Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

Polarised IR-microscope spectra of guanidinium hydrogensulphate single crystal

Polarised IR-microscope spectra of C(NH(2))(3)*HSO(4) small single crystal samples were measured at room temperature. The spectra are discussed on the basis of oriented gas model approximation and group theory. The stretching nuOH vibration of the hydrogen bond with the Ocdots, three dots, centeredO distance of 2.603A gives characteristic broad AB-type absorption in the IR spectra. The changes of intensity of the AB bands in function of polariser angle are described. Detailed assignments for bands derived from stretching and bending modes of sulphate anions and guanidinium cations were performed. The observed intensities of these bands in polarised infrared spectra were correlated with theoretical calculation of directional cosines of selected transition dipole moments for investigated crystal. The vibrational studies seem to be helpful in understanding of physical and chemical properties of described compound and also in design of new complexes with exactly defined behaviors.     

Polarized IR-microscope spectra of guanidinium hydrogenselenate single crystal

The polarized IR-microscope spectra of C(NH2)3.HSeO4 small single crystal samples were measured at room temperature. The spectra are discussed with the framework of oriented gas model approximation and group theory. The stretching nuOH vibration of the hydrogen bond with the O...O distance of 2.616 A gives characteristic broad AB-type absorption in the IR spectra. The changes of intensity of the AB bands in function of polarizer angle are described. Detailed assignment for bands derived from stretching and bending modes of selenate anions and guanidinium cations were performed. The observed intensities of these bands in polarized infrared spectra were correlated with theoretical calculation of directional cosines of selected transition dipole moments for investigated crystal. The vibrational studies seem to be helpful in understanding of physical and chemical properties of described compound and also in design of new complexes with exactly defined behaviors.     

Raman spectroscopic study of the molecular structure of the uranyl mineral zippeite from Jáchymov (Joachimsthal), Czech Republic

Raman spectra at 298 and 77K and infrared spectra of the uranyl sulfate mineral zippeite from Jáchymov (Joachimsthal), Czech Republic, K(0.6)(H(3)O)0.4[(UO(2))6(SO(4))3(OH)7].8H2O, were studied. Observed bands were tentatively attributed to the (UO(2))2+ and (SO(4))2- stretching and bending vibrations, the OH stretching vibrations of water molecules, hydroxyls and oxonium ions, and H(2)O, oxonium, and delta U-OH bending vibrations. Empirical relations were used for the calculation of U-O bond lengths in uranyl R (A)=f(nu(3) or nu(1)(UO(2))2+). Calculated U-O bond lengths are in agreement with U-O bond lengths from the single crystal structure analysis and those inferred for uranyl anion sheet topology of uranyl pentagonal dipyramidal coordination polyhedra. The number of observed bands supports the conclusion from single crystal structure analysis that at least two symmetrically distinct U6+ (in uranyls) and S6+ (in sulfates), water molecules and hydroxyls may be present in the crystal structure of the zippeite studied. Strong to very weak hydrogen bonds present in the crystal structure of zippeite studied were inferred from the IR spectra.     

Low-temperature Fourier transform infrared spectra and hydrogen bonding in polycrystalline L-alanine

The 400-4000 cm(-1) FTIR spectra of pure NH and isotopically substituted (10 and 90% doped ND/NH) polycrystalline L-alanine were recorded in the temperature range 10-300 K. The observed temperature dependence and isotopic shifts behavior enabled to identify, in the spectra of the doped crystals, three well-separated bands ascribable to either the NH or ND stretching vibrations associated with the three different types of hydrogen bonds existing in the crystal. The observed red shifts of these bands relative to the frequency of a reference "free" NH (or ND) stretching mode were found to correlate well with the H-bond distances found in the crystal and provide an indirect way of estimating the enthalpies associated with each type of H-bond found in the crystal. In the low-frequency deformation and torsional spectral region (below 2000 cm(-1)), several bands, which were found to be affected by isotopic substitution, were identified as belonging to the NH3(+) group. Several bands show splitting at low temperatures, indicating the occurrence of a significant reorganization in the crystal structure, which with all probability results mainly from changes in the proton positions. Finally, the literature assignments of the IR spectra of both crystalline NH3(+) and ND3(+) L-alanine were revised taking into consideration their temperature dependence and behavior upon deuteration.     

