Spectroscopic and structural analysis of Ca substituted La orthoferrite

Samples of orthoferrites La_1−xCa_xFeO₃ (0.15≤x≤0.45) were synthesized by double sintering ceramic technique. X-ray diffraction and infrared spectroscopy experiments were carried out and discussed for the investigated samples. The data showed the formation of single-phase orthorhombic structure of space group Pbnm. The FTIR spectra were performed in the region (1200–200 cm⁻¹). Four main absorption bands were present with some side bands and shoulders in the range (1200–400 cm⁻¹). Another four bands were appeared in the range (400–200 cm⁻¹). The positions, intensities and values of the absorptions bands vary depending on the Ca content in the samples. The first absorption band appeared at about 920 cm⁻¹ was assigned to the La–O stretching vibration.     

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of 2-hexyne

The infrared spectra (3500–50 cm⁻¹) of the gas and solid and the Raman spectra (3500–50 cm⁻¹) of the liquid and solid have been recorded for 2-hexyne, CH₃–CC–CH₂CH₂CH₃. Variable temperature studies of the infrared spectrum (3500–400 cm⁻¹) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti/gauche conformer pairs, the anti(trans) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm⁻¹ (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range −105 to −150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH₃ group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ζ, have been determined. The results are compared to similar properties of some corresponding molecules.     

The effect of hydrogen bonding interactions between 2-[4-(dimethylamino)phenyl]-3-hydroxy-4H-chromene-4-one in the ground and excited states and dimethylsulfoxide or methanol on electronic absorption and emission transitions

The surface state of optically pure polydisperse TiO₂ (anatase and rutile) was determined by infra-red (IR) spectroscopy analysis in the temperature range of 100–453 K. Anatase A300 spectrum, contrary to rutile R300 one, has a broad three-component absorption band with peaks at 1048, 1137 and 1222 cm⁻¹ in the spectral range of δ(Ti–O–H) deformation vibrations. For rutile R300 we observed a very weak band at 1047 cm⁻¹, and for the thermal treated rutile R900 these bands were not appeared at all. The analysis of temperature dependencies for the mentioned absorption bands revealed the spectral shift of 1222 cm⁻¹ band towards the high frequencies, when the temperature increased, but the spectral parameters of 1137 and 1048 cm⁻¹ bands remained the same. The temperature of 1222 cm⁻¹ band maximum shift was 373–393 K and correlated with DSC data. Obtained results allowed to assign 1222 cm⁻¹ band to the deformation vibrations of OH-groups, bounded to the surface adsorbed water molecules by weak hydrogen bonds (5 kcal/mol). During the temperature growth these molecules desorbed, which also resulted in the intensity decreasing of stretching OH-groups vibration IR-bands at 3420 cm⁻¹. The destruction and desorption of surface water complexes led to Ti–O–H bond strengthening. IR bands at 1137 and 1048 cm⁻¹ were attributed to the stronger bounded adsorbed water molecules, which are also characterized with stretching OH-groups vibration bands at 3200 cm⁻¹. These surface structure were additionally stabilized by hydrogen bonds with the neighbouring TiO₂ lattice anions and other OH-groups, and desorbed at higher temperatures.     

Raman spectroscopy of the acetates of sodium, potassium and magnesium at liquid nitrogen temperature

A comprehensive Raman spectroscopic study of the acetates of potassium, sodium and magnesium in the solid state have been made at both 298 and 77 K. Band separation of the C=O stretching region was not achieved in the 298 K spectra but was in the 77 K spectra. The CO stretching vibration is observed as a single band in both the 298 and 77 K spectra and its frequency is cation dependent. Single C–C stretching bands are observed for the acetates in the 77 K spectra. The OCO deformation vibrations were also cation dependent. Low frequency vibrations of magnesium acetate are observed at 338, 253 and 268 cm⁻¹ and are assigned to the MgO stretching vibration of the magnesium bisacetato complex. Low frequency bands were also observed for sodium acetate at 219, 277 and 288 cm⁻¹.     

