Micro‐Raman investigation of tin dioxide nanostructured material based on annealing effect

Rutile‐structured nanocrystalline tin dioxide (SnO₂) powder was synthesized by the chemical precipitation method using the precursor SnCl₂• 5H₂O. The SnO₂ powder was annealed at different temperatures, namely, 600, 800 and 1000 °C. Micro‐Raman spectra were recorded for both the as‐grown and annealed SnO₂ nanocrystalline samples. Micro‐Raman spectral measurements on the SnO₂ nanoparticle show the first‐order Raman modes A_1g (633 cm⁻¹), E_1g (475 cm⁻¹) and B_2g (775 cm⁻¹), indicating that the grown SnO₂ belongs to the rutile structure. The first‐order A_1g mode is observed as an intense band, whereas the other two modes show low intensity. The full width at half‐maximum and band area of the Raman lines of SnO₂ nanoparticle annealed at various temperatures were calculated. The effect of high‐temperature annealing on the vibrational modes of SnO₂ was studied. The optical image of SnO₂ nanocrystalline material was used to understand the surface morphology effect. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman spectroscopy of 4‐tert‐butylpyridine on a silver electrode

We report the observation of large surface‐enhanced Raman scattering (SERS) (10⁶) for 4‐tert‐butylpyridine molecules adsorbed on a silver electrode surface in an electrochemical cell with electrode potential set at − 0.5 V. A decrease in electrode potential to − 0.3 V was accompanied by a decrease in relative intensities of the vibrational modes. However, there were no changes in vibrational wavenumbers. Comparison of both normal solution Raman and SERS spectra shows very large enhancement of the intensities of a₁, a₂, and b₂ modes at laser excitation of 488 nm. Enhancement of the non‐totally symmetric modes indicates the presence of charge transfer as a contributor to the enhancement. Copyright © 2011 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and DFT calculations of di‐amino acid peptides: α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu in the solid state

Experimental vibrational spectroscopic studies and density functional theory (DFT) calculations of the di‐amino acid peptide derivatives α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu have been undertaken. Raman and infrared spectra have been recorded for samples in the solid state. DFT simulations were conducted using the B3‐LYP correlation functional and the cc‐pVDZ basis set to determine energy minimized/geometry optimized structures (based on a single isolated molecule in the gaseous state). Normal coordinate calculations have provided vibrational assignments for fundamental modes, including their potential energy distributions. Significant differences are observed between α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu both in the computed structures and in the vibrational spectra. The combination of experimental and calculated spectra provide an insight into the structural and vibrational spectroscopic properties of di‐amino acid peptide derivatives. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopy and characterisation of α‐gallium oxyhydroxide and β‐gallium oxide nanorods

Raman spectroscopy complemented by infrared spectroscopy was used to characterise both gallium oxyhydroxide (α‐GaO(OH)) and gallium oxide (β‐Ga₂O₃) nanorods synthesised with and without the surfactants using a soft chemical methodology at low temperatures. Nano‐ to micro‐sized gallium oxyhydroxide and gallium oxide materials were characterised and analysed by both X‐ray diffraction and Raman spectroscopy. Rod‐like GaO(OH) crystals with average length of ∼2.5 µm and width of 1.5 µm were obtained. Upon thermally treating gallium oxyhydroxide GaO(OH) to 900 °C, β‐Ga₂O₃ was synthesised retaining the initial GaO(OH) morphology. Raman spectroscopy has been used to study the structure of nanorods of GaO(OH) and Ga₂O₃ crystals. Raman spectroscopy shows bands characteristic of GaO(OH) at 950 and ∼1000 cm⁻¹ attributed to Ga OH deformation modes. Bands at 261, 275, 433 and 522 cm⁻¹ are assigned to vibrational modes involving Ga OH units. Bands observed at 320, 346, 418 and 472 cm⁻¹ are assigned to the deformation modes of Ga₂O₆ octahedra. Two sharp infrared bands at 2948 and 2916 cm⁻¹ are attributed to the GaO(OH) symmetric stretching vibrations. Raman spectroscopy of Ga₂O₃ provides bands at 630, 656 and 767 cm⁻¹ which are assigned to the bending and stretching of GaO₄ units. Raman bands at 417 and 475 cm⁻¹ are attributed to the symmetric stretching modes of GaO₂ units. The Raman bands at 319 and 347 cm⁻¹ are assigned to the bending modes of GaO₂ units. Copyright © 2008 John Wiley & Sons, Ltd.     

