Change In Linewidth Research Articles

High temperature 17O MAS NMR study of calcia, magnesia, scandia and yttria stabilized zirconia

High-resolution 17O MAS NMR can provide unique constraints on local structure and oxide ion dynamics in conductive zirconia ceramics of interest for fuel cells and other technologies. We describe here NMR and bulk conductivity measurements for scandia, yttria, calcia, and magnesia stabilized zirconias, including MAS NMR spectra collected in situ at temperatures up to 700 °C. All of the cubic compounds with high dopant levels showed line narrowing and coalescence in this temperature range, and the temperature-induced changes in line widths are qualitatively correlated with the bulk conductivities. A monoclinic zirconia with 2% Sc 2O 3 dopant level (expected to have relatively low ionic mobility) showed no motional averaging of its two 17O NMR peaks even at 600 °C, but instead is observed to begin to transform to a disordered, possibly cubic or tetragonal phase at 600 to 700 °C. 17O MAS NMR spectra of calcia stabilized zirconia were analyzed in detail and the exchange frequencies as a function of temperature, conductivity, and activation energy were estimated and compared with bulk conductivities. The activation energy estimated from NMR exchange frequencies is somewhat lower than that of bulk conductivity but the conductivities estimated from NMR appear to be lower than bulk conductivity.

Cavity linewidth narrowing and broadening due to competing linear and nonlinear dispersions

We experimentally demonstrate cavity linewidth control by manipulating dispersion of the intracavity medium. By making use of the dramatic change of Kerr nonlinearity near electromagnetically induced transparency resonance in a three-level atomic system, the cavity transmission linewidth can be greatly modified. As the cavity input intensity increases, the cavity linewidth changes from below to above empty cavity linewidth, corresponding to subluminal and superluminal photon propagation in the cavity, respectively.

Magnetic properties of the tetranitrosyl-iron complex Fe2(SC3H5N2)2(NO)4

The magnetic properties of the binuclear nitrosyl-iron complexes Fe2(SC3H5N2)2(NO)4 are investigated. It is demonstrated that several types of particles, such as dimers with a pair of spins 1/2, dimers with a pair of spins 5/2, and paramagnetic particles with spin 3/2, make a contribution to the magnetic properties of the complexes. A decrease in the temperature below 25 K leads to a change in the shape of the EPR spectra corresponding to these dimers, so that Lorentzian lines (homogeneous broadening) transform into Gaussian lines (inhomogeneous broadening). This is accompanied by a stepwise change in the EPR line width and g factors. The change in the line shape indicates that complexes become asymmetric at low temperatures, possibly, due to the decrease in the spin exchange frequency below the frequency of the microwave field of the spectrometer.

Effects on transition temperature and Raman spectra of substitution of Cr and Al for Mg in MgB2

AbstractMg1−x Mx B2 (M = Cr, Al) polycrystalline bulk samples with 0 ≤ x ≤ 5% have been synthesized by a solid state reaction and studied by X‐ray diffraction, SEM and Raman spectroscopy. By comparing with the results of Sc‐substituted MgB2, it is found that all these atomic substitutions for Mg depress Tc, and Cr and Sc substitutions depress Tc even more quickly than the one of Al doping. It is suggested that the Tc changes of the M‐substituted MgB2 can be understood by the competing/cooperating effects of the hole‐filling and the disorder. The Raman peak linewidth decreases for Al‐substituted MgB2, which represents an opposite trend to the linewidth change of Mg1−x Crx B2 and shows an evidence of the disorder caused by the atomic substitution and the different arrangement of the substituted atoms in the lattice. Meanwhile, different frequency changes of the Raman peak for the Cr‐ and Al‐substitute MgB2 are discovered and understood by the competing/cooperating effects of the electron‐phonon coupling, the grain size, and the lattice contraction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultraviolet photon absorption in single- and double-wall carbon nanotubes and peapods: Heating-induced phonon line broadening, wall coupling, and transformation

Ultraviolet photon absorption has been used to heat single- and double-wall carbon nanotubes and peapods in vacuum. By increasing the laser intensity up to $500\phantom{\rule{0.3em}{0ex}}\mathrm{mW}$, a downshift and a broadening of the optical phonons are observed corresponding to a temperature of $1000\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The UV Raman measurements are free of blackbody radiation. We find that the linewidth changes for the ${G}_{+}$ and ${G}_{\ensuremath{-}}$ bands differ considerably in single-wall carbon nanotubes. This gives evidence that the phonon decay process is different in axial and radial tube directions. We observe the same intrinsic linewidths of graphite (highly oriented pyrolytic graphite) for the $G$ band in single- and double-wall carbon nanotubes. With increasing temperature, the interaction between the walls is modified for double-wall carbon nanotubes. Ultraviolet photon induced transformations of peapods are found to be different on silica and diamond substrates.

