The identification of two entrance channels in the reaction of metastable helium He(23S,21S) with SO2

The energy spectrum of electrons emitted in the reaction of He(2³S) and He(2¹S) with SO₂ indicates that in addition to the covalent entrance channel a strongly attractive ionic channel plays a role. We find upper limits for the well depth of the potential curve that corresponds to the latter channel of D_e ? 3.5 eV and D_e ? 4.3 eV for He(2³S) and He(2¹S) as the reaction partner, respectively. The partitioning between the two entrance channels can be understood by assuming the coupling matrix between both channels to depend strongly on the orientation of the SO₂ molecule with respect to the incident metastable He*.     

Measurement of the astrophysical S factor for dd interaction at ultralow deuteron-collision energies using the inverse Z pinch

This paper is devoted to measurement of the astrophysical S factor and cross sections of the d + d → ³He + n reaction at ultralow deuteron-collision energies. Formation of the flow of the accelerated deuterons incident on the CD₂ solid-state target was made within the scheme of the inverse Z pinch. The liner in the initial state was a hollow supersonic deuterium jet of radius of 15 mm and length of 20 mm. The experiment was carried out at the pulsed high-current accelerator (I=950 kA, τ=80 ns) of the Institute of High-Current Electronics (Tomsk, Russia). Measurement of the deuteron energy distribution was performed through an analysis of the time distributions of the intensity of the liner radiation (H_α and H_β lines) generated during the liner radial movement from the axis. Recording of this radiation was carried out by optical detectors placed along the direction of the liner moving from its axis. The measured value of the astrophysical S factor for the dd reaction at the average deuteron collision energy E _coll=3.69 keV was equal to S(E _coll=3.69 keV)=58.2±18.1 keV b. The dd-reaction cross section calculated using the found value of the S factor and known representation of the reaction cross section as the product of the barrier factor and the astrophysical S factor was σ _dd ⁿ (E _coll=3.69 keV)=(1.33±0.41)×10^?30 cm².     

ESR study of pyrrhotite iron vacancies and the adsorption of CO and H2S

The ESR spectra were determined for pyrrhotite in vacuum, under CO, H₂S and a CO/H₂S mixture. The singlet signal observed in vacuum at room temperature is split into a doublet in H₂S and when heated in vacuum or CO. The g-values are dependent upon the nature of the adsorbing gas. The catalytic effect in H₂S-CO mixture is explained by a two step reaction: (i) H₂S⁺ and CO^- adsorption, (ii) interaction of chemisorbed H₂S⁺ with chemisorbed CO^- on the surface of catalyst to form active hydrogen.     

Triplet-singlet interaction in the 1s 2s3S1 hyperfine splitting of he-like Li+

The hyperfine structure (hfs) interaction between the metastable 2³ S ₁ and 2¹ S ₀ states in^{6, 7}Li⁺ causes very small equal and opposite energy level shifts,δ, in the two levels having the same total angular momentum quantum numberF=I. This amounts to 12ppm with respect to the total hfs splitting of 30 GHz for the⁷Li⁺ 2³S₁ state and has been measured for the first time directly for the case of a core-free electronic system by combined laser-microwave spectroscopy. A new calculation ofδ with accurate integral-transform 2¹ S ₀ and 2³S₁ wave functions is reported. Configuration interactions and electron exchange and correlation effects, which differ for parallel (³ S ₁) and antiparallel (¹ S ⁰) spins, are treated in detail in order to obtain very good agreement between measured and theoretical values for this tiny perturbation. A complete understanding ofδ is indispensable for extracting fundamental constants from two-electron spectroscopic data.     

Lack of oxygen substitution in the chevrel compound Mo6S8

We present results from x-ray powder diffraction and lithium intercalation cells on samples of nominal composition “Cu₂Mo₆S₆O₂” and “Mo₆S₆O₂”. Our results show that it is not possible to prepare these materials with any significant fraction of the sulfur substituted by oxygen as claimed by Umarji et al.¹ Instead, the high temperature (1250°C) products from starting materials of CuO, Cu, S, MoO₂ and/or Mo are MoO₂, Mo and Cu_yMo₆S₈ with y>2.     

