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991.
Unusual cases of effective coordination of substituted 4-thioxochromones with lanthanide shift reagents have been studied. It is shown that the necessary condition for such coordination is the presence in the 3-hetaryl substituent of a pyridine type nitrogen atom next to the bond between the heterocyclic fragments. Coordination with the lanthanide shift reagents is explained by the formation of chelates of the shift reagents with substrate molecule. Calculations on the structures of these complexes have been carried out.Taras Shevchenko Kiev University, Ukraine; e-mail: ovl@bhf2.kiev.ua. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, 605–610, May, 2000. 相似文献
992.
Introduction Various ethylene/ α- olefin copolymers such as LLDPE,VLDPE/ ULDPE,EPR,EPDMetc.have a wide application in polymer materials science and engineering.The properties ofthose copolymers are greatly influenced by the type,content and distributions of thecomonomer branches.The effects of different kinds of chain branches,which were derivedfrom comonomerincorporationsin themain chain of the ethylene/α- olefin copolymers on theirproperties and studied by many authors,have sh… 相似文献
993.
Spectral-luminescent properties and photoinduced transformations of bisanthene and bisanthenequinone
Based on the study of photochemical transformations of bisanthene in oxygen-containing solutions, it was established that
the final product of this reaction is bisanthenequinone. It is shown that in the course of this oxidation reaction the intermediate
compounds endomonoperoxide and bisanthene endobiperoxide are formed. Quantum-chemical calculation of the geometrical structure
and electronic spectra of the endoperoxides has shown that they have a nonplanar structure, and their absorption spectra experience
a large hypsochromic shift. The absorption and fluorescence spectra of solutions of bisanthene in different solvents at 300
and 77 K were investigated. The large Stokes shift of the fluorescence spectra of the solutions of bisanthene in benzene and
in its methyl derivatives is explained by the action of intermolecular interactions. The quasi-line fluorescence spectra of
solutions of bisanthene in the matrices of saturated hydrocarbons were recorded.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 176–182, March–April, 2000. 相似文献
994.
V. A. Yurevich 《Journal of Applied Spectroscopy》2000,67(5):924-928
We have explored the possibility of observing bistability of the frequency dependence of transmission of a thin (less than the wavelength of the acting laser radiation) surface layer of active atoms. For the external field strength corresponding to the transition saturation, we predict the hysteresis behavior of transmission on separate portions of the dependence and sharp asymmetry of resonance curves of absorption if the influence on the dielectric constant of the medium of a layer of transitions adjacent to the resonance one and capable of interacting with radiation is taken into account. 相似文献
995.
996.
Based on the quantum confinement-luminescence center model, we focus on the relationship between the photoluminescence (PL) spectra and sizes of nanoscale silicon particles.We find that when there are two kinds of luminescence centers (LC) in the oxide layer surrounding the silicon particles, both the integrated PL intensity and the spectral peak position swing with reducing the sizes of silicon particles, which is different from the monotonous blueshift of peak position predicted by quantum confinement model. By changing the concentrations of LC we find the correlation between the spectral peak position and the integrated PL intensity when the size of silicon particles is reduced. The effects of other parameters such as the half width of size distribution and the position of photon emission levels of LC are also found to be important. 相似文献
997.
Nuclear magnetic moments provide a sensitive test of nuclear wave functions, in particular those of neutrons, which are not
readily obtainable from other nuclear data. These are taking added importance by recent proposals to study parity non-conservation
(PNC) effects in alkali atoms in isotopic series. By taking ratios of the PNC effects in pairs of isotopes, uncertainties
in the atomic wave functions are largely cancelled out at the cost of knowledge of the change in the neutron wave function.
The Bohr–Weisskopf effect (B–W) in the hyperfine structure interaction of atoms measures the influence of the spatial distribution
of the nuclear magnetization, and thereby provides an additional constraint on the determination of the neutron wave function.
The added great importance of B–W in the determination of QED effects from the hfs in hydrogen-like ions of heavy elements,
as measured recently at GSI, is noted. The B–W experiments require precision measurements of the hfs interactions and, independently,
of the nuclear magnetic moments. A novel atomic beam magnetic resonance (ABMR) method, combining rf and laser excitation,
has been developed for a systematic study and initially applied to stable isotopes. Difficulties in adapting the experiment
to the ISOLDE radioactive ion beam, which have now been surmounted, are discussed. A first radioactive beam measurement for
this study, the precision hfs of 126Cs, has been obtained recently. The result is 3629.515(∼0.001) MHz. The ability of ABMR to determine with high precision nuclear
magnetic moments in free atoms is a desideratum for the extraction of QED effects from the hfs of the hydrogen-like ions.
We also point out manifestations of B–W in condensed matter and atomic physics.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
998.
Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λF) values whereas the effect is moderate at the absorption maximum (λabs) values. The molecular electrostatic potential (MESP) at the metal center (VM) and the most electron rich region indicated by MESP minimum (Vmin), located at the oxygen of phenoxide ring exhibit excellent correlations with the λF and Stokes shift (λF−λabs) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the Vmin or VM emerge as theoretical quantities to measure the same. 相似文献
999.
1000.
Fumiko Akagi Masaki MukohMasafumi Mochizuki Junko UshiyamaTakuya Matsumoto Harukazu Miyamoto 《Journal of magnetism and magnetic materials》2012,324(3):309-313
Thermally assisted magnetic recording (TAR) with bit-patterned media was investigated by micromagnetic simulation. The media were assumed to be FePt layers. The effective head-field margin as well as the increase in temperature margin and down-track shift margin was investigated. Conditions of the head and medium that lead to a recording density beyond 5 Tb/in2 were proposed. 相似文献