Redox-Dependent Sodium Binding by the Na+-Translocating NADH:Quinone Oxidoreductase from Vibrio harveyi

Relaxation characteristics of the 23Na nuclei magnetization were used to determine the sodium-binding properties of the Na+-translocating NADH:quinone oxidoreductase from Vibrio harveyi (NQR). The dissociation constant of Na+ for the oxidized enzyme was found to be 24 mM and for the reduced enzyme about 30 microM. Such large (3 orders in magnitude) redox dependence of the NQR affinity to sodium ions shows that the molecular machinery was designed to use the drop in redox energy for creating an electrochemical sodium gradient. Redox titration of NQR monitored by changes in line width of the 23Na NMR signal at 2 mM Na+ showed that the enzyme affinity to sodium ions follows the Nernst law for a one-electron carrier with Em about -300 mV (vs SHE). The data indicate that energy conservation by NQR involves a mechanism modulating ion affinity by the redox state of an enzyme redox cofactor.

The effect of magnetic order and thickness in the Raman spectra of oriented thin films ofLaMnO3

Low-temperature Raman studies on (100)-orientedLaMnO3 thin films of different thicknesses deposited onLaAlO3(100) substrate by using the pulsed laser deposition technique are presented. The phonon modefrequencies depend strongly on the thickness of the film and in comparison to theLaMnO3 single crystal shift to higher values with decreasing thickness. The broadening of Ramanline widths was also observed with decreasing film thickness. Anomalous softening of theB2g mode (Jahn–Teller distortion activated) was observed for all films below the magnetic orderingtemperature. A signature of lattice anomalies in the form of changes in line width of theB2g mode correlated with the magnetic ordering temperature was also seen. The results wereinterpreted by considering strong spin–phonon coupling and reduction in Jahn–Tellerdistortion driven polarons due to magnetic order.

Role of cationic gemini surfactants toward enhanced ninhydrin–tryptophan reaction

AbstractIn this paper we report the effect of dicationic ‘gemini’ surfactants (CH3)2C16H33N+ (CH2)mN+C16H33(CH3)2, 2Br− (where m = 4, 5, 6) on the reaction of ninhydrin with DL‐tryptophan. The gemini surfactant micellar media are comparatively more effective than their conventional monomeric counterpart cetyltrimethylammonium bromide (CTAB) micelles. Also, whereas typical rate constant (kψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produce a third region of increasing kψ at higher concentrations. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in 1H NMR line widths. Quantitative kinetic analysis of the rate constant–[surfactant] data has been performed on the basis of modified pseudophase model. Copyright © 2007 John Wiley & Sons, Ltd.

1H and 7Li NMR in defect cobaltite Li0.6CoO2

Within a temperature range of 120–330 K, 7Li NMR spectra in Li0.6CoO2 are obtained. It is shown that as the temperature increases, both smooth and stepwise variation of 7Li NMR contact shifts occurs. The observed effects are explained by the occupation of the excited levels of cobalt ions. The stepwise change of the resonance line width depending on the temperature is revealed. It is driven by the features of the diffusive motion of lithium ions. The calculation of the 1H NMR line shape provides the determination of the ratio of one-, two-, and three-spin proton clusters in Li0.6CoO2·xH2O.

