Hot band spectroscopy of CCO in the C–O stretching region: The (ν1 + 2ν3) − 2ν3 and (2ν1 + ν3) − (ν1 + ν3) bands

Two C–O stretching hot bands, (ν₁ + 2ν₃) − 2ν₃ and (2ν₁ + ν₃) − (ν₁ + ν₃), of the CCO radical in the ground electronic state were measured. These hot bands are red shifted by approximately 70 cm⁻¹ compared to the C–O stretching fundamental. CCO was produced in a discharge through a flowing mixture of carbon suboxide and helium. The spectra were recorded using a diode laser spectrometer. The band origins were determined to be 1904.32512(62) and 1902.69130(56) cm⁻¹ for (ν₁ + 2ν₃) − 2ν₃ and (2ν₁ + ν₃) − (ν₁ + ν₃), respectively. The measurements in this band together with previously reported frequencies in the C–C and C–O stretching regions were analysed to determine harmonic frequencies and anharmonicity constants.     

A Raman spectroscopic study of the antimonite mineral peretaite Ca(SbO)4(OH)2(SO4)2·2H2O

Raman spectra of mineral peretaite Ca(SbO)₄(OH)₂(SO₄)₂·2H₂O were studied, and related to the structure of the mineral. Raman bands observed at 978 and 980 cm^?1 and a series of overlapping bands observed at 1060, 1092, 1115, 1142 and 1152 cm^?1 are assigned to the SO₄^2? ν₁ symmetric and ν₃ antisymmetric stretching modes. Raman bands at 589 and 595 cm^?1 are attributed to the SbO symmetric stretching vibrations. The low intensity Raman bands at 650 and 710 cm^?1 may be attributed to SbO antisymmetric stretching modes. Raman bands at 610 cm^?1 and at 417, 434 and 482 cm^?1 are assigned to the SO₄^2? ν₄ and ν₂ bending modes, respectively. Raman bands at 337 and 373 cm^?1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO₄^2? and SbO stretching vibrations support the concept of the non-equivalence of these units in the peretaite structure.     

Vibrational interactions in dimethylgold(III) halides and carboxylates

The far-infrared and Raman spectra of binuclear molecules [Me₂AuX]₂ (X = Cl, Br, I) and [Me₂Au(OOCR)]₂ (R = Me, CF₃, Bu^t, Ph) in the 600–70 cm⁻¹ region are reported. The experimentally measured vibrational frequencies of [Me₂AuX]₂ are in a good agreement with density functional theory predictions. The Au…Au vibrational interactions predicted to be in the 270–60 cm⁻¹ region of [Me₂AuX]₂ far-IR and Raman spectra have been observed. The Raman-active Au…Au vibrations of the [Me₂Au(OOCR)]₂ molecules were found to be in the same region as those of [Me₂AuX]₂. The Au–X stretching modes were observed between 100 and 250 cm⁻¹ in accordance with the DFT predictions. Their frequencies in the IR spectra of [Me₂AuX]₂ increase in the sequence I < Br < Cl while the AuC₂ stretching frequencies decrease in the same order. This fact might be an evidence of the decreasing covalent character of the gold-halogen bridges. The Au–O stretching bands of dimethylgold(III) carboxylates have been observed in the 500–250 cm⁻¹ region, and Au–C stretching frequencies of both [Me₂AuX]₂ and [Me₂Au(OOCR)]₂ compounds have been found between 600 and 500 cm⁻¹.     

Electronic and vibrational circular dichroism spectroscopic study of non-covalent interactions of meso-5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin with (dG-dC)10 and (dA-dT)10

The non-covalent interactions of (dG-dC)₁₀ and (dA-dT)₁₀ with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) were studied using the combination of electronic circular dichroism (ECD), vibrational circular dichroism (VCD) spectroscopy, and UV–vis and IR absorption spectroscopy at different ratios of both components r = [oligonucleotide]/[TMPyP] = 2/1–10/1 where [oligonucleotide] and [TMPyP] are the amount concentrations of oligonucleotide per base-pair and TMPyP, respectively. It was shown that TMPyP with (dG-dC)₁₀ provided hemiintercalative binding mode for r = 4/1 that is manifested in vibrational spectra: The absorption band assigned to the C6O6 stretching vibration of guanine is shifted from 1683 to 1672 cm⁻¹, the corresponding VCD couplet from 1694(−)/1674(+) to 1684(−)/1663(+) cm⁻¹ and its intensity decreases. The absorption band assigned to the C2O2 stretching vibration of cytosine is shifted from 1652 to 1644 cm⁻¹ and its intensity increases. TMPyP with (dA-dT)₁₀ provided three binding modes: (i) external binding to the phosphate backbone, (ii) external minor groove binding for the ratios >6/1 and (iii) external major groove binging associated with the partial B- to Z-transition for the ratios <4/1. The major groove binding is manifested in VCD spectra by the intensity decrease of the bands 1655 and 1638 cm⁻¹ assigned to the thymine vibrations while the bands assigned to the adenine vibrations are unchanged. In the (dA-dT)₁₀–TMPyP complexes, the external binding to the phosphate backbone accompanied by self-stacking of porphyrins along the phosphate backbone chain is preferred at temperatures higher than 40 °C.     

The Raman OH stretching bands of liquid water

In this work, from the discussion on water structure and clusters, it can be deduced that the OH stretching vibration is closely related to local hydrogen-bonded network for a water molecule, and different OH vibrations can be assigned to OH groups engaged in various hydrogen bonding. At ambient condition, the main local hydrogen bonding for a molecule can be classified as DDAA (double donor–double acceptor), DDA (double donor–single acceptor), DAA (single donor–double acceptor) and DA (single donor–single acceptor) and free OH vibrations. As for water at 290 K and 0.1 MPa pressure, the OH stretching region of the Raman spectrum can be deconvoluted into five sub-bands, which are located at 3014, 3226, 3432, 3572, and 3636 cm⁻¹, and can be assigned to ν_DAA-OH, ν_DDAA-OH, ν_DA-OH, ν_DDA-OH, and free OH₂ symmetric stretching vibrations, respectively.     

