Infrared and Raman spectra of 2,4-dithiobiuret and its normal vibrations

The infrared spectra of 2,4-dithiobiuret(DTB), N-deuterated dithiobiuret(DTB-d5) and the laser Raman spectrum of DTB are reported. Normal coordinate treatments of DTB and DTB-d5 have been carried out to aid the assignment of the vibrational frequencies. A trans—cis conformation is favoured for DTB molecule in the solid state.

On the conformation of cyclohexane-1,4-dione and its derivatives—I : Infrared and raman spectra of cyclohexane 1,4-dione and infrared spectrum of its octadeutero analogue

Raman spectra of cyclohexane 1,4-dione (I), in chloroform, benzene and water solutions have been recorded. Temperature effect on the spectrum has been studied. The IR spectra of I and its octadeutero analogue in the solid state have also been studied. The spectra have been found on the basis of selection rules applicable for Raman and IR spectra, to be consistent with a single conformer of C2 symmetry. Plausible causes of conformational preference have been discussed.

Infra-red and raman spectra of BaCl2.2H2O and BaCl2.2D2O

The infra-red and Raman spectra of ordinary and deuterated barium chloride dihydrate have been studied to throw light on the intramolecular hydrogen bonds in these two crystals. The frequencies of the stretching, bending and librational modes observed in infra-red and Raman spectra exclude the possibility of at least one of the OH.... Cl hydrogen bonds, contrary to the results of NMR and neutron diffraction studies.

Temperature dependence of infrared and Raman modes in polymeric RbC60

Temperature dependence of the intra-molecular vibrational modes Of C-60 in the quasi-1D polymeric RbC60, across the low temperature transition at similar to50 K, has been probed through infrared (IR) and Raman spectroscopies. With the lowering of temperature, the split IR modes of RbC60 are seen to harden but below 50 K a small but definitive signature of an anomalous softening is observed. In addition, the background IR transmission shows an increase below 50 K with the opening of a well defined gap in the electronic spectrum. The implications of these results, along with those of Raman measurements, are discussed in terms of the interaction of intra-molecular phonons with electrons and spin excitations in the system. (C) 2002 Published by Elsevier Science Ltd.

Study on the structure and vibrational spectra of efavirenz conformers using DFT: Comparison to experimental data

Efavirenz, (S)-6-chloro-4-(cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3 ,1-benzoxazin-2-one, is an anti HIV agent belonging to the class of the non-nucleoside inhibitors of the HIV-1 virus reverse transcriptase. A systematic quantum chemical study of the possible conformations, their relative stabilities and vibrational spectra of efavirenz has been reported. Structural and spectral characteristics of efavirenz have been studied by vibrational spectroscopy and quantum chemical methods. Density functional theory (DFT) calculations for potential energy curve, optimized geometries and vibrational spectra have been carried out using 6-311++G(d,p) basis sets and B3LYP functionals. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of the most stable form of efavirenz. A complete analysis of the experimental infrared and Raman spectra has been reported on the basis of wavenumber of the vibrational bands and potential energy distribution. The infrared and the Raman spectra of the molecule based on OFT calculations show reasonable agreement with the experimental results. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. (C) 2011 Elsevier B.V. All rights reserved.

Study of molecular structure and vibrational spectra of poly (beta,-1-malic acid) PMLA] using DFT approach

Poly (beta-L-malic acid) (PMLA) is a biodegradable polymer and it has various important applications in the biomedical field. In the present work the structural and spectral characteristics of PMLA have been studied by methods of infrared. Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) using oligomeric approach employing B3LYP with complete relaxation in the potential energy surface using 6-311++G (d, p) basis set. Based on results, we have discussed the correlation between the vibrational modes and the structure of the PMLA. A complete analysis of the experimental infrared and Raman spectra has been reported on the basis of wavenumber of the vibrational bands and potential energy distribution. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The calculated infrared and the Raman spectra of the polymer based on DFT calculations show reasonable agreement with the experimental results. (c) 2012 Elsevier Ltd. All rights reserved.

Vibrational Spectra and Normal Coordinate Analysis of N-Methyl Thiourea

The infrared spectra of N-methylthiourea (NMTU) and its N-deuterated and S-methylated species were measured. Assignment of the infrared and Raman spectra of NMTU has been accomplished by correlation with thiourea and by use of infrared band shifts on N-deuteration as well as S-methylation. Normal coordinate analysis was performed for all the fundamentals of NMTU and NMTU-d3, the assignments obtained from the force field calculations being discussed in relation to those in other related thioureas and thioamides. The potential barriers to the internal rotations for the �NH2, �CH3, and �CN groups were estimated from the force constants.