IR spectra of long-chain α,ω-alkanediols: 1,22-docosanediol and 1,44-tetratetracontanediol

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH₂)₂₂OH and HO(CH₂)₄₄OH, in the spectral range of 400–5000 cm^?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm^?1 (rocking vibrations of CH₂ groups) and 1463–1473 cm^?1 (bending vibrations of CH₂ groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH₂ wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.     

Polarised vibrational studies of the α-glycine single crystal: Part I. Polarised Raman spectra—the Problem of effective local Raman tensors for the glycine zwitterions

Complete (full) set of the polarised Raman spectra for the α-glycine single crystal at room temperature are presented. For the strongest bands arising from the ν_sCH₂, ν_aCH₂, δCH₂, τCH₂, νCOO⁻, δCOO and ν_sCCN vibrations effective local Raman tensors are determined applying the Tsuboi approach. The obtained results are compared to literature data available on this problem. Unfortunately, significant differences are observed between our data and other published results. This is due to the improper single crystal sample preparation for polarised Raman spectra measurements in the past. The obtained results are presented in forms which allow to apply these data for the polarised Raman spectra of other crystals of glycine compounds.     

NH stretching vibrations of pyrrole clusters studied by infrared cavity ringdown spectroscopy

The IR spectra for various sizes of pyrrole clusters were measured in the NH stretching vibration region by infrared cavity ringdown spectroscopy. The hydrogen-bonded structures and normal modes of the pyrrole clusters were analyzed by a density functional theory calculation of the B3LYP/6-311+G(d,p) level. Two types of pulsed nozzles, a slit and a large pinhole, were used to generate different cluster size distributions in a supersonic jet. A rotational contour analysis of the NH stretching vibration for the monomer revealed that the slit nozzle provides a warmer jet condition than the pinhole one. The IR spectra, measured under the warmer condition, showed the intense bands at 3444, 3392, and 3382 cm(-1), which were assigned to hydrogen-bonded NH stretching vibrations due to the dimer, the trimer, and the tetramer, respectively. On the other hand, the IR spectra measured under a lower temperature condition by a pinhole nozzle showed a broad absorption feature in addition to sharp bands. This broad absorption was reproduced by the sum of two Gaussians peaks at 3400 and 3372 cm(-1) with widths of 30 and 50 cm(-1) (FWHM), respectively. Compared with the spectra of the condensed phase, two bands at 3400 and 3372 cm(-1) were assigned to hydrogen-bonded NH stretching vibrations of larger clusters having liquid-like and solid-like structures, respectively.     

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.     

A new assignment of IR vibrational modes in mullite

A new assignment of IR absorption bands of mullite is presented on the basis of empirical studies in the 1400–400 cm⁻¹ vibrational range of mullite-type compounds in the systems Al₂O₃–SiO₂, Al₂O₃–GeO₂, Ga₂O₃–GeO₂, and Al₂O₃–Me₂O, Ga₂O₃–Me₂O (Me=Na, K, Rb). The powder samples were prepared by heat treatment of sol–gel derived precursor powders and by reaction sintering of oxide powders. The FTIR powder spectra of Al–Si, Al–Ge, and Ga–Ge mullite compounds are characterized by three band groups, designated as (a), (b) and (c). Due to the lack of group (a) bands in the alkaline aluminate and gallate spectra, this high-energetic band group is assigned to Si---O and Ge---O stretching vibrations. Group (b) bands are essentially determined by Al---O and Ga---O stretching vibrations with Al and Ga on T sites in tetrahedral coordination and by T---O---T bending modes, while the low-energetic group (c) bands are due to Al---O and Ga---O stretching vibrations in octahedral structural units. Details of the vibrational modes are discussed on the basis of the deconvoluted spectra.     

Infrared spectra of the hydrogen bond in pimelic acid crystals: polarization and temperature effects.

