Vibrational spectroscopy study of essential oils from Plectranthus amboinicus Lour. Spreng and Vanillosmopsis arborea Baker

Essential oils are aroma compounds extracted from plants with pharmacology and mecial uses, being also utilized as perfumes, cosmetics and for flavoring foods. In this work, Fourier Transform-Raman and Attenuated Total Reflection-infrared spectra of essential oils from Plectranthus amboinicus Lour. Spreng (Labiateae) and Vanillosmopsis arborea Baker (Asteraceae) were investigated at room temperature. The analysis of the vibrational spectra of the major constituents performed on the basis of density functional theory (DFT) calculations allowed us to assign the normal modes of these essential oils. Our analyses show that vibrational spectra of these essential oils in the spectral region of lower wavenumber (<1500 cm⁻¹) present bands with characteristic profile of their main chemical constituents. Additionally, this study also shows that compounds which participated in an essential oil composition in relatively low percentage can have a significant influence on the Raman and infrared spectra of these essential oils, in particular in the high wavenumber spectral region.     

Vibrational spectroscopy and DFT calculations of 1,3-dibromo-2,4,6-trimethylbenzene: Anharmonicity,coupling and methyl group tunneling

The Raman, IR and INS spectra of 1,3-dibromo-2,4,6-trimethylbenzene (DBMH) were recorded in the 80–3200 cm⁻¹ range. The molecular conformation and vibrational spectra of DBMH were computed at the MPW1PW91/LANL2DZ level. Except for the methyl 2 environment, the agreement between the DFT calculations and the neutron diffraction structure is almost perfect (deviations < 0.01 Å for bond lengths, <0.2° for angles). The frequencies of the internal modes of vibration were calculated with the harmonic and anharmonic approximations; the later method yields results that are in remarkable agreement with the spectroscopic data, resulting in a confident assignment of the vibrational bands. Thus, no scaling is necessary. The coupling, in phase or anti-phase, of the motions of symmetrical CBr and CMe bonds is highlighted. Our DFT calculations suggest that the torsion of methyl groups 4 and 6 is hindered in deep wells, whereas methyl group 2 is a quasi-free rotor. The failure of the calculations to determine the frequencies of the methyl torsional modes is explained as follows: DFT does not consider the methyl spins and assumes localization of the protons, whereas the methyl groups must be treated as quantum rotors.     

Complementary optical and neutron vibrational spectroscopy study of bromanilic acid: 2,3,5,6-tetramethylpyrazine (1:1) cocrystal

Complementary structural and vibrational spectroscopy study of bromanilic acid:2,3,5,6-tetramethylpyrazine (BrA:TMP) 1:1 cocrystal is reported. The crystallographic structure was determined by means of single-crystal X-ray diffraction and can be described as a stacked net of hydrogen-bonded TMPH⁺⋯BrA⁻⋯BrA⁻⋯TMPH⁺ moieties. The structural analysis was supported by ¹³CP/MAS NMR study. The complementary vibrational analysis was performed by combining optical (infrared, Raman, terahertz) and inelastic neutron scattering spectroscopy with the state-of-the-art solid–state density functional theory (DFT) computations, which have proven to be superior to the hybrid cluster modeling approach. An excellent agreement between theoretical and experimental data was observed over the entire spectral range, allowing for deep understanding of the vibrational properties. While the primary hydrogen-bonding interactions are limited to the above quoted structural units, the system revealed very little dispersion of the phonon branches, manifested mainly in the intermolecular vibrations range. Moreover, the studied phase does not exhibit any mechanical instability, which could suggest a displacive structural transformation tendency.     

Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440cm(-1) is assigned to the nu(3) CO(3)(2-) antisymmetric stretching vibration. An additional band is resolved at 1335cm(-1). An intense sharp Raman band at 1092cm(-1) is assigned to the CO(3)(2-) symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442cm(-1) shifting to lower wavenumbers with thermal treatment. A band observed at 870cm(-1) with a band of lesser intensity at 842cm(-1) shifts to higher wavenumbers upon thermal treatment and is observed at 865cm(-1) at 400 degrees C and is assigned to the CO(3)(2-)nu(2) mode. No nu(2) bending modes are observed in the Raman spectra for smithsonite. The band at 746cm(-1) shifts to 743cm(-1) at 400 degrees C and is attributed to the CO(3)(2-)nu(4) in phase bending modes. Two infrared bands at 744 and around 729cm(-1) are assigned to the nu(4) in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO(6) octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991cm(-1) in both the IE and infrared spectra are attributed to combination bands.     

Vibrational spectroscopy of selected minerals of the rosasite group

Minerals in the rosasite group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by a combination of infrared and Raman spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at approximately 3401 and 3311 cm-1. Two intense bands observed at approximately 1096 and 1046 cm-1 are assigned to nu1(CO3)2- symmetric stretching vibration and the delta OH deformation mode. Multiple bands are found in the 800-900 and 650-750 cm-1 regions attributed to the nu2 and nu4 bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C2v or Cs. A band at approximately 560 cm-1 is assigned to a CuO stretching mode.     

Structural and optical properties of ZnMgO nanostructures formed by Mg in-diffused ZnO nanowires

ZnMgO nanostructures with wurtzite phase were prepared by thermal diffusion of Mg into the ZnO nanowires. As ZnO light-emitting devices have been operated by using ZnMgO layers as energy barrier layers to confine the carriers, it is essential to realize the characterization of ZnMgO particularly. In this work, the Mg content in Zn_1−xMg_xO alloy determined by X-ray diffraction (XRD) and photoluminescence (PL) shows a good coincidence. The variation of lattice constant and the blueshift of near-band-edge emission indicate that Zn²⁺ ions are successfully substituted by Mg²⁺ ions in the ZnO lattice. In Raman-scattering studies, the change of E₂(high) phonon line shape in ZnO:Mg nanostructures reveals the microscopic substitutional disorder. In addition to the host phonons of ZnO, two additional bands around 383 and 510 cm⁻¹ are presumably attributed to the Mg-related vibrational modes.     

Vibrational spectroscopic study of hydrated uranyl oxide: Curite

Raman and infrared spectra of the uranyl oxyhydroxide hydrate: curite is reported. Observed bands are attributed to the (UO₂)²⁺ stretching and bending vibrations, U–OH bending vibrations, H₂O and (OH)⁻ stretching, bending and librational modes. U–O bond lengths in uranyls and O–H…O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. These bond lengths are close to the values inferred and/or predicted from the X-ray single crystal structure. The complex hydrogen-bonding network arrangement was proved in the structures of the curite minerals. This hydrogen bonding contributes to the stability of these uranyl minerals.     

Structural Characterization,Vibrational Studies and Electrical Properties of 2-Amino-3-benzyloxy Pyridinium Perchlorate

A title organic-inorganic hybrid material 2-amino-3-benzyloxy pyridinium perchlorate was synthesized by slow evaporation at room temperature using 2-amino-3-benzyloxypyridine as the structure-directing agent. The structure of the title compound was determined by means of single-crystal X-ray diffraction at 293 K. The results show that this compound crystallizes in the centrosymetric monoclinic system with a space group of P2₁/n and lattice parameters of a=0.7025(5) nm, b=1.2635(5) nm, c=1.5766(5) nm, Z=4 and V=1.3905(2) nm³. The crystal structure has been determined and refined to R₁=0.0367 and wR₂=0.1022 using 2326 independent reflections and can be described as a succession of organic and inorganic layers parallel to the bc plane. In this arrangement, hydrogen bonds and van der Waals interactions between different species play an important role in the two-dimensional(2D) network cohesion. This compound was also characterized by means of infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis-differential thermal analysis(TG-DTA). Moreover, protonic conduction of this compound determined by an impedance analyzer has been studied in the temperature range of 303-373 K.     

