O<Subscript>2</Subscript> photodesorption from AuO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and Au<Subscript>2</Subscript>O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>

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.     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

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.     

Hyperfine Interactions in Pb<Superscript>3+</Superscript>F<Stack><Subscript>8</Subscript><Superscript>−</Superscript></Stack>F<Stack><Subscript>a</Subscript><Superscript>−</Superscript></Stack> clusters in fluorite crystals

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.     

EIT Ground State Cooling Scheme of <Superscript>171</Superscript>Yb<Superscript>+</Superscript> Based on the <Superscript>2</Superscript>S<Subscript>1/2</Subscript>→<Superscript>2</Superscript>P<Subscript>1/2</Subscript> Cooling Transition

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).     

<Superscript>57</Superscript>Fe emission Mössbauer spectroscopy following dilute implantation of <Superscript>57</Superscript>Mn into In <Subscript>2</Subscript>O<Subscript>3</Subscript>

Emission Mössbauer spectroscopy has been utilised to characterize dilute ⁵⁷Fe impurities in In ₂O₃ following implantation of ⁵⁷Mn (T _1/2 = 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.     

Analysis of the vector form factors f<Superscript>+</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) and f<Superscript>-</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) with light-cone QCD sum rules

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     

<Superscript>151</Superscript>Eu Mössbauer study of multiferroic Eu<Subscript>0.75</Subscript>Y<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript>

We are herewith reporting the ¹⁵¹Eu Mössbauer spectra collected on a polycrystalline powder sample of Eu_0.75Y_0.25MnO₃ from 15 K to room temperature. All the spectra consist of a single line, whose shape and related sample thickness are dependent on the temperature T. The thermal trend of the mean square displacement of Eu ion, obtained from the spectra analysis, clearly reveals a large low-temperature anharmonicity and in concomitance with the onset of the magnetic ordering consists in a linear strong decrease interrupted by two narrow wells at 29.5 K and 40 K. This behavior is interpreted in connection with the transfer of spectral weight from the 120 cm^-1 optical phonon to the electromagnonic modes. The T-trend of the central shift shows that Eu³⁺ electronic ground state in the magnetically ordered phase differs from the one in the paramagnetic state. Finally, the temperature dependence of the hyperfine field under T _N gives a contribution to interpret some controversial features regarding the phase-diagram.     

<Superscript>16</Superscript>O/<Superscript>18</Superscript>O oxygen isotope exchange kinetics in MnO<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> as probed by <Superscript>55</Superscript>Mn NMR

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.     

<Superscript>10</Superscript>B–<Superscript>11</Superscript>B isotope substitution and superconductivity in ZrB<Subscript>12</Subscript>

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, Zr^natB₁₂, and Zr¹¹B₁₂ dodecaborides, the electron density of states and the electronphonon coupling constant, λ_e-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.     

Odd autoionizing 2p<Subscript>1/2</Subscript><Superscript>5</Superscript>n(s<Superscript>′</Superscript>/d<Superscript>′</Superscript>) resonances of Ne excited from the 2p<Superscript>5</Superscript>3p[K]<Subscript>J</Subscript> states

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 2p_1/2 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 ²P_3/2 and ²P_1/2 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 2p_x levels. For the 2p₁ level the resonance structure and the partial cross sections are strongly influenced by a Cooper-Seaton minimum in the d_3/2 ^′ channel,located just above the ²P_1/2 ionization limit.     

Analysis of Ω<Subscript>c</Subscript><Superscript>*</Superscript>(css) and Ω<Subscript>b</Subscript><Superscript>*</Superscript>(bss) with QCD sum rules

In this article, we calculate the masses and residues of the heavy baryons Ω_c ^*(css) and Ω_b ^*(bss) with spin–parity with the QCD sum rules. The numerical values are compatible with the experimental data and other theoretical estimations. PACS 14.20.Lq, 14.20.Mr     

Λ<Subscript>b</Subscript>→Λℓ<Superscript>+</Superscript>ℓ<Superscript>-</Superscript> decay in universal extra dimensions

We study the exclusive Λ_b→Λℓ⁺ℓ^- 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 Λ_b→Λℓ⁺ℓ^- (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 Λ_b→Λℓ⁺ℓ^- 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     

CO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> radicals in synthetic hydroxyapatite

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.     

Conserved vector current and decays τ<Superscript>−</Superscript> → η(η′)π<Superscript>−</Superscript>π<Superscript>0</Superscript>ν<Subscript>τ</Subscript>

We use experimental data on e ⁺ e ^? → (η′)π⁺π^? and conservation of vector current to estimate the branching fractions of τ^? decay to η(η′)π^?π⁰ν_τ. The obtained values are compared to the experimental results.     

Photoluminescence of sol–gel-derived Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> thin-film phosphors with Mg<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-doping

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     

110 W ceramic Nd<Superscript>3+</Superscript> : Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> laser

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     

Calix[4]arene Based Dual Fluorescent Sensor for Al<Superscript>3+</Superscript> and S<Subscript>2</Subscript>O<Subscript>7</Subscript><Superscript>2−</Superscript>

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 S₂O₇ ^2? 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 S₂O₇ ^2? 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 S₂O₇ ^2? and their binding constants were calculated as 12.1?×?10⁴ and 8.3?×?10³ respectively. Complexes were also characterized through FT-IR spectroscopy.

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Graphical Abstract ?

     

On the energy of the 8<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> 1479-keV level in <Superscript>178</Superscript>Hf

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.     

Mössbauer spectroscopy of <Superscript>57</Superscript>Fe in <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> following implantation of <Superscript>57</Superscript>Mn<Superscript>*</Superscript>

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.