This paper deals with the polarized IR spectra of the hydrogen bond in pimelic acid crystals and their quantitative interpretation. The spectra were measured for the vO-H and vO-D band frequency regions, at temperatures of 298 and 77 K, for the 'alpha' crystalline form of pimelic acid. Two kinds of transmission spectra were obtained, for the beam perpendicular to the two different crystalline faces: 'ac' and 'ab'. The spectra of the hydrogen and the deuterium bonded systems were quantitatively reproduced, with sufficient accuracy, on the basis of the 'strong-coupling' model, assuming the (COOH)2 cycles to be the structural units responsible for the basic spectral properties. It was found that the spectra could be reproduced only, when assuming spectral activity in the IR of the totally symmetric proton stretching vibrations in centrosymmetric cyclic dimers of hydrogen bonds. The polarization effects in the crystal spectra were interpreted as directly connected with the hydrogen bond orientation in the crystal. However, in the pimelic acid crystalline spectra there were not observed another polarization effects characteristic for another carboxylic acid crystals, depending on differentiation of the long- and of the short-wave branch properties of each of the vO-H and vO-D bands. The temperature variation only affect the intensity ratio between the lower- and the higher-frequency branches of the vO-H and vO-D bands. These spectral effects were ascribed to less strained hydrogen bond structures in the pimelic acid lattices of the alpha' crystalline form and a relatively low concentration of defects in the lattices.     

IR spectroscopy of hydrogen-bonded 2-fluoropyridine-methanol clusters

The electronic and infrared spectra of 2-fluoropyridine-methanol clusters were observed in a supersonic free jet. The structure of hydrogen-bonded clusters of 2-fluoropyridine with methanol was studied on the basis of the molecular orbital calculations. The IR spectra of 2-fluoropyridine-(CH3OH)n(n = 1-3) clusters were observed with a fluorescence-detected infrared depletion (FDIR) technique in the OH and CH stretching vibrational regions. The structures of the clusters are similar to those observed for 2-fluoropyridine-(H2O)n (n = 1-3) clusters. The existence of weak hydrogen bond interaction through aromatic hydrogen was observed in the IR spectra. The theoretical calculation also supports the result. The vibrational frequencies of CH bonds in CH3 group are affected by hydrogen bond formation although these bonds do not directly relate to the hydrogen bond interaction. The B3LYP/6-311 ++G(d,p) calculations reproduce well the vibrational frequency of the hydrogen-bonded OH stretching vibrations. However, the calculated frequency of CH stretching vibration could not reproduce the IR spectra because of anharmonic interaction with closely lying overtone or combination bands for nu3 and nu9 vibrations. The vibrational shift of nu2 vibration is reproduced well with molecular orbital calculations. The calculation also shows that the frequency shift of nu2 vibration is closely related to the CH bond length at the trans position against the OH bond in hydrogen-bonded methanol.     

Structure and optical properties of the 4-cyano-4′-n-pentylbiphenyl dimers and trimers

ABSTRACT

The variation of the spectral characteristics of liquid crystal molecules based on 4-cyano-4′-n-pentylbiphenyl (5CB) was analysed depending on its associates structure using the quantum–chemical density functional hybrid potential methods B3LYP/6-31G and B3LYP/6-31G**. The electronic absorption spectra and IR spectra of dimers and trimers 5CB were calculated. It was shown that spectra are sensitive to the associates’ structure. We can observe the appearance of new bands in spectra and splitting characteristic CN stretching vibrations (1–5 cm^?1) in the vibrational spectra.     

Structure-acidity-IR spectra correlations for p-substituted N-phenylsulfonylbenzamides

The wavenumbers of the IR absorption bands of the C=O, S=O and N-H stretching vibrations for a series of p-substituted N-phenylsulfonylbenzamides were measured in trichloromethane. The bond orders, Mulliken charges, charge densities and heats of formation were calculated using the PM3 method. Fifty significant mutual mono parameter (MP) and six dual parameter (DP) correlations were found for the IR spectral, theoretical structural data, substituent constants and previously reported dissociation constants in five polar organic solvents. The transmission of the substituent effects has been discussed and the solvent effect on the slopes of some linear correlations was evaluated using different solvent parameters. The results showed that the factors describing the electronic structure and controlling the dissociation equilibrium and the IR spectra properties of p-substituted N-phenylsulfonylbenzamides must be the same.     

Polarized infrared and Raman spectra of a CsHSO4 single crystal

The polarized absorption infrared (IR) and polarized Raman spectra of a CsHSO₄ single crystal at room temperature are presented and discussed in relation to the X-ray crystal structure. Breakdown of the selection rules for the X-ray determined C_2h factor group is observed. The vibrational factor group appears to be C₂. This implies C₁ site symmetry for the SO²⁻₄ ions. The polarization features of the HSO⁻₄ ion vibrations are predicted assuming that the longest S---OH bond vibrates independently of the SO₃ group vibrations. The ABC structure of the IR and Raman band arising from the νOH stretching vibration is explained on the basis of Fermi resonance.     