Vibrational study of [(CH3)4N]2Cu0.5Zn0.5Cl4

[(CH3)4N]2Zn0.5Cu0.5Cl4 shows an orthorhombic system at ambient temperature with P2(1)nb space group. At room temperature, the crystal consists of three sublattices constituted by MCl4 (M=Cu and Zn) and two tetramethylammoniums N1(CH3)4 and N2(CH3)4, which give rise to a total of 372 vibrational modes that transform according to the four irreductible representations of the C2v point group in the following way: Gamma(vib)=93(A1+A2+B1+B2). The infrared and Raman spectra of polycrystalline samples have been investigated at room temperature. The assignment of the observed bands is discussed.     

Mixed complexes of alkaline earth uranyl carbonates: a laser-induced time-resolved fluorescence spectroscopic study

The interaction of the alkaline earth ions Mg(2+), Sr(2+) and Ba(2+) with the uranyl tricarbonato complex has been studied by time-resolved laser-induced fluorescence spectroscopy. In contrast to the non-luminescent uranyl tricarbonato complex at ambient temperature the formed products show luminescence properties. These have been used to determine the stoichiometry and complex stabilities of the formed compounds. As the alkaline earth elements are located in an outer shell of the complex the influence of the type of the alkaline earth element on the stability constant is not very drastic. The stability constants range from logbeta(113) degrees =26.07+/-0.13 to logbeta(113) degrees =26.93+/-0.25 for the first reaction step and from logbeta(213) degrees =29.73+/-0.47 to logbeta(213) degrees =30.79+/-0.29 for the overall complex formation with two alkaline earth ions.     

Walsh’s contributions to molecular spectroscopy and its instrumentation

Alan Walsh made major contributions to molecular spectroscopy and its instrumentation, particularly with his invention of the multiple monochromator, which greatly improved the performance of infrared spectrometers.     

Molecular conformations of a partially halogenated ether: A study based on infrared spectroscopy and density functional theory calculations

A new partially halogenated ether (ClCF₂CF(CF₃)OCF₂CH₃) has been synthesized and characterized using DSC, GC, ¹H and ¹⁹F NMR, IR. The experimental infrared spectra of this “flexible” molecule have been successfully interpreted on the basis of reliable Density Functional Theory calculations. An efficient method useful for the identification of the many stable conformers has been developed and applied. Infrared spectra of the stable conformers have been simulated after full geometry optimization. The results obtained allow detection of conformation-sensitive bands, making possible the interpretation of fine details in the spectra.     

INS,IR, RAMAN, 1H NMR and DFT investigations on dynamical properties of l-asparagine

Results of inelastic neutron scattering (INS), infra-red (IR), Raman and ¹H NMR spectroscopy used for investigations on the l-asparagine dynamics are reported. The crystallographic structure and experimental vibrational spectra are compared with those calculated by the DFT methods applied to the solid state. Very good conformity of the experimental and theoretical structures has been found. The NH₃⁺ torsional vibration mode is observed in the INS spectra at 494 cm⁻¹, while the bands assigned to the vibrations of the strong NH⋯O hydrogen bonds are observed at 2849, 2650, and 2480 cm⁻¹ in the IR spectrum. A ¹H NMR investigation has been carried out at 26.75 MHz in the temperature range 150–300 K. For l-asparagine the activation energy needed for the NH₃⁺ group reorientation is equal 5.6 kcal/mol.     

In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.     

Phonon spectra and phonon-dependent properties of AgSO4, an unusual sulfate of divalent silver

Phonon spectra of recently synthesized Ag(II)SO₄ have been measured using infrared absorption and Raman scattering spectroscopy, and theoretically predicted using density functional theory calculations. Excellent agreement between experimental and theoretical results with correlation coefficient of 1.05 allowed for full assignment of the experimentally observed vibrational bands, as well as calculation of standard vibrational entropy of AgSO₄ (118.2 J mol⁻¹ K⁻¹), vibrational heat capacity at constant volume (99.1 J mol⁻¹ K⁻¹), zero-point energy (48.3 kJ mol⁻¹). The experimental cut-off frequency of the phonon spectrum equals 1116 cm⁻¹ which translates to the Debye temperature of 1606 K. High frequencies of S–O stretching modes render sulfate connections of Ag(II) attractive precursors of high-T_C superconductors.     

