Raman Intensities (raman + intensity)

Distribution by Scientific Domains


Selected Abstracts


Monitoring oxidation of multiwalled carbon nanotubes by Raman spectroscopy

JOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2007
Sebastian Osswald
Abstract Multiwalled carbon nanotubes (MWCNTs) were oxidized in air and acids while varying the treatment time and/or temperature. The goal of this approach was to create the highest density of carboxyl groups with moderate sample loss, which is necessary for nanocomposite applications. In situ Raman experiments allowed real-time observation of the structural changes in MWCNTs upon oxidation. The ratio of the Raman intensities of the D and G bands was used to estimate the concentration of defects. It was found that while an oxidation for 6 h in H2SO4/HNO3 provided the strongest effect, a ,flash oxidation' in air (15 min at 550 °C) also leads to an efficient functionalization in a cost-effective and environmentally friendly way. Transmission electron microscopy, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis and electrophoretic mobility analysis were used to study the oxidized nanotubes. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Vibrational spectroscopic studies, conformations and quantum chemical calculations of 3,3,3-trifluoropropyl- silane and 3,3,3-trifluoropropylsilane- d3,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 1-3 2006
Peter Klaeboe
Abstract Infrared spectra of 3,3,3-trifluoropropylsilane (CF3CH2CH2SiH3) and 3,3,3-trifluoropropylsilane- d3 (CF3 CH2CH2SiD3) were obtained in the vapour, liquid, and crystalline solid phases in the range 4000,50 cm,1. Additional spectra in argon matrices at 5 K were recorded before and after annealing to temperatures 20,34 K. Raman spectra of the compounds as liquids were recorded at various temperatures between 296 and 183 K and spectra of the amorphous and crystalline solids were obtained. The spectra revealed the existence of two conformers (anti and gauche) in the fluid phases and in the matrices. When the two vapours were shock-frozen on a cold finger at 78 K, they turned partly crystalline immediately. After subsequent annealing to 140,150 K, ca 7,9 Raman bands of both molecules present in the liquids vanished in the crystal. Similar variations in intensity were observed in the corresponding infrared spectra before and after annealing. The spectra revealed the existence of one conformer (anti) in the crystal. From Raman intensity variations of three independent pairs of anti and gauche bands between 298 and 173 K for the parent compound, and 298 and 183 K for the deuterated analogue, the values ,confHo(gauche,anti) = 4.1 ± 0.3 kJ mol,1 for the parent compound and the same value for the deuterated species were obtained in the liquid state. Annealing experiments in the matrices show that the gauche bands vanish after annealing, demonstrating that the anti conformer also has the lower energy here and that the barrier to gauche , anti inter-conversion is around 5,6 kJ mol,1. The spectra of both conformers have been interpreted in detail. Ab initio and DFT calculations at the HF/6,311G**, B3LYP/6,311 G** and MP2/6,311 G** levels gave optimized geometries, infrared and Raman intensities and vibrational wavenumbers for the anti and gauche conformers. The conformational enthalpy difference derived from the calculations was between 6.0 and 4.1 kJ mol,1 with anti being the low energy conformer. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Indole ring orientations of Trp189 in the ground and M intermediate states of bacteriorhodopsin as studied by polarized UV resonance Raman spectroscopy,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 1-3 2006
Kazuhiro Asakawa
Abstract Polarized resonance Raman spectroscopy provides a means for orientation analysis of proteins in aligned samples. Previously, we developed a Raman linear intensity difference (RLID) method to determine the orientations of aromatic amino acid side chains in flow-oriented or membrane-bound proteins. In this study, we have applied the RLID method to Trp189 in bacteriorhodopsin (BR), a transmembrane protein that acts as a light-driven proton pump. Among the eight Trp residues in BR, the Raman spectrum of Trp189 has been extracted by subtracting the spectrum of the Trp189 , Phe mutant from that of wild-type BR. By examining the 251.3-nm-exited polarized resonance Raman intensities of two indole ring vibrations of Trp189, the directions of the La and Bb transition moments have been determined with respect the membrane normal in the light-adapted ground state (BR568) and a photo-excited intermediate (M). Comparison of the orientations of the Trp189 indole ring derived from the La and Bb inclination angles has shown that the indole ring slightly but significantly reorients toward the ionone ring of the retinal chromophore in the M intermediate. The reorientation of Trp189 is consistent with the previous observation that helix F, on which Trp189 is located, undergoes an outward tilt and the hydrophobic interaction of Trp189 increases in the M intermediate. The RLID method combined with 251.3 nm excitation and point mutation is useful for detecting even a small reorientation of a targeted Trp residue. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Solvent effects on sunscreen active ingredients using Raman spectroscopy

JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2003
L. Beyere
Abstract We present Raman spectra of five sunscreen active ingredients in 10 solvents. Shifts in the UV absorption maxima and the CO Raman mode wavenumber are observed for some of the sunscreens as a function of solvent. Correlations between the observed wavenumber shifts and solvent properties indicate that hydrogen bonding is a key interaction between sunscreen active ingredients and solvent. Interestingly, the relative Raman intensities are also sensitive to the hydrogen-bonding and polarizability properties of the solvent, reflecting differential stabilization of the sunscreen's resonance structures. These results suggest an ,expanded polarizability' view of the solvent's effect on the solute. The observed wavenumber and relative intensity changes were also utilized to identify the active agents present in commercial sunscreen preparations from their in situ Raman spectra. Copyright © 2003 John Wiley & Sons, Ltd. [source]


First and second optical transitions in single-walled carbon nanotubes: a resonant Raman study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007
H. Telg
Abstract Resonant Raman spectroscopy was performed to study electron,phonon coupling in single-walled carbon nanotubes separated in solution. By varying the excitation energy from 1.26 eV to 1.93 eV we obtained radial breathing mode resonance profiles of the first and second optical transitions E11 and E22 of the (9,1) and (8,3) tubes. We observe up to 16 times stronger Raman intensities for the E11 transitions which can mostly be attributed to a two times broader linewidth of the E22 transition. Comparison of the matrix element ratio ,11/,22 to theoretical predictions on the electron,phonon coupling show a deviation of a factor 1.7 which might be associated with the change of the exciton,photon matrix element. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Raman intensities of the first optical transitions in carbon nanotubes

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006
H. Telg
Abstract We performed resonant Raman spectroscopy on the lowest optical transition ES11 of separated single-walled carbon nanotubes by studying the radial-breathing mode (RBM) spectra for excitation energies between 1.15 and 1.48 eV. We were able to extend the experimental Kataura plot to these energies by adding the ES11 transition energies of 11 nanotube chiralities. We discuss also the relative Raman intensities; they are more similar for different family index , than those of the corresponding transitions of the ES22 [1]. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Raman scattering of vanadium ladder compounds from first principles

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
J. Spitaler
Abstract We investigate phonon Raman scattering of the Ag modes in NaV2O5 and CaV2O5. We perform firstprinciples calculations within density functional theory (DFT) to obtain the ground state with relaxed atomic positions. Thereupon we determine eigenvectors and frequencies of the 8 Ag modes within the frozen phonon approach and compute the dielectric functions ,(,) for structures distorted according to the phonon eigenvectors. Raman intensities are obtained using the derivatives of ,(,) with respect to the normal coordinates Q taken at the incident photon energy ,I. For NaV2O5 the peak positions and the relative intensities of the theoretical results for the experimentally used frequency ,I = 2.5 eV excellently agree with measured data. Moreover, for the three different scattering geometries a strong dependency of the Raman intensity on ,I is revealed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Theoretical Simulation of Vibrational Sum-Frequency Generation Spectra from Density Functional Theory: Application to p -Nitrothiophenol and 2,4-Dinitroaniline