The submillimeter wave spectrum of 32S16O2, 32S16O2(ν2), and 34S16O2

Extensive new measurements in the region 400–1000 GHz have been made on ³²S¹⁶O₂, ³²S¹⁶O₂(ν₂), and ³⁴S¹⁶O₂. These measurements represent almost a threefold extension in the frequency region for which high-resolution microwave data are available. These data have been combined with the previously available microwave data for this analysis. The results, when extrapolated into the far infrared, compare favorably with recent results obtained from high-resolution FIR spectroscopy.     

Phase transitions and colossal magnetoresistance in CuVxCr1−x S2 layered disulfides

New substances CuV_xCr_1?x S₂ are synthesized in which colossal magnetoresistance (T _C = 95 K, δ_H = ?60%, H = 7 kOe), as well as the sequence of phase transitions with change in the conduction type and magnetic order, is observed as temperature is varied. The change found in the magnetic and electric properties of the CuV_xCr_1?x S₂ compounds may be a consequence of a specific disintegration into Cu⁺Cr³⁺S₂ and Cu²⁺Cr²⁺S₂ and a change in the concentration relation between these electronic phases in the substance bulk.     

Observation of a new resonance at 2000 MeV in the K S K S system

This article continues a series of publications devoted to previously unknown narrow resonances in the K _S K _S system that are observed in experimental data coming from the 6-m spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The experimental data on the production of K _S pairs were obtained in π ^? p interactions at 40 GeV by using a neutral trigger. In the K _S K _S system, a maximum of width not exceeding 15 MeV is observed at a mass of about 2000 MeV, the statistical significance of this maximum being not less than five standard deviations. With a high degree of reliability, the spin-parity of this structure is J ^P = 4⁺. The observed phenomenon may be interpreted as a resonance whose parameters are equal to the above values.     

Astrophysical S factor for dd interaction at ultralow energies

Experimental results are presented that were obtained by measuring the astrophysical S factor for dd interaction at very low deuteron collision energies by using the liner-plasma technique. The experiment was performed at the high-current generator of the High-Current Electronics Institute (Tomsk, Russia). The values found for the S factor at the deuteron collision energies of 1.80, 2.06, and 2.27 keV are S _dd=114±68, 64±30, and 53±16 keV b, respectively. The corresponding dd cross sections obtained as the product of the barrier factor and the measured astrophysical S factor are σ _dd ⁿ (E _col=1.80 keV)=(4.3±2.6)×10^?33cm², σ _dd ⁿ (E _col=2.06 keV)=(9.8±4.6)×10^?33cm², and σ _dd ⁿ (E _col=2.27 keV)=(2.1±0.6)×10^?32cm².     

Excitation transfer from He(235,21,S) into bound and continuum states of CS2 studied by electron and optical spectroscopy and by coincidence measurements

For the reaction of He(2³ S, 2¹ S) with CS₂ we present a large body of experimental data: electron spectra, fluorescence spectra, electron-ion and electron-photon coincidence spectra. The combination of all these data allows us to characterize the reaction in great detail in a way which is rather direct and free of speculations. As for other molecules with positive electron affinity the charge exchanged channel He⁺ + CS ₂ ^? plays an important role as intermediate state. It is possible to isolate experimentally the electron energy spectra which correspond to formation of the individual electronic CS ₂ ⁺ states out of the intermediate He⁺ + CS ₂ ^? state. This has not been achieved so far for CS₂ or any other molecule by straightforward evaluation of experimental data.     

Photoluminescence of cobalt in CdIn2S4

The photoluminescence of cobalt (0.05 mol %) doped CdIn₂S₄ has been measured in the range 8500–16500 cm^-1. Luminescence is observed from both tetrahedrally and octahedrally coordinated Co²⁺ ions in the partially inverted spinel. Vibrationally assisted transitions from the ²E(G) state of both of these sites are identified. The ⁴A₂(F) level of the tetrahedrally coordinated Co²⁺ is found to be 1927 cm^-1 above the CdIn₂S₄ valence band and the spin-orbit splitting factor is measured to be λ = -133 cm^-1.     

