State of bismuth in BaBiO3 and BaBi1-xPbxO3: Bi 4f photoemission and Bi L3 absorption spectroscopic studies

The 2p 6d feature in the Bi L3 spectra has different energies in the semiconducting (0.0≤x<0.7) and the superconducting (x=0.75) compositions of BaBi1−xPbxO3. The Bi 4f core level spectrum shows distinct features ascribable to Bi III and Bi V in BaBiO3 and in the semiconducting compositions; the width of the 4f peaks is also considerably larger in these compositions compared to that in BaBi0.25Pb0.75O3, which shows a single sharp Bi 4f feature.

DFT study of structure and vibrational spectra of ceramide 3: comparison to experimental data

The Fourier transform Raman and infrared (IR) spectra of the Ceramide 3 (CER3) have been recorded in the regions 200-3500 cm(-1) and 680-4000 cm(-1), respectively. We have calculated the equilibrium geometry, harmonic vibrational wavenumbers, electrostatic potential surfaces, absolute Raman scattering activities and IR absorption intensities by the density functional theory with B3LYP functionals having extended basis set 6-311G. This work is undertaken to study the vibrational spectra of CER3 completely and to identify the various normal modes with better wavenumber accuracy. Good consistency is found between the calculated results and experimental data for the IR and Raman spectra.

Two-Dimensional Correlation Analysis of Temperature-Dependent FT-IR Spectra of Oleic Acid

In the present study, variable temperature FT-IR spectroscopic investigations were used to characterize the spectral changes in oleic acid during heating oleic acid in the temperature range from -30 degrees;C to 22 degrees C. In order to extract more information about the spectral variations taking place during the phase transition process, 2D correlation spectroscopy (2DCOS) was employed for the stretching (C?O) and rocking (CH2) band of oleic acid. However, the interpretation of these spectral variations in the FT-IR spectra is not straightforward, because the absorption bands are heavily overlapped and change due to two processes: recrystallization of the ?-phase and melting of the oleic acid. Furthermore, the solid phase transition from the ?- to the a-phase was also observed between -4 degrees C and -2 degrees C. Thus, for a more detailed 2DCOS analysis, we have split up the spectral data set in the subsets recorded between -30 degrees C to -16 degrees C, -16 degrees C to 10 degrees C, and 10 degrees C to 22 degrees C. In the corresponding synchronous and asynchronous 2D correlation plots, absorption bands that are characteristic of the crystalline and amorphous regions of oleic acid were separated.

Valence band electronic structure of Nd1-xYxMnO3 using X-ray absorption, photoemission and GGA plus U calculations

The electronic structures of Nd1-xYxMnO3 (x=0-0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L-3,L-2- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L-3,L-2-edge with doping, suggests a decrease in the occupancy of Mn 3d orbitals. The O K-edge XANES shows a depletion of unoccupied states above the Fermi energy. The changes in the O K-edge spectra due to doping reflects an increase in the Jahn-Teller distortion. The VB-PES shows broadening of the features associated with Mn 3d and O 2p hybridized states and the shift of these features to a slightly higher binding energy in agreement with our GGA + U calculations. The system shows a net shift of the occupied and unoccupied states away from the Fermi energy with doping. The shift in theoretical site-projected density of states of x=0.5 composition with respect to x=0 suggest a subtle change from a charge transfer to Mott-Hubbard type insulator. (C) 2013 Elsevier B.V. All rights reserved.

Electronic structure of Nd1-xYxMnO3 from Mn K edge absorption spectroscopy and DFT methods

The electronic structure of Nd1-xYxMnO3 (x-0-0.5) is studied using x-ray absorption near-edge structure (XANES) spectroscopy at the Mn K-edge along with the DFT-based LSDA+U and real space cluster calculations. The main edge of the spectra does not show any variation with doping. The pre-edge shows two distinct features which appear well-separated with doping. The intensity of the pre-edge decreases with doping. The theoretical XANES were calculated using real space multiple scattering methods which reproduces the entire experimental spectra at the main edge as well as the pre-edge. Density functional theory calculations are used to obtain the Mn 4p, Mn 3d and O 2p density of states. For x=0, the site-projected density of states at 1.7 eV above Fermi energy shows a singular peak of unoccupied e(g) (spin-up) states which is hybridized Mn 4p and O 2p states. For x=0.5, this feature develops at a higher energy and is highly delocalized and overlaps with the 3d spin-down states which changes the pre-edge intensity. The Mn 4p DOS for both compositions, show considerable difference between the individual p(x), p(y) and p(z)), states. For x=0.5, there is a considerable change in the 4p orbital polarization suggesting changes in the Jahn-Teller effect with doping. (C) 2013 Elsevier Ltd. All rights reserved.