Infrared depletion spectroscopy of the doubly hydrogen-bonded aniline–(tetrahydrofuran)2 complex produced in supersonic jet

The vibrational frequencies of the N–H stretching modes of aniline after forming a strong doubly H-bonded complex with tetrahydrofuran (THF) are measured with infrared depletion spectroscopy that uses cluster-size-selective resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry. Two strong infrared absorption features observed at 3355 and 3488 cm⁻¹ are assigned to the symmetric and antisymmetric N–H stretching vibrations of the 1:2 aniline–THF complex, respectively. The red-shifts of the N–H stretching vibrations of aniline agree with the ab initio calculated (MP2/6-31G**) aniline-(THF)₂ structure in which both aniline N–H bonds interact with the oxygen atom of THF through two hydrogen bonds. The calculated binding energy is found to be 29.6 kJ mol⁻¹ after corrections for basis set superposition error (BSSE) and zero-point energy. The calculated structure revealed that the angle between the N–H bonds in the NH₂ group increased to 112.5° in the aniline–(THF)₂ complex from that of 109.8° in the aniline. The electronic 0–0 band origin for the S₁ ← S₀ transition is observed at 32,900 cm⁻¹ in the aniline–(THF)₂ complex, giving a red-shift of 1129 cm⁻¹ from that of the aniline molecule.     

Far infrared spectra, conformational equilibria, vibrational assignments, ab initio calculations and structural parameters for 2-bromoethanol

The far infrared spectrum from 370 to 50 cm⁻¹ of gaseous 2-bromoethanol, BrCH₂CH₂OH, was recorded at a resolution of 0.10 cm⁻¹. The fundamental O–H torsion of the more stable gauche (Gg′) conformer, where the capital G refers to internal rotation around the C–C bond and the lower case g to the internal rotation around the C–O bond, was observed as a series of Q-branch transitions beginning at 340 cm⁻¹. The corresponding O–H torsional modes were observed for two of the other high energy conformers, Tg (285 cm⁻¹) and Tt (234 cm⁻¹). The heavy atom asymmetric torsion (rotation around C–C bond) for the Gg′ conformer has been observed at 140 cm⁻¹. Variable temperature (−63 to −100°C) studies of the infrared spectra (4000–400 cm⁻¹) of the sample dissolved in liquid xenon have been recorded. From these data the enthalpy differences have been determined to be 411±40 cm⁻¹ (4.92±0.48 kJ/mol) for the Gg′/Tt and 315±40 cm⁻¹ (3.76±0.48 kJ/mol) for the Gg′/Tg, with the Gg′ conformer the most stable form. Additionally, the infrared spectrum of the gas, and Raman spectrum of the liquid phase are reported. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental frequencies have been obtained from ab initio calculations utilizing different basis sets at the restricted Hartree–Fock or with full electron correlation by the perturbation method to second order. The theoretical results are compared to the experimental results when appropriate. Combining the ab initio calculations with the microwave rotational constants, r₀ adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg′ conformers.     

Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignments for 2-chloroethyl silane

The infrared (3500–30 cm⁻¹) spectra of gaseous and solid and the Raman (3500–10 cm⁻¹) spectra of liquid with quantitative depolarization ratios and solid 2-chloroethyl silane, ClCH₂CH₂SiH₃, have been recorded. Similar data have been recorded for the Si–d₃ isotopomer. These data indicate that two conformers, trans and gauche, are present in the fluid states but only one conformer, trans, is present in the solid. The mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (−55 to −100°C) has been recorded. The enthalpy difference between the conformers has been determined to be 181±12 cm⁻¹ (2.17±0.14 kJ/mol) with the trans rotamer the more stable form. From the isolated Si–H frequencies from the Si–d₂ isotopomer the r_o Si–H distances of 1.484 and 1.483 Å for the trans and 1.481 for the gauche conformers have been obtained. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G** from which structural parameters and conformational stabilities have been determined. With all the basis sets the trans form is predicted to be the more stable conformer which is consistent with the experimental results. These results are compared to the corresponding quantities for the carbon analogue.     

