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1.
M. Gutowski I. Dabkowska J. Rak S. Xu J.M. Nilles D. Radisic K.H. Bowen Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):431-439
The photoelectron spectra (PES) of anions of uracil-glycine and uracil-phenylalanine complexes reveal broad features with
maxima at 1.8 and 2.0 eV. The results of ab initio density functional B3LYP and second order M?ller-Plesset theory calculations indicate that the excess electron occupies a
π* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT)
from the carboxylic group of glycine to the O8 atom of uracil. As a result, the four most stable structures of the anion of
uracil-glycine complex can be characterized as the neutral radical of hydrogenated uracil solvated by the anion of deprotonated
glycine. The similarity between the PES spectra for the uracil complexes with glycine and phenylalanine suggests that the
BFPT is also operative in the case of the latter anionic species. The BFPT to the O8 atom of uracil may be related to the
damage of nucleic acid bases by low energy electrons because the O8 atom is involved in a hydrogen bond with adenine in the
standard Watson-Crick pairing scheme.
Received 6 April 2002 Published online 13 September 2002 相似文献
2.
The Raman spectroscopic studies of two rare earth trihydrides: Y H3, HoH3, have been performed in the pressure range from ambient up to 16 GPa and 25 GPa respectively. For the first time samples of REH3 in the form of powder have been studied by Raman spectroscopy using the Diamond Anvil Cell (DAC) technique. A rapid decrease of Raman activity has been observed for the hydrides under pressure values in the vicinity of structural phase transition. Metallization as a possible reason for the observed dramatic change of the REH3 Raman activity has been discussed. 相似文献
3.
The electronic structure and magnetism of SmCo7-xZrx alloy are investigated using the spin-polarized MS-X. method. The results show that a few of electrons are transferred to the Sm(5d0) orbital due to orbital hybridization between Sm and Co atoms. The exchange interactions between 3d and 5d electrons are more important than the polarization effects of the conductive electrons, thus it is the main reason resulting in the long-range ferromagnetic order in SmCo7-xZrx. The Curie temperature of SmCo7-xZrx is generally lower than that of corresponding pure Co, which may be explained by the weaker average coupling strength between Co lattices due to some negative couplings mainly occurring of 2e site. The calculated results for the Sm5Co32Zr2 cluster may lead to a better understanding of why SmCo7-xZrx is stable phase. Since the spin-up DOS peak of d electrons at EF arises and the bonding of electrons at EF strengthens with increasing Zr concentration, which results in the internal energy of the system decrease, the stable ferromagnetic order forms in SmCo7-xZrx. 相似文献
4.
We perform the ab initio calculation for obtaining the density of states and magnetic properties of ZrFe2 Laves phase compound based on the method of augmented plane waves plus local orbital The results indicate that the ferromagnetic state is more stable than the paramagnetic one, but with a slightly larger volume. The 3d - 4d exchange interactions between Fe and Zr electrons lead to the antiparallel coupling for Fe 3d and Zr 4d states, which is responsible for the ferrimagnetic ordering of the compound. The resulting magnetic moment of about 1.98μB for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin states causes a moment of about -0.44 μB. Moreover, the resulting magnetic moments with the generalized gradient approximation are more consistent with experimental values than that of the local-spin density approximation. 相似文献
5.
The influence of the substitution of Ga atoms for Co atoms in DyCo2 compounds on magnetocaloric properties has been investigated. A series of DyCo2−xGax alloys with x=0, 0.03, 0.06, 0.1, 0.15, and 0.2 was prepared by the arc-melting method for this investigation. Experimental results revealed that the Ga substitution for Co in DyCo2 can form a single phase with the cubic Laves phase structure up to x=0.2. As the Ga content x increases, the lattice parameter and the Curie temperature Tc increases from 143 to 196 K linearly. The maximum magnetic entropy changes in a low field change of 0-1.5 T, increasing from 8.24 to 10.61 J/K kg when the Ga content x increases from 0 to 0.03, but decreasing gradually to 3.51 J/K kg as the Ga content further increases to x=0.2. All the samples show a relatively large magnetic entropy change with very small hysteresis loss. 相似文献
6.
Although SiO2 crystals have been used in electroluminescence devices and thermoluminescence (TL) dosimeters, the emission mechanism of TL has not yet been clearly explained. Recently, as we could get amorphous and highly pure SiO2 prepared by the sol-gel method, we have investigated the TL emission mechanism using Al3+- and/or Eu3+-doped SiO2 crystalline samples prepared by the heat-treatment under much lower temperature that the melting point of SiO2. The TL spectrum of the Eu3+-doped sample displayed several peaks, including two main peaks due to the electron transitions from 5D2 to 7F5 (ca. 570 nm) and from 5D0 to 7F2 (ca. 610 nm). As doping concentration increased, all the peak intensities reduced from maximum values except that due to the electron transition from 5D0 to 7F2. These observations are thought to result from a cross-relaxation process due to the lack of inversion symmetry at the Eu3+ site. 相似文献
7.
We report frequency stabilization of diode lasers using modulation transfer spectroscopy of an acetylene transition (13C2H2, 1+3, P(16)) at 1542 nm. We realize modulation-free acetylene-stabilized lasers with a frequency stability of about 10–11 and an absolute frequency accuracy of about 20 kHz.This revised version was published online in March 2005. In the previous version, the published online date was missing 相似文献
8.
J. Henningsen 《Applied physics. B, Lasers and optics》2003,76(4):451-456
A 7.4-μm difference frequency spectrometer is used for analysing the headspace above the liquid surface of a sample of red
wine for SO2. The analysis is based on previously determined line parameters for a number of SO2 lines of the ν3 band, and allows fast, interference-free determination of the concentration without the need for any calibration against
a standard of known concentration. The potential for developing this technique into a method for determining free and total
sulphur dioxide in beverages is discussed.
Received: 16 January 2003 / Revised version: 19 February 2003 / Published online: 9 April 2003
RID="*"
ID="*"Corresponding author. Fax: +45-4593/1137, E-mail: jh@dfm.dtu.dk 相似文献
9.
V. Matolín J. Libra I. Matolínová V. Nehasil L. Sedlá?ek F. Šutara 《Applied Surface Science》2007,254(1):153-155
The reactive vacuum deposition of CeO2 on Cu(1 1 1) surface in oxygen atmosphere provides high quality epitaxial ceria overlayers. We report the growth characteristics of Ce oxide, the structures, and the temperature stability of the oxide phases as investigated by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy. We find that Ce oxide on the Cu(1 1 1) grows initially in the form of islands giving sharp hexagonal LEED pattern of the CeO2(1 1 1) structure corresponding to the (1.5 × 1.5) structure. The CeO2-Cu(1 1 1) films exhibited mixed valence states and temperature dependent CeO2-Ce2O3 transition above 900 K due to the vacuum annealing. The transition progressed more rapidly at the surface, probably by formation of oxygen vacancies. 相似文献
10.
RPdIn (R = La-Nd) compounds were studied by means of magnetic susceptibility, specific heat and photoelectron spectroscopy measurements. The results prove that CePdIn is an antiferromagnetic Kondo lattice with TN below 1.7 K. The Pr-based indide remains paramagnetic down to 1.7 K, and the lack of any magnetic ordering may be due to the presence of a singlet as the crystalline electric field ground state or/and strong hybridization between Pr 4f states and Pd 4d states. In turn, NdPdIn exhibits ferromagnetism below about 26 K. In contrast to CePdIn, for the Pr- and Nd-based compounds any significant enhancement of the electronic specific heat coefficient was observed. 相似文献