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.     

The evaluation of the branching ratios of the decays φ(1020)→2π<Superscript>+</Superscript>2π<Superscript>−</Superscript>π<Superscript>0</Superscript>, π<Superscript>+</Superscript>π<Superscript>−</Superscript>3π<Superscript>0</Superscript>

Combining the Okubo-Zweig-Iizuka rule in the decay φ→ρπ→π⁺π^?π⁰ with the ρ→4π decay amplitudes, we calculate the φ→2π⁺2π^?π⁰ and φ→π⁺π^?3π⁰ ones. The partial widths of the above φ decays are evaluated, and the excitation curves in e⁺e^? annihilation are obtained, assuming reasonable particular relations among the parameters characterizing the anomalous terms of the HLS Lagrangian. The evaluated branching ratios B_φ→π⁺_π^?_3π⁰ ≈ 2 × 10^?7 and B_φ→2π⁺_2π^?_π⁰ ≈ 7 × 10^?7 are such that, with the luminosity L=500 pb^?1 attained at DAΦNE φ factory, one may already possess about 1685 events of the decays φ→5π.     

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.     

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.     

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     

Negative ions Ar<Superscript>−</Superscript>, Kr<Superscript>−</Superscript>, and Xe<Superscript>−</Superscript> in superfluid helium

The catalogue of negative ions in superfluid helium has been extended using the example of Ar⁻, Kr⁻, and Xe⁻. Such objects cannot exist in vacuum, since the polarization attraction of an electron to the inert A atom is insufficient for the formation of the bound state A⁻. However, these objects exist in helium as stable or metastable with a very long lifetime. The effect is due to the electron localization in liquid helium. If a mixture of excited A* atoms and electrons is prepared in the gas phase above liquid helium, the reaction A* + e = A*⁻ becomes possible for all atoms of the periodic table. Such charges can be immersed into liquid helium by the electric field. In this case, the radiative decay A*⁻ = A + e allowed in vacuum can be forbidden in liquid. This leads to the formation of the new unique objects A⁻, which can exist in liquid helium but are absent in nature. The size of such charged formations has been determined and is close the radius of a usual electron bubble in helium.     

F<Stack> <Subscript>3</Subscript> <Superscript>−</Superscript> </Stack> molecular ions in fluoride crystals

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.     

Neutron-induced molecular defect O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> in beryllium orthogermanate

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.     

High repetition rate LiF<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>: Color center laser

The efficient oscillation of LiF:F₂⁻ color center laser pumped by a compact LD-pumped Nd:YVO₄ acousto optically Q-switched laser with 30 kHz pulse repetition rate was demonstrated. The broadband oscillation with 75 μJ pulse energy and 37 kW peak power with the slope efficiency 20% was obtained. The average output power as high as 230 mW was reached. The narrow line tunable from 1.10 to 1.29 μm laser radiation with 10% conversion efficiency in the maximum of the tuning curve was achieved under pumping with 1.6 W average pump power.     

<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.     

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.     

Processes e<Superscript>+</Superscript>e<Superscript>−</Superscript> → π<Superscript>0</Superscript>(π<Superscript>0</Superscript>′) γ in extended NJL model

The processes of electron-positron annihilation into π⁰γ and into π′(1300)γ are considered within an extended NJL model. The intermediate vector mesons ρ ⁰, ω ρ′(1450), and ω(1420) are taken into account. The latter two mesons are treated as the first radial excited states. They are incorporated into the NJL model by means of a polynomial form factor. Numerical predictions for the cross-sections of these processes are received for the center-of-mass energies below 2 GeV. Our results for the π⁰γ production are in agreement with experimental data obtained in the energy region 600–1020 MeV.     

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.     

Optimized semiempirical potential energy surface for H<Subscript>2</Subscript><Superscript>16</Superscript>O up to 26000 cm<Superscript>−1</Superscript>

A semiempirical potential energy surface is obtained for the major isotopologue of the water molecule H₂ ¹⁶O that allows the vibration-rotation energy levels in the range of 0–26000 cm⁻¹ to be calculated with an accuracy almost equal to the average experimental accuracy of measurements in the infrared and visible ranges. Variational calculations using this potential energy surface reproduce the experimental energy values of more than 1500 vibration-rotation levels of H₂ ¹⁶O with the total angular momentum quantum number J = 0, 2, and 5 in the indicated range with a standard deviation of 0.022 cm⁻¹. The potential was obtained by optimizing a starting ab initio surface using a combination of two approaches, i.e., (1) the multiplication of the starting ab initio surface by a morphing function whose parameters were optimized and (2) the optimization of parameters of the ab initio surface using both the experimental values of energy levels and the results of quantum-chemical electronic structure calculations.     