Local disorder investigation in NiS2-xSex using Raman and Ni K-edge x-ray absorption spectroscopies

We report on Raman and Ni K-edge x-ray absorption investigations of a NiS2-xSex (with x = 0.00, 0.50/0.55, 0.60, and 1.20) pyrite family. The Ni K-edge absorption edge shows a systematic shift going from an insulating phase (x = 0.00 and 0.50) to a metallic phase (x = 0.60 and 1.20). The near-edge absorption features show a clear evolution with Se doping. The extended x-ray absorption fine structure data reveal the evolution of the local structure with Se doping which mainly governs the local disorder. We also describe the decomposition of the NiS2-xSex Raman spectra and investigate the weights of various phonon modes using Gaussian and Lorentzian profiles. The effectiveness of the fitting models in describing the data is evaluated by means of Bayes factor estimation. The Raman analysis clearly demonstrates the disorder effects due to Se alloying in describing the phonon spectra of NiS2-xSex pyrites.

Solid-state optical absorption from optimally tuned time-dependent range-separated hybrid density functional theory

We present a framework for obtaining reliable solid-state charge and optical excitations and spectra from optimally tuned range-separated hybrid density functional theory. The approach, which is fully couched within the formal framework of generalized Kohn-Sham theory, allows for the accurate prediction of exciton binding energies. We demonstrate our approach through first principles calculations of one- and two-particle excitations in pentacene, a molecular semiconducting crystal, where our work is in excellent agreement with experiments and prior computations. We further show that with one adjustable parameter, set to produce the known band gap, this method accurately predicts band structures and optical spectra of silicon and lithium fluoride, prototypical covalent and ionic solids. Our findings indicate that for a broad range of extended bulk systems, this method may provide a computationally inexpensive alternative to many-body perturbation theory, opening the door to studies of materials of increasing size and complexity.

Electron spin resonance absorption in organic metal polyaniline and its blend with PMMA

The electron spin resonance absorption in the synthetic metal polyaniline (PANI) doped with PTSA and its blend with poly(methylmethacrylate) (PMMA) is investigated in the temperature range between 4.2 and 300 K. The observed line shape follows Dyson's theory for a thick metallic plate with slowly diffusing magnetic dipoles. At low temperatures the line shape become symmetric and Lorentzian when the sample dimensions are small in comparison with the skin depth. The temperature dependence of electron spin relaxation time is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.

Spectroscopic investigations of manganese ions in microwave-prepared NaPO3-PbO glasses

The EPR spectra of microwave-prepared 70NaPO(3):30PbO glasses containing different weight percentages of manganese ions have been studied. The EPR spectra exhibit a well-resolved hyperfine pattern at g(eff) approximate to 2.0. Optical absorption, fluorescent emission and excitation spectra of the glasses have been examined. The absorption spectrum exhibits a peak near 500 nm and this has been attributed to the spin-allowed E-5(g) --> T-5(2g) transition of Mn3+ ions. The emission spectrum shows a band at 595 nm which has been assigned to the T-4(1g)(G) --> (6)A(1g)(S) spin-forbidden transition of Mn2+ ions in octahedral coordination. Concentration quenching of fluorescence was found to occur above 0.75 wt% of Mn2+ ions. The excitation spectra exhibit four bands characteristic of Mn2+ ions in octahedral coordination. From the observed band positions of the excitation spectra, the crystal field parameter D-q and the Racah interelectronic repulsion parameters, B and C have been calculated. A structural model is proposed based on the IR, Raman and MASNMR studies according to which Mn2+ ions are likely to occupy sites similar to Na+ ions in these glasses.

1H and 13C NMR spectra of some unsymmetric N,N-dipyridyl ureas: spectral assignments and molecular conformation

Abstract: The H-1 NMR spectra of N-(2-pyridyl), N'-(3-pyridyl)ureas and N-(2-pyridyl), N'-(4-pyridyl)ureas in CDCl3 and (CD3)(2)CO have been assigned with the aid of COSY and NOE experiments and chemical shift and coupling constant correlations, The C-13 NMR spectra in CDCl3 were analysed utilizing the HETCOR and proton coupled spectra, The H-1 NMR spectra, NOE effects and MINDO/3 calculations have been utilized to show that the molecular conformation of these compounds has the 2-pyridyl ring coplanar with the urea plane with the N-H group hydrogen bonded to the nitrogen of the 2-pyridyl group on the other urea nitrogen while the 3/4-pyridyl group rotates rapidly about the N-C-3/N-C-4 bond.