Near-infrared spectroscopy: A powerful tool in studies of acid-treated clay minerals

The benefit of near-infrared (NIR) spectroscopy in studies of acid-treated clay minerals is demonstrated. The effects of mineral type, composition and content of non-swelling interlayers on the dissolution rate are investigated. Detailed analysis of the NIR region is performed by comparing the first overtone (2ν_OH) and combination (ν + δ)_OH bands with the fundamental stretching (ν) and bending (ν) vibrations. Spectra of acid-treated samples show a gradual decrease in the intensities of the structural OH overtone (near 7100 cm^?1) and combination (4600–4300 cm^?1) bands reflecting a fewer number of octahedral atoms. The appearance of the 2ν_SiOH vibration for terminal (isolated) SiOH groups near 7315 cm^?1 indicates the formation of a protonated silica phase. The band near 7130 cm^?1 remaining in the spectra of acid-treated samples is assigned to 2ν_HOSiOH of geminal silanol groups. Thus the creation of geminal silanols, previously detected by ²⁹Si MAS-NMR spectroscopy in acid-treated hectorite, is confirmed also by NIR spectroscopy. The assignment of the 4555 cm^?1 band to the (ν + δ)_SiOH combination enabled calculation of the wavenumber for the SiO–H bending vibration (～810 cm^?1) that is not observable in the mid-IR region due to overlapping with the Si–O band of amorphous silica (～800 cm^?1). The NIR spectra confirm that trioctahedral hectorite is much more susceptible to dissolution in HCl than dioctahedral nontronite. The dissolution rate of kaolinite present in the Badin clay as an admixture is lower than that of the main mineral nontronite. The accessibility of the interlayers for protons significantly influences the stability of clay minerals in HCl. Mixed-layered mineral illite/smectite with only 30% of swelling interlayers dissolves more slowly than smectite of similar chemical composition containing mainly swelling interlayers.     

Raman study of natural berlinite from a geological phosphate deposit

Natural berlinite from a heated sedimentary sequence in Cioclovina Cave (Romania) was studied using Raman spectroscopy complemented with infrared techniques. Vibrational data acquired at room temperature were compared with those reported for synthetic berlinite in ambient conditions. The symmetry of the (PO₄)^3? units is confirmed by the observation of characteristic bands attributed to the ν₁(PO₄)^3? stretching mode, both the ν₄ and ν₂ bending regions at 500–595 cm^?1, and 350–500 cm^?1, respectively. The berlinite Raman fingerprint was unambiguously identified at 1111 and 1104 cm^?1, confirming the identity of the species and elucidating some controversial reports in the mineralogy field.The vibrational data of natural berlinite relates to its crystallography, and along with the spectra–structure correlation, confirmed an almost ideal natural berlinite crystal.     

The spectroscopic characterization of the sulphate mineral ettringite from Kuruman manganese deposits,South Africa

The mineral ettringite has been studied using a number of techniques, including XRD, SEM with EDX, thermogravimetry and vibrational spectroscopy. The mineral proved to be composed of 53% of ettringite and 47% of thaumasite in a solid solution. Thermogravimetry shows a mass loss of 46.2% up to 1000 °C. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1072 cm⁻¹ attributed to a carbonate symmetric stretching mode, confirming the presence of thaumasite. The observation of multiple bands in the ν₄ spectral region between 700 and 550 cm⁻¹ offers evidence for the reduction in symmetry of the sulphate anion from T_d to C_2v or even lower symmetry. The Raman band at 3629 cm⁻¹ is assigned to the OH unit stretching vibration and the broad feature at around 3487 cm⁻¹ to water stretching bands. Vibrational spectroscopy enables an assessment of the molecular structure of natural ettringite to be made.     

Vapor deposited ethanol–H2O ice mixtures investigated by micro-Raman scattering

Solid deposits have been formed at 88 K and 10⁻¹ Torr from ethanol–water gas collected above aqueous solutions of ethanol (EtOH) (0.6, 2, 4.5, 9 and 17 mol%). The composition of different gas mixtures varying between 1:16 and 1:0.8 EtOH:H₂O are determined at 295 K using our experimental vapor–liquid equilibrium (VLE) data in combination with the Wilson model [28]. The Wilson constants derived at this temperature are Λ₁₂ = 0.37(4) and Λ₂₁ = 0.58(5). The concentration of EtOH in the ice mixture can be calculated using these data and a kinetic model of condensation. It is found to vary between 9 and 65 mol% EtOH. The ice mixtures are analyzed in situ in a modified cryostage by micro-Raman spectroscopy. The distinct vibrational signatures of pure EtOH, EtOH aqueous solutions and EtOH–ice mixtures are identified in the 400–3800 cm⁻¹ spectral range. Internal vibrational motions of EtOH molecules are affected by temperature and concentration. The presence of amorphous EtOH–ice phases at 88 K is demonstrated by the characteristic vibrational signatures of the ν_OH stretching modes. The crystallization of an EtOH hydrate is proposed during annealing at ∼140 K of a 65 mol% EtOH–ice mixture. According to our preliminary X-ray diffraction work, this phase has apparently a distinct structure from that of solid EtOH or from EtOH–clathtrate structures usually found in frozen aqueous solutions. For ice mixtures of lower EtOH content, a distinct hydrate phase crystallizes at ∼170 K. These results suggest that ice mixtures obtained by vapor deposition reflect the existence of EtOH clusