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 AunO2− with analogous data on AgnO2− 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
A series of 30 adenosine derivatives with three different substituents at the N6-position were prepared in order to evaluate their potential to inhibit the pathogenic protozoa Plasmodium falciparum and Trypanosoma brucei in vitro. The rationale for synthesis of these structures was the high probability of interactions with multiple adenosine
associated targets and the assumption that N6-substitutents should increase stability against adenosine deaminases and allow the molecules to diffuse across parasite membranes.
Starting from inosine, the new compounds were prepared as single isomers using a polymer-assisted acylation protocol enabling
the straightforward isolation of the target compounds in pure form. Three of the compounds displayed anti-plasmodial and one
anti-trypanosomal activity in the single digit micromolar concentration range. 相似文献
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
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
In this article, we calculate the vector form factors f+Kπ(Q2) and f-Kπ(Q2) within the framework of the light-cone QCD sum rule approach. The numerical values of f+Kπ(Q2) are compatible with existing theoretical calculations, and the central value of f+Kπ(0) (f+Kπ(0)=0.97) is in excellent agreement with the values from chiral perturbation theory and lattice QCD. The values of |f-Kπ(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+Kπ(Q2) and |f-Kπ(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
Emission Mössbauer spectroscopy has been utilised to characterize dilute 57Fe impurities in In 2O3 following implantation of 57Mn (T1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In 3+, however the spectra are dominated by spectral lines due to paramagnetic Fe2+. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe2+ state in In 2O3. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In 2O3. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature. 相似文献
Red-light-emitting Y2O3:Eu3+ thin-film phosphors were synthesized using a sol–gel process. The effect of Mg2+ and Al3+ co-dopants on the Y2O3:Eu3+ thin-film phosphor photoluminescence (PL) property was investigated. At a certain concentration, both Mg2+ and Al3+ co-dopants were found to further enhance the PL emission intensity of Y2O3:Eu3+ thin-film phosphors. The optimum PL emission intensity was observed in Y2O3:12%Eu3+, 7%Mg2+ and Y2O3:12%Eu3+, 2%Al3+ phosphor films. From our results, the enhancement of the emission intensity by the Mg2+ and Al3+ co-dopants is explained in terms of the creation of defect states near the Y(4d+5s) conduction band, which overlap with the Eu3+ charge-transfer state (CTS). The overlapping leads to CTS broadening and consequently induces higher absorption and hence an increase of the emission intensity. From X-ray diffraction results, we have found that there is no additional phase formed in the co-doped phosphor films. PACS 68.55.Ln; 78.55.-m; 81.20.Fw 相似文献
The parameters of hyperfine interactions in Pb3+F8?Fa? 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 Fa? 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 Fa? ion leads to anomalously large parameters of this interaction for MeF2 crystals. These results are in agreement with experimental data. 相似文献
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 CO2? radicals, namely, the axial CO2? radicals and the orthorhombic CO2? 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 CO2? 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
A novel blue–green emitting phosphor Ba2ZnSi2O7: Eu2+ was prepared by a combustion synthesis (CS) method. An efficient green emission under conditions ranging from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 503 nm, which corresponds to the 4f65d1→4f7 transition of Eu2+. The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu2+ in Ba2ZnSi2O7:Eu2+ phosphor is about 0.05 mol. The corresponding concentration quenching mechanism is verified to be a dipole–dipole interaction. The value of the critical transfer distance is calculated as 19 Å, which is in good agreement with the value (20 Å) derived from the experimental data. 相似文献
Specific functionalized calix[4]arene based fluorescent chemosensor was synthesized for cations and anions binding efficiency examination. Receptor C4MA displayed strong affinity for Al3+and S2O72? with enhanced fluorescence intensity. The selective response of C4MA was investigated in the presence of different co-existing competing ions. The limit of detection (LOD) of Al3+and S2O72? was calculated as 2.8?×?10?6 M and 2.6?×?10?7 M respectively. Sensor C4MA forms (1:1) stoichiometric complex with both Al3+ and S2O72? and their binding constants were calculated as 12.1?×?104 and 8.3?×?103 respectively. Complexes were also characterized through FT-IR spectroscopy.