CHEMPHYSCHEM, Issue 12 2009
Julien Guthmuller Dr.
Abstract The molecular orientation of adsorbed molecules forming self-assembled monolayers can be determined by combining vibrational sum-frequency generation (SFG) measurements with quantum chemical calculations. Herein, we present a theoretical methodology used to simulate the SFG spectra for different combinations of polarizations. These simulations are based on calculations of the IR vectors and Raman tensors, which are obtained from density functional theory computations. The dependency of the SFG vibrational signature with respect to the molecular orientation is presented for the molecules p -nitrothiophenol and 2,4-dinitroaniline. It is found that a suitable choice of basis set as well as of exchange-correlation (XC) functional is mandatory to correctly simulate the SFG intensities and consequently provide an accurate estimation of the adsorbed molecule orientation. Comparison with experimental data shows that calculations performed at the B3LYP/6-311++G(d,p) level of approximation provide good agreement with experimental frequencies, and with IR and Raman intensities. In particular, it is demonstrated that polarization and diffuse functions are compulsory for reproducing the IR and Raman spectra, and consequently vibrational SFG spectra, of systems such as p -nitrothiophenol. Moreover, the investigated XC functionals reveal their influence on the relative intensities, which show rather systematic variations with the amount of Hartree,Fock exchange. Finally, further aspects of the modeling are revealed by considering the frequency dependence of the Raman tensors. [source]


Applicability of laser-induced Raman microscopy for in situ monitoring of imine formation in a glass microfluidic chip

JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2003
Moonkwon Lee
Abstract Laser-induced Raman microscopy has been used to illustrate its applicability for the in situ monitoring of imine formation reaction in a glass microfluidic chip. In order to monitor the diffusion process in a micro channel, the Raman spectra were measured at various points along the channel with a constant flow rate of 2.7 µl min,1. Time-dependent Raman spectra were also measured without flow in order to monitor the variation of Raman peaks to a complete conversion. The disappearance of the CO stretching peak at 1700 cm,1 of the reactant, benzaldehyde, and the appearance of the Raman peak for the product, an imine, at 1628 cm,1 were successfully monitored. In addition, the intensity increases of three phenyl stretching modes in the 1550,1630 cm,1 region were also observed. The increase in Raman intensity for this vibrational mode is caused by an effective ,-electron conjugation between two phenyl rings through the ,CN,bridging group of the product. Laser-induced Raman microscopy enables us to monitor in situ product formation and to obtain detailed structural information in a glass microfluidic chip. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Drug-induced corneal hydration changes monitored in vivo by non-invasive confocal Raman spectroscopy

JOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2001
Roel J. Erckens
It is well established that the state of corneal hydration plays a crucial role in maintaining optimal vision. Therefore, any knowledge that can be obtained non-invasively about the status of corneal hydration could be of significant clinical value. A novel confocal Raman spectroscopic technique was used to monitor non-invasively drug-induced hydration changes in the rabbit cornea. The spectroscopic technique enables one to monitor the changes in water content of the cornea while the confocal probing reduces interference of signals from adjacent tissues and allows for measurement of corneal hydration at various depths. The corneal hydration is altered by applying a dehydrating agent (Muro 128®) topically on the cornea. To determine the corneal hydration status, the OH/CH ratio between the Raman intensity of the water OH mode at 3390 cm,1 and the protein CH stretching mode at 2945 cm,1 is calculated. In the middle of the corneal stroma after 10 min, Muro 128® -treated corneas show an average decrease of about 30% in the OH/CH ratio (1.27 ± 0.13) compared with the untreated corneas (1.76 ± 0.09). In this in vivo model it is possible to monitor the hydration status of the living cornea using the Raman spectroscopic technique. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison with X-ray Diffraction

