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1.
An accurate calculation of the lowest negative electronic state of H 2 - (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H -. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H2 dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.  相似文献   

2.
The difference in the 332-and 326-keV transition energies from 178Ta decay is measured with a magnetic β spectrometer and a γ spectrometer. The energy of the 332-keV transition (E(332) = 331 607 ± 4 eV) and the energy of the 8 2 ? 1479-keV level in 178Hf (E(1479) = 1479001 ± 6 eV) are determined with high accuracy.  相似文献   

3.
The parameters of hyperfine interactions in Pb3+F 8 ? F a ? tetragonal clusters of MeF2 crystals (Me=Ca, Sr, Ba) are interpreted. The contributions of the spin polarization to the parameters of the proper hyperfine interaction and additional (ligand) hyperfine interactions are calculated in the approximation of weak binding between a charge-compensating ion F a ? and a cubic fragment in the tetragonal cluster. It is demonstrated that correct inclusion of the contributions from the spin polarization to the ligand isotropic hyperfine interaction for the F a ? ion leads to anomalously large parameters of this interaction for MeF2 crystals. These results are in agreement with experimental data.  相似文献   

4.
Using time-resolved photoelectron spectroscopy, the decay channels of AuO2 and Au2O2 following photoexcitation with 3.1-eV photons have been studied. For AuO2, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption can be excluded. For Au2O2, the spectra indicate O2 desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on Au n O2 with analogous data on Ag n O2 clusters, a discernible pattern emerges: for dissociatively bound O2(AuO2, Ag3O2), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au2O2, Ag2O2, Ag4O2, Ag8O2), the 3.1-eV photoexcitation triggers fast O2 desorption with a high quantum yield.  相似文献   

5.
A new model is proposed for a local transition in a Jahn-Teller impurity center in a crystal with a ferroelastic (ferroelectric) phase transition. This model is based on direct interaction of the order parameter of the phase transition in the matrix with the Jahn-Teller impurity degrees of freedom. It is shown that, under these conditions, the order parameter field can induce lifting of degeneracy of the electronic states active in the Jahn-Teller effect, which is accompanied by a transition from the Jahn-Teller effect to the pseudo-Jahn-Teller effect with its subsequent suppression. As a result, a decrease in temperature gives rise to a structural local transition in the region of the low-symmetry ferroelastic (ferroelectric) matrix phase from the many-well local adiabatic to a single-well potential. The model proposed allows interpretation of experimental data obtained in an EPR study of the molecular impurity ion MnO 4 2? in the K3Na(CrO4)2 ferroelastic.  相似文献   

6.
A crystal of the Cs5H3(SO4)4 · xH2O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by 2H NMR spectroscopy. The temperature and orientation dependences of the 2H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature T g = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point T g . However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.  相似文献   

7.
The specific heat of the ZrB12 compound in the normal and superconducting states (T C ≈ 6 K) has been studied in the 1.9–7 K temperature range for high-quality single crystals with different relative contents of boron isotopes. For Zr10B12, ZrnatB12, and Zr11B12 dodecaborides, the electron density of states and the electronphonon coupling constant, λe-ph ∼ 0.4, are found. The dependence of the thermodynamic and upper critical fields, as well as of the Ginzburg-Landau parameter (κ = 0.8–1.14) on temperature and isotope composition is determined. The results suggest the existence of the magnetic field induced phase transition at T* = 4–5 K, which is not related to the transition from type-I to type-II superconductivity. The possibilities of the existence of two-gap superconductivity and a structural phase transition at T* in zirconium dodecaboride are discussed.  相似文献   

8.
Powders of the B-type synthetic apatite exposed to gamma or ultraviolet irradiation were investigated using EPR spectroscopy. It was shown that ultraviolet irradiation leads to the appearance of the EPR spectrum near g = 2, which is similar to the spectrum observed upon gamma irradiation. The decomposition of the EPR spectra into components and the simulation of the shape of the experimental EPR signals revealed that these signals are associated primarily with two types of CO 2 ? radicals, namely, the axial CO 2 ? radicals and the orthorhombic CO 2 ? radicals. The differences in the shapes of the EPR spectra of the samples exposed to gamma and ultraviolet irradiation were explained by different ratios between the axial and orthorhombic CO 2 ? radicals. It was established that thermal annealing results in an increase in the relative contribution to the total EPR spectrum. This increase was explained by the transformation of the orthorhombic radicals into the axial radicals.  相似文献   

