NMR study of one-dimensional ionic conductor with hollandite-type structure. II. Frequency dependence of spin-lattice relaxation time of 27Al

Frequency dependence of spin-lattice relaxation time T₁ of ²⁷Al in one-dimensional K⁺ ion conductor, K-Al-priderite, was measured at 45 K in the frequency range from 10.1 MHz to 55 MHz. It is found that T₁ is proportional to ω^1.49±0.05 and agrres well with the $\text{ω}{}^{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}$ dependence derived by the continuum diffusion model. The intrinsic activation energy is determined to be 0.058 eV by doubling the slope E_NMR=0.029 eV of the d(ln T₁)/dT curve in the low temperature region. The frequency dependence of T₁ in the high temperature region measured in the frequency range from 11.5 MHz to 20.8 MHz shows a tendency that the frequency dependence becomes smaller than the $\text{ω}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ dependence as temperature is raised above 450 K.     

Raman spectra of IVB and VIB transition metal disulfides using laser energies near the absorption edges

In this paper, we present Raman spectra of ZrS₂, HfS₂, MoS₂ and WS₂ using laser energies near the energies of the absorption edges. The Raman spectra probe the properties of the first-excited electronic state and the nature of the electron-phonon coupling. The spectra of the IVB disulfides are independent of the laser excitation energy, suggesting weak electron-phonon interaction. In contrast, additional Raman bands appear in the spectra of the VIB disulfides as the laser energy approaches the band gap energy. The new modes in the spectra of MoS₂ and WS₂ cannot be assigned as first-order processes nor as combination bands of the phonons with zero momentum. The resonance Raman scattering of MoS₂ is analyzed in terms of second-order scattering due to the coupling of phonon modes of nonzero momentum with an electronic transition associated with excitonic states.     

EPR of atomic hydrogen 1H and 2H in α-quartz

Detailed EPR measurements of the spin-Hamiltonian parameters for the hydrogen atom H⁰ in its principal low-temperature trapping site in X-irradiated α-quartz have been made at several temperatures in the range 40–100 K. Besides the Zeeman splitting matrix ? and the proton hyperfine matrix $\text{A}$_H, the parameters include the super-hyperfine ²⁹Si matrix describing interaction between these cavity wall atoms and H⁰. The measured spin-Hamiltonian parameters for the isotopes ¹H⁰ and ²H⁰ are compared. The trapping site has been identified and is discussed. The hydrogen atom is mobile within this complex cavity comprised of various silicon and oxygen ions.     

Determination of the diffusion path in the ionic conductor LaF3

LaF₃ is an F^? conductor; its crystal structure is described elsewhere. In the space group P$\text{3}$cl we distinguish 3 symmetrically independent F^? ions which exist. The F1^? and F3^?ions contribute mainly to the ionic conductivity of this compound. Our results indicate an essentially one-dimensional diffusion path in the crystallographic c-direction.     

Microwave spectral study of the axial and equatorial conformers of cyanocyclopentane

The microwave spectrum of cyanocyclopentane has been observed and analyzed in the 26.5 to 40.0-GHz frequency region. Rotational transitions were assigned for both an axial and an equatorial conformer. These data and those for the molecule deuterated in the 1-position (1-d-cyanocyclopentane) show that both conformers adopt the C_s envelope structure. For the normal isotopic species the rotational constants have the following values, in megahertz: axial, A = 4297.196, B = 2210.245, C = 2057.205; equatorial, A = 6324.905, B = 1790.937, C = 1497.792. Relative intensity measurements indicate that the ground-state energy difference of the two conformers is 0 ± 200 cal/mole. The low-frequency (pseudorotational) potential surface has been discussed and compared with that of chlorocyclopentane.     

A speckle-shearing interferometer: A tool for measuring derivatives of surface displacements

A speckle-shearing interferometer is developed using a sheared Michelson interferometer. The tool, like speckle interferometry, utilizes the speckle effect of coherent light. However, while speckle interferometry measures surface displacements, the speckle-shearing interferometer determines the derivatives of the surface displacements. Hence, it eliminates the necessity of differentiating the measured displacements to obtain strain.     