Synthesis, X-ray structures, and spectroscopic and electrochemical properties of (mu-oxo)bis(mu-carboxylato)diruthenium complexes having six imidazole bases as terminal ligands

Complexes [Ru2O(O2CR)(2)(1-MeIm)(6)](ClO4)(2) (la-c), [Ru2O(O2CR)(2)(ImH)(6)](ClO4)(2) (2a,b), and [Ru2O(O2CR)(2)(4-MeImH)(6)](ClO4)(2) (3a,b) with a (mu-oxo)bis(mu-carboxylato)diruthenium(III) core have been prepared by reacting Ru2Cl(O2CR)(4) with the corresponding imidazole base, viz. 1-methylimidazole (1-MeIm), imidazole (ImH), and 4-methylimidazole (4-MeImH) in methanol, followed by treatment with NaClO4 in water (R: Me, a; C6H4-p-OMe, b; C6H4-p-Me, c). Diruthenium(III,IV) complexes [Ru2O(O2CR)(2)(1-MeIm)(6)](ClO4)(3) (R: Me, 4a; C6H4-p-OMe, 4b; C6H4-p-Me, 4c) have been prepared by one-electron oxidation of 1 in MeCN with K2S2O8 in water. Complexes la, 2a . 3H(2)O, and 4a . 1.5H(2)O have been structurally characterized. Crystal data for the complexes are as follows: la, orthorhombic, P2(1)2(1)2(1), a = 7.659(3) Angstrom, b = 22.366(3) Angstrom, c = 23.688(2) Angstrom, V = 4058(2) Angstrom(3), Z = 4, R = 0.0475, and R-w = 0.0467 for 2669 reflections with F-o > 2 sigma(F-o); 2a . 3H(2)O, triclinic, , a = 13.735(3) Angstrom, b = 14.428(4) Angstrom, c = 20.515(8) Angstrom, alpha = 87.13(3)degrees, beta = 87.61(3)degrees, gamma = 63.92(2)degrees, V = 3646(2) Angstrom(3), Z = 4, R = 0.0485 and R-w = 0.0583 for 10 594 reflections with F-o > 6 sigma(F-o); 4a . 1.5H(2)O triclinic, , a = 11.969(3) Angstrom, b = 12.090(6) Angstrom, c = 17.421(3) Angstrom, alpha = 108.93(2)degrees, beta = 84.42(2)degrees, gamma = 105.97(2)degrees, V = 2292(1) Angstrom(3), Z = 2, R = 0.0567, and R-w = 0.0705 for 6775 reflections with F-o > 6 sigma(F-o). The complexes have a diruthenium unit held by an oxo and two carboxylate ligands, and the imidazole ligands occupy the terminal sites of the core. The Ru-Ru distance and the Ru-O-oxo-Ru angle in la and 2a . 3H(2)O are 3.266(1), 3.272(1) Angstrom and 122.4(4), 120.5(2)degrees, while in 4a . 1.5H(2)O these values are 3.327(1) Angstrom and 133.6(2)degrees. The diruthenium(III) complexes 1-3 are blue in color and they exhibit an intense visible band in the range 560-575 nm. The absorption is charge transfer in nature involving the Ru(III)-d pi and O-oxo-p pi orbitals. The diruthenium(III,IV) complexes are red in color and show an intense band near 500 nm. The diruthenium(III) core readily gets oxidized with K2S2O8 forming quantitatively the diruthenium(III,IV) complex. The visible spectral record of the conversion shows an isosbestic point at 545 nm for 1 and at 535 nm for 2 and 3. Protonation of the oxide bridge by HClO4 in methanol yields the [Ru-2(mu-OH)(mu-O2CR)(2)](3+) core. The hydroxo species shows a visible band al 550 nm. The pK(a) value for la is 2.45. The protonated species are unstable. The 1-MeIm species converts to the diruthenium(III,IV) core, while the imidazole complex converts to [Ru(ImH)(6)](3+) and some uncharacterized products. Complex [Ru(ImH)(6)](ClO4)(3) has been structurally characterized. The diruthenium(III) complexes are essentially diamagnetic and show characteristic H-1 NMR spectra indicating the presence of the dimeric structure in solution. The diruthenium(III,IV) complexes are paramagnetic and display rhombic EPR spectral features. Complexes 1-3 are redox active. Complex 1 shows the one-electron reversible Ru-2(III)/(RuRuIV)-Ru-III, one-electron quasireversible (RuRuIV)-Ru-III/Ru-2(IV), and two-electron quasireversible Ru-2(III)/Ru-2(II) couples near 0.4, 1.5, and -1.0 V vs SCE In MeCN-0.1 M TBAP, respectively, in the cyclic and differential pulse voltammetric studies. Complexes 2 and 3 exhibit only reversible Ru-2(III)/(RuRuIV)-Ru-III and the quasireversible (RuRuIV)-Ru-III/Ru-2(IV) couples near 0.4 and 1.6 V vs SCE, respectively, The observation of a quasireversible one-step two-electron transfer reduction process in 1 is significant considering its relevance to the rapid and reversible Fe-2(III)/Fe-2(II) redox process known for the tribridged diiron core in the oxy and deoxy forms of hemerythrin.

