Intermolecular potential and lattice dynamics of orthorhombic acetylene

The crystal structure and lattice dynamics of orthorhombic acetylene have been calculated with an intermolecular potential consisting of atom-atom and multipole-multipole interactions and including a hydrogen bond. A new assignment of the Raman lattice vibrations is discussed and utilized in the refinement of the potential parameters. The non-transferability of the potential to the cubic phase is attributed to the breaking of the hydrogen bond at the phase transition, and to the large anharmonicity expected for the high-temperature phase.     

Application of the dimer approach for the analysis of vibrational spectra of BEDT—TTF-based charge-transfer salts

The dimer approach was proposed for the normal coordinate analysis of BEDT—TTF⁺ molecular vibrations. It was shown that, within the framework of the approximation used, the appearance of additional bands in the IR as well as in Raman spectra may be explained as due to the reduction of symmetry of the dimerized system in comparison with the monomeric one. The strength of intermolecular interaction in the dimer was estimated by adjusting the calculated frequencies to the observed positions of intense “vibronic” bands recorded in the IR spectra of BEDT—TTF-based monovalent charge transfer salts. It was found that for the reproduction of “vibronic shifts” observed for some vibrations it should be assumed that the intermolecular interaction takes effect not only on the totally symmetric a_g modes, but also on the vibrations of other symmetry species.     

Vibrational studies of monosubstituted halogenated pyridines

Infrared and Raman spectra of 2- and 3-iodopyridine and 2-fluoropyridine have been measured. Complete vibrational assignments for the three molecules are proposed. Linear relationships between X-sensitive vibrations and structural parameters are shown to be valid for the 2- and 3-halopyridines as well as for the halobenzenes. The assignments for the halopyridines are correlated with one another and with those for the halobenzenes. It is concluded that, in most cases, the ring vibrations of the pyridine derivatives are closely parallel to those of the phenyl derivatives, but the hydrogen deformation frequencies are generally higher in the substituted pyridines than in the corresponding monosubstituted benzenes.     

Effect of anharmonicity and vibrations resonance interaction in the vibrational spectra of H-bonded crystals

On the basis of the absorption coefficient calculation it is shown that strong optical and mechanical anharmonicity of the OH group vibrations and the interaction between the main tone and the overtone of the other vibration of the same OH group and the same symmetry (Fermi-resonance) leads to the formation of two-phonon bound states (biphonons) seen in spectra as “additional” sharp bands. The IR and Raman bands half-width and shape of the main tone and the bound state is measured as a function of temperature and a possible theoretical treatment is proposed. The anharmonicity parameters and low-frequency vibrations responsible for the temperature behavour of the main tone and the biphonons are determined.     

IR, 1H NMR, mass, XRD and TGA/DTA investigations on the ciprofloxacin/iodine charge-transfer complex

Raman and infrared spectra of two polymorphous minerals with the chemical formula Fe3+(SO4)(OH)·2H2O, monoclinic butlerite and orthorhombic parabutlerite, are studied and the spectra assigned. Observed bands are attributed to the (SO4)2- stretching and bending vibrations, hydrogen bonded water molecules, stretching and bending vibrations of hydroxyl ions, water librational modes, Fe-O and Fe-OH stretching vibrations, Fe-OH bending vibrations and lattice vibrations. The O-H?O hydrogen bond lengths in the structures of both minerals are calculated from the wavenumbers of the stretching vibrations. One symmetrically distinct (SO4)2- unit in the structure of butlerite and two symmetrically distinct (SO4)2- units in the structure of parabutlerite are inferred from the Raman and infrared spectra. This conclusion agrees with the published crystal structures of both mineral phases.     

High-resolution Raman spectroscopy study of phonon modes in LiBH4 and LiBD4

We have performed micro Raman measurements on LiBH4 and LiBD4 powders for temperatures between 5 and 300 K. At the lowest temperature, the peak energies agree very well with the results of a calculation within the density functional theory for the orthorhombic structure. The spectra are dominated by three separated bands: the external modes, the internal bending, and the internal stretching vibrations. Internal refers to vibrations within the BH 4 tetrahedrons, whereas external modes imply motions of Li and BH 4. The temperature dependence of the observed phonons corroborates the strong anharmonicity of the system. Due to the anharmonicity, Fermi resonances occur between the first order stretching modes and the second order bending modes of LiBH4. Moreover, the linewidths of the observed modes in LiBH4 have an Arrhenius-like component, with activation energies ranging from 250 to 500 K.     