DFT and Raman spectroscopy of porphyrin derivatives: Tetraphenylporphine (TPP)

Raman spectrum of the meso tetraphenylporphine (TPP) deposited onto smooth copper surface as thin film were recorded in the region 200–1700 cm⁻¹. To investigate the effect of meso-phenyl substitution rings on the vibrational spectrum of free base porphyrin, we calculated Raman and infrared (IR) spectra of the meso-tetraphenylporphine (TPP), meso tetramethylporphine (TMP), copper (II)porphine (CuPr) and free base porphine (FBP) at the B3LYP/6-311+G(d,p) level of the density functional theory (DFT). The observed Raman spectrum of the TPP is assigned based on the calculated its Raman spectrum in connection with the calculated spectra of the TMP, CuPr and FBP by taking into account of their corresponding vibrational motions of the Raman modes of frequencies. Results of the calculations clearly indicated that the meso tetraphenyl substitution rings are totally responsible for the observed Raman bands at ∼1593, 1234 and 1002 cm⁻¹. The calculated and observed Raman spectra also suggested that the observed Raman band with a medium intense at 962 cm⁻¹ might result from the surface plasmon effect. Furthermore, the observed Raman bands with medium intense at ∼334 and ∼201 cm⁻¹ are as results of the dimerization or aggregation of the TPP or would be that related to intramolecular interaction. We also calculated IR spectra of these molecules at same level of the theory. To investigate the solvent effect on the vibrational spectrum of porphine, the Raman and IR spectra of the TPP and FBP are calculated in solution phase where water used as solvent. The results of these calculation indicated that there is no any significant effect on the vibrational spectrum of the TPP.     

Structural Investigation of Small Nickel-Ethanol Clusters Using Vibrational Spectroscopy in a Molecular Beam

The structural identification of small nickel clusters with ethanol can help to understand fundamental steps for heterogenous catalysis. We investigate the rows [Ni_x(EtOH)₁]⁺ with x=1–4, and [Ni₂(EtOH)_y]⁺ with y=1–3 via IR photodissociation spectroscopy in a molecular beam experiment. Analyzing the CH- and OH-stretching frequencies and comparing these experimental results with density functional theory (DFT) calculations on the PW91/6-311+G(d,p) level leads to the identification of intact motifs for all clusters and hints for C−O cleavage of the ethanol in two particular cases. Furthermore, we analyze the effects of frequency shifts with the increasing clusters sizes using the results of natural bond orbitals (NBO) analyses and an energy decomposition method.     

Structural and conductivity changes during the pyrolysis of polyaniline base

Polyaniline base has been exposed to various temperatures between 100 °C and 1000 °C for 2 h in air. The mass loss has increased with increasing temperature. FTIR and Raman spectroscopies show the gradual destruction of the PANI structure, the possible formation of intermediate oxime and nitrile groups, and the final conversion to graphitic material. The elemental analysis confirmed the dehydrogenation while the content of nitrogen was nearly constant even after treatment at 800 °C. The conductivity of PANI base, 10⁻⁸ S cm⁻¹, increased to ∼10⁻⁴ S cm⁻¹ after treatment at 1000 °C; most of the products, however, were non-conducting. Another series of experiments involved the polyaniline base heated at 500 °C for 1-8 h. The studies were performed in connection with the potential flame-retardant application of polyaniline.     

Vibrational and electrical investigations of a uniaxially stretched polystyrene/carbon nanotube composite

Multiwall carbon nanotube (MWCNT)/polystyrene (PS) composite materials were prepared in the absence and in the presence of a surfactant. TEM analysis reveals the formation of chains made of several nanotubes tied up together upon application of the surfactant while an almost random distribution is observed without any treatment. These nanotubes are seen to be highly oriented in the uniaxially stretched composite. It is shown that the presence of the surfactant and the alignment reduce electrical conductivity while polymer chain orientation remains insensitive to these parameters.