Vibrational modes of acid hydrogen in CsH<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> and NaH<Subscript>5</Subscript>P<Subscript>2</Subscript>O<Subscript>6</Subscript>: inelastic neutron scattering

The vibrational modes of hydrogen bonds in CsH₅(PO₄)₂ and NaH₅P₂O₆ compounds are analyzed via inelastic incoherent neutron scattering in a wide range of temperatures and Raman light scattering at room temperature. The energy ranges have been determined for the γ, jg, and ? bands of the vibrational modes of acid hydrogens of these compounds. The dependences of the energy on the length of hydrogen bonds in CsH₅(PO₄)₂ have been revealed.     

Raman scattering by Hg<Subscript>2</Subscript>F<Subscript>2</Subscript> polycrystals

The Raman spectra of Hg₂F₂ polycrystals are experimentally measured for the first time. The spectra of Hg₂F₂ are interpreted using X-ray diffraction analysis and group-theoretical treatment. The results obtained are discussed in comparison with the spectra of Hg₂Hal₂ crystals.     

Inelastic neutron scattering in Zr<Subscript>2</Subscript>NiH<Subscript>1.9</Subscript> and Zr<Subscript>2</Subscript>NiH<Subscript>4.6</Subscript>

In this paper we report the results obtained from inelastic neutron scattering measurements on Zr₂NiH_1.9 and Zr₂NiH_4.6 using triple-axis spectrometer at Dhruva reactor, Trombay. The spectrum up to 35 meV represents largely the lattice modes of Zr and Ni atoms. The vibrational frequencies of hydrogen atoms are expected predominantly at higher energies. The phonon spectra from 35–180 meV were recorded using a Be filter as analyser. In order to analyse the observed neutron spectra, we assume a set of Ein-stein modes due to the hydrogen atoms which are delta functions in energy. These delta functions are broadened by the resolution of the instrument. The vibrational frequencies obtained from the fitting of the observed phonon spectra have been assigned to various tetrahedral sites in both the compounds.     

Computer calculations for thermal behavior of Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Li<Subscript>2</Subscript>CO<Subscript>3</Subscript> melt

The thermal behavior of Na₂CO₃+Li₂CO₃ melt is studied by the method of thermodynamic simulation. The equilibrium compositions of the gas and salt phases are calculated at different temperatures in the initial argon atmosphere. Basic trends of the variation in the compositions of the melts and the gas phase above the melts in the presence of carbon are determined. The obtained results characterizing the stability of carbonate components in the melt are analyzed.     

Vibrational spectrum and elastic properties of KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> crystals

The Raman spectra and elastic moduli of KPb₂Cl₅ crystals were studied experimentally. The results are interpreted using a parameter-free model of the crystal lattice dynamics with inclusion of the multipole moments of the electron shells of ions. The calculated and experimental results are in good agreement. It is shown that not only the halogen ions but also the heavy cations make a significant contribution to the eigenvectors of high-frequency lattice vibration modes, which accounts for the relatively low frequencies of these modes.     

Soft X-ray resonant scattering study of single-crystal LaSr<Subscript>2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>7</Subscript>

Soft X-ray resonant scattering studies at the Mn L_{II, III}- and the La M_{IV, V}- edges of single-crystal LaSr₂Mn₂O₇ are reported. At low temperatures, below T_N ≈ 160 K, energy scans with a fixed momentum transfer at the A-type antiferromagnetic (0 0 1) reflection around the Mn L_{II, III}-edges with incident linear σ and π polarizations show strong resonant enhancements. The splitting of the energy spectra around the Mn L_{II, III}-edges may indicate the presence of a mixed valence state, e.g., Mn³⁺/Mn⁴⁺. The relative intensities of the resonance and the clear shoulder-feature as well as the strong incident σ and π polarization dependences strongly indicate its complex electronic origin. Unexpected enhancement of the charge Bragg (0 0 2) reflection at the La M_{IV, V}-edges with σ polarization has been observed up to 300 K, with an anomaly appearing around the orbital-ordering transition temperature, T_OO ≈ 220 K, suggesting a strong coupling (competition) between them.     

Application of R-matrix method to electron-H<Subscript>2</Subscript>S collisions in the low energy range

Electron-H₂S collision process is studied using the R-matrix method. Nine low-lying states of H₂S molecule are considered in the R-matrix formalism to obtain elastic integral, differential, momentum transfer and excitation cross sections for this scattering system. We have represented our target states using configuration interaction (CI) wavefunctions. We obtained adequate representation of vertical spectrum of the target states included in the scattering calculations. The cross sections are compared with the experiment and other theoretical results. We have obtained good agreement for elastic and momentum transfer cross sections with experiment for entire energy range considered. The differential cross sections are in excellent agreement with experiment in the range 3–15 eV. A prominent feature of this calculation is the detection of a shape resonance in ²B₂ symmetry which decays via dissociative electron attachment (DEA). Born correction is applied for the elastic and dipole allowed transition to account for higher partial waves excluded in the R-matrix calculation. The electron energy range is 0.025–15 eV.     