Nuclear-medium modification of the ρ0(1S) and ρ′(2S) mesons in coherent photo-and electroproduction: Coupled-channel analysis

We study medium modifications of the dilepton e ⁺ e ^? and μ⁺μ^? mass spectra in coherent photo-and electroproduction of ρ⁰(1S)-and ρ′(2S)-meson resonances on nuclear targets. The analysis is performed within the coupled ρ⁰(1S), ρ′(2S), ... channel formalism, where nuclear modifications derive from off-diagonal rescatterings. We find that the effect of off-diagonal rescatterings on the shape of the dilepton-mass spectrum in the ρ⁰(1S)-meson mass region is only marginal, but it is very important in the ρ′(2S) mass region. The main off-diagonal contribution in the ρ′(2S) mass region comes from the sequential mechanism γ* → ρ⁰(1S) → ρ′(2S), which dominates ρ′(2S) production for heavy nuclei. Our results also show that, in the ρ′(2S) mass region, there is a considerable interference of the Breit-Wigner tail of the amplitude for the decay ρ⁰(1S) to e ⁺ e ^? and μ⁺μ^? with the amplitude for the decay of ρ′(2S) to e ⁺ e ^? and μ⁺μ^?.     

Magnetotransport and magnetic properties of sulfospinels Zn x Fe1−x Cr2S4

Cr-based chalcogenide spinels, which do not have heterovalency and distortion-induced ions such as manganese oxides with perovskite structure, have demonstrated the existence of colossal magnetoresistance. In order to investigate the magnetotransport phenomena and magnetic properties of sulfospinels Zn _x Fe_1?x Cr₂S₄, polycrystalline Zn _x Fe_1?x Cr₂S₄ samples were synthesized in the 0?≤?x?≤?0.2 range by a solid reaction method. The crystal structure for x?=?0.05, 0.1, and 0.2 turned out to be cubic at room temperature by X-ray diffraction measurement. In magnetoresistance measurement, Zn _x Fe_1?x Cr₂S₄ samples indicate that this system is semiconducting below about 150 K. The temperature of maximum magnetoresistance is almost consistent with Curie temperature. The isomer shift and the electric quadrupole shift of Zn _x Fe_1?x Cr₂S₄ samples by Mössbauer experiment show that Fe²⁺ ions occupy the tetrahedral site in the spinel structure. As the Zn ions are substituted for Fe ions, the Jahn–Teller relaxation slows down and the electric quadrupole shift increases. The magnetotransport phenomena of Zn _x Fe_1?x Cr₂S₄ is related to Jahn–Teller effect and half-metallic electronic structure, which are different from the double exchange interactions of the manganite La–Ca–Mn–O system or the triple exchange interactions of sulfospinel Cu _x Fe_1?x Cr₂S₄.     

Low-lying states of trinuclear mixed-valence cluster: [Fe3S4]0

Low-lying energy states of the [Fe₃S₄]⁰ cluster have been calculated by taking into account the double exchange, superexchange and vibronic interaction. It was found that the adiabatic potential of the excited state withS=0 corresponds to the full delocalization of the “excess” charge. From the analysis of experimental data of Mössbauer spectroscopy and the temperature dependence of the magnetic susceptibility the double exchange parametert≥4000 cm^?1 and the vibronic interaction parameter λ₂/2k cm^?1 have been estimated.     

Electronic to ionic conductivity of glasses in the Li2S–Sb2S3–P2S5 system

There is great interest in sulfide glasses because of their high lithium ion conductivity. New sulfide glasses in the Li₂S–Sb₂S₃–P₂S₅ system have been synthesized by classical quenching technique. The glass domain relays on the medium-lithium content (up to 50% molar).Electrical conductivities of the samples have been determined by Impedance Spectroscopy. The isothermal conductivity curves exhibit two regions on dependence of lithium content implying that the conductivity mechanisms in these two regions are different. The compositions of low lithium content (below 20% mol.) have presented low electronic conductivities close to 10^− 8 S/cm at room temperature. The compositions of medium lithium content (30–50% mol.) could be mixed ionic–electronic conductors with predominant ionic conductivities with a maximum close to 10^− 6 S/cm for sample with 50% Li₂S at room temperature. Arrhenius exponential behavior is verified between 25 °C and T_g for all glasses. The activation energies, determined from temperature dependence, are 0.55–0.64 eV. A comparative study with glasses belonging to the other chalcogenide systems has been undertaken on base of the weak electrolyte model and the values of decoupling index, R_τ, are reported. The impedance of the 0.5Li₂S–0.3Sb₂S₃–0.2P₂S₅ ionic conductor can be described by an equivalent circuit R(RQ)(RQ).     

