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1.
2.
A.K. Kazansky L. Yu Sergeeva 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,37(4):305-313
The method of an accurate calculation of vibrational excitation cross sections of a two-mode molecule by slow electrons within the framework of the local theory (the ‘boomerang’ model) is applied for a model study of the excitation of the symmetrical stretching vibrational modes of carbon dioxide in the two-mode approximation (i.e., only the symmetrical stretch and bending modes are included in the consideration). It is shown that the 'boomerang’ oscillations in the cross section are strongly suppressed due to the decay of the one-dimensional ‘boomerang' state caused by the anion wave packet sliding from the linear configuration ridge. Consequently, the bending motion in CO2 molecule should to be taken into account even if only the processes without the final bending excitation are considered. A simple quasi one-dimensional model describing the system sliding from the ridge is put forward which treats this phenomenon as a decay of the initial wave packet via the series of diabatic resonant states related to unstable trajectory. 相似文献
3.
Specific sorption sites for nitrogen, N2, in NaLSX and LiLSX zeolites were investigated using a DRIFT spectroscopic method. Sorption of molecular hydrogen, H2, by NaLSX or LiLSX zeolite at 77 K with DRIFT control of perturbation of sorbed molecules allowed to discriminate two or three different types of specific sorption sites in the respective zeolites. Their H–H stretching frequencies are 4077 and 4081 cm–1 for NaLSX, and 4061, 4084 and 4129 cm–1 for LiLSX. With reference to an independent investigation by methods of both sorption thermodynamics and molecular modeling for N2 sorption on LiLSX, the first two of the corresponding bands were ascribed to H2 sorption on lithium cations, Li+, localized in supercages of the faujasite, FAU, zeolite framework at sites SIII and SIII, while the latter band most likely belongs to H2 sorption on Li+ cations at sites SII, and on hydroxyl groups, OH. Sorption of N2 by Li+ cations at sites SIII and SIII is the strongest, resulting in a decrease of intensity of the corresponding DRIFT bands that stem from subsequent H2 sorption. Nitrogen sorption by Li+ cations at sites SII is much weaker. Sorption of N2 on Na+ cations at sites SIII in NaLSX zeolite is also stronger than by Na+ cations at sites SII. 相似文献
4.
A DRIFT study of ethane adsorbed by zinc cations in ZnZSM-5 prepared by chemical reaction of the hydrogen form of the zeolite with zinc vapor at 770 K, or by wet ion exchange, reveals unusual spectra of adsorbed C2H6 species. In addition to the weakly perturbed narrow bands in the region of C-H stretching vibrations, these spectra exhibit a very intense broad IR band with a frequency that is more than 200 cm(-1) lower than those of the C-H stretching vibrations of gaseous or physically adsorbed ethane. The very high relative intensity of this band indicates a very strong polarizability of the corresponding vibrational mode. It is concluded that these strongly polarized vibrations are closely connected with the subsequent heterolytic dissociation of ethane at moderately elevated temperatures, resulting in the formation of acidic hydroxyl groups and zinc ethyl fragments. At higher temperatures, the zinc ethyl fragments decomposed, resulting in the formation of zinc hydrides and ethylene. The unusual DRIFT spectrum of the molecular form of ethane adsorption by zinc cations represents a first example of anisotropy of polarizability of adsorbed molecules, which may provide a new explanation for selectivity of the acid-catalyzed reactions. In this connection, it is suggested to use the relative intensities of IR bands of adsorbed molecules as a reactivity index that is directly connected with chemical activation of adsorbed molecules via their polarization by the active sites. 相似文献
5.
A remarkable effect of circular dichroism, i.e., a difference in photoelectron spectra produced by right and left circularly polarized light in two-color multiphoton ionization of atoms, is predicted for the case when the atom is ionized by an extreme ultraviolet or x-ray femtosecond pulse in the field of a strong infrared laser pulse, both pulses being circularly polarized. We show that the sidebands formed in the spectra exhibit different circular dichroism often of different signs both in angle-resolved and angle-integrated experimental conditions. The effect can be used for detecting and measuring circular polarization of x rays in a spectral range where other methods are not effective. 相似文献
6.
