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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

<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.     

Absorption spectrum of H<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> near 1.06 μm

The absorption spectra of molecular hydrogen plasma excited by electric hollow-cathode and high-frequency discharges are measured. The spectra in the region of 1.06 μm were recorded using a neodymium intracavity laser spectrometer with a resolution of 0.03 cm^?1 and an absorption sensitivity of 10^?8 cm^?1. The absorption lines that can be attributed to the transitions to vibrational states in the molecule are recorded.     

Stereodynamics of the reaction He+H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> → HeH<Superscript>+</Superscript> + H: a theoretical study

Quasiclassical trajectory method for the title reaction He +H₂⁺ → HeH⁺ + H was carried out on the potential energy surface which was revised by Aquilanti et al. [Chem. Phys. Lett. 469, 26 (2009)]. The initial vibrational quantum number of reactant was set as v=1, v=2 and v=3. Stereodynamics information of the reaction was obtained, such as the distributions of product angular momentum P(θ _r ), P(ϕ _r ),p(ϕ _r , θ _r ) and the two commonly used polarization-dependent differential cross sections (PDDCSs) (2π/σ)(dσ ₀₀/dω _t ) and (2π/σ)(dσ ₂₀/dω _t ), to get the alignment and orientation of product molecules. The results show that the influence of both the collision energy and vibrational quantum number (v) to the reaction are highly sensitive.     

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.     

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 ?

     

Influence of configuration interaction on splitting of multiplets of TmF<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> and TmCl<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> molecular complexes

The Stark structure of elpasolites activated by Tm³⁺ ions is analyzed with the help of standard and modified crystal field theories. Application of the modified approach reduces considerably the root-mean-square deviation between theoretical and experimental energy values. Crystal field and covalence parameters are determined, the latter being in good agreement with the covalence parameters calculated using microscopic models.     

“Alpha decays” of <Stack><Subscript>Λ</Subscript><Superscript>10</Superscript></Stack>Be and <Stack><Subscript>Λ</Subscript><Superscript>10</Superscript></Stack>B hypernuclei: Phenomenological analysis and role of nuclear structure

Hypernuclei are used to study the baryon-baryon weak interaction and associated effective weak Hamiltonian. We will show how the proper choice of hypernucleus can be used to pick out components of the effective weak Hamiltonian. It is well known that removing one nucleon from ⁹Be or ⁹B results in ⁸Be* with a subsequent αα decay. Through this unique process, it would be possible to identify final states of the residual nucleus. So, due to these specific properties of the core nuclei ⁹Be and ⁹B, it may be possible to measure the branching fractions Γ _ααi ^n(p) for the exclusive decays of the _Λ ¹⁰ Be ( _Λ ¹⁰ B) hypernuclei.     

On the delay mechanism of Cl<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> diatomic anion dissociation up to the microsecond timescale

The dissociative capture of slow electrons by tetrachlorethylene (C₂Cl₄) has been investigated by resonant electron capture negative ion mass spectrometry. Metastable ions with fractional mass numbers 7.5, 17.5, and 19 corresponding to the C₂Cl₄⁻ → Cl⁻ + C₂Cl₃ and Cl₂⁻ → Cl⁻ + Cl decays occurring at the microsecond timescale have been detected. It has been revealed that Cl₂⁻ anions, which are fragment ions, can dissociate at the microsecond timescale, which is very surprising for a system with one internal degree of freedom. This process is assumingly attributed to the rotational excitation of Cl₂⁻ anions. Thus, the experimental estimate of the time of rovibronic relaxation in the Cl₂⁻ anion has been obtained.