Ultraviolet resonance Raman spectroscopy of a β‐sheet peptide: a model for membrane protein folding

The partitioning of a hydrophobic hexapeptide, N‐acetyl‐tryptophan‐pentaleucine (AcWL5), into self‐associated β‐sheets within a vesicle membrane was studied as a model for integral membrane protein folding and insertion via vibrational and electronic spectroscopy. Ultraviolet resonance Raman spectroscopy allows selective examination of the structures of amino acid side chains and the peptide backbone and provides information about local environment and molecular conformation. The secondary structure of AcWL5 within a vesicle membrane was investigated using 207.5‐nm excitation and found to consist of β‐sheets, in agreement with previous studies. The β‐sheet peptide shows enhanced Raman scattering cross‐sections for all amide modes as well as extensive hydrogen‐bonding networks. Tryptophan vibrational structure was probed using 230‐nm excitation. Increases in Raman cross‐sections of tryptophan modes W1, W3, W7, W10, W16, W17, and W18 of membrane‐incorporated AcWL5 are primarily attributed to greater resonance enhancement with the B_b electronic transition. The W17 mode, however, undergoes a much greater enhancement than is expected for a simple resonance effect, and this observation is discussed in terms of hydrogen bonding of the indole ring in a hydrophobic environment. The observed tryptophan mode frequencies and intensities overall support a hydrophobic environment for the indole ring within a vesicle, and these results have implications for the location of tryptophan in membrane protein systems. Copyright © 2009 John Wiley & Sons, Ltd.     

MgB2 and AlB2 at high pressures

We have studied the effect of pressure on vibrational and electronic properties of MgB₂ and AlB₂ by ab initio calculations and Raman spectroscopy. The comparison between the calculations and the Raman data puts the common assignment of a broad spectral feature near 600 cm^?1 in MgB₂ to the E _2g phonon into question. At variance with MgB₂ the Raman spectra of AlB₂ exhibit a well-defined E _2g mode indicating that the anomalous Raman spectrum encountered in MgB₂ is not related to the metallicity of the samples nor is it intrinsic to crystals of the AlB₂ structure type. A theoretical estimate of the pressure dependence of T _c in MgB₂ shows that the experimentally observed decrease of T _c under pressure is predominantly due to phonon frequency shifts.     

Raman studies and optical properties of some (PbO)x(Bi2O3)0.2(B2O3)0.8−x glasses

Five (PbO)_x(Bi₂O₃)_0.2(B₂O₃)_0.8−x glasses, where x = 0, 0.2, 0.3, 0.4 and 0.6, were prepared. The dilatometric glass transition temperature (T_g) was found in the region 470 (x = 0)≥ T_g ( °C) ≥ 347 (x = 0.6), and the density (ρ) varied within 4.57 (x = 0) ≤ ρ (g/cm³) ≤ 8.31 (x = 0.6). Raman spectra indicated the conversion of BO₃ to BO₄ entities for low x values but for x > 0.3, namely, for x → 0.6, back‐conversion occurred, most probably. From the measurements of the optical transmission on very thin bulk samples, the room temperature optical gap values (E_g) were determined to be in the range 4.03 (x = 0)≥ E_g (eV) ≥ 3.08 (x = 0.6). The temperature (T) dependence of the optical gap (E_g(T)) in the region 300 ≤ T(K) ≤ 600 was examined and approximated by a linear relationship of the form of E_g(T) = E_g(0)− γT, where γ × 10⁻⁴(eV/K) varied from 5.1 to 6.8. The non‐linear refractive index (n₂) was estimated from the optical gap values and it was found to correspond to the n₂ values calculated from the experimental third‐order non‐linear optical susceptibility taken from the literature. Copyright © 2008 John Wiley & Sons, Ltd.     

