Catalytic dioxygen activation by (nitro)(meso-tetrakis(2-n-methylpyridyl)porphyrinato)cobalt(III) cation derivatives electrostatically immobilized in nafion films: an experimental and DFT investigation

Complexes of the (nitro)( meso-tetrakis(2- N-methylpyridyl)porphyinato)cobalt(III) cation, [LCoTMpyP(2)(NO 2)] (4+), in which L = water or ethanol have been immobilized through ionic attraction within Nafion films (Naf). These immobilized six-coordinate species, [LCoTMPyP(2)(NO 2)/Naf], have been found to catalyze the oxidation of triphenylphosphine in ethanol solution by dioxygen, therefore retaining the capacity to activate dioxygen catalytically without an additional reducing agent as was previously observed in nonaqueous solution for the non-ionic (nitro)cobalt porphyrin analogs. Heating these immobilized six-coordinate species under vacuum conditions results in the formation of the five-coordinate nitro derivatives, [CoTMPyP(2)(NO 2)/Naf] at 85 degrees C and [CoTMPyP(2)/Naf] at 110 degrees C. The catalytic oxidation of gas-phase cyclohexene with O 2 is supported only by the resulting immobilized five-coordinate nitro complex as was previously seen with the corresponding solution-phase catalyst in dichloromethane solution. The simultaneous catalytic oxidation of triphenylphosphine and cyclohexene with O 2 in the presence of the Nafion-bound six-coordinate ethanol nitro complex is also observed; however, this process is not seen for the CoTPP derivative in dichloromethane solution. The oxidation reactions do not occur with unmodified Nafion film or with Nafion-supported [BrCo(III)TmpyP]/Naf or [Co(II)TmpyP]/Naf, indicating the necessity for the nitro/nitrosyl ligand in the oxidation mechanism. The existence of a second reactive intermediate is indicated because the two simultaneous oxidation reactions depend on two distinct oxygen atom-transfer steps having different reactivity. The absence of homogeneous cyclohexene oxidation by the six-coordinate (H 2O)CoTPP(NO 2) derivatives in the presence of Ph 3P and O 2 in dichloromethane solution indicates that the second reactive intermediate is lost by an unidentified route only in solution, implying that the immobilization of it in Nafion allows it to react with cyclohexene. Although direct observation of this species has not been achieved, a comparitive DFT study of likely intermediates in several catalytic oxidation mechanisms at the BP 6-31G* level supports the possibility that this intermediate is a peroxynitro species on the basis of relative thermodynamic accessibility. The alternate intermediates evaluated include the reduced cobalt(II) porphyrin, the dioxygen adduct cobalt(III)-O 2 (-), the oxidized cobalt(II) pi-cation radical, and the nitrito complex, cobalt(III)-ONO.     

Estimate of B(B(over) -->Xgamma) at O(alpha(s)2)

Combining our results for various O(alpha[s]) corrections to the weak radiative B-meson decay, we are able to present the first estimate of the branching ratio at the next-to-next-to-leading order in QCD. We find B(B[over ]-->X[s]gamma)=(3.15+/-0.23) x 10(-4) for Egamma>1.6 GeV in the B[over ]-meson rest frame. The four types of uncertainties:nonperturbative (5%), parametric (3%), higher-order (3%), and m(c)-interpolation ambiguity (3%) have been added in quadrature to obtain the total error.     

Investigation of isomeric ratios in high-energy reactions

Experimental data on the isomeric ratios of cross sections for products originating from the interaction of ¹²C ions (E 12 _C = 26.4 GeV), protons (E _p = 3.65 GeV), and deuterons (E _d = 7.3 GeV) with targets enriched in the tin isotopes ¹¹²Sn, ¹¹⁸Sn, ¹²⁰Sn, and ¹²⁴Sn are presented. The dependence of the isomeric ratios on the interaction mechanism, projectile type and energy, and nuclear properties of the final-state nucleus are discussed. The dependence of the isomeric ratios on the degree of deformation of the product nucleus is also considered.     

Gas sensors made of multiwall carbon nanotubes modified by tin dioxide

Thin film gas sensors made of nanocomposite MWCNT·SnO₂(1:66), semiconductor compound WO₃·SnO₂(1:9), and also multicomponent structure MWCNT·SnO₂(1:66)/WO₃·SnO₂(1:9) have been fabricated by high-frequency magnetron sputtering and electron-beam deposition methods. Sensitivity of the prepared sensors to influence of gases, such as hydrogen, methane, butane, and also ethanol vapors, was investigated. Sensors made of MWCNT·SnO₂(1:66) and WO₃·SnO₂(1:9) show appreciable sensitivity to hydrogen and alcohol vapors already at working body temperature 100–150°C. Sensors made of MWCNT·SnO₂(1:66)·WO₃·SnO₂(1:9) can be used for detection of low concentrations of hydrogen and ethanol vapors; besides, monotonous increase in the structure sensitivity with increase in content of the alcohol vapors allows one to apply these sensors also for fast detection of concentration of these vapors in air.     

