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Vibrational Properties (vibrational + property)
Selected AbstractsChemInform Abstract: Ba2In2O4(OH)2: Proton Sites, Disorder and Vibrational PropertiesCHEMINFORM, Issue 23 2008Jean-Raphael Martinez Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Hydrogen Bond in Layered Materials: Structural and Vibrational Properties of Kaolinite by a Periodic B3LYP Approach.CHEMINFORM, Issue 27 2006Sergio Tosoni Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] ChemInform Abstract: Theoretical Study of Structural and Vibrational Properties of Al3N3, Ga3N3, and In3N3.CHEMINFORM, Issue 37 2001Anil K. Kandalam Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Electronic and Vibrational Properties of Fluorenone in the Channels of Zeolite LCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2004André Devaux Dr. Abstract Fluorenone (C13H8O) was inserted into the channels of zeolite L by using gas-phase adsorption. The size, structure, and stability of fluorenone are well suited for studying host,guest interactions. The Fourier transform IR, Raman, luminescence, and excitation spectra, in addition to thermal analysis data, of fluorenone in solution and fluorenone/zeolite L are reported. Normal coordinate analysis of fluorenone was performed, based on which IR and Raman bands were assigned, and an experimental force field was determined. The vibrational spectra can be used for nondestructive quantitative analysis by comparing a characteristic dye band with a zeolite band that has been chosen as the internal standard. Molecular orbital calculations were performed to gain a better understanding of the electronic structure of the system and to support the interpretation of the electronic absorption and luminescence spectra. Fluorenone shows unusual luminescence behavior in that it emits from two states. The relative intensity of these two bands depends strongly on the environment and changes unexpectedly in response to temperature. In fluorenone/zeolite L, the intensity of the 300 nm band (lifetime 9 ,s) increases with decreasing temperature, while the opposite is true for the 400 nm band (lifetime 115 ,s). A model of the host,guest interaction is derived from the experimental results and calculations: the dye molecule sits close to the channel walls with the carbonyl group pointing to an Al3+ site of the zeolite framework. A secondary interaction was observed between the fluorenone's aromatic ring and the zeolite's charge-compensating cations. [source] A Comparative Study of the Structural, Electronic, and Vibrational Properties of NH3BH3 and LiNH2BH3: Theory and ExperimentCHEMPHYSCHEM, Issue 11 2009Seung Mi Lee Dr. Abstract Herein, we systematically investigate the structural, electronic, and vibrational properties of ammonia borane (NH3BH3, AB) and lithium amidoborane (LiNH2BH3, LAB) through both density functional calculations and experiments. AB and LAB samples are generated and their vibrational spectra are obtained by using Fourier transformed infrared spectroscopy (FTIR). The measured vibrational spectra are in good agreement with the calculated ones. Our calculations show that the Li-related vibration modes are primarily found in the low-frequency region (<1000 cm,1), and that the intermolecular interactions significantly influence the vibrational spectra. Electronic structure calculations provide insights into the differences between the binding natures of AB and LAB and their influence on the vibrational properties of these compounds. [source] Vibrational properties of four consecutive carbon picotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008Nils Rosenkranz Abstract Four different picotubes have been synthesized up to now. These highly symmetric, ringlike hydrocarbons are closely related to the smallest armchair nanotubes available. We investigate vibrational properties of the different picotubes using first principles calculations and polarization-dependent Raman spectroscopy. Our results emphasize the strong relationship between picotubes and nanotubes. In this context, two features in the picotube spectra are of particular interest: The high-energy bands and breathing-like modes. Vibrational patterns calculated for the high-energy modes of picotubes are similar to the axial and transversal high-energy vibrations of armchair nanotubes. Concerning the radial breathing modes of picotubes, our calculations suggest a d,1 -dependence of the radial breathing mode (RBM) frequency, which is again in analogy to nanotubes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibrational properties of single walled carbon nanotubes under pressure from Raman scattering experiments and molecular dynamics simulationsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007In-Hwan Choi Abstract