Micro‐Raman study of exfoliated Bi2Sr2CaCu2O8+δ single crystals with different thicknesses

Exfoliated Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) single crystals were prepared by micromechanical cleavage of bulk Bi‐2212 single crystals on SiO₂/Si substrates. Room temperature micro‐Raman spectra were collected using a 532‐nm laser source. The evolutions of the spectra of A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) Raman modes with different thicknesses of the samples were studied. The refractive index of Bi‐2212 single crystal was obtained by studying the intensity evolutions based on the interference effect. The observed wavenumber shifts of the A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental and theoretical FT‐IR and FT‐Raman spectroscopic analysis of N1‐methyl‐2‐chloroaniline

In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C₇H₈NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. ¹³C and ¹H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 John Wiley & Sons, Ltd.     

Absorption and resonance Raman spectroscopy of the 1Bu state of trans‐1,3,5‐hexatriene including vibronic coupling

The vibronic coupling between the first excited S₁ (2¹A_g) and the second excited S₂ (1¹B_u) singlet electronic states in spectroscopy of trans‐1,3,5‐hexatriene molecule is investigated on the basis of a model consisting of two electronic states coupled by two vibrational modes. Employing a perturbation theory that treats the intramolecular couplings in a perturbative manner, the absorption and resonance Raman cross sections and excitation profiles of this molecule are calculated using the time‐correlation function formalism. The non‐Condon corrections are included in evaluation of cross sections. The multidimensional time‐domain integrals that arise in these calculations have been evaluated for the case in which S₀ (1¹A_g) S₂ (1¹B_u) electronic transition takes place between displaced and distorted harmonic potential energy surfaces. The calculated spectra are in good agreement with the experimental ones. Copyright © 2011 John Wiley & Sons, Ltd.     

Detailed analysis of the charge transfer complex N,N‐dimethylaniline–SO2 by Raman spectroscopy and density functional theory calculations

Although the amine sulfur dioxide chemistry was well characterized in the past both experimentally and theoretically, no systematic Raman spectroscopic study describes the interaction between N,N‐dimethylaniline (DMA) and sulfur dioxide (SO₂). The formation of a deep red oil by the reaction of SO₂ with DMA is an evidence of the charge transfer (CT) nature of the DMA–SO₂ interaction. The DMA–SO₂ normal Raman spectrum shows the appearance of two intense bands at 1110 and 1151 cm⁻¹, which are enhanced when resonance is approached. These bands are assigned to ν_s(SO₂) and ν(ϕ N) vibrational modes, respectively, confirming the interaction between SO₂ and the amine via the nitrogen atom. The dimethyl group steric effect favors the interaction of SO₂ with the ring π electrons, which gives rise to a π–π* low‐energy CT electronic transition, as confirmed by time‐dependent density functional theory (TDDFT) calculations. In addition, the calculated Raman DMA–SO₂ spectrum at the B3LYP/6‐311 + + g(3df,3pd) level shows good agreement with the experimental results (vibrational wavenumbers and relative intensities), allowing a complete assignment of the vibrational modes. A better understanding of the intermolecular interactions in this model system can be extremely useful in designing new materials to absorb, detect, or even quantify SO₂. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman tensor elements for multiferroic BiFeO3 with rhombohedral R3c symmetry

A quantitative assessment of the Raman spectrum emitted from a coarse‐grained polycrystal of multiferroic BiFeO₃ has been carried out by means of a polarized Raman microprobe. The dependence of the intensity of Raman phonon modes has been first theoretically modeled as a function of crystal rotation. Then, the Raman tensor elements have been experimentally determined from the analysis of the A_g and E_g vibrational modes. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman polarization analysis of highly crystalline polyethylene fiber