The partition function zeros of the anisotropic Ising model with multisite interactions on a zigzag ladder

It is shown that the spin- anisotropic Ising model with multisite interactions on a zigzag ladder may be mapped into the one dimensional spin- Axial-Next-Nearest-Neighbor Ising (ANNNI) model with multisite interactions. The partition function zeros of the ANNNI model with multisite interactions are investigated. A comprehensive analysis of the partition function zeros of the ANNNI model with and without three-site interactions on a zigzag ladder is done using the transfer matrix method. Analytical equations for the distribution of the partition function zeros in the complex magnetic field (Yang-Lee zeros) and temperature (Fisher zeros) planes are derived. The Yang-Lee and Fisher zeros distributions are studied numerically for a variety of values of the model parameters. The densities of the Yang-Lee and Fisher zeros are studied and the corresponding edge singularity exponents are calculated. It is shown that the introduction of three-site interaction terms in the ANNNI model leads to a simpler distribution of the partition function zeros. For example, the Yang-Lee zeros tend to a circular distribution when increasing by modulus the three-site interactions term coefficient. It is found that the Yang-Lee and Fisher edge singularity exponents are universal and equal to each other, .     

Difference frequency generation by optical rectification of femtosecond laser pulse in GaAs crystal with a periodic domain structure

We study the influence of spatial boundedness of a femtosecond laser pulse (FLP) on the efficiency of generation of difference frequency radiation (DFR) in a GaAs crystal with a periodic domain structure. It is shown that at propagation of DFR a spectral-angular filtration occurs in the transverse distribution of the beam. An expression is obtained for the frequency-angular spectrum of DFR. For a pump pulse with the duration of 100 fs, the beam radius of 24μm, the energy of 30 nJ, and the wavelength of 1.98μm propagating in 1.716-mm long GaAs crystal with the domain structure period of 74.6μm the efficiency of generation of DFR at the wavelength of 14μm is calculated to be close to 2×10⁻⁶.     

Influence of additional electric field on the birefringence of a nematic liquid crystal

Influence of the longitudinal voltage applied along the semiconductor substrate of a planar-oriented liquid crystal cell on the birefringence of a nematic liquid crystal (NLC) was investigated. It is shown that for a fixed magnitude of the transverse field the application of a longitudinal voltage creates an additional possibility to control the electro-optically induced phase incursion of the radiation passing through NLC. Dependence of the phase incursion on the control voltages is obtained. The results of simulation of the longitudinal voltage effect on the NLC reorientation are described. The obtained results can be used in development and designing of NLC phase modulators.     

Recording of geometric phase elements based on liquid crystal polymers

A technique is developed for recording the centrally-symmetric liquid crystal phase plates with the anisotropic orientation of molecules providing a smooth change of the optical axis in a thin film of liquid crystal polymer. The technique enables one to record the elements with the cylindrically-symmetric and planar-symmetric distributions. Such structures can be used to develop the optical elements with the new functional possibilities. Using the developed techniques, the polarization-sensitive Fresnel lens is realized which is functioning either as a collecting or as a scattering lens for the light beams with the orthogonal circular polarizations.     

Photonuclear reactions on 112,118,124Sn,natTe, and natHf targets

The yields of products of photonuclear reactions on tin targets enriched in the isotopes ^112,118,124Sn and on Te and HfO₂ targets of natural isotopic composition were measured. The targets were irradiated at the linear electron accelerator of the A.I. Alikhanian National Science Laboratory (Yerevan Physics Institute) at the electron energy of E _e = 40 MeV. The dependence of the product yields on the nucleonic composition of the targets was discussed. The isomeric ratios were obtained for the ^119m,g Te, ^121m,g Te, ^117m,g In, and ^123m,g Sn products. The experimental data in question were compared with their theoretical counterparts calculated on the basis of the TALYS 1.4 code. The dependence of the isomeric ratios on the photon energy and on the mass number of the product is considered.     

Special features of isomeric ratios in nuclear reactions induced by various projectile particles

Calculations for (p, n) and (α, p3n) reactions were performed with the aid of the TALYS-1.4 code. Reactions in which the mass numbers of target and product nuclei were identical were examined in the range of A = 44–124. Excitation functions were obtained for product nuclei in ground and isomeric states, and isomeric ratios were calculated. The calculated data reflect well the dependence of the isomeric ratios on the projectile type. A comparison of the calculated and experimental data reveals, that, for some nuclei in a high-spin state, the calculated data fall greatly short of their experimental counterparts. These discrepancies may be due to the presence of high-spin yrast states and rotational bands in these nuclei. Calculations involving various level-density models included in the TALYS-1.4 code with allowance for the enhancement of collective effects do not remove the discrepancies in the majority of cases.