Ab initio studies of solvent effect on conformational equilibria and vibrational spectra of dipropionamide

Systematic ab initio molecular orbital studies of the conformational equilibria and vibrational spectra of dipropionamide using the basis sets 6-31g(d) and 6-31++G(d,p) have been carried out. The vibrational spectra of dipropionamide have been satisfactorily interpreted taking into account the agreement between the calculated frequencies, infrared and Raman band intensities and the shifts in the spectra of deuterated molecules with those observed. The previous assignments of most of the vibrational bands are well confirmed, a few bands need reassignment, however. The solvent effects were investigated by self-consistent reaction field theory using dipole and self-consistent isodensity polarized continuum model methods. The introduction of a dielectric medium has only a marginal effect on the conformational equilibria and vibrational spectra. However, the calculated changes in geometry and vibrational spectra on going from the gas phase to the solution phase are in accord with the increasing weight of the dipolar resonance structure in polar solvents. (C) 2002 Elsevier Science B.V. All rights reserved.

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

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

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO2 thin films

Titanium dioxide (TiO2) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO2 films were investigated. The refractive index of TiO2 films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO2 film is of anatase phase after annealing at 300 degrees C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications. (C) 2012 Elsevier B.V. All rights reserved.

Conformation and orientation of alkyl chains in the layered organic-inorganic hybrids: (CnH2n+1NH3)(2)PbI4 (n=12,16,18)

Layered organic inorganic hybrids based on perovskite-derived alkylammonium lead halides have been demonstrated as important new materials in the construction of molecular electronic devices. Typical of this class of materials are the single-perovskite slab lead iodides of the general formula (CnH2n+1NH3)(2)PbI4. While for small n, these compounds are amenable to single-crystal structure determination, the increasing degree of disorder in the long chain (n = 12,14...) compounds makes such an analysis difficult. In this study, we use powder X-ray diffraction, and vibrational and C-13 NMR spectroscopies to establish the conformation, orientation and organization of hydrocarbon chains in the series of layered alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4 (n = 12,16,18). We find that the alkyl chains adopt a tilted bilayer arrangement, while the structure of the inorganic layer remains invariant with respect to the value of n. Conformation-sensitive methylene stretching modes in the infrared and Raman spectra, as well as the C-13 NMR spectra indicate that bonds in the methylene chain are in trans configuration. The skeletal modes of the alkyl chain in the Raman spectra establish that there is a high degree of all-trans conformational registry for the values of n studied here. From the orientation dependence of the infrared spectra of crystals of (CnH2n+1NH3)(2)PbI4 ( n = 12,16), we find that the molecular axis of the all-trans alkyl chains are tilted away from the interlayer normal by an angle of 55degrees. This value of this tilt angle is consistent with the dependence of the c lattice expansion as a function of n, as determined from powder X-ray diffraction.

Normal vibrations of N,N-dimethylacetamide

Infrared and Raman spectra of N,N-dimethylacetamide (DMA) are recorded and the normal vibrational analysis of the DMA skeleton as well as the entire molecule carried out employing the Urey-Bradley and modified Urey-Bradley force fields. Vibrational frequencies are assigned on the basis of the normal coordinate calculations and are compared with those of related molecules. Infrared spectra of metal complexes are examined to substantiate the band assignments.

Normal vibrations of N,N-dimethylacetamide

Infrared and Raman spectra of N,N-dimethylacetamide (DMA) are recorded and the normal vibrational analysis of the DMA skeleton as well as the entire molecule carried out employing the Urey-Bradley and modified Urey-Bradley force fields. Vibrational frequencies are assigned on the basis of the normal coordinate calculations and are compared with those of related molecules. Infrared spectra of metal complexes are examined to substantiate the band assignments.

Raman and polarized infrared spectra of pyridine-2-thione

Polarized i.r. spectra of oriented polycrystals and the i.r. and Raman spectra of polycrystalline samples of pyridine-2-thione have been obtained. The Raman spectra of a solution of pyridine-2-thione has also been measured and the polarization of many lines determined. The i.r. spectra of S-methyl and N-deuterated compounds have also been investigated. A complete assignment of all the observed peaks has been possible. The results are correlated with the assignments available for related systems.

Effect of curve crossing on absorption and resonance Raman spectra: analytical treatment for delta-function coupling in parabolic potentials

We propose an exactly solvable model for the two-state curve-crossing problem. Our model assumes the coupling to be a delta function. It is used to calculate the effect of curve crossing on the electronic absorption spectrum and the resonance Raman excitation profile.