9.
Two Fe/MCM-41 systems, one of them sylilated, were obtained to be used as catalysts in Fischer–Tropsch reaction. They have more than 90% of the iron species located inside the support channels, leading to a narrow crystal size distribution accessible to reactive gases. The samples were characterized by X-ray diffraction, atomic absorption spectroscopy, N2 adsorption, Mössbauer spectroscopy and Fourier transformer infrared spectroscopy. Mössbauer spectroscopy allowed us to demonstrate that the catalytic active species were the same in both catalysts. The only difference between them was the surface hydrophobicity, which decreases the “water gas shift reaction” in the sylilated catalyst. Besides, this solid is more active for hydrocarbon production, with a lower methane yield.  相似文献   

10.
We propose a method for EIT ground state cooling of 171Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).  相似文献   

11.
In this article, we calculate the vector form factors f+ (Q2) and f- (Q2) within the framework of the light-cone QCD sum rule approach. The numerical values of f+ (Q2) are compatible with existing theoretical calculations, and the central value of f+ (0) (f+ (0)=0.97) is in excellent agreement with the values from chiral perturbation theory and lattice QCD. The values of |f- (0)| are very large compared to the theoretical calculations and experimental data, and they cannot give any reliable prediction. At large momentum transfer with Q2 > 5 GeV2, the form factors f+ (Q2) and |f- (Q2)| can either show the asymptotic behavior of or decrease more quickly than ; more experimental data are needed to select the ideal sum rules. PACS 12.38.Lg; 12.38.Bx; 12.15.Hh  相似文献   

12.
We study the exclusive Λb→Λℓ+- decay in the Appelquist, Chang, Dobrescu model with a single universal extra dimension. We investigate the sensitivity of the branching ratio, lepton polarization and forward–backward asymmetry to the compactification parameter 1/R. We obtain the result that the branching ratio for the Λb→Λℓ+- (ℓ=μ,τ) decay changes about 25% compared to the SM value when 1/R=250 GeV, and the zero position of the forward–backward asymmetry is shifted to the left compared to the SM result. Therefore, measurement of the branching ratio of Λb→Λℓ+- decay and determination of the zero position of are very useful in looking for new physics in the framework of the UED models. PACS 12.60.-i; 13.30.-a; 14.20.Mr  相似文献   

13.
14.
The Λ 7 He hypernucleus is considered within the Λ 5 He + n + n cluster model. The hyperon—nucleon interaction is described by a one-boson-exchange potential that is constructed on the basis of the NSC97f model. Phenomenological potentials are used to describe the αΛ and αN interactions. For the Λ 5 Hen interaction, use is made of the folding-model potential. The calculations of the hyperon binding energy in the ground state of the Λ 7 He hypernucleus on the basis of Faddeev equations in configuration space yield a result (5.35 MeV) that agrees well with preliminary experimental data (5.4 MeV). The problem of calculating the hyperon binding energy within the three-body approach is discussed. In calculating the energy spectrum of Λ 7 He, use is made of a version of the method of analytic continuation in the coupling constant. Low-lying excited states of this nucleus can be classified as an analog of the corresponding states of the 6He nucleus with allowance for the clustering of the Λ 5 He+n+n system in the 6He(J π)+Λ(s) form.  相似文献   

15.
The UV absorption spectra of F3? molecular ions in LaF3, SrF2, CaF2, and BaF2 crystals doped with rare-earth elements are studied. Comparison of radiation-colored and additively colored crystals reveals the absorption bands of F3? hole centers in the region near 6 eV. Nonempirical calculations of optical transitions agree well with experimental results.  相似文献   

16.
Absolute photoionization cross sections for Ne atoms in the excited levels (Paschen notation ) were calculated at near threshold energies within the configuration interaction Pauli-Fock approach including core polarization. The computed spectra and the lineshape parameters of the odd parity 2p1/2 5ns/d autoionizing resonances are found to be in good agreement with high resolution laser spectroscopic results. Guided by the theoretical results, improved analyses of the measured spectra by superimposed Fano-type profiles were achieved. Theoretical predictions are presented for resonances which have not yet been studied experimentally. In addition, we report the absolute partial photoionization cross sections for the 2P3/2 and 2P1/2 channel at photoelectron energies up to 7 eV. Except for the highest lying 2p1(1S0) level, these cross sections monotonically decrease with energy (as reported earlier in single-electron calculations for the Ne(2p53p) configuration) with branching ratios which essentially reflect the core composition of the 2px levels. For the 2p1 level the resonance structure and the partial cross sections are strongly influenced by a Cooper-Seaton minimum in the d3/2 channel,located just above the 2P1/2 ionization limit.  相似文献   

17.
The effect of the 16O ? 18O substitution in the coordination sphere of permanganate anion MnO 4 ? on the chemical shift of 55Mn nuclei have been studied by 17O and 55Mn NMR. Time constants τ n,k of oxygen exchange in the water–permanganate anion system have been estimated. In nearly neutral solutions (pH ≈ 6.8–7.2), the oxygen exchange time is on the order of tens of hours. Bubbling gaseous HCl through this solution for a few seconds leads to the equilibrium distribution of oxygen isotopes in the manganese coordination sphere. The observed temperature dependences of isotope-induced 55Mn NMR shifts in Mn16 O 44-n 18 O n (n = 0–4) have been treated as a result of rovibrational averaging of Mn–O bond lengths. The change in the Mn—O bond length in caused by the 16O → 18O isotope substitution is on the order of 10–4 Å.  相似文献   

18.
19.
Be2GeO4 polycrystalline samples preliminarily irradiated by fast neutrons (E ~ 1 MeV, Φ = 4.5 × 1017 cm?2) were studied by photoluminescence spectroscopy using synchrotron radiation pulses for excitation. The neutron-induced luminescence band observed at 1.7 eV in the spectra of the irradiated samples is assigned to the radiative relaxation of a molecular ion O 2 ? . The luminescence of these defects in the Be2GeO4 structure is effectively excited by 4.7-and 5.2-eV photons. At low temperatures (10 K), the profiles of the photoluminescence and excitation bands have a fine structure characteristic of electron-vibration interactions. The vibration frequencies for the ground state (v1 = 161 cm?1) and two excited states (v2 = 672 cm?1 and v3 = 887?1451 cm?1) were measured. Potential curves of the energy states of the O 2 ? center are constructed in terms of the Morse model using the experimental data. The optical spectrum fine structure is shown to be predominantly due to intrinsic vibrations of the molecular defect.  相似文献   

20.
Yttrium aluminium borate single crystals, doped with 1 and 4 mol% of Pr3+, were analyzed in the wave number range 500–25000 cm−1 and temperature range 9–300 K by means of high-resolution Fourier transform spectroscopy. In spite of the complex spectra, exhibiting broad and split lines, the energy level scheme was obtained for several excited manifolds. The careful analysis of the spectra as a function of the temperature allowed us to identify most of the sublevels of the ground manifold. The thermally induced line shift, well described by a single-phonon coupling model, could be exploited to provide information about the energy of the phonons involved. The orientation of the dielectric ellipsoid and of the dipole moments associated to a few transitions was also determined from linear dichroism measurements. The experimental data were fitted in the framework of the crystal-field theory, but the agreement was not satisfactory, as already reported for Pr3+ ion in other matrices. Additional discrepancies came from the dichroic spectra analysis and the line splitting, possibly associated to hyperfine interaction. Some causes which might be responsible for the difficulties encountered in the Pr3+ ion theoretical modelling are discussed.  相似文献   

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