We have investigated theoretically and experimentally the pressure dependent structural and vibrational properties of single-walled carbon nanotubes (SWNT). Bundles of SWNTs are studied inside a diamond anvil high pressure cell with micro-Raman scattering. The tube diameter and size distribution are determined from the radial breathing modes (RBM) of the tubes. The pressure coefficient and linewidth of one of the high frequency C,C bond stretching modes was found to change suddenly at ,3 GPa which is well below the structural transformation pressure (Pc) for the tubes in our sample. Molecular dynamics simulations were used to calculate the vibrational density of states of SWNTs as a function of pressure. Our simulations suggest that the experimental results can be explained by a softening of a low-frequency optical mode of the SWNTs , the "squashing" mode , and the dynamical effect of this softening on other phonon modes. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibrational properties of InP under pressure: a molecular-dynamics studyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007Paulo S. Branício Abstract Dynamical properties of InP in the zincblende (ZB) are investigated using isothermal,isobaric molecular-dynamics simulations based on a proposed interaction potential for InP consisting of two- and three-body terms. The two-body term represents steric repulsion, Coulomb interactions due to charge transfer, induced charge,dipole interaction, and van der Waals dipole,dipole interaction. The three-body term represents covalent bond bending and stretching. The model is fitted to reproduce crystalline lattice constant, cohesive energy, and the structural transition pressure from ZB to rocksalt. The effects of hydro- static pressure and temperature on the vibrational density-of-states, phonon anharmonicity, dynamic Debye,Waller factor, thermal expansion coefficient are described as well as the pressure induced structural phase transformation. Results are consistent with available experimental data, in particular the calculated equation of state and phonon density-of-states have very good agreement. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibrational properties of GaP and GaP1,xNx under hydrostatic pressures up to 30 GPaPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007M. P. Jackson Abstract We report on Raman scattering of the vibrational modes of GaP and the dilute nitride ternary GaP0.979N0.021 under hydrostatic pressures of up to 30 GPa. We measured the pressure induced shift of the TO and LO modes of GaP up to the phase transition (I,II) and determined mode Grüneisen parameters of 1.12 and 0.98. The phase transition was observed near to 24.5 GPa. We have also studied the dependence of the vibrational spectrum of the GaP0.979N0.021 up to 20 GPa. The zincblende optical phonons of the ternary alloy show great similarities to those of binary GaP, with no significant changes to the Grüneisen parameters or the phase transition. The pressure-induced shift of local nitrogen mode frequency in GaP0.979N0.021 was studied up to 10 GPa and found to be considerably larger than that of the phonon modes in GaN, indicating that the local mode does not show a GaN-like behaviour under pressure. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the performance of eleven DFT functionals in the description of the vibrational properties of aluminosilicatesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2010Raffaella Demichelis Abstract The performance of eleven DFT functionals in describing the equilibrium structure and the vibrational spectra at the , point of pyrope (Mg3Al2Si3O12), forsterite (,-Mg2SiO4), ,-quartz (,-SiO2) and corundum (,-Al2O3) is discussed. The four systems, for which accurate experimental data are available, are here used as a representative sample of the large aluminosilicates family. Calculations were performed with the periodic ab initio CRYSTAL code by using all-electron Gaussian-type basis sets. All the functionals here considered provide reasonable structural predictions, the hybrid PBE0 giving the least deviation from the experimental unit cell volumes (from ,0.3% to +0.6%). At the other extreme, SVWN and SPWLSD (,,3%) and PBE and PW91 (, +3%) provide the largest volume under- and over-estimation, respectively. Vibrational frequencies are more accurate when computed with hybrid functionals, with the best performance provided by B3LYP and WC1LYP (mean absolute differences with respect to experiments evaluated on a set of 134 vibrational frequencies, ||t , 5.5 cm,1). The three recently proposed GGA functionals, PBEsol, SOGGA-PBE and WC-PBE, provide a good description of the vibrational spectra, of the same quality as the one provided by PBE0 and B1WC (||t , 10 cm,1), whereas poorer results