A study on the formation mechanism of graphite fluorides by Raman spectroscopy

Raman spectra were measured of highly fluorinated graphite samples prepared at room temperature, 380 and 515 °C. C_xF prepared at room temperature showed a novel downshifted band at 1555–1542 cm⁻¹ along with G band at 1593–1583 cm⁻¹. Similar behavior is also observed for samples prepared at 380 and 515 °C at early stages of fluorination, after which the Raman shifts completely disappeared. Raman spectra as well as X-ray diffraction (XRD) analysis suggest that graphite fluorides, (CF)_n and (C₂F)_n are formed via fluorine-intercalated phase with planar graphene layers.     

Low frequency vibrational spectra of some amino acids

Far-IR absorption and reflection spectra, as well as laser Mandelshtam–Brillouin and Raman scattering spectra of -glycine, β-alanine, -histidine, -tryptophane single crystals in the 0.2–400 cm⁻¹ range were investigated. It was revealed that the far-IR and Raman spectra of the amino acids under study contain more bands than predicted by factor-group analysis, thus indicating a possible contribution of low-energy intramolecular vibrations and overtones, as well as an emergence of forbidden vibrations. Some of the low-frequency bands have never, to our knowledge, been detected previously.     

Conformational studies of cyclopropylmethyl isocyanate from temperature dependent FT-IR spectra of xenon solutions and ab initio calculations

Variable temperature (−55 to −100 °C) studies of the infrared spectra (3200 to 100 cm⁻¹) of cyclopropylmethyl isocyanate, c-C₃H₅CH₂NCO, dissolved in liquefied xenon, have been carried out. The infrared spectra (gas and solid) as well as the Raman spectrum of the liquid have been recorded from 3200 to 100 cm⁻¹. By analyzing six conformer pairs in xenon solutions, an enthalpy difference of 193 ± 19 cm⁻¹ (2.31 ± 0.23 kJ/mol) was obtained with the gauche–cis rotamer (the first designation indicates the orientation of the CNCO group with respect to the three-membered ring, the second designation indicates the relative orientation of the NCO group with respect to the bridging CC bond) the more stable form and the only form present in polycrystalline solid. The abundance of the cis–trans conformer present at ambient temperature is 16 ± 1%. The potential function governing the conformational interchange has been obtained from B3LYP/6-31G(d) calculations and the two-dimensional potential has been obtained. From MP2 ab initio calculations utilizing various basis sets with diffuse functions, the gauche–cis conformer is predicted to be more stable by 223 to 269 cm⁻¹, which is consistent with the experimental results. However, without diffuse functions the predicted conformational energy differences are much smaller (77–166 cm⁻¹). Similar diffuse function dependency affects density functional theory calculations by the B3LYP method to a lesser extent. A complete vibrational assignment for the gauche–cis conformer is proposed and several fundamentals for the cis–trans conformer have been identified. The structural parameters, dipole moments, conformational stability, vibrational frequencies, infrared intensities and Raman activities have been predicted from ab initio calculations and r₀ structural parameters are estimated. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.     

Strong antiferromagnetism in the dinuclear 2-pyridone complex with N–C–O bridges: A paddle-wheel analogue of the dinuclear tetracarboxylates

A novel dinuclear complex [Cu₂(μ-L)₄(HL)₂] (1) was isolated from starting 2-pyridone (HL) via a resonance and a tautomeric transformation. Each copper centre is in a square-pyramidal coordination sphere, defined by two oxygen atoms (Cu–O4 1.978(5), Cu–O11 1.964(4) Å) and two nitrogen atoms (Cu–N2 2.003(5), Cu–N3 2.007(5) Å) of four bridging deprotonated pyridin-2-olates and an oxygen atom on the top from a neutral 2-pyridone (Cu–O2 2.227(5) Å), analogous to tetracarboxylate paddle-wheel complexes. Compound 1 was compared with mixed pyridin-2-olato/methanoato analogues [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] · 2CH₃CN (2) and [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] (2a) (2a is an air stable form obtained from 2 outside mother-liquid). The EPR spectra of air stable 1 and 2a show three signals H_z1, H₂ and H_z2, typical for the binuclear systems with spin S = 1, both revealing strong antiferromagnetism 2J = −334 (1) and −324 cm⁻¹ (2a). Interestingly, only for 1 additional H₁ signal at 100 mT is noticed (D(1) = 0.293 cm⁻¹ < hν = 0.320 cm⁻¹ < D(2a) = 0.347 cm⁻¹). On the other hand, several broad signals in the 100–450 mT region, only in the high temperature spectrum for 2a are observed. These results are in agreement with the magnetic susceptibility analysis.     