Study of the binding sites in the biomass of <Emphasis Type="Italic">Aspergillus niger</Emphasis> wild-type strains by FTIR spectroscopy

Fourier transform infrared (FTIR) spectroscopy studies were performed to confirm and to provide information on the identity and binding characteristics of the chemical groups responsible for the binding of elements using Aspergillus niger (A. niger) wild-type strains. Two absorption bands in the 3690–3615 and 2970–2895 cm^?1 regions can characterize stretching vibrations OH and CH groups in fatty acids, respectively, and intensive bands around of 1600 cm^?1 and by 1048 cm^?1 correspond to stretching vibrations of C=O groups of amides (amide I) or stretching vibrations ν(C–N). The FTIR results confirmed that no extra differences between IR spectra of A. niger in raw biomass and in solid rest after extraction with chloroform were observed. The small differences were observed in IR spectra of A. niger in chloroform after extraction.     

Molecular dynamics simulation of liquid methanol. II. Unified assignment of infrared, Raman, and sum frequency generation vibrational spectra in methyl C-H stretching region

Vibrational spectra of methyl C-H stretching region are notoriously complicated, and thus a theoretical method of systematic assignment is strongly called for in condensed phase. Here we develop a unified analysis method of the vibrational spectra, such as infrared (IR), polarized and depolarized Raman, and ssp polarized sum frequency generation (SFG), by flexible and polarizable molecular dynamics simulation. The molecular model for methanol has been developed by charge response kernel model to allow for analyzing the methyl C-H stretching vibrations. The complicated spectral structure by the Fermi resonance has been unraveled by empirically shifting potential parameters, which provides clear information on the coupling mechanism. The analysis confirmed that for the IR, polarized Raman, and SFG spectra, two-band structure at about 2830 and 2950 cm(-1) results from the Fermi resonance splitting of the methyl C-H symmetric stretching and bending overtones. In the IR spectrum, the latter, higher-frequency band is overlapped with prominent asymmetric C-H stretching bands. In the depolarized Raman spectrum, the high frequency band at about 2980 cm(-1) is assigned to the asymmetric C-H stretching mode. In the SFG spectrum, the two bands of the splitted symmetric C-H stretching mode have negative amplitudes of imaginary nonlinear susceptibility χ(2), while the higher-frequency band is partly cancelled by positive imaginary components of asymmetric C-H stretching modes.     

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.     

Study of polarized IR spectra of the hydrogen bond system in crystals of styrylacetic acid

We have investigated the polarized IR spectra of the hydrogen bond system in crystals of trans-styrylacetic acid C(6)H(5)CHCHCH(2)COOH, and also in crystals of the following three deuterium isotopomers of the compound: C(6)H(5)CHCHCH(2)COOD, C(6)H(5)CHCHCD(2)COOH and C(6)H(5)CHCHCD(2)COOD. The spectra were measured at room temperature and at 77K by a transmission method. The spectral studies were preceded by determination of the X-ray crystal structure. Theoretical analysis of the results concerned linear dichroic effects, the H/D isotopic and temperature effects, observed in the solid-state IR spectra of the hydrogen and of the deuterium bond, at the frequency ranges of the nu(OH) and the nu(OD) bands, respectively. Basic spectral properties of the crystals can be interpreted satisfactorily in terms of the "strong-coupling" theory, when based on a hydrogen bond dimer model. This model sufficiently explained not only a two-branch structure of the nu(OH) and the nu(OD) bands, and temperature-induced evolution of the crystalline spectra, but also the linear dichroic effects observed in the band frequency ranges. A vibronic mechanism was analyzed, responsible for promotion of the symmetry-forbidden transition in the IR for the totally symmetric proton stretching vibrations in centrosymmetric hydrogen bond dimers. It was found to be of minor importance, when compared with analogous spectral properties of arylcarboxylic acid, or of cinnamic acid crystals. These effects were ascribed to a substantial weakening of electronic couplings between the hydrogen bonds of the associated carboxyl groups and the styryl radicals, associated with the separation of these groups in styrylacetic acid molecules by methylene groups in the molecules.     

Structure and properties of hydroxylated surfaces of oxides

A review of works dealing with the IR spectra and structure of hydroxylated surfaces of oxides is presented. Influence of crystal structure and other factors on OH stretching modes, as well as data about bending vibrations of hydroxy groups are discussed. Experimental results are compared with data of computer simulations.