The complex orientation dependence in space of Raman active vibrations in the orthorhombic structure of polyethylene (PE) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. Building upon the symmetry assignment of these vibrational modes, we systematically studied, from both theoretical and experimental viewpoints, the changes of polarized intensity for the A_g and the B_2g + B_3g vibrational modes with respect to PE molecular orientation. After explicitly expanding the Raman selection rules associated with the A_g and the B_2g + B_3g modes, introducing them into general expressions of the orientation distribution function, and validating them by means of a least‐square fitting procedure on experimental data, we compare here two mesostructural models for a highly crystallized and self‐aligned PE fiber structure. Stereological arguments are shown concerning the arrangement of orthorhombic fibrils in such a sample that unfold the correct values of five independent Raman tensor elements for orthorhombic PE. Copyright © 2010 John Wiley & Sons, Ltd.     

Organic cyclic difluoramino‐nitramines: infrared and Raman spectroscopy of 3,3,7,7‐tetrakis(difluoramino)octahydro 1,5‐dinitro‐1,5‐diazocine (HNFX)

We present the first vibrational structure investigation of 3,3,7,7‐tetrakis(difluoramino)octahydro‐1,5‐dinitro‐ 1,5‐diazocine (HNFX)—and, more generally, of a member of the new class of gem‐bis(difluoramino)‐substituted heterocyclic nitramine energetic materials—using combined theoretical and experimental approaches. Optimized molecular structure and vibrational spectra of the Ci… symmetry conformer constituting the HNFX crystal were computed using density functional theory methods. Fourier transform infrared and Raman spectra of HNFX crystalline samples were also collected at ambient temperature and pressure. The average deviation of calculated structural parameters from X‐ray diffraction data is ∼1% at the B3LYP/6‐311 + + G(d,p) level of theory, suggesting the absence of significant molecular distortion induced by the crystal field. Very good agreement was found between simulated and measured spectra, allowing reliable assignment of the fundamental normal modes of vibration of the HNFX crystal. Detailed analysis of the normal modes of the C–(NF₂)₂ and N–NO₂ moieties was performed due to their critical importance in the initial steps of the molecular homolytic fragmentation process. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman tensor analysis of hexagonal polyoxymethylene and its application to study the molecular arrangement in highly crystalline electrospun nanofibers

The orientation dependence in space of Raman‐active vibrations in the hexagonal structure of polyoxymethylene (POM) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. The variation of polarized intensity for the A₁ and the E₁ vibrational modes with respect to the POM molecular orientation is systematically studied, from both theoretical and experimental viewpoints, according to the symmetry assignments of each vibrational mode. A set of working equations including the Raman selection rules associated with the A₁ and the E₁ modes and the orientation distribution function are explicitly formulated and validated by means of a least‐square fitting procedure on experimental data. In addition, an approach based on the introduction of orientation distribution functions is applied to quantitatively assess and compare on a statistical base the molecular orientation of two different types of electrospun POM nanofibers. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman Spectroscopic Study of the Molybdate Mineral Szenicsite and Comparison with Other Paragenetically Related Molybdate Minerals

Abstract

The molybdate‐bearing mineral szenicsite, Cu₃(MoO₄)(OH)₄, has been studied by Raman and infrared spectroscopy. A comparison of the Raman spectra is made with those of the closely related molybdate‐bearing minerals, wulfenite, powellite, lindgrenite, and iriginite, which show common paragenesis. The Raman spectrum of szenicsite displays an intense, sharp band at 898 cm^?1, attributed to the ν₁ symmetric stretching vibration of the MoO₄ units. The position of this particular band may be compared with the values of 871 cm^?1 for wulfenite and scheelite and 879 cm^?1 for powellite. Two Raman bands are observed at 827 and 801 cm^?1 for szenicsite, which are assigned to the ν₃(E _g ) vibrational mode of the molybdate anion. The two MO₄ ν₂ modes are observed at 349 (B _g ) and 308 cm^?1 (A _g ). The Raman band at 408 cm^?1 for szenicsite is assigned to the ν₄(E _g ) band. The Raman spectra are assigned according to a factor group analysis and are related to the structure of the minerals. The various minerals mentioned have characteristically different Raman spectra.     