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003
Shin-ichi Nakashima
Raman scattering measurements have been made on SiC ceramics prepared from two powdered by sintering at different temperatures. The Raman spectra of starting powders have also been measured. The volume contents of the 4H and 15R polytype phases relative to that of the 6H phase in the ceramics are inferred from the Raman intensity of folded modes of the acoustic branches and compared with those determined from X-ray diffraction (XRD) analysis. A strong correlation is found between the results obtained from the two analyses. The 4H polytype contents estimated by Raman measurement for specimens prepared from one powder show a good agreement with those obtained by the XRD analysis. For the 15R polytype component there is a correlation between the contents inferred by the two techniques when the content is not very small. The results obtained by the two techniques demonstrate that the Raman spectroscopy as well as the XRD analysis is useful to study the natures and preparation conditions of SiC ceramics. [source]


Raman tensor analysis of baddeleyite single-crystal and its application to define crystallographic domains in polycrystalline zirconia

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010
Kyoju Fukatsu
Abstract The angular dependence of polarized Raman intensity for the Ag and Bg modes was investigated and the full set of Raman tensor elements defined for a baddeleyite single-crystal, namely the monoclinic polymorph of zirconia (ZrO2). Based on the quantitative knowledge of the tensor elements, a method has been proposed for the determination of unknown crystallographic textures in monoclinic zirconia. An application of this method is also shown, which consists of a Raman analysis of crystal orientation on the microscopic scale in polycrystalline ZrO2 after its tetragonal-to-monoclinic (t,m) polymorphic transformation (i.e., occurred under an externally applied stress field). This working example not only confirms the well-known phenomenon of stress-induced phase transformation in polycrystalline zirconia, but also proves the existence of textured domain patterns in the monoclinic phase on a scale larger than that of individual grains. This finding might suggest that the structural and functional properties of polycrystalline zirconia after partial phase transformation should be reinterpreted with taking into account a crystallographic reorientation effect. [source]


Raman scattering of vanadium ladder compounds from first principles

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
J. Spitaler
Abstract We investigate phonon Raman scattering of the Ag modes in NaV2O5 and CaV2O5. We perform firstprinciples calculations within density functional theory (DFT) to obtain the ground state with relaxed atomic positions. Thereupon we determine eigenvectors and frequencies of the 8 Ag modes within the frozen phonon approach and compute the dielectric functions ,(,) for structures distorted according to the phonon eigenvectors. Raman intensities are obtained using the derivatives of ,(,) with respect to the normal coordinates Q taken at the incident photon energy ,I. For NaV2O5 the peak positions and the relative intensities of the theoretical results for the experimentally used frequency ,I = 2.5 eV excellently agree with measured data. Moreover, for the three different scattering geometries a strong dependency of the Raman intensity on ,I is revealed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Time-resolved resonance Raman study on ultrafast structural relaxation and vibrational cooling of photodissociated carbonmonoxy myoglobin

BIOPOLYMERS, Issue 4-5 2002
Teizo Kitagawa
Abstract A localized small structural change is converted to a higher order conformational change of protein and extends to a mesoscopic scale to induce a physiological function. To understand such features of protein, ultrafast dynamics of myoglobin (Mb) following photolysis of carbon monoxide were investigated. Recent results are summarized here with a stress on structural and vibrational energy relaxation. The core expansion of heme takes place within 2 ps but the out of plane displacement of the heme iron and the accompanying protein conformational change occur in 10 and 100 s of the picosecond regimes, respectively. Unexpectedly, it was found from UV resonance Raman spectra that Trp7 in the N-terminal region and Tyr151 in the C-terminal region undergo appreciable structural changes upon ligand binding,dissociation while Tyr104, Tyr146, and Trp14 do not. Because of the communication between the movements of these surface residues and the heme iron, the rate of spectral change of the iron-histidine (Fe- His) stretching band after CO photodissociation is influenced by the viscosity of solvent. Temporal changes of the anti-Stokes Raman intensity demonstrated immediate generation of vibrationally excited heme upon photodissociation and its decay with a time constant of 1,2 ps. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 67: 207,213, 2002 [source]