Vibrational dynamics of the organometallic compound triarylorganoantimony (V) SbPh<Subscript>3</Subscript>[O<Subscript>2</Subscript>CC(OH)Ph<Subscript>2</Subscript>]<Subscript>2</Subscript>

A complete normal coordinate analysis was performed for five-coordinate non-rigid triarylantimony diester SbPh₃(O₂CR)₂, known to be a bioactive molecule, using Wilson G-F matrix method and Urey Bradley force field. The study of vibrational dynamics was performed using the concept of group frequencies and band intensities.      

First-principles calculations of SO<Subscript>2</Subscript> sensing with Si nanowires

High chemical reactivity and large surface-to-volume ratio have recently led to growinginterest in the employment of silicon nanowires (SiNWs) in sensing applications forchemical species detection. The working principle of SiNWs sensors resides in thepossibility to induce modifications in their electronic properties via molecularinteraction. A detailed analysis of the interaction of Si with molecular compounds is thenrequired to design and optimize NW-based sensors. Here we study the mechanisms ofadsorption on SiNWs of SO₂, an air pollutant with pernicious effects on humans.First-principles density-functional calculations are performed to calculate the electronicstructure of a SO₂molecule adsorbed at a silicon surface in case of undoped substrate and in presence ofsubstitutional subsurface and deep boron impurities. Comparing the results with the caseof NO₂ adsorption –a similar molecule that, nonetheless has a very different interaction with a Si surface –,we show the specific traits of SO₂ interaction: formation of localized states in theband-gap and absence of reactivation of pre-existing and passivated sub-surfaceimpurities. A connection between the modifications in the system electronic structure andthe strength of the molecular interaction is discussed.     

Temperature dependence of the order parameter and of diffuse scattering in the Hg<Subscript>2</Subscript>Cl<Subscript>2</Subscript> model ferroelastics

The fundamental and diffuse x-ray reflections from Brillouin zone-edge X points of the paraelastic phase of Hg₂Cl₂ crystals (whose integrated intensity is related to the order parameter and its fluctuations) were studied. Information was obtained on the temperature dependence of the order parameter and of diffuse scattering, and the critical exponents were determined. The conclusion is drawn that the ferroelastic phase transition in these crystals is close to the tricritical point.     

Photoaccumulating film systems based on TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript> and TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript>:V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoheterostructures

The thin-film photocatalysts TiO₂/MoO₃ and TiO₂/MoO₃:V₂O₅ obtained by a combination of sol–gel and sintering techniques were studied using the photooxidation of probing dyes, EPR spectroscopy, X-ray diffraction analysis, and electron microscopy. It was shown that due to charge accumulation caused by UV irradiation, these photocatalysts retain their oxidative activity and ability for self-sterilization in the dark for a long time after irradiation was terminated (up to 5 h for TiO₂/MoO₃:V₂O₅).     

Raman scattering spectroscopy of inclusions of carbon in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films and its solid solutions with HfO<Subscript>2</Subscript>

We apply Raman scattering spectroscopy to study the nature of carbon inclusions in Al₂O₃ and (HfO₂) _x (Al₂O₃)_{1 ? x} films deposited using volatile complex compounds. Raman spectra of the films under investigation contain D and G vibrational modes, which indicate that carbon clusters of the sp ² configuration tend to form in the films. We estimate the size of clusters from the integrated intensity ratio I _D /I _G and find it to be in the range of 14–20 Å. The content of hydrogen in carbon clusters is calculated from the height of the photoluminescence pedestal and is found to vary from 14 to 30 at % depending on the regime of the film’s synthesis.     

Vibrational spectrum of CF<Subscript>4</Subscript> isotopes in an algebraic model

In this paper the stretching vibrational modes of CF₄ isotopes are calculated up to first overtone using the one-dimensional vibron model for the first time. The model Hamiltonian so constructed seems to describe the C-F stretching modes accurately using a relatively small set of well-defined parameters.     

Low-frequency Raman scattering from CeO<Subscript>2</Subscript> nanoparticles

Raman scattering measurements were performed on CeO₂ nanoparticles at room temperature. Low-frequency modes are assigned to confined acoustic vibrations of spherical CeO₂ nanoparticles. Frequencies of these vibrational modes have been calculated in the elastic continuum approximation, which considers a nanoparticle as a homogeneous elastic sphere. We assumed stress-free boundary conditions. The specific dependence of the vibrational frequency on the particle diameter enables the determination of the particle size from the experimental Raman frequency. The particle size value calculated in this way agrees well with the value acquired from the phonon confinement model. PACS 61.46.Df; 73.63.Bd; 63.22.+m     

Coherent semilinear oscillator with Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript>:Sb crystals

We present experimental results for the semilinear oscillator geometry based on Sn₂P₂S₆:Sb photorefractive crystals. The samples with strong two-wave mixing gain demonstrate degenerate oscillation regime. A mirrorless oscillation is also observed.