are obtained with PBE (||t , 17 cm,1). © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Wavelet transform analysis of ab initio molecular dynamics simulation: Application to core-excitation dynamics of BF3JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2007Takao Otsuka Abstract We propose a novel analysis method of ab initio molecular dynamics (AIMD) simulation using a continuous wavelet transform (c-WT) technique. The c-WT technique, one of the time-frequency signal analysis methods, provides a clear view of the dynamical information in time developments. Combined with the auto-correlation function of velocity by AIMD simulation, c-WT analysis enables us to well understand dynamical distribution, such as the vibrational properties following a change of electronic structure in a molecular system. As a practical application, AIMD simulation of core-excited BF3 (B1s , 2a) is illustrated. AIMD simulation leads to the change of vibrational motion as well as structural deformation by core-excitation. The c-WT analysis clarifies the relationship between structural deformation and the related significant vibrational modes in core-excitation within 50 fs. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] XRD studies, vibrational spectra, and molecular structure of 1H-imidazo [4,5-b]pyridine based on DFT quantum chemical calculationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2010L. Dymi Abstract The molecular structures and vibrational properties of 1H -imidazo[4,5-b]pyridine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the X-ray diffraction (XRD), infrared (IR), and Raman studies. The theoretical data are discussed on the basis of density functional theory (DFT) quantum chemical calculations using Lee,Yang,Parr correlation functional (B3LYP) and 6-31G(d,p) basis. This compound crystallizes in orthorhombic structure, space group Pna21(C2v9) and Z = 4. The planar conformation of the skeleton and presence of the NH···N hydrogen bond was found to be characteristic for the studied system. The temperature dependence of IR and Raman modes was studied in the range 4,294 K and 8,295 K, respectively. The normal modes, which are unique for the imidazopyridine derivatives are identified. Copyright © 2009 John Wiley & Sons, Ltd. [source] Vibrational and optical properties of a one-dimensional organic,inorganic crystal [C6H14N]PbI3JOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2008S. Elleuch Abstract Self-assembled organic,inorganic [C6H14N]PbI3 crystals were synthesized. The crystal structure consists of one-dimensional semiconductor chains formed by infinite PbI6 face-sharing octahedra aligned along the a -axis. The organic cations are linked to the inorganic chains by NH· · ·I hydrogen bonds and act as insulator barriers. The vibrational properties of [C6H14N]PbI3 were studied using polarized Raman scattering and infrared (IR) absorption. The observed Raman and IR spectral features were identified by comparison with the vibrational properties of homologous compounds and with the vibrational wavenumbers calculated using the ab initio PM3 method. Moreover, the photoluminescence and diffuse reflectance of [C6H14N]PbI3 single crystals, along with the UV-Vis absorption of spin- coated films, were measured. A strong green-blue luminescence due to radiative recombinations of 1D excitons is observed. The Stokes shift is estimated at 70 meV. Copyright © 2008 John Wiley & Sons, Ltd. [source] Pressure- and temperature-dependent Raman studies of KNbW2O9 hexagonal tungsten bronzeJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2003czka Abstract Pressure- and temperature-dependent Raman studies were performed on KNbW2O9 ferroelectric hexagonal tungsten bronze single crystal. The results suggest that some structural changes, possibly phase transitions, connected with tilting of the WO6 octahedra occur in this material at around 290,350 K and 1.0,1.4 GPa. No changes in the spectra could be observed at the 523 and 543,553 K phase transitions. The data indicate that these phase transitions lead to only weak changes in the vibrational properties of KNbW2O9, which were not observed owing to the large bandwidth of the Raman bands. The Raman studies suggest, therefore, that the structure of the unknown phase, existing below 553 K, differs slightly form the orthorhombic structure present above 553 K. The pressure-dependent study revealed that the 52 cm,1 band, assigned to external vibrations of the WO6 octahedron, consists at ambient temperature and pressure of two overlapping bands. These bands become well separated at high pressure. Copyright © 2003 John Wiley & Sons, Ltd. [source] Isotope and disorder effects in the Raman spectra of LiHxD1,x crystalsJOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2001V. G. Plekhanov Most of