correctly predict that Au⁺ and Au^? ion yields are much more strongly enhanced by oxygen in dilute Au-Al alloys than in pure gold.     

Decay of 17-min, 19/2−129mSb

A 17.1min, 19/2^? isomer has been established in¹²⁹Sb at 1851 keV. It is fed by levels populated in the decay of the 6.2min, 11/2^?129Sn isomer. This isomer decays by an M4, 723keV internal transition and by β^? decay to levels in¹²⁹Te. The 723keV transition is 20 times slower than 11/2^?→3/2⁺ M4 transitions in the adjacent odd-N nuclides and is 10 times faster than the M4 transition from the 19/2^? isomer in¹³⁵Cs. A partial level scheme for the decay of the 11/2^?,¹²⁹Sn isomer is given showing levels that populate the 19/2^? isomer along with a partial level scheme for¹²⁹ Te.     

Intervalley magnetophonon resonance peak of thermoelectric power in the phonon drag region of p-Te

A large peak is found at 3.2 Tesla (T) in the second derivative curve of longitudinal magneto-Seebeck coefficient (-?²α₆/?H² of p-type tellurium below 20 K under the magnetic field H6c. The peak height is rapidly increasing with decreasing temperature, in contrast to disappearance of the usual oscillation due to LO phonon which is observed between 20 and 100 K. A small peak is also appreciable in the second derivative of longitudinal magnetoresistance (-?²?₆/?H² at the same field of 3.2 T. The peaks both in -?²α₆/?H² and -?²?₆/?H² are interpreted as a resonance peak due to the intervalley scattering by longitudinal acoustic (LA) phonon between the two valleys split off by inversion asymmetry splitting (μ_BGH). This interpretation gives a value of G as 5.5 in good agreement with the value of G = 5 ± 1 determined by the Shubnikov-de Haas experiment. It is explained by t he phonon drag effect based on this interpretation that the peak of -?²α₆/?H² is much more prominent than that of -?²?₆/?H² and increases with decreasing temperature.     

Sers measurement of oxidation-reduction reactions of adsorbates on gold microstructures

The use of surface enhanced Raman scattering (SERS) to study oxidation-reduction and complexation chemical reactions on Au surfaces is illustrated by: (1) the reaction of Au(CN)₂^? adsorbed on a Au colloid (2140 cm^?) to form Au(CN)₃^2? (2131 cm^?1) on the surface in excess CN^?; (2) the oxidation of Au(CN)₂^? by HNO₃, Cl₂, or Br₂ solutions to form Au(CN)₄^? (2190 cm^?) on a Au colloid; and (3) the dissolution of Au in excess CN^? with O₂. Unlike with Ag surfaces, no SERS is observed when Au powder is exposed to NO, NO₂, SO₂, CO, or CO₂ gases. The surface chemistry of Au is discussed in the light of these reactions.     

The weight,shape, and speed of the universe

Present astronomical data indicate an unbound universe with density ～1.6 × 10^?31 g cm^?3 in which galaxies could not have formed gravitationally. We show how magnetohydrodynamic (MHD) processes allow galaxy formation in an open anisotropic MHD universe with shear, rotation, and fluid flow. The dipole anisotropy of the microwave background radiation sets their respective first-order values at 3.7×10^?15 yr^?1, 10^?14 yr^?1, and 5×10^?4 c. Second-order effects of Maxwell and Reynolds stresses require that the magnetic field, shear, and Hubble expansion be 10^?8 G, 3.7×10^?15 yr^?1, and 10^?10 yr^?1 (100 km sec^?1 Mpc^?1). The model is rigidly self-consistent, predicting both the recent value of the Hubble expansion above and of the shear (? 9×10^?15 yr^?1) given by the microwave background's recently measured quadrupole anisotropy.     