Theoretical and spectroscopic study of infrared spectra of hydrogen-bonded 1-methyluracil crystal and its deuterated derivative

Theoretical simulation of the band shape and fine structure of the N-H(D) stretching band is presented for 1-methyluracil and its deuterated derivative taking into account anharmonic coupling between the high-frequency N-H(D) stretching and the low-frequency N...O stretching vibrations, resonance interaction between two equivalent hydrogen bonds in the dimer, anharmonicity of the potentials for the low-frequency vibrations in the ground and excited state of the N-H(D) stretching mode, Fermi resonance between the N-H(D) stretching and the first overtone of the N-H(D) bending vibrations, and electrical anharmonicity. The effect of deuteration has been successfully reproduced by our model calculations. Infrared, far-infrared, Raman, and low-frequency Raman spectra of the polycrystalline 1-methyluracil have been recorded. The geometry and experimental frequencies are compared with the results of harmonic and anharmonic B3LYP6-311++G(**) calculations.     

Ultraviolet absorption and vibrational spectra of 2-fluoro-5-bromopyridine

The ultraviolet absorption spectrum in the range 340-185 nm in the vapour and solution phase has been measured for 2-fluoro-5-bromopyridine. Three fairly intense band systems identified as the pi* <-- pi transitions II, III and IV have been observed. A detailed vibronic analysis of the vapor and solution spectra is presented. The first system of bands is resolved into about sixty-two distinct vibronic bands in the vapour-phase spectrum. The 0,0 band is located at 35944 cm(-1). Two well-developed progressions, in which the excited state frequencies nu'25 (283 cm(-1)) and nu'19 (550 cm(-1)) are excited by several quanta, have been observed. The corresponding excited state vibrational and anharmonicity constants are found to be omega'i = 292 cm(-1), x'ii = 4.5 cm(-1) (i = 25) and omega'i = 563.8 cm(-1), x'ii = 6.9 cm(-1) (i = 19). The other two band systems show no vibronic structure, the band maxima being located at 48346 and 52701 cm(-1), respectively. The oscillator strength of the band systems in different solutions and the excited state dipole moments associated with the first two transitions have been determined by the solvent-shift method. The infrared spectrum in the region 4000-130 cm(-1) and the laser Raman spectrum of the molecule in the liquid state have been measured and a complete vibrational assignment of the observed frequencies is given. A correlation of the ground and excited state fundamental frequencies observed in the UV absorption spectrum with the Raman or infrared frequencies is presented.     

Theoretical model for a tetrad of hydrogen bonds and its application to interpretation of infrared spectra of salicylic acid

Theoretical model of vibrational interactions in hydrogen-bonded salicylic acid dimer is presented which takes into account the adiabatic couplings between high- and low-frequency O-H and O...O stretching vibrations, resonance interactions between both intermolecular hydrogen bonds and between inter- and intramolecular hydrogen bonds, and Fermi resonance between the O-H stretching fundamental and the first overtone of the O-H in-plane bending vibrations. The model is used for theoretical simulation of the nu(s) stretching bands of salicylic acid and its OD derivative at 300 K. The effect of deuteration is successfully reproduced by our model. Infrared, far infrared, Raman, and low-frequency Raman spectra of the polycrystalline salicylic acid and its deuterated derivative have been measured. The geometry and experimental frequencies are compared with the results of density-functional theory calculations performed at the B3LYP6-31 ++ G**, B3LYP/cc-pVTZ, B3PW916-31 ++ G**, and B3PW91/cc-pVTZ levels. O-H, O-D, and O...O stretching frequencies are used in theoretical simulation of the nu(s) stretching bands.     

Molecular vibrations of [n]oligoacenes (n=2-5 and 10) and phonon dispersion relations of polyacene

As model compounds for nanosize carbon clusters, the phonon dispersion curves of polyacene are constructed based on density functional theory calculations for [n]oligoacenes (n=2-5, 10, and 15). Complete vibrational assignments are given for the observed Fourier-transform infrared and Raman spectra of [n]oligoacenes (n=2-5). Raman intensity distributions by the 1064-nm excitation are well reproduced by the polarizability-approximation calculations for naphthalene and anthracene, whereas several bands of naphthacene and pentacene at 1700-1100 cm(-1) are calculated to be enhanced by the resonance Raman effect. It is found from vibronic calculations that the coupled a(g) modes between the Kekulé deformation and joint CC stretching give rise to the Raman enhancements of the Franck-Condon type, and that the b(3g) mode corresponding to the graphite G mode is enhanced by vibronic coupling between the (1)L(a)((1)B(1u)) and (1)B(b)((1)B(2u)) states. The phonon dispersion curves of polyacene provide a uniform foundation for understanding molecular vibrations of the oligoacenes in terms of the phase difference. The mode correlated with the defect-sensitive D mode of the bulk carbon networks is also found for the present one-dimensional system.     