the physical properties of a solid depend on its isotopic composition in some way or another. Scientific interest, technological promise and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled crystals. A great number of stable isotopes and well-developed methods for their separation have made it possible to grow crystals of C, LiH, ZnO, ZnSe, CuCl, GaN, GaAs, CdS, Cu2O, Si, Ge and ,-Sn with a controllable isotopic composition. Among these compounds, LiH possesses the largest value of the isotope effect. The great number of theoretical and experimental data suggest that the isotopic composition of a crystal lattice exerts some influence on the vibrational properties of crystals. These effects are fairly large and can be readily measured by modern experimental techniques (ultrasound, Brillouin and Raman scattering and neutron scattering). In addition, crystals of different isotopic compositions possess different Debye temperatures. This difference between an LiH crystal and its deuterated analogue exceeds a 100 K. Very pronounced and general effects of isotopic substitution are observed in phonon spectra. The scattering lines in isotopically mixed crystals are not only shifted (the shift of LO lines exceeds 100 cm,1) but are also broadened. This broadening is related to the isotopic disorder of the crystal lattice. It is shown that the degree of a change in the scattering potential is different for different isotopic mixed crystals. In the case of germanium and diamond crystals, phonon scattering is weak, which allows one to apply successfully the coherent potential approximation (CPA) for describing the shift and broadening of scattering lines. In the case of lithium hydride, the change in the scattering potential is so strong that it results in phonon localization, which is directly observed in experiments. The common nature of the isotopic and disorder effects in a wide range of crystals is emphasized. Copyright © 2001 John Wiley & Sons, Ltd. [source] Depth profiling of optical and vibrational properties in GaN/AlN quantum dot superlatticesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009A. Cros Abstract Spatially resolved confocal ,-Raman and ,-photoluminescence experiments were performed to analyze the vibrational and optical properties of GaN/AlN quantum dots as a function of depth. Two approaches have been followed. First, spectra were taken by defocusing the microscope objective at various depths on the sample surface. In a second set of experiments a bevel at an angle of 20° with respect to the surface normal was prepared by mechanical polishing of the surface, and spectra were taken across the bevel. The E2h vibrational modes ascribed to the GaN QDs and the AlN spacer redshift towards the surface, indicating the progressive relaxation of the QDs and a considerable increase of the tensile strain in the AlN spacer. The photoluminescence is found to blueshift and narrow towards the surface. This behaviour is ascribed to the decrease of the QD internal electric field as a consequence of the relaxation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical study of the electronic structure and the totally symmetric vibrations of selected CoMoCat carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008Kürti Abstract In situ Raman spectroelectrochemical studies of CoMo-Cat single-walled carbon nanotubes enriched in (6,5) tubes have been carried out recently. We performed calculations on the density functional level using local density approximation for the electronic and vibrational properties of the most abundant tubes in these samples. The following chiral semiconducting tubes were investigated: (6,4), (7,3), (6,5), (9,1), (8,3) and (7,5). The calculated and the measured frequencies of the RBM and G, modes agree within several wave numbers. The calculated E11, E22 transition energies -after 30% and 20% upscaling, respectively- are comparable with the experimental values. The quenching of the RBM band with p- and n-doping can be interpreted within the rigid band approximation. The validity of the rigid band approximation was shown by calculating the density of states for neutral and charged tubes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibrational properties of four consecutive carbon picotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008Nils Rosenkranz Abstract Four different picotubes have been synthesized up to now. These highly symmetric, ringlike hydrocarbons are closely related to the smallest armchair nanotubes available. We investigate vibrational properties of the different picotubes using first principles calculations and polarization-dependent Raman spectroscopy. Our results emphasize the strong relationship between picotubes and nanotubes. In this context, two features in the picotube spectra