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排序方式: 共有71条查询结果,搜索用时 15 毫秒
1.
Yevgen Posokhov Alexander Gorski Jens Spanget-Larsen Fritz Duus Poul Erik Hansen Jacek Waluk 《Chemphyschem》2004,5(4):495-502
Thioacetylacetone and its variously deuterated isotopomers have been investigated using electronic and vibrational spectroscopy combined with quantum chemical calculations. Thioacetylacetone is known for its photochromic properties, but the structures of the initial and final forms have been the subject of a long debate. Analysis of the IR spectra recorded in low-temperature argon and xenon matrices, room-temperature solutions, and in the gas phase has allowed us to establish the nature of the photochromic species and of its precursor. Similar to the case of another beta-thioxoketone, monothiodibenzoylmethane, the photo-product has been assigned to the nonchelated SH exo-rotamer of the (Z)-enethiol tautomeric form, whereas the dominant ground-state species corresponds to the chelated (Z)-enol tautomeric form. Detailed vibrational assignments have been proposed for both forms based on quantum chemical calculations and polarization experiments. In the case of the chelated (Z)-enol species prevailing in the ground state, a second-order perturbative anharmonic analysis at the B3LYP/cc-pVTZ level indicated strong anharmonic effects associated with the intramolecular hydrogen bond, leading to a shift of more than 600 cm-1 of the wavenumber of the OH-stretching vibration. A small fraction of the SH endo-rotameric chelated (Z)-enethiol form was also detected under unperturbed conditions. The (Z)-enethiol form can be converted into the (Z)-enol form by irradiation at 290 nm. 相似文献
2.
Experimental and Theoretical Investigation of the First‐Order Hyperpolarizability of Octupolar Merocyanine Dyes 下载免费PDF全文
Dr. Frédéric Castet Dr. Mireille Blanchard‐Desce Frédéric Adamietz Yevgen M. Poronik Prof. Dr. Daniel T. Gryko Prof. Dr. Vincent Rodriguez 《Chemphyschem》2014,15(12):2575-2581
Hyper‐Rayleigh scattering experiments and quantum chemical calculations are combined to investigate the second‐order nonlinear optical responses of a series of three‐arm merocyanine derivatives. They exhibit an octupolar hyperpolarizability response with lower amplitude than crystal violet due to a lower extent of the photoinduced charge transfer and reduced bond length alternation. Strong effects on the second‐order optical response measured close to the two‐photon absorption level are clearly evidenced; for example, the effective measured polarization ratio deviates below the ideal octupolar value of 3/2 even at very low excitation power. These effects are attributed to two‐photon absorption resonance, which we believe modifies dynamically the population of the ground state versus that of the excited state. 相似文献
3.
E. F. Venger T. Ya. Gorbach L. A. Matveeva S. V. Svechnikov 《Journal of Experimental and Theoretical Physics》1999,89(5):948-954
We present the results of studies of electroreflection in the 1.1–4.4 eV spectral range, of electron Auger spectroscopy, and
of electron diffraction involving the photoluminescent Si-SiO2 system prepared via anisotropic chemical etching of the Si(100) surface. These results are explained on the basis of a four-layer
model of the band structure and energy transition diagram for a system with a quantum well at the silicon surface, surface
electron states at the boundary, and a gradient of the band potential in the transition layer. We find that light-emitting
silicon remains an indirect-gap semiconductor and that the visible photoluminescence is due to direct recombinations of the
light-excited electrons and holes in the quantum well at the center of the Brillouin zone with the participation of the band
of deep localized states, which is due to the presence of oxygen at the silicon surface.
Zh. éksp. Teor. Fiz. 116, 1750–1761 (November 1999) 相似文献
4.
Bhanushree Gupta Rahul Sharma Namrata Singh Yevgen Karpichev Manmohan L. Satnami Kallol K. Ghosh 《Journal of Physical Organic Chemistry》2013,26(8):632-642
Kinetic studies of the reactions of tertiary oximes (monoisonitroso acetone; MINA and butane 2,3 dione monooxime; BDMO) with some carboxylate (p‐nitrophenyl acetate and p‐nitrophenyl benzoate), phosphate (p‐nitrophenyl diphenyl phosphate and bis (2,4‐dinitrophenyl) phosphate) and sulfonate (p‐nitrophenyl p‐toluene sulphonate) esters in gemini surfactants have been conducted. The observed first‐order rate constant versus surfactant profiles show micelle‐assisted bimolecular reactions involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. Experimental results showed that MINA exhibited better nucleophilic activity towards ester cleavage than BDMO. Pseudophase model has been applied in order to determine micellar second‐order rate constants and binding constants. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
5.