Rigid lattice NMR spectra of proton conductors H(H2O)nSbO3

The “rigid lattice” ¹H NMR spectra of H(H₂O)_nSbO₃ have been interpreted for n=0.20, 0.92 and 1. For n?0.92 the compounds contain deformed H₃O⁺ ions and OH groups. For n=1 the real formula is (H₃O)_0.7H_0.3SbO₃,0.3 H₂O. The results are discussed in relation to the level of proton conductivity.     

A new electron spectrometer design:II

A novel charged particle energy analyzer of simple geometry is described. Expressions for the potential distribution and electric field components defined by the geometry are given. A raytrace program using these components is discussed and results of its application are presented in graphical and tabular form. Also presented are experimental results for two versions of the analyzer in the form of representative spectra of well known species (Ar⁺, H₂⁺, O₂⁺). Finally, a comparison of the new instrument with the well known cylindrical mirror analyzer is outlined which suggests the superiority of the new instrument under the specific conditions given.     

A mirror-free cavity configuration for a CW ring dye laser

A new cavity configuration without mirrors is described for a CW ring dye laser. The cavity design is based on a new type of focusing prism which uses the Brewster angle of incidence and total internal reflection. Special roof prisms allow wavelength tuning. All of these elements are made from uncoated quartz thus allowing dye laser operation over a large range of wavelengths. CW operation as well as synchronously pumped mode locked operation with intracavity doubling is reported using the Rhodamine 6G dye.     

A comparison between shake-up and UV charge-transfer transitions

The He(II) spectra of the unsubstituted metallocenes {M(η-C₅H₅)₂}, M  V, Cr, Mn, Fe, Co, Ni and Ru, and of {Mn(η-C₅H₄Me)₂} are reported; both He(I) and He(II) spectra of some decamethylmetallocenes {M(η-C₅Me₅)₂}, where M  Mg, V, Cr, Mn, Fe, Co and Ni, are also given. Intensity changes between the He(I) and He(II) spectra are shown to provide a reliable guide to band assignment. A ligand field treatment of the decamethylmanganocene cation, including limited configuration interaction, gives values for Δ₂, B and C; these values are also in good agreement with the photoelectron spectra of {M(η-C₅Me₅)₂} where M  V, Cr and Fe. Overlap between the ligand and metal “d” band structures prevents complete assignment in the cases of Co and Ni.     

Transferability of dipole moment derivatives: A general method for the calculation of absolute rotational contributions

A general method for the calculation of absolute rotational corrections for the dipole moment derivatives is given based on the definition of pure geometrical distortions. The method is generally valid and allows the rotational contributions to be calculated for all modes of any molecule. The relation between absolute and relative corrections is discussed and the method is demonstrated by calculating the rotational corrections for a few asymmetrical molecules.     

Modelling the voltammetric study of intercalation in a host structure: application to lithium intercalation in RuO2

Intercalation process kinetics have been studied theoretically for the case of potential sweep voltammetry. The influence of the thickness (or the particle radius) of the “host” material and the potential sweep rate has been determined between the limits of thin film diffusion and semi-infinite diffusion for a reversible process. Experimental data have been obtained with the cell: RuO₂/LiClO₄-PEO/Li. The theoretical results have been used to calculate the diffusion coefficient of lithium in the “host” structure RuO₂ at 80°C, giving an approximate value of 1.6 × 10^?11 cm² s^?1     

Vibrational study of H3OUO2PO4·3 H2O (HUP) and related compounds. Phase transitions and conductivity mechanism: Part II,H3OUO2PO4·3 H2O

Infrared and Raman spectra of polycrystalline H₃OUO₂PO₄·3 H₂O (HUP) and its D and P¹⁸O₄ derivatives, in the form of dense transparent disks and wet powder, have been investigated at various temperatures in the 100–300 K region. The bands due to framework vibrations are similar to those of KUP, whereas those for the protonic species are different. OH stretching and bending bands of the oxonium ion have been identified at 2920, 1740 and 1160 cm^?1 in the low-temperature spectrum of HUP. Differential scanning calorimetry (DSC) and infrared (IR) intensity investigations show a phase transition between 274 and 260 K. The mechanism of the phase transition consists, as in the case of KUP, of ordering of the protonic species, which induces ordering of PO₄ tetrahedra. The ordering can be influenced by excess water content, stacking faults and stress (ferroelastic behaviour is evidenced). The conductivity mechanism in HUP is discussed.     