Vibrational states of chlorophyll and related compound molecules. Metal complexes of octaethylchlorin

Fine-structure fluorescence spectra and i.r. spectra of the model compound chlorophyll-Zn-octaethylchlorin (Zn OEC), and its three deuterated derivatives at meso-positions and Zn OEC-¹⁵N₄ have been obtained. Polarization measurements for individual zero-phonon lines show that in the vibronic spectra of the above compounds the totally symmetric vibrations are mainly active. A joint analysis of the experimental data and calculation results of normal vibrations has served as a basis for the interpretation of the spectra obtained as well as resonance Raman spectra. It is pointed out that the vibrations of ethyl substituents largely form a vibrational structure of the vibronic Zn OEC spectrum. An assignment of some lines in a fine-structure spectrum of chlorophyll a is discussed.     

Transient resonance Raman spectra and vibrational assignments of the S1 state of trans-stilbene and its deuterated analogues

Raman spectra of S₁ trans-stilbene and its deuterated analogues were observed. Assignments of the three olefinic vibrations have been made on the basis of the isotopic frequency shifts. The S₁ Raman spectra are interpreted according to the newly established vibrational assignments, which are different from those proposed previously.     

Comparison of experimental and density functional study on the molecular structure, infrared and Raman spectra and vibrational assignments of 6-chloronicotinic acid

The experimental and theoretical study on the structures and vibrations of 6-chloronicotinic acid (6-CNA, C(6)H(4)ClNO(2)) are presented. The Fourier transform infrared spectra (4,000-50 cm(-1)) and the Fourier transform Raman spectra (3,500-50 cm(-1)) of the title molecule in solid phase have been recorded, for the first time. The geometrical parameters and energies have been obtained for all four conformers from DFT (B3LYP) with different basis sets calculations. There are four conformers, C1, C2, C3, and C4 for this molecule. The computational results diagnose the most stable conformer of 6-CNA as the C1 form. The vibrations of the two stable and two unstable conformers of 6-CNA are researched with the aid of quantum chemical calculations. The molecular structure, vibrational frequencies, infrared intensities and Raman scattering activities and theoretical vibrational spectra were calculated a pair of molecules linked by the intermolecular OH...O hydrogen bond. The spectroscopic and theoretical results are compared to the corresponding properties for 6-CNA stable monomers and dimer of C1 conformer.     

Vibrational spectroscopic study on polymorphism and molecular aggregation states in polyoxymethylene

Polarized Raman spectra of the moth-shaped single-crystal of orthorhombic polyoxymethylene (metastable phase) have been investigated by means of the Raman microprobe technique in the frequency range covering both molecular and lattice vibrations. The observed polarizations of the Raman bands are found to be strongly influenced by the optical alignment in the microscope, mainly by the polarization scrambling effect. By taking the optical effect into account, the orientation of the crystal axes in the single-crystal is investigated. Normal mode analysis of the orthorhombic crystal is performed based on the newly obtained polarization data. Raman spectra of two crystalline samples of trigonal polyoxymethylene (stable phase) differing in their morphology and in their structural orderliness are compared. In the spectrum of the needle-like crystal consisting of the fully extended molecules, measured at low temperature, eight Raman bands due to the E₂ symmetry species are newly detected     

Quantum chemistry-based analysis of the vibrational spectra of five-coordinate metalloporphyrins [M(TPP)Cl

Vibrational properties of the five-coordinate porphyrin complexes [M(TPP)(Cl)] (M = Fe, Mn, Co) are analyzed in detail. For [Fe(TPP)(Cl)] (1), a complete vibrational data set is obtained, including nonresonance (NR) Raman, and resonance Raman (RR) spectra at multiple excitation wavelengths as well as IR spectra. These data are completely assigned using density functional (DFT) calculations and polarization measurements. Compared to earlier works, a number of bands are reassigned in this one. These include the important, structure-sensitive band at 390 cm(-1), which is reassigned here to the totally symmetric nu(breathing)(Fe-N) vibration for complex 1. This is in agreement with the assignments for [Ni(TPP)]. In general, the assignments are on the basis of an idealized [M(TPP)]+ core with D(4h) symmetry. In this Work, small deviations from D(4h) are observed in the vibrational spectra and analyzed in detail. On the basis of the assignments of the vibrational spectra of 1, [Mn(TPP)(Cl)] (2), and diamagnetic [Co(TPP)(Cl)] (3), eight metal-sensitive bands are identified. Two of them correspond to the nu(M-N) stretching modes with B(1g) and Eu symmetries and are assigned here for the first time. The shifts of the metal sensitive modes are interpreted on the basis of differences in the porphyrin C-C, C-N, and M-N distances. Besides the porphyrin core vibrations, the M-Cl stretching modes also show strong metal sensitivity. The strength of the M-Cl bond in 1-3 is further investigated. From normal coordinate analysis (NCA), force constants of 1.796 (Fe), 0.932 (Mn), and 1.717 (Co) mdyn/A are obtained for 1-3, respectively. The weakness of the Mn-Cl bond is attributed to the fact that it only corresponds to half a sigma bond. Finally, RR spectroscopy is used to gain detailed insight into the nature of the electronically excited states. This relates to the mechanism of resonance enhancement and the actual nature of the enhanced vibrations. It is of importance that anomalous polarized bands (A(2g) vibrations), which are diagnostic for vibronic mixing, are especially useful for this purpose.     