Substituting CF2 for O4′ in Components of Nucleic Acids: Towards Systems with Reduced Propensity to Form Abasic Lesions 下载免费PDF全文
Dr. Yevgen P. Yurenko Dr. Jan Novotný Prof. Dr. Vladimir Sklenář Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17933-17943
Intrinsic structural features and energetics of nucleotides containing variously fluorinated sugars as potential building blocks of DNA duplexes and quadruplexes are explored systematically using the modern methods of density functional theory (DFT) and quantum chemical topology (QCT). Our results suggest that fluorination at the 2′‐β or 2′‐α,β positions somewhat stabilizes in vacuo the AI relative to the BI conformations. In contrast, substitution of the CF2 group for the O4′ atom (O4′‐CF2 modification) leads to a preference of the BI relative to AI DNA‐like conformers. All the studied modifications result in a noticeable increase in the stability of the glycosidic bond [estimated by the relaxed force constants (RFC) approach], with particularly encouraging results for the O4′‐CF2 derivative. Consequently, the O4′‐CF2 modified systems are suggested and explored as promising scaffolds for the development of duplex and quadruplex structures with reduced propensity to form abasic lesions and to undergo DNA damage. 相似文献
6.
This work deals with the investigation of dielectric and optical properties of discontinuous metal films over a wide range
of filling factors each side of the percolation threshold. A phenomenological two-parameter representation is used for the
effective permittivity &εtilde; of such systems. In order to test the proposed approach, we have taken for gold films on a
glass substrate the transmittance spectra in the visible and near-IR regions. It is shown that the representation used for
the effective permittivity enables us to adequately describe the experimental transmittance spectra. The parameters entering
the above representation are determined and the relationship between them and film microgeometry is discussed.
Received: 6 November 2000 / Accepted: 30 May 2001 / Published online: 25 July 2001 相似文献
7.
A. A. Belyaev E. F. Venger V. G. Lyapin R. V. Konakova V. V. Milenin Yu. A. Tkhorik I. Hotovy G. N. Kashin 《Technical Physics》1998,43(1):56-59
Peculiarities of contact formation in the system NbN-GaAs upon a change in the structural-phase state of the deposited metal
are investigated. It is shown that the role of the chemical factor in the processes of contact formation decreases as the
degree of structural perfection of the NbN alloy increases. The causes of the corresponding changes in the electronic structure
of the interface as a result of the phase transition NbN-Nb4N3 are discussed. The Auger spectrum and current-voltage and capacitance-voltage characteristics of NbN-GaAs surface-barrier
structures are measured before and after annealing in vacuum at T=850 °C for 10 s.
Zh. Tekh. Fiz. 68, 63–66 (January 1998) 相似文献
8.
E. F. Venger A. V. Goncharenko O. S. Gorya N. L. Dmitruk V. P. Romanyuk 《Journal of Applied Spectroscopy》1999,66(4):493-500
We studied phonon-polariton modes in long-period GaAs/GaPAs semiconductor superlattices using the methods of frustrated total
internal reflection and IR spectroscopy in the region of residual rays. The excitation of waveguide, real, and virtual surface
and volume phonon polariton modes was observed experimentally. Their dispersion relations were calculated and compared with
experimental data, and the excitation nature was identified with the aid of the spectra of permittivity and a normal component
of the wave vector in heterostructure layers.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 460–466, July–August, 1999. 相似文献
9.
The purpose of this work is to extend a typical creep-damage model in order to describe material behavior under variable thermal and mechanical loading in wide stress range. The model basis is creep constitutive law in form of hyperbolic sine stress response function proposed by Nadai. The constitutive law is extended to assume the damage process under creep and fatigue by the introduction of scalar damage parameters and appropriate evolution equations according to Kachanov-Rabotnov concept. The material constants for model are identified by fitting the experimental creep and low-cycle fatigue data for the steel AISI type 316 at the range of temperatures 500°C – 750°C. The development of such model is motivated by the well described failure case study of high-temperature components at unit 1 of Eddystone power plant, which have operated during 130520 hours under creep-fatigue interaction conditions. The main steam piping (MSP) from this power plant is selected for thermo-mechanical creep-fatigue analysis applying the proposed material model. The estimated values of damage parameters comply with the real location of the component failure and a scatter of experimental data on creep-fatigue interaction diagram. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
Many materials exhibit a stress range dependent creep behavior. The power–law creep observed for a certain stress range changes to the viscous type creep if the stress value decreases. Recently published experimental data for advanced heat resistant steels indicate that the high creep exponent (in the range 5–12 for power–law behaviour) may decrease to the low value of approximately 1 within the stress range relevant for engineering structures. The aim of this paper is to confirm the necessity of the assumption of the stress range dependent power–law–viscous creep transition for the solution of stress relaxation problems affected by creep behavior at elevated temperatures. A constitutive model for the minimum creep rate is introduced to describe both the linear and the power law creep depending upon the stress level. The proposed constitutive model includes a strain hardening function to describe the primary creep stage. To demonstrate the existence of the linear creep behaviour in the low stress range of application area and the influence of the primary creep behaviour on relaxation, several solutions of a uniaxial stress relaxation problem are presented for the loading values relevant to engineering applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献