Infrared and Raman Spectra, conformations, ab initio calculations and spectral assignments of 1,3‐disilabutane (SiH3CH2SiH2CH3)

AbstractRaman spectra of 1,3‐disilabutane (SiH3CH2SiH2CH3) as a liquid were recorded at 293 K and as a solid at 78 K. In the Raman cryostat at 78 K an amorphous phase was first formed, giving a spectrum similar to that of the liquid. After annealing to 120 K, the sample crystallized and large changes occurred in the spectra since more than 20 bands present in the amorphous solid phase vanished. These spectral changes made it possible to assign Raman bands to the anti or gauche conformers with confidence. Additional Raman spectra were recorded of the liquid at 14 temperatures between 293 and 137 K. Some Raman bands changed their peak heights with temperature but were countered by changes in linewidths, and from three band pairs assigned to the anti and gauche conformers, the conformational enthalpy difference ΔconfH(gauche–anti) was found to be 0 ± 0.3 kJ mol−1 in the liquid. Infrared spectra were obtained in the vapor and in the liquid phases at ambient temperature and in the solid phases at 78 K in the range 4000–400 cm−1. The sample crystallized immediately when deposited on the CsI window at 78 K, and many bands present in the vapor and liquid disappeared. Additional infrared spectra in argon matrixes at 5 K were recorded before and after annealing to temperatures 20–34 K. Quantum chemical calculations were carried out at the HF, MP2 and B3LYP levels with a variety of basis sets. The HF and DFT calculations suggested the anti conformer as the more stable one by ca 1 kJ mol−1, while the MP2 results favored gauche by up to 0.4 kJ mol−1. The Complete Basis Set method CBS‐QB3 gave an energy difference of 0.1 kJ mol−1, with anti as the more stable one. Scaled force fields from B3LYP/cc‐pVQZ calculations gave vibrational wavenumbers and band intensities for the two conformers. Copyright © 2007 John Wiley & Sons, Ltd.

Raman scattering and tunable electron–phonon coupling in single layer graphene

Graphene, the two-dimensional hexagonal lattice of carbon atoms, is promising for future electronic devices and for studies of fundamental interactions. New behaviors are linked to the extreme reduction in dimensionality to the atomic level and to the presence of Dirac fermion charge carriers. Here we review our recent work on Raman scattering studies in single layer graphene in which carrier densities are gate-modulated by the electric-field-effect (EFE). The couplings of long wavelength optical phonons (the G -band) with Dirac fermions display remarkable changes in energy and line-width that are tunable by the EFE. In these studies Raman methods emerge as tools for studies of unique properties of charge carriers in graphene such as particle–hole symmetry of Dirac fermions and the impact of disorder.

EPR results and Raman spectroscopy as a complementary characterization of isolated Yb ions and Yb pairs in CaF2:Yb single crystals

Raman spectrum of the CaF 2 :Yb crystal irradiated with γ-rays shows the localized phonon centred at about 64 cm -1 being an evidence of the ytterbium pairs presence. There are not observed absorption bands characteristic for Yb 2+ ions in the absorption spectrum of as-grown (not irradiated or not annealed) CaF 2 :Yb (5 mol%) crystal. Electron paramagnetic resonance measurements of CaF 2 :Yb (5 mol%) single crystals were carried out for lattice sites substituted by Yb 3+ ions and also for the possibility of ytterbium pairs arising. Among eight of EPR lines observed for as-grown crystal, mainly the lines originating from different Yb 3+ isotopes can be distinguished: 170 Yb 3+ Ι = 0, 171 Yb 3+ 1= 1/2 and 1?3 Yb 3+ Ι=5/2. The lines originating from Yb 3+ pairs cannot be excluded. All of the lines do not move with angular variation in the planes parallel and perpendicular to the axis. The extra line in the magnetic field orientation in every plane at 45°, with B 0 ∼ 191 mT is observed. This unidentified line corresponds to a non-axial Yb 3+ centre or unknown impurity. The components of A and g tensors of the spin Hamiltonian for cubic symmetry were calculated. Temperature dependence of the EPR lines shows the agreement with the Curie law until the temperature of 18 K. The peak-to-peak linewidth changes continuously within 20 mT range for as-grown crystals, while shows significant linear increase above 18 K for γ-irradiated ones. It suggests the presence of Yb 2+ ions, being created due to Compton electron capture. So, Yb 3+ co-exists with Yb 2+ after the Yb 3+ → Yb 2+ conversion under influence of γ-irradiation. It seems the Yb 2+ centres arising in CaF 2 :Yb (5 mol%) single crystal irradiated with γ-quanta are related to Yb 3+ , as an effect of recharging one of Yb 3+ ion from a pair, or form Yb 3+ -Yb 2+ pair when Compton electron is captured by one of isolated neighbour Yb 3+ ions.