Conduction transients in single-crystal octadecane

Charge transients were measured in high-quality single-crystal octadecane after electron beam irradiation. The signals produced were of significantly greater duration than the ionization pulse but were not interpretable by conventional uniform field time-of-flight analysis. By assuming that the specimens contained a strong inbuilt polarization field, it was possible to predict the properties of the observed charge transients and obtain values for the positive and negative drift mobilities. The results indicated a positive species with a mobility of 0.7 × 10^?4 m² V^?1 s^?1 and a negative carrier value of 1.6 × 10^?4 m² V^?1 s^?1. The standard deviations observed in the data were large, being 0.3 × 10^?4 m² V^?1 s^?1 and 0.8 × 10^?4 m² V^?1 s^?1, respectively. This scatter was significantly in excess of the estimated experimental error.     

Effect of additional metal ions on the ratio between the rates of the transformation of the intermediate products of the hydrolysis of adenosine-5′-triphosphoric acid catalyzed the Cu2+ ion (Communication 2: Mathematical modeling of the kinetics of the hydrolysis in the presence of additional Mg2+ ions)

It was previously shown that the hydrolysis of the (CuATP^2? · OH₂)₂ dimeric complex to CuADP^? and an inorganic phosphate occurs in a sequence of two rapid and irreversible steps. Along with the hydrolysis through a common intermediate product, (CuATP^2?)₂OH^?-(DOH^?), the OH^? nucleophile at the Cu²⁺ ion is replaced by OH^? at the positively charged phosphorus atom to form an IntK pentacovalent intermediate (step 1). A mathematical modeling of the kinetics of the hydrolysis catalyzed by the Cu²⁺ base metal ion in the presence of additional Mg²⁺ ions at two pH values, 6.48 and 6.71 (at the ascending branch of the dependence of the initial rate of the hydrolysis on the pH value) is performed. Additional ions affect only the pathway of coupling of the conformational conversion of DOH^?. The rate constant for the forward reaction (IntK→ DOH^?), k ₁, increases from 2 · 10⁷ L mol^?1 min^?1 in the absence of Mg²⁺ to 2.9 · 10⁷ L mol^?1 min^?1 upon introduction of Mg²⁺ ions; rate constant of the reverse reaction IntK → DOH→, k ^?1, decreases from 1 · 10⁵ L mol^?1 min^?1 in the absence of Mg²⁺ to 3 · 10⁴ L mol^?1 min^?1 in the presence of Mg²⁺. The relative concentrations of the intermediate products are demonstrated to change during the irreversible hydrolysis. In the presence of Mg²⁺, IntK emerges at much earlier stages of the hydrolysis, the fraction of formed IntK in the balance of NuP₀ is substantially higher, and the growth of its relative concentration with time in the earlier stages of hydrolysis is much more dramatic.     

A search for K−p → Λγ and K−p → Σ0γ at rest

A search has been made for photons from the reactions K^?p → Λγ and K^?p → Σ⁰γ produced by K^? stopping in a liquid hydrogen target. No signal from these reactions was found; upper limits on the branching ratios are K^?p → Λγ/K^?p → anything ? 4 × 10^?4, K^?p → Σ⁰γ/K^?p → anything ? 4 × 10^?3. The first of these is in conflict with a theoretical prediction using recent values for coupling constants and scattering amplitudes. This may reflect the influence of the Λ(1405) on the radiative capture.     

Lepton charge and model of weak interactions with μ-e transitions

The gauge model of weak interactions is proposed and μ^±?e^? transitions predicted by the model are discussed. Estimates are given for μ^±→e^? transitions on hadrons like K⁺→π^?μ⁺e⁺ with Γ (K⁺→π^?μ⁺e⁺) ? 10^?11Γ(K⁺ and μ^? capture on nuclei with W(μ^?→e⁺) ? 10^?12W(μ^? → ν). Single μ^± production in e^? beams with a cross section δ ～ 10^?42?10^?41 cm² is predicted.     