Improper hydrogen bonding and motional narrowing in binary mixtures of 2‐ and 3‐bromopyridine in methanol probed by polarized Raman study and DFT calculations

A concentration‐dependent Raman study of the ν(C Br) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH₃OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm⁻¹in the case of 2Br‐p and at ∼618 cm⁻¹ in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(C Br) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd.     

The vibrational spectra of the cyanide ligand revisited: the ν(CN) infrared and Raman spectroscopy of Prussian blue and its analogues

A careful analysis of the Raman spectra of the M′_x[M(CN)₆]_y Prussian blue species has enabled a general model for the interpretation of the ν(CN) vibrational spectra. The spectral patterns are derived from those of the metal ions with local O_h symmetry. Two limiting models are discussed. A ‘localized mode’ model, involving matrix‐isolated species, is in much better accord with the observations than a ‘factor group’ model. The use of the infrared feature as fingerprint of specific M CN M′ units arises from the axis‐specific nature of individual T_1u modes. The interpretation of the A_1g and E_g Raman features is done in terms of localized vibrations, with involvement of additional energy terms from the lattice motions. Copyright © 2011 John Wiley & Sons, Ltd.     

Solvent‐dependent structural dynamics of 2(1H)‐pyridinone in light absorbing S4(ππ*) state

The B‐band resonance Raman spectra of 2(1H)‐pyridinone (NHP) in water and acetonitrile were obtained, and their intensity patterns were found to be significantly different. To explore the underlying excited state tautomeric reaction mechanisms of NHP in water and acetonitrile, the vibrational analysis was carried out for NHP, 2(1D)‐pyridinone (NDP), NHP–(H₂O)_n (n = 1, 2) clusters, and NDP–(D₂O)_n (n = 1, 2) clusters on the basis of the FT‐Raman experiments, the B3LYP/6‐311++G(d,p) computations using PCM solvent model, and the normal mode analysis. Good agreements between experimental and theoretically predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands in both the FT‐Raman and the resonance Raman spectra. The results indicated that most of the B‐band resonance Raman spectra in H₂O was assignable to the fundamental, overtones, and combination bands of about ten vibration modes of ring‐type NHP–(H₂O)₂ cluster, while most of the B‐band resonance Raman spectra in CH₃CN was assigned to the fundamental, overtones, and combination bands of about eight vibration modes of linear‐type NHP–CH₃CN. The solvent effect of the excited state enol‐keto tautomeric reaction mechanisms was explored on the basis of the significant difference in the short‐time structural dynamics of NHP in H₂O and CH₃CN. The inter‐molecular and intra‐molecular ESPT reaction mechanisms were proposed respectively to explain the Franck–Condon region structural dynamics of NHP in H₂O and CH₃CN.Copyright © 2015 John Wiley & Sons, Ltd.     

A Combined Experimental and Theoretical Study on the Formation of Ag Filaments on β‐Ag2MoO4 Induced by Electron Irradiation

A combined experimental and theoretical study is presented to understand the novel observed nucleation and early evolution of Ag filaments on β‐Ag₂MoO₄ crystals, driven by an accelerated electron beam from an electronic microscope under high vacuum. The growth process, chemical composition, and the element distribution in these filaments are analyzed in depth at the nanoscale level using field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) with energy‐dispersive spectroscopy (EDS) characterization. To complement experimental results, chemical stability, structural and electronic aspects have been studied systematically using first‐principles electronic structure theory within a quantum theory of atoms in molecules (QTAIM) framework. The Ag nucleation and formation on β‐Ag₂MoO₄ are a result of structural and electronic changes of the AgO₄ tetrahedral cluster as a constituent building block of β‐Ag₂MoO₄, consistent with Ag metallic formation. The formation of Ag filament transforms the β‐Ag₂MoO₄ semiconductor from n‐ to p‐type concomitant with the appearance of Ag defects.