are of particular interest: The high-energy bands and breathing-like modes. Vibrational patterns calculated for the high-energy modes of picotubes are similar to the axial and transversal high-energy vibrations of armchair nanotubes. Concerning the radial breathing modes of picotubes, our calculations suggest a d,1 -dependence of the radial breathing mode (RBM) frequency, which is again in analogy to nanotubes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The effects of inhomogeneous isotope distribution on the vibrational properties of isotope enriched double walled carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007V. Zólyomi Abstract The radial breathing mode in the Raman spectrum of 13C isotope enriched single walled carbon nanotubes is inhomogeneously broadened due to the random distribution of isotopes. We study this effect theoretically using density functional theory within the local density approximation and compare the result with experiments on isotope engineered double walled carbon nanotubes in which the inner tubes were grown from a mixture of 13C enriched fullerenes and natural fullerenes. As explained by the calculations, this synthesis procedure leads to an increased inhomogeneity compared to a case when only enriched fullerenes are used. The good agreement between the measurements and calculations shows the absence of carbon diffusion along the tube axis during inner tube growth, and presents a strong support of the theory that inner tube growth is governed by Stone,Wales transformations following the interconnection of fullerenes. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Compositional dependence of optical and vibrational properties of strontium barium niobate (SrxBa1,xNb2O6)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007C. David Abstract The index of refraction, the optical band edge and the Raman scattering of strontium barium niobate, SrxBa1,xNb2O6 with 0.38 < x < 0.77 have been studied. The ordinary refractive index does not depend on x, while the extra-ordinary one increases with increasing x. The band edge is almost unaffected by the Ba- or Sr-content and shows a weak band bowing. Both the index of refraction and the band edge may be used for an optical determination of the composition of the crystal. Raman spectra show the typical behavior of tungsten bronze type crystals with broad bands and complicated spectral shapes. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibrational properties of single walled carbon nanotubes under pressure from Raman scattering experiments and molecular dynamics simulationsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007In-Hwan Choi Abstract We have investigated theoretically and experimentally the pressure dependent structural and vibrational properties of single-walled carbon nanotubes (SWNT). Bundles of SWNTs are studied inside a diamond anvil high pressure cell with micro-Raman scattering. The tube diameter and size distribution are determined from the radial breathing modes (RBM) of the tubes. The pressure coefficient and linewidth of one of the high frequency C,C bond stretching modes was found to change suddenly at ,3 GPa which is well below the structural transformation pressure (Pc) for the tubes in our sample. Molecular dynamics simulations were used to calculate the vibrational density of states of SWNTs as a function of pressure. Our simulations suggest that the experimental results can be explained by a softening of a low-frequency optical mode of the SWNTs , the "squashing" mode , and the dynamical effect of this softening on other phonon modes. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Lattice dynamics of CuAlO2 under high pressure from ab initio calculationsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007P. Rodríguez-Hernández Abstract The density functional perturbation theory is employed to study the vibrational properties of CuAlO2 under pressure. The calculations are preformed using the pseudopotential wave method and the local density approximation for the exchange-correlation (XC) potential. The d electrons of Cu are treated as valence states. We present the phonon dispersion curves. Our results are in good agreement with the available experimental Raman scattering experiments. Ab initio calculations show the presence of a dynamical instability, possibly related with the experimentally observed phase transition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Raman and transmission electron microscopy characterization of InN samples grown on GaN/Al2O3 by molecular beam epitaxyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006J. Arvanitidis Abstract Raman spectroscopy and transmission electron microscopy were employed to study the vibrational properties and the microstructure of epitaxially