Infrared studies of chromones—I Carbonyl and hydroxyl regions

Quantitative IR solution data in carbon tetrachloride and chloroform are recorded for the CO and OH regions of 31 chromones. In the 1580–1700 cm⁻¹ region, 5-hydroxychromones show three main maxima, the two of highest frequency, at 1663 ± 3 cm⁻¹ and 1630 ± 5 cm⁻¹ in CCl₄ (1661 ± 2 cm⁻¹ and 1627 ± 5 cm⁻¹ in CHCl₃), being sufficiently intense as to possess high CO character. Typically, 5-alkoxychromones exhibit two intense maxima in this region, 1663 ± 3 cm⁻¹ and 1613 ± 7 cm⁻¹ in CCl₄ (1657 ± 2 cm⁻¹ and 1608 ± 12 cm⁻¹ in CHCl₃). Diagnostically useful changes in contour and principal peak positions can be seen for substituted and annellated 5-hydroxychromones. In the 2500–3650 cm⁻¹ region, the stretching frequencies of OH groups at the most commonly encountered positions (C-5, C-7, and 2-CH₂OH) in natural chromones, are identified.     

Vibrational analysis of 3-trifluoromethylphenol

The molecular geometry and molecular vibrations of 3-trifluoromethylphenol have been investigated by means of quantum chemical calculations and vibrational spectroscopy. The computations indicated the preference of the conformer with the OH hydrogen pointing in the direction of the trifluoromethyl group by 0.9 kJ/mol with respect to the anti conformer. FT-IR spectra of the vapour and CCl₄ solution as well as FT-IR and FT-Raman spectra of the pure liquid have been recorded in the range of 4000–150 cm⁻¹. The interpretation of the spectra was based on a scaled quantum mechanical (SQM) analysis for which the initial force field was calculated at the Becke3-Lee-Yang-Parr (B3LYP) DFT level supplemented with a 6-311++G** basis set. Using 11 scale factors refined in the present study an rms deviation of 7.6 cm⁻¹ between the experimental and SQM frequencies has been achieved. On the basis of the computations 40 of the total of 42 fundamentals of the title compound have been assigned.     

Raman scattering study of highly fluorinated graphite

Raman spectra of highly fluorinated C_xF samples (1<x<2) prepared at room temperature and 515°C were measured. C_xF samples prepared at room temperature exhibited two Raman bands at 1593–1583 and 1555–1542 cm⁻¹. Graphite samples fluorinated at 515°C for 1 and 2 min also gave similar bands at 1581–1580 and 1550–1538 cm⁻¹. However, graphite samples fluorinated from 15 min to 10 h at 515°C no longer showed such spectra. The Raman peaks shifted to lower frequencies with increasing fluorine concentration in C_xF. This trend is due to the weakening of the C---C bonds of the graphene layers. Observation of both kinds of Raman bands suggests the coexistence of two highly fluorinated phases, C₂F and C₁F, in the samples. The process of formation of graphite fluoride is discussed on the basis of the Raman spectra of C_xF samples obtained at 515°C.     

Sensitive photoacoustic overtone spectroscopy of acetylene with a multipass photoacoustic cell and a colour centre laser at 1.5 μm

Sensitive Doppler-limited overtone spectra of acetylene in the spectral region 6300–6400 cm⁻¹ have been recorded using a single mode NaCl---OH⁻ colour centre laser and a radial resonant photoacoustic multipass cell. We observed some very weak bands which have not been recorded up to now. By comparing our signal strength with direct absorption measurements of some stronger bands, we were able to calculate a minimum detectable absorption coefficient _min ≈ 10⁻⁹ cm⁻¹.     