Halogen-substituted barium indate Ba2In2O5 based brownmillerites Ba1.95In2O4.9F0.1 and Ba1.95In2O4.9Cl0.1 have been synthesized. It has been verified radiographically that the single-phase condition is satisfied. The effect of the substituent ion nature on parameters of the crystalline lattice and lengths of In–O bonds has been revealed. The propensity of the phases under study for hydration and formation of energetically unequal ОН– groups in the structure has been proved. In both the cases of doping, the degree of hydration decreased as compared to barium indate Ba2In2O5, which is caused by the participation of the halide ion in the tetrahedral site of indium. 相似文献
Ca2B2O5:RE (RE = Eu3+, Tb3+, Dy3+) nanofibers were synthesized by the hydrothermal reaction method. The structural refinement was conducted on the base of the X-ray powder diffraction (XRD) measurements. The surface properties of the Ca2B2O5:RE (RE = Eu3+, Tb3+, Dy3+) nanofibers were investigated by the measurements such as the scanning electron microscope (SEM), transmission electron microscope (TEM), and the energy dispersive spectrum (EDS). The nanofiber has a diameter of about 100 nm and a length of several micrometers. The luminescence properties such as photoluminescence excitation (PLE) and emission spectra (PL), decay lifetime, color coordinates, and the absolute internal quantum efficiency (QE) were reported. Ca2B2O5:Eu3+ nanofibers show the red luminescence with CIE coordinates of (x = 0.41, y = 0.51) and the luminescence lifetime of 0.63 ms. The luminescence of Ca2B2O5:Tb3+ nanofibers is green color (x = 0.29, y = 0.53) with the lifetime of 2.13 ms. However, Dy3+-doped Ca2B2O5 nanofibers present a single-phase white-color phosphor with the fluorescence decay of 3.05 ms. Upon near-UV excitation, the absolute quantum efficiency is measured to be 65, 35, and 37 % for Eu3+-, Tb3+-, Dy3+-doped Ca2B2O5 nanofibers, respectively. It is suggested that Ca2B2O5:RE (RE = Eu3+, Tb3+, Dy3+) nanofibers could be an efficient phosphor for lighting and display. 相似文献
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 Tg = 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 Tg. 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
Relative coefficients of collisional broadening caused by N2O molecules and their temperature dependences are determined for absorption lines (1000–0001 transition, R-branch) of the CO2 molecule. 相似文献
A high-power, continuous-wave 0.6% Nd3+-doped ceramic Y3Al5O12 (Nd:YAG) laser has been developed. 110 W laser output at 1064 nm was obtained, with a slope efficiency of about 41%. The M2 factor was found to be around 6. The laser performance of the ceramic laser material was found to compare favorably with that obtained with single crystal Nd:YAG. PACS 42.55.-f; 42.55.Xi; 42.70.Hj 相似文献
The temperature dependences of the quenching rate constants of the states
N2 (${\rm C} \ {^{3}{
\rm \Pi }_{u}}${\rm C} \ {^{3}{
\rm \Pi }_{u}} v′=0,1) by N2 (X) and of the state
N2 (${\rm C} \ {^{3}{
\rm \Pi }_{u}} \ v^{\prime}=0${\rm C} \ {^{3}{
\rm \Pi }_{u}} \ v^{\prime}=0) by O2 (X) are studied.
Time-resolved light emission from the gas was analyzed in the temperature
range from 300 K to 210 K keeping the gas at constant density. In case of
quenching by N2 (X), the quenching rate constant for the vibrational
level v′= 0 increases by (13 ±3)% with gas cooling whereas the
quenching rate constant for v′= 1 decreases by (5.0 ±2.5)% in this
temperature range. For quenching by O2 (X), the quenching rate constant
decreases by (3 ±2)% with gas cooling. The temperature variation of
the N2 (C 3Πu v′=0) emission intensity for pure nitrogen
and dry air are calculated using the obtained quenching rate constants and
is compared with the experimental data available in the literature. 相似文献
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 82? 1479-keV level in 178Hf (E(1479) = 1479001 ± 6 eV) are determined with high accuracy. 相似文献
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 O2?. 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 O2? 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