Raman study of alloy potential fluctuations inMgxZn1−xO nanopowders

The blueshift of near-band-edge emission and excitonic absorption indicate thatZn2+ ions are successfullysubstituted by Mg2+ ions in MgxZn1−xO nanopowders for 0≤x≤0.14. The changes in Raman spectral linewidth and the asymmetry of theE2 (high) mode for various Mg contents can be well described by a modified spatial correlationmodel that considers the grain size distribution. With increasing Mg concentration, the alloypotential fluctuations lead to a decrease in the grain size, which is induced by the surplusMg2+ that could form MgO clusters surrounding the crystalline MgZnO.

EPR study of local ordering in DMAAlS and DMAGaS crystals

X-band electron paramagnetic resonance (EPR) investigations of single crystals of Cr3+-doped dimethylammonium aluminium sulphate hexahydrate (DMAAlS) and dimethylammonium gallium sulphate hexahydrate (DMAGaS) are presented from room temperature down to liquid helium temperature. Both crystals undergo an order-disorder phase transition to ferroelectric phase at T C1 = 152 K and T C1 = 134 K, respectively. Additionally, DMAGaS undergoes a first-order transition into a low temperature non-ferroelectric intermediate phase at T C2 = 116 K and into a low temperature antiferroelectric phase at about T C3 = 60 K. The spin Hamiltonian parameters have been determined for all observed in both crystal phases. Remarkable EPR line width changes with observed triplets confirm the order-disorder character of the ferroelectric phase transition and demonstrate freezing-out of dimethyl ammonium reorientations, which is a primary reason for this transition. The doubled number of EPR lines in comparison to the paraelectric and ferroelectric phases in DMAGaS indicates a unit cell doubling in antiferroelectrics phase below 60 K.

Magnetic Properties on Ferromagnetic FeAlO$_3$

FeAlO3 polycrystalline sample was fabricated by the sol-gel method. The crystallographic and magnetic properties of the sample were measured using X-ray diffractometer, Mossbauer spectroscopy, and vibrating sample magnetometer (VSM). The crystal structure was found to be an orthorhombic with the space group Pna21, which has four cation sites labeled Fe1, Fe2, Al2(octahedral sites), and Al1(tetrahedral site). Magnetic hysteresis curves of FeAlO3 showed the ferromagnetic phase and a pinched-like shape at low temperature, which is similar to those of 'exchange-spring magnet'. The Curie temperature was determined to be 250 K. Mossbauer spectra were measured from 4.2 to 295 K. The isomer shifts at room temperature are 0.32 mm/s and 0.11 mm/s relative to alpha-Fe metal, which is consistent with ferric state in oxide materials. Mossbauer spectra showed line broadening and the changes in linewidth with increasing temperature, we have examined the cation distribution and anisotropy energy difference of Fe1, Fe2, Al2, and Al1 sites. From the analysis of Mossbauer spectrum at 4.2 K, the occupancies of Fe ion on Fe1, Fe2, Al1, and Al2 sites are determined to be 41.15%, 38.7%, 7.8%, and 12.4%, respectively

15N MAS NMR Studies of Cph1 Phytochrome: Chromophore Dynamics and Intramolecular Signal Transduction

Solid-state nuclear magnetic resonance (NMR) is applied for the first time to the photoreceptor phytochrome. The two stable states, Pr and Pfr, of the 59-kDa N-terminal module of the cyanobacterial phytochrome Cph1 from Synechocystis sp. PCC 6803 containing a uniformly 15N-labeled phycocyanobilin cofactor are explored by 15N cross-polarization (CP) magic-angle spinning (MAS) NMR. As recently shown by 15N solution-state NMR using chemical shifts [Strauss, H. M.; Hughes, J.; Schmieder, P. Biochemistry 2005, 44, 8244], all four nitrogens are protonated in both states. CP/MAS NMR provides two additional independent lines of evidence for the protonation of the nitrogens. Apparent loss of mobility during photoactivation, indicated by the decrease of line width, demonstrates strong tension of the entire chromophore in the Pfr state, which is in clear contrast to a more relaxed Pr state. The outer rings (A and D) of the chromophore are significantly affected by the phototransformation, as indicated by both change of chemical shift and line width. On the other hand, on the inner rings (B and C) only minor changes of chemical shifts are detected, providing evidence for a conserved environment during phototransformation. In a mechanical model, the phototransformation is understood in terms of rotations between the A-B and C-D methine bridges, allowing for intramolecular signal transduction to the protein surface by a unit composed of the central rings B and C and its tightly linked protein surroundings during the highly energetic Pfr state.