Highly sensitive electrochemical detection of dopamine and uric acid on a novel carbon nanotube-modified ionic liquid-nanozeolite paste electrode

A novel biosensor has been constructed by incorporating modified nanosized natural zeolite and 3-hydroxypropanaminium acetate (HPAA) as a novel room temperature ionic liquid, supported on multiwalled carbon nanotube (MWCNTs) and employed for the simultaneous determination of dopamine (DA) and uric acid (UA). A detailed investigation by transmission electron microscopy and electrochemistry is performed in order to elucidate the preparation process and properties of the composites. The voltammetric studies using the modified carbon paste electrode show two well-resolved anodic peaks for DA and UA with a potential difference of 160 mV, revealing the possibility of the simultaneous electrochemical detection of these compounds. The modified carbon paste electrode shows good conductivity, stability, and extraction effect due to the synergic action of HPAA, MWCNTs, and iron ion-doped natrolite zeolite. Under optimized conditions, the peak currents are linear from 8.12?×?10^?7 to 3.01?×?10^?4?mol?L^?1 and from 9.31?×?10^?7 to 3.36?×?10^?4?mol?L^?1 with detection limits of 1.16?×?10^?7 and 1.33?×?10^?7?mol?L^?1 for DA and UA using the differential pulse voltammetric method, respectively. Finally, the modified carbon paste electrode proved to have good sensitivity and stability and is successfully applied for the simultaneous determination of DA and UA in human blood serum and urine samples.     

The adsorption of ammonia on a Fe(110) single crystal surface studied by high resolution electron energy loss spectroscopy (EELS)

EELS spectra of ammonia adsorbed on a Fe(110) single crystal surface at 120 K reveal four different molecular adsorption states:1. At very low exposures (0.05 L) three vibrational losses at 345 cm^?1, 1170 and 3310 cm^?1 are observed which are attributed to the symmetric Fe-N stretching-, N-H₃ deformation and N-H₃ stretching modes of chemisorbed molecular ammonia, respectively. The observation of only three vibrational losses indicates an adsorption complex of high symmetry (C_3v).2. Further exposures up to 0.5 L cause the appearance of additional losses at 1450 cm^?1, 1640 cm^?1 and 3370 cm^?1. The latter two are interpreted as the degenerate NH₃ deformation and - stretching modes of molecularly adsorbed NH₃. The 1450 cm^?1 loss is a combination of the losses at 345 cm^?1 and 1105 cm^?1. The observation of 5 vibrational losses is consistent with an adsorption complex of C_s symmetry.3. In the exposure range from 0.5 to 2 L adsorption of molecular ammonia in a second layer is observed. This phase is characterized by a symmetric deformation mode at 1190 cm^?1 and by two additional very intense modes at 160 cm^?1 and 350 cm^?1 which are due to rotational and translational modes.4. Exposures above 2 L cause multilayer condensation of ammonia characterized by translational and rotational bands at 190 cm^?1, 415 cm^?1 and 520 cm^?1, and a symmetric deformation mode at 1090 cm^?1. A broad loss feature around 3300 cm^?1 is attributed to hydrogen bonding in the condensed layer.Thermal processing of a Fe(110) surface ammonia covered at 120 K leads to decomposition of the ammonia into hydrogen and nitrogen above 260 K. No vibrational modes due to adsorbed NH or HN₂ species were detected.     

Molecular dynamics simulation of methane in sodium montmorillonite clay hydrates at elevated pressures and temperatures

Computer simulation has been used to study the structure and dynamics of methane in hydrated sodium montmorillonite clays under conditions encountered in sedimentary basins. Systems containing approximately one, two, three and four molecuiar layers of water have followed gradients of 150 bar km^?1 and 30Kkm^?1, to a maximum burial depth of 6 km (900 bar and 460 K). Methane is coordinated to approximately 19 oxygen atoms, of which typically 6 are provided by the clay surface. Only in the three- and four-layer hydrates is methane able to leave the clay surface. Diffusion depends strongly on the porosity (water content) and burial deth self-diffusion coefficients are in the range 0.12 × 10^?9m²S^?1 < D < 12.65 × 10^?9m²s^?1 for water and 0.04 × 10^?9m²s^?1 < D < 8.64 × 10^?9m²s^?1 for methane. Bearing in mind that porosity decreases with burial depth, it is estimated that maximum diffusion occurs at around 3 km. This is in good agreement with the known location of methane reservoirs in sedimentary basins.