Self-Absorption and Focusing Effects in Carrier Relaxation Dynamics under Depletion Conditions

The effect of a one-dimensional field (1) on the self-absorption characteristics and (2) when we have a finite numerical aperture for the objective lens that focuses the laser beam on the solid are considered here. Self-absorption, in particular its manifestation as an inner filter for the emitted signal, has been observed in luminescence experiments. Models for this effect exist and have been analyzed, but only in the absence of space charge. Using our previous results on minority carrier relaxation in the presence of a field, we obtain expressions incorporating inner filter effects. Focusing of a light beam on the sample, by an objective lens, results in a three-dimensional source and consequently a three-dimensional continuity equation to be solved for the minority carrier concentration. Assuming a one-dimensional electric field and employing Fourier-Bessel transforms, we recast the problem of carrier relaxation and solve the same via an identity that relates it to solutions obtained in the absence of focusing effects. The inner filter effect as well as focusing introduces new time scales in the problem of carrier relaxation. The interplay between the electric field and the parameters which characterize these effects and the consequent modulation of the intensity and time scales of carrier decay signals are analyzed and discussed.

Difference spectroscopic studies on binding of Cibacron blue F3GA to ribosome inactivating proteins: effect of beta-mercaptoethanol on the interaction with ricin

The interaction of Cibacron blue F3GA with ribosome inactivating proteins, ricin, ricin A-chain and momordin has been investigated using difference absorption spectroscopy. Ricin was found to bind the dye with a 20- and 2-fold lower affinity than ricin A-chain and momordin, respectively. A time dependent increase in the amplitude of Cibacron blue difference spectrum in the presence of ricin was observed on addition of beta-mercaptoethanol. Analysis of the kinetic profile of this increase showed a biphasic phenomenon and the observed rates were found to be independent of the concentration of beta-mercaptoethanol. Kinetics of reduction of the intersubunit disulphide bond in ricin by beta-mercaptoethanol showed that reduction pet se is a second order reaction. Therefore, the observed changes in the difference spectra of Cibacron blue probably indicate a slow change in the conformation of ricin, triggered by reduction of the intersubunit disulphide bond.

Improved assessment of aerosol absorption using OMI-MODIS joint retrieval

The Ozone Monitoring Instrument (OMI) aboard EOS-Aura and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard EOS-Aqua fly in formation as part of the A-train. Though OMI retrieves aerosol optical depth (AOD) and aerosol absorption, it must assume aerosol layer height. The MODIS cannot retrieve aerosol absorption, but MODIS aerosol retrieval is not sensitive to aerosol layer height and with its smaller pixel size is less affected by subpixel clouds. Here we demonstrate an approach that uses MODIS-retrieved AOD to constrain the OMI retrieval, freeing OMI from making an a priori estimate of aerosol height and allowing a more direct retrieval of aerosol absorption. To predict near-UV optical depths using MODIS data we rely on the spectral curvature of the MODIS-retrieved visible and near-IR spectral AODs. Application of an OMI-MODIS joint retrieval over the north tropical Atlantic shows good agreement between OMI and MODIS-predicted AODs in the UV, which implies that the aerosol height assumed in the OMI-standard algorithm is probably correct. In contrast, over the Arabian Sea, MODIS-predicted AOD deviated from the OMI-standard retrieval, but combined OMI-MODIS retrievals substantially improved information on aerosol layer height (on the basis of validation against airborne lidar measurements). This implies an improvement in the aerosol absorption retrieval, but lack of UV absorption measurements prevents a true validation. Our study demonstrates the potential of multisatellite analysis of A-train data to improve the accuracy of retrieved aerosol products and suggests that a combined OMI-MODIS-CALIPSO retrieval has large potential to further improve assessments of aerosol absorption.

On the dielectric dispersion and absorption in nanosized manganese zinc mixed ferrites

The temperature and frequency dependence of dielectric permittivity and dielectric loss of nanosized Mn1-xZnxFe2O4 (for x = 0, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The impact of zinc substitution on the dielectric properties of the mixed ferrite is elucidated. Strong dielectric dispersion and broad relaxation were exhibited by Mn1-xZnxFe2O4. The variation of dielectric relaxation time with temperature suggests the involvement of multiple relaxation processes. Cole-Cole plots were employed as an effective tool for studying the observed phenomenon. The activation energies were calculated from relaxation peaks and Cole-Cole plots and found to be consistent with each other and indicative of a polaron conduction.