Complex formation of HCONH 2 in CH 3OH environment and investigation of linewidth changes of ν(C [dbnd]O) stretching and NH 2 bending modes

The isotropic part of the Raman bands corresponding to NH 2 bending and ν(C O) stretching modes of formamide (HCONH 2) at ∼1593 and 1668 cm −1, respectively, in neat HCONH 2 as well as in binary mixtures with methanol (CH 3OH) were reinvestigated. Variations of their linewidths exclusively with mole fractions of HCONH 2, in the range C = 0.1–0.9 were studied. The linewidth variation of the NH 2 bending mode shows a departure from the trend expected on the basis of concentration fluctuation model and this has been explained using a recently suggested empirical model by invoking the concept of microviscosities of the solute, HCONH 2 and the solvent, CH 3OH. The other peak at ∼1668 cm −1 shows a peculiar variation of the linewidth with concentration having two minima at C = 0.8 and 0.4, which have been explained in terms of formation of hydrogen bonded complexes, NH 2HCO⋯HOCH 3, and NH 2HCO⋯(HOCH 3) 2 and the two phenomena, namely motional narrowing and diffusion dynamics being simultaneously operative. The equilibrium constants have been evaluated from the spectral data and their variation with total molar concentration has been presented.

A New Approach to Explain Concentration-Dependent Changes of Isotropic Raman Line Width in the Associated Binary Mixtures

We report on a new empirical relationship to explain the concentration-dependent isotropic Raman line width changes of a vibrational mode in uniform binary mixtures. The factors contributing to the intrinsic line width and several other broadening mechanisms are, in general, concentration-dependent. Concentration fluctuation in a microscopic volume and microviscosity are the two factors that are known to cause a concentration-dependent line width variation. These two factors combined in a specific manner successfully explain the variation of the line width with concentration strongly associated with binary systems. A readily usable empirical relationship for line width is suggested. It has been demonstrated that it can successfully explain the line width variation with concentration in a given class of hydrogen-bonded systems taking some representative binary mixtures.

Solvent response and dielectric relaxation in supercooled butyronitrile

We have measured the dynamics of solvation of a triplet state probe, quinoxaline, in the glass-forming dipolar liquid butyronitrile near its glass transition temperature T(g)=95 K. The Stokes shift correlation function displays a relaxation time dispersion of considerable magnitude and the optical linewidth changes along the solvation coordinate in a nonmonotonic fashion. These features are characteristic of solvation in viscous solvents and clearly indicate heterogeneous dynamics, i.e., spatially distinct solvent response times. Using the dielectric relaxation data of viscous butyronitrile as input, a microscopic model of dipolar solvation captures the relaxation time, the relaxation dispersion, and the amplitude of the dynamical Stokes shift remarkably well.

Disease-associated Sequence Variations Congregate in a Polyanion Recognition Patch on Human Factor H Revealed in Three-dimensional Structure

Mutations and polymorphisms in the regulator of complement activation, factor H, have been linked to atypical hemolytic uremic syndrome (aHUS), membranoproliferative glomerulonephritis, and age-related macular degeneration. Many aHUS patients carry mutations in the two C-terminal modules of factor H, which normally confer upon this abundant 155-kDa plasma glycoprotein its ability to selectively bind self-surfaces and prevent them from inappropriately triggering the complement cascade via the alternative pathway. In the current study, the three-dimensional solution structure of the C-terminal module pair of factor H has been determined. A binding site for a fully sulfated heparin-derived tetrasaccharide has been delineated using chemical shift mapping and the C3d/C3b-binding site inferred from sequence comparisons and computational docking. The resultant information allows assessment of the likely consequences of aHUS-associated amino acid substitutions in this critical region of factor H. It is striking that, excepting those likely to perturb the three-dimensional structure, aHUS-associated missense mutations congregate in the polyanion-binding site delineated in this study, thus potentially disrupting a vital mechanism for control of complement on self-surfaces in the microvasculature of the kidney. It is intriguing that a single nucleotide polymorphism predisposing to age-related macular degeneration occupies another region of factor H that harbors a polyanion-binding site.