Paramagnetic species on catalytic surfaces--DFT investigations into structure sensitivity of the hyperfine coupling constants

Structure sensitivity of the hyperfine coupling constants was investigated by means of DFT calculations for selected surface paramagnetic species. A *CH2OH radical trapped on silica and intrazeolite copper nitrosyl adducts encaged in ZSM-5 were taken as the examples. The surface of amorphous silica was modeled with a [Si5O8H10] cluster, whereas the zeolite hosting sites were epitomized by [Si4AlO5(OH)10]- cluster. Three different coordination modes of the *CH2OH radical were considered and the isotropic 13C and 1H hyperfine constants of the resultant van der Waals complexes, calculated with B3LYP/6-311G(d), were discussed in terms of the angular deformations caused by hydrogen bonds with the cluster. The magnetic parameters of the eta1-N[CuNO]11 and eta1-O[CuNO]11 linkage isomers were calculated at the BPW91/LanL2DZ and 6-311G(df) level. For the most stable eta1-N adduct a clear dependence of the spin density distribution within the Cu-NO moiety on changes in the Cu-N-O angle and the Cu-N bond distance was observed and accounted for by varying spin polarization and delocalization contributions.     

Photogeneration of reactive oxygen species over ultrafine TiO2 particles functionalized with rutin–ligand induced sensitization and crystallization effects

Research on Chemical Intermediates - Interaction of amorphous and crystalline TiO2 ultrafine particles (2–6 nm) with rutin results in the formation of colored nanomaterials of an...     

微波消解-原子吸收光谱法测定虎耳草中的重金属

建立了虎耳草铅、镉、砷、铜、汞含量测定的方法.采用微波消解处理虎耳草药材,以原子吸收光谱法测定样品中的铅、镉、砷、铜、汞重金属元素的含量.所测不同地区虎耳草样品中除砷合格外,其他元素各有不同程度的超标.方法简便、快速、准确,能有效测定虎耳草药材中铅、镉、砷、铜、汞的含量.     

Strangeness exchange reaction on nuclei

Population of hypernuclear states has been observed in recoiless Λ production of the strangeness exchange reaction (K^?, π^?) on ⁹Be, ¹²C, ¹⁶O, ³²S and ⁴⁰Ca.     

Relativistic density functional calculations of EPR g tensor for eta1{CuNO}(11) species in discrete and zeolite-embedded states

Spin-unrestricted zeroth order regular approximation (ZORA) and the scalar relativistic method based on Pauli Hamiltonian implemented in the Amsterdam Density Functional suite were used to calculate the electronic g tensor for isolated covalent {CuNO}(11) and electrostatic {q-NO}(1) species and for various model molecular and nonmolecular {CuNO}(11)-containing systems, epitomizing copper nitrosyl cage adducts in the ZSM-5 zeolite. The predicted g tensor values using the ZORA/VWN scheme were in satisfactory agreement with experimental EPR results. Relativistic, diamagnetic, and paramagnetic contributions to the calculated g tensor were quantified. The nature of the observed Deltag shifts was discussed in terms of the molecular orbital contributions due to the magnetic field-induced couplings and their structure sensitivity. The influence of basis set and exchange-correlation functional on the results was also briefly evaluated.     

Some aspects of thermal destruction of polyurethanes

A number of Polyurethane elastomers were investigated by means of non-isothermal thermogravimetry to set a general procedure for numerical estimation of kinetic parameters. The value of an assumed objective function. determining the accuracy of the estimation depends on many factors as: the considered region of a TG-curve, the method of choosing points from the curve, and the initial values of the pre-exponential factor and the reaction order. After the optimal conditions were evaluated, the minimum values of the objective function and the corresponding triplet values of kinetic parameters were obtained. Among these, only the activation energy can be considered as a semiquantitative estimate of thermal stability.

---

Zusammenfassung Eine Anzahl von Polyurethan-Elastomeren wurde mittels nichtisothermer Thermogravimetrie untersucht, um eine allgemeingültige Verfahrensweise zur numerischen Abschätzung kinetischer Parameter abzuleiten. Der Wert einer angenommenen objektiven Funktion zur Bestimmung der Genauigkeit der Abschätzung hängt von mehreren Faktoren ab: von dem in Betracht gezogenen Teil der TG-Kurve, von der Auswahlmethode für die berücksichtigen Meßpunkte, und von den anfänglichen Werten des Präexponentiellen Faktors und der Reaktionsordnung. Nachdem die optimalen Bedingungen ermittelt waren, wurden die minimalen Werte der objektiven Funktion und die entsprechenden Wertetripel für die kinetischen Parameter erhalten. Von diesen kann nur die Aktivierungsenergie als halbquantitatives Maß für die thermische Stabilität betrachtet werden.

---

, . - , , , , . , . , .

     

Carrier transport mechanisms in the ZnO based heterojunctions grown by MBE

This paper presents a review of models of the current transport in different kind of heterojunctions (HJs) and their characteristics. In order to effectively deduce the dominant electron transport for the HJs based on ZnO or Zn_1?xMg_xO layers grown on Si substrate by MBE a comparison is performed – which type of the HJ exhibits better electrical properties. The current–voltage characteristics for the studied HJs were measured within 280–300 K. The transport properties of the HJs are explained in terms of Anderson model with reference to aforementioned current transport models. It is found, that the mechanisms of current transport for all of the studied HJs are similar. At a low forward voltage bias the tunneling current dominates while at medium voltage bias (0.5–1 V) multitunneling capture-emission prevails with the electron trap located at 0.1–0.25 eV below the bottom of a ZnO (Zn_1?xMg_xO) conduction band. Beyond this voltage bias space charge limited current governs the current transport.     

Suche nach intermediären Substrukturen im Spaltungsquerschnitt von232Th+n

The resonances in the²³²Th(n, f) reaction atE _n =1.61 and 1.72 MeV were examined for fine structure. With the experimental resolution of 8 keV no resolved fine structure was observed.