Type IIB Green-Schwarz superstrings in AdS 5 × S 5 from the supercoset approach

We consider superstrings moving in the AdS ₅ × S ⁵ space-time and find their Green-Schwarz action using the supercoset approach based on the supergroup PSU(2, 2|4). We describe several parametrizations of the relevant supercoset and present the action in different κ-symmetry gauges. In particular, we discuss a gauge where all the fermionic coordinates corresponding to the conformal (S) supercharges are gauged away and also a light-cone type gauge where half of the Q and S supercoordinates are gauged away. The resulting action contains terms that are quadratic and quartic in fermions. In the flat-space limit, it reduces to the standard light-cone Green-Schwarz action. We comment on the possibility of fixing the bosonic light-cone gauge and of reformulating the action in terms of two-dimensional Dirac spinors.     

Highly resolved electronic absorption and luminescence spectra of some phenanthrolines in Shpolskii matrices: Part II. Fluorescence and S1←S0 absorption spectra

Highly resolved fluorescence and S₁←S₀ absorption spectra of some phenanthrolines in n-alkane matrices were obtained at 77 K. The vibrational analysis of the spectra was carried out. Mirror symmetry distortions of the fluorescence and absorption spectra were attributed to vibronic coupling between ¹(π, π¹) states. It was shown that vibronic mixing of S₁(π, π¹) and S₂(π, π¹) states occurs in phenanthroline molecules with S₁-S₂ energy gap not exceeding 3000 cm^-1 (i.e., 4,7-, 1,7- and 1,10-Phen), whereas in other phenanthrolines the coupling of S₁ and S₃(π, π¹) plays a dominant role. Fluorescence quantum yields of phenanthroline liquid solutions were measured. Changes of luminescence efficiencies due to the change of the polarity of the media point to a weak coupling of the lowest ¹(π, π¹) and ¹(n, π¹) states.     

Luminescent crystals of MIIGa2S4:Er3+ (MII = Eu, Yb, Ca)

We have studied the photoluminescent properties of M^IIGa₂S₄:Er³⁺ polycrystals (M^II = Eu, Yb, Ca) for excitation by radiation with λ = 976 nm as a function of temperature. The samples were obtained by solid-state reaction. We have studied the comparative characteristics of the anti-Stokes and IR luminescence of these luminophores. We have determined the mechanisms for anti-Stokes emission of M^IIGa₂S₄:Er³⁺ crystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 332–335, May–June, 2007.     

The visible absorption spectrum of S2O

The visible absorption spectrum of S₂O vapor has been studied by spectrographic and laser optoacoustic techniques. Magnetic rotation spectroscopy was used to establish the triplet-singlet nature of the transition. Vibrational analysis gave ν′₁ = 1089, ν′₂ = 505, and ν′₃ = 332 cm⁻¹.     

Spin relaxation of the8 S 7/2 ground state of europium in noble gases

Spin relaxation of the 4f ⁷ 6s ^{2 8} S _7/2 ground state of the Eu atom in noble gases was investigated by the direct, continuous optical pumping method. Transient signals could be observed by pulsed saturation of rf Zeeman transitions within theF= 6 hfs level of the stable Eu isotopes. The time constant of the transient signals can be related to the electronic spin depolarization cross section for Eu-noble gas collisions, yielding noble gas He Ne Ar Kr Xe σ₁in 10^?20 cm² 0.99(10) 5.1(5) 15(1.5) 43(4) 97(10) These cross sections exceed those measured forS-states of alkalies by three orders of magnitude. They can be explained by perturbations of theS-ground state configuration of Eu due to the admixture of excited state non-spherical wave functions.