<Emphasis Type="Italic">J</Emphasis><Superscript>π</Superscript>0<Superscript>−</Superscript> levels in <Superscript>156</Superscript>Gd and <Superscript>158</Superscript>Gd

The 0^? states in the ¹⁵⁶Gd nucleus at E = 1952.38 keV and in the ¹⁵⁸Gd nucleus at E = 2269.16 keV are established on the basis of an analysis of available data on even-even deformed nuclei. From data on the deexcitation of the levels and on the probability of their population by beta transitions, it is found that these states have a two-particle proton structure. A comparison of our data with information about the 0^? levels in the ¹⁷⁰Yb and ¹⁷⁶Hf nuclei makes it possible to conclude that J^π0^? two-particle states exist at an excitation energy of about 2 MeV and higher.     

Long <Emphasis FontCategory="NonProportional">K</Emphasis><Superscript>π</Superscript> = 0<Superscript>+</Superscript> and 4<Superscript>−</Superscript> bands in deformed nuclei

Experimental data on some long bands in N=88–98 deformed nuclei are analyzed on the basis of a method systematizing the energies of levels and inertial parameters and a method employing the analogy between neighboring. Beta bands built on low-lying 0 ₂ ⁺ levels are identified in N=90 isotones, including the ¹⁵⁸Er, ¹⁶⁰Yb, and ¹⁶²Hf nuclei. Some of intermediate members of these bands have not been found yet. The systematic properties of 4^? bands are presented, and the dynamics of the inertial parameters of these bands in N=88–98 isotones is revealed. The bands are identified in ¹⁵⁸Yb, ¹⁵⁶Dy, ¹⁵⁶Er, ¹⁶²Yb, and ¹⁶⁶Hf.     

Laser control of low-temperature reaction <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> + O<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

A theory is developed to describe dissociative recombination of a slow electron with a ground-state molecular ion of oxygen driven by a strong monochromatic electromagnetic field. Mathematically, the theory is based on the time-independent formalism of radiative scattering matrix whose poles correspond to dressed intermediate states of the complex. The analysis embraces both transitions to dissociative states and laserinduced nonadiabatic transitions to intermediate bound states of valence configurations. Key reaction mechanisms are considered, and a classification is given of all allowed transitions to dissociative states. Partial and total reaction cross sections are calculated by taking into account the contributions from Rydberg, valence, and dissociative states of O₂^**. A detailed discussion of results is presented, and feasibility of laser control of the reaction is demonstrated.     

Magnetooptical properties of a molecular D<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>-ion in a quantum wire

In the framework of a model of zero-range potential, the problem of bound states of an electron in the field of two D0 centers (a two-center problem) in a semiconductor quantum wire is considered in the presence of a longitudinal magnetic field. It is shown that the magnetic field produces a significant shift of g and u terms and stabilizes the D ₂ ^? states in quantum wires. It is found that, in the case of transverse polarization of light, the spectral dependence of the photoionization cross section of a D ₂ ^? center exhibits the quantum-confined Zeeman effect with strongly pronounced oscillations of interference nature.     

Inversion of the <Emphasis Type="Italic">K</Emphasis><Superscript>π</Superscript>=1<Superscript>−</Superscript> states in <Superscript>156</Superscript>Gd and <Superscript>170</Superscript>Yb

For the ¹⁵⁶Gd and ¹⁷⁰Yb nuclei, where the inversion of levels in the K^π=1^? bands is observed, the energies of rotational levels are calculated on the basis of the Coriolis interaction model for the states of two bands whose quantum numbers are K^π=1^?. New 0^? levels are introduced in ¹⁷⁰Yb, and the structure of ¹⁷⁰Er is refined. The interaction parameters calculated for six nuclei are considered within the structure predicted by the quasiparticle-phonon model.     

Two photons into π<Superscript>0</Superscript>π<Superscript>0</Superscript>

We perform a theoretical study based on dispersion relations of the reaction γγ → π ⁰ π ⁰ emphasizing the low-energy region. We discuss how the ƒ ⁰(980) signal emerges in γγ → ππ within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ → ππ amplitude above the threshold. This allows us to make sharper predictions for the cross-section at lower energies and our results could then be used to distinguish between different ππ isoscalar S-wave parameterizations with the advent of new precise data on ππ → π ⁰ π ⁰. We compare our dispersive approach with an updated calculation employing the unitary chiral perturbation theory (U _gC PT). We also pay special attention to the role played by the σ-resonance in γγ → ππ and calculate its coupling and width to γγ, for which we obtain Γ(σ → γγ) = (1.68 ± 0.15) keV.