Gas phase and solid state X-ray photoelectron spectra of the substituted acetylenes (SF5)n C2 (CF3)2−n (n = 0, 1, 2): A comparison of the pentafluorosulfur and trifluoromethyl groups

The core level X-ray photoelectron spectra (XPS) of CF₃CCCF₃, CF₃CCSF₅ and SF₅CCSF₅ have been measured in the solid state. Gas phase spectra of CF₃CCCF₃ and CF₃CCSF₅ have also been obtained. The XPS data, interpreted with the point charge potential model and semiempirical MNDO (minimum neglect of differential overlap) molecular orbital calculations, indicate that the electron withdrawing effect of the ?CF₃ group is greater than that of the ?SF₅ group. Results further suggest that sulfur 3d orbitals do not play a detectable role in the bonding or charge distribution in these molecules. Carbon 1s linewidths of ?CF₃ carbon atoms are found to be much narrower than those arising from the acetylenic carbon atoms. The narrower lines correlate with the much higher binding energy of the ?CF₃ carbon atoms. Large shifts (nearly 1 eV) in heteroatom core level binding energy differences (for example, F 1s — C 1s) between the gas phase and solid state data are observed. These shifts are attributed to solid state effects (Madelung potential, intermolecular bonding interactions, and/or extramolecular relaxation contributions). From these comparisons it is clear that solid state effects are not uniform in their influence on the photoionized sites in these molecules.     

Study of the phase transitions in ammonium bromide by Raman spectroscopy

A complete Raman scattering study of an oriented NH₄Br single crystal has been carried out and new results are reported for temperature between 45 to 410°K. The study includes measurements and interpretations of the Raman spectral bandwidths, intensities and frequencies of the lattice and internal modes as a function of temperature. Because of the ability of generating a single domain crystal, unambiguous assignments of the Raman active modes are made. From the present data together with those presented previously significant information on the behavior of the ordering and crystal structure associated with the phase transitions in NH₄Br is obtained.     

Surface relaxation and reconstruction in diamond-like crystals

The MNDO semiempirical method has been used to study the structure of the (111) surface of diamond-like crystals employing two model clusters. Numerical results are in agreement with previous computations for the small X₄H₉ clusters and become very similar to experimental data when employing the larger X₉H₁₅ clusters. These latter clusters allow also the study of surface reconstruction. Our results suggest that the Haneman model of 2 × 1 reconstruction could be equally valid for silicon and diamond, but in the latter case the difference in vertical shifts is too small to be experimentally observed.     

Collisional redistribution of radiatively-excited levels of Tl and Ga atoms in an O2-acetylene-Ar flame

Several useful expressions for the population ratios of collisionally excited levels have been derived and different transitions of Tl and Ga atoms, seeded in a premixed atmospheric flame, have been excited in order to verify that the levels higher than the laser-excited level are populated approximately according to a Boltzmann equilibrium. This result confirms the possibility of using thermally assisted flourescence lines to measure local temperatures in flames. The Einstein spontaneous emission probability for the transition 6S_1/2→4P_3/2 at 2719.65Å of Ga has also been calculated (A_2719.65=0.41×10⁸s^-1) to fit the experimental point.     

Generation of paramagnetic centres in crystalline quartz by ultraviolet irradiation

Irradiation of α-quartz crystals with ultraviolet light (4.0–5.0 eV) results in ionization of alkali-compensated aluminum tetroxide impurity centres, as observed by electron paramagnetic resonance spectroscopy of the hole centres created or of the germanium tetroxide electron centres formed when Ge is present.