Temperature sensitivity of Ge-B-SiO(2) waveguide Bragg gratings on a crystallized glass substrate 总被引:1,自引:0,他引:1
Waveguide Bragg gratings were fabricated by plasma-enhanced chemical-vapor deposition followed by irradiation with KrF excimer laser light through a phase mask. The period of the Bragg grating was 0.53 mum, and the Bragg wavelength was ~1.53 mum . The temperature dependence of the Bragg wavelength was 11 pm/ degrees C for a 10GeO(2) -90SiO(2)(mol.%) core waveguide on a Si substrate, and the Bragg wavelength shift was successfully reduced to 5.0pm/ degrees C by use of a 14GeO(2)-12B(2)O(3)-74SiO(2) (mol.%) core and a crystallized glass substrate with a thermal-expansion coefficient of -2.0x10(-6)(/ degrees C) . 相似文献
7.
A theoretical study of the electron dynamics in image potential states on Cu(1 0 0) surfaces with different types of adsorbates is presented. Scattering of the image state electron by an adsorbate induces inter-band and intra-band transitions leading respectively to the population decay and to the dephasing of the image state. We compare results obtained with low coverage (typically 1 adsorbate atom per 1000 surface atoms) Cs, Ar, and a model electronegative adsorbates. As follows from our results, Cs adsorbates lead to both appreciable dephasing and decay, while electronegative adsorbates mostly affect the dephasing rate. The effect of low coverage Ar adsorbates is small, consistent with their neutrality. 相似文献
8.
L. A. Bondar L. M. Kustov I. P. Beletsky V. B. Kazansky 《Reaction Kinetics and Catalysis Letters》1993,50(1-2):193-198
Microporous silica gels containing small amounts of titanium ions have been synthesized. Porous structure and surface active sites of silica gels have been studied. It has been found that the titanium ions are distributed uniformly in silica gel matrix, substituting silicon ions isomorphically. 相似文献
9.
Greater than 20%-efficient frequency doubling of 1532-nm nanosecond pulses in quasi-phase-matched germanosilicate optical fibers 总被引:2,自引:0,他引:2
Pruneri V Bonfrate G Kazansky PG Richardson DJ Broderick NG de Sandro JP Simonneau C Vidakovic P Levenson JA 《Optics letters》1999,24(4):208-210
We fabricated second-order nonlinear gratings in D-shaped germanosilicate fibers, using thermal poling and periodic electrodes defined by standard photolithography. These gratings, which are up to 75 mm long, were used for efficient quasi-phase-matched frequency doubling of 1.532-mum nanosecond pulses from a high-power erbium-doped fiber amplifier. Average second-harmonic powers as high as 6.8 mW and peak powers greater than 1.2 kW at 766 nm were generated, with average and peak conversion efficiencies as high as 21% and 30%, respectively. 相似文献
10.
J.P.?GauyacqEmail author A.G.?Borisov A.K.?Kazansky 《Applied Physics A: Materials Science & Processing》2004,78(2):141-147
The local density of states of two model systems formed by an individual adsorbate (Cs or Ar) on a Cu(111) surface is investigated using a wave-packet propagation approach. In both cases a sharp peak appears at the threshold of the 2D Shockley surface-state continuum. This peak is attributed to quasi-stationary states located just below the 2D continuum. Following the existence criterion for a bound state in two dimensions by Simon, such states splitting off the surface-state bottom should appear whenever the surface-state continuum is perturbed by an attractive potential, independently of the existence of atomic-like states bound by the perturbing potential. These findings are discussed in connection with recent observations of peaks located at the surface-state threshold in scanning tunnelling microscopy experiments. PACS 68.37.Ef; 73.20.At; 73.20.Hb; 68.43.-h 相似文献