Laser Raman and infrared spectral studies of dl-phenylalaninium nitrate

The vibrational band assignments of dl-phenylalaninium nitrate in the crystalline state are made by recording the infrared and Raman spectra at room temperature. The presence of carbonyl (C=O) group has been identified. The prominent marker bands of the aromatic amino acid phenylalanine have been observed and the various modes of vibration have been assigned. The extensive intermolecular hydrogen bonding in the crystal has been identified by the shifting of bands due to the stretching and bending modes of the various functional groups. The nitrate group forms the anion. The stretching and bending wave numbers of the NO(3)(-) anion are different from those observed for free ion state and the degenerating mode of vibrations is also lifted. These reveal that the crystalline field has influenced the symmetry of the nitrate ion.     

Phase transition in single crystal Cs2Nb4O11

We studied temperature dependence of complex capacitance, impedance, and polarized Raman spectra of single crystal Cs2Nb4O11. First, we observed a sharp lambda-shaped peak at 165 degrees C in the complex capacitance, then found drastic changes in the Raman spectra in the same temperature range. Utilizing the pseudosymmetry search of structure space group, we attributed the observed anomalies to a structural change from the room temperature orthorhombic Pnn2 to another orthorhombic Imm2. We also measured room temperature polarized Raman spectra in different symmetries of normal vibrations and assigned high wavenumber Raman bands to the internal vibrations of NbO6 octahedra and NbO4 tetrahedra.     

Vibrational structures of methylamine isotopomers in the predissociative ~A states: CH3NHD, CD3NH2, CD3NHD, and CD3ND2

Mass-resolved two-photon (1+1) resonance-enhanced multiphoton ionization spectra of the ~A-X transitions of various methylamine isotopomers (CH(3)NHD, CD(3)NH(2), CD(3)NHD, and CD(3)ND(2)) cooled in the supersonic jet expansion have been measured and analyzed. The band analysis using the Hamiltonian for the internal and overall rotational motions provides the accurate vibrational band positions, allowing for unambiguous assignments for all observed vibrational bands of methylamine isotopomers in the ~A states. Amino wagging (nu(9)) and methyl rocking (nu(7)) modes are found to be Franck-Condon active, and associated anharmonicity constants are precisely determined to give the detailed shape of the potential energy surface in the vicinity of the minimum electronic molecular structure. The barrier height for the nearly free internal rotation about the C-N bond in the ~A state is calculated to be strongly dependent on the excitation of the other higher-frequency vibrational modes, and it is found that the trend is consistent with the experiment. Experimentally measured spectroscopic constants are compared with ab initio calculations, confirming all vibronic assignments. Experimental and theoretical results on all possible HD isotopomers of methylamine in this work, with the earlier report on CH(3)NH(2) and CH(3)ND(2) Baek et al., [J. Chem. Phys. 118, 11026 (2003)], provide the complete spectroscopic characterization of the A state of methylamine.     

Δ-2 thiazoline et alkyl-2 Δ-2 thiazolines: etude vibrationnelle infrarouge et Raman.conformation

Raman spectra (liquid state) and infrared spectra of 2-Δ thiazoline and its 2-alkyl derivatives (vapor, liquid, solution and solid states) have been analysed between 4000 and 200 cm⁻¹. The assignments proposed for the fundamental vibrations of these heterocycles agree with a planar or a very little distorted conformation of the cycle.     

DFT studies of structure and vibrational frequencies of isotopically substituted diamin uranyl nitrate using relativistic effective core potentials

The infrared and Raman spectra of UO(2)(NH(3))(2)(NO(3))(2) with (14)NH(3)/(15)NH(3) isotopic substitution were measured. The structure was optimized and the vibrational spectrum was calculated by DFT (B3LYP/6-31G(d)) methodology using relativistic effective core potential for U atom. The results for force constant and vibrational frequencies support the experimental assignments and the proposed model, mainly in the far-infrared region, where the metal-ligand bond and lattice vibrations are observed. Based on the theoretical findings and the observed spectra a structure of distorted D(2h) symmetry with the nitrate group acting like bidentate ligands for the UO(2)(NH(3))(2)(NO(3))(2) is proposed.