grown InN films on GaN/Al2O3 templates. The variations of the InN lattice constants, as deduced by electron diffraction analysis, along with the red-shifted E22 mode frequency reveal that InN films exhibit residual tensile stress, strongly dependent on the epilayer growth temperature. Threading dislocations are the dominant structural defects in the films, having a density in the order of 109,1010 cm,2. Profile analysis of the E22 Raman peak by means of the Spatial Correlation Model provides useful information concerning the effective mean length for free phonon propagation (L), which is a measure of the structural quality of the samples. In all the studied samples, L monotonically increases with decreasing threading dislocation density of pure screw and mixed type character. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a -plane GaNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006V. Darakchieva Abstract Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a -plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A1(TO) mode. These results are compared with previous theoretical and experimental findings and discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescence and vibrational properties of erbium-implanted nanoporous GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008C. B. Soh Abstract Implantation of erbium (Er) into GaN is useful in creating selected areas to emit at the green, yellow and infrared wavelengths. Enhanced erbium activation is obtained when erbium is implanted into porous GaN formed by electrochemical etching than into as-grown GaN. This is due to the increase in surface areas for light extraction and the availability of more free surfaces to accommodate strain when it is annealed. Furnace annealing at 1100 °C for 30 mins in nitrogen gives rise to higher band-edge photoluminescence intensity. Apart from the host GaN phonon modes, we have also observed disorder-induced lattice vibrations at 170, 200 and 350-365 cm,1 from Er-implanted porous GaN. The E2 (high) mode of GaN also shifts towards higher energy at higher annealing temperatures, indicative of more erbium occupying the VGa site (ionic radii of Er > Ga) and hence increasing the compressive stress in the GaN crystal lattice. The prominent defect-induced local vibrational modes in Er-doped nanoporous GaN are also observed in ultraviolet resonant Raman scattering. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Comparative Study of the Structural, Electronic, and Vibrational Properties of NH3BH3 and LiNH2BH3: Theory and ExperimentCHEMPHYSCHEM, Issue 11 2009Seung Mi Lee Dr. Abstract Herein, we systematically investigate the structural, electronic, and vibrational properties of ammonia borane (NH3BH3, AB) and lithium amidoborane (LiNH2BH3, LAB) through both density functional calculations and experiments. AB and LAB samples are generated and their vibrational spectra are obtained by using Fourier transformed infrared spectroscopy (FTIR). The measured vibrational spectra are in good agreement with the calculated ones. Our calculations show that the Li-related vibration modes are primarily found in the low-frequency region (<1000 cm,1), and that the intermolecular interactions significantly influence the vibrational spectra. Electronic structure calculations provide insights into the differences between the binding natures of AB and LAB and their influence on the vibrational properties of these compounds. [source] Observation and characterization of a specific vibrational circular dichroism band in phenyl glycosides,CHIRALITY, Issue 3-4 2008Tohru Taniguchi Abstract Application of vibrational circular dichroism (VCD) spectroscopy to structural analysis of carbohydrates has recently progressed. However, few studies on glycoconjugates VCD have thus far been reported, despite the fact that naturally occurring carbohydrates exist as various glycoconjugates. To further explore the application of the VCD technique, we have measured a series of aromatic glycosides and found that axial aromatic glycosides exhibited a negative band at around 1230 cm,1 while equatorial ones showed flat features in this region. This is the first structure,spectra relationship on glycoconjugate VCD that distinguishes the stereochemistry of the sugar anomers. Several model compounds were prepared and their vibrational properties calculated by using the density functional theory (DFT) method, which assigned the vibrational mode of this band based on the stretching motion of the glycosidic oxygen and aromatic carbon. This concept that aglycan parts can reflect stereochemical information of sugar moieties may encourage further VCD studies on glycoconjugates to realize practical structural analysis of carbohydrates. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] |