Quantum chemical determination of molecular geometries and interpretation of FTIR and Raman spectra for 2,3,4-and 2,3,6-tri-fluoro-benzonitriles

Raman and FTIR spectra for 2,3,4- and 2,3,6-tri-fluoro-benzonitriles have been recorded in the regions 50–4000 cm⁻¹ and 400–4000 cm⁻¹, respectively. Measurement of depolarization ratios for the Raman lines has also been made. Optimized geometrical parameters, charge distributions and vibrational wavenumbers were calculated using ab initio quantum chemical method. Normal coordinate analysis has also been carried out to help assign the fundamentals of these molecules. Each vibration has been assigned using observed wavenumbers in the IR and Raman spectra and their relative intensities, depolarization ratios of the Raman lines, the calculated frequencies, vector displacements and potential energy distributions (PEDs).     

Spectroscopy of C–H stretching vibrations of gas-phase cyclohexene

The fundamental and overtone spectra of the C–H stretching of cyclohexene in the gas phase have been measured using FTIR spectroscopy in the range 2800–11 500 cm⁻¹ (Δv=1–4) and intracavity dye laser spectrometry in the range 12 900–17 500 cm⁻¹ (Δv=4–7). Up to Δv=6, the spectra show disturbed structure. The transitions observed are mainly interpreted on the basis of a comparative study with the previous experimental and theoretical work relative to 3,3,6,6-d₄-cyclohexene. Ab initio calculations of molecular geometries and fundamental vibrational frequencies have also been performed in a molecule-fixed cartesian coordinates to calculate the first derivative of the dipole moment function and of the polarisability tensor in order to reproduce the fundamental infrared and Raman spectra. In the overtone spectra, possibility of Fermi resonances between the methylenic C–H bond stretchings and combination states involving other low-frequency modes is qualitatively discussed.     

FTIR investigation of the conformational properties of the cyanide bound human hemoglobin

Infrared spectra at 4 cm⁻¹ resolution of the cyanide ligated human methemoglobin (Hb-CN) were examined in the C---N stretching region. The FTIR spectra of hemoglobin ligated with the various isotopomeric forms of the cyanide ion support the existence of three conformational states for Hb-CN. In potassium phosphate buffer at pH of 7.5, the three bands were observed at 2116, 2122 and 2127 cm⁻¹ for natural abundance Hb-CN. These bands shift to 2086, 2091 and 2095 cm⁻¹ for Hb-¹²C¹⁵N and 2073, 2077 and 2081 cm⁻¹ for Hb-¹³C¹⁴N. Two extra bands have been identified in the IR spectra of solid Hb-CN in KBr pellets. The peaks persist in the pH range between 3.5 and 10.5 with small changes in frequency and intensity. The appearance of several C---N stretching bands is consistent with C---N vibrators residing in different environment and support the hypothesis that Hb-CN assumes multiple conformers under the conditions studied.     

Polarized infrared and Raman spectra of CsHSeO4 and CsDSeO4 single crystals

The polarized absorption infrared spectra of CsHSeO₄ and CsDSeO₄ single crystals and polarized Raman spectra of the CsHSeO₄ single crystal were measured at room temperature. The polarization features of the internal vibrations of the HSeO⁻₄ ions are predicted on the basis of the X-ray structure assuming strong couping between the vibrations of the two shortest Se---O bonds and an intermediate Se---O bond. The bending methods γOH and δOH of a hydrogen bond appear at 805 cm⁻ and 1258 cm⁻¹, respectively. The νOH absorption has the ABC structure due to Fermi resonance of νOH with the overtones of the δOH and γOH vibrations. A similar shape of the νOH band is observed in the Raman spectra. The νOD absorption has a different shape from that of νOH. Intra-chain coupling was observed for the νOH and νOD vibrations.     

Born–Oppenheimer molecular dynamics of phenol in a water cluster

Born–Oppenheimer molecular dynamics for a phenol molecule in a cluster with 32 water molecules is reported. The results for the dynamics provide new theoretical informations on the role played by phenol as an hydrophobic/hydrophylic probe. Significant differences between the short-time hydrogen bond dynamics related to water–water and phenol–water interactions are observed. The vibrational spectra calculated from the Fourier transform of time correlation functions were compared with experimental data on phenol–water clusters and it was found that the average red-shift of the phenol ν_OH frequency (78 ± 36 cm⁻¹) is less important than what is observed in small phenol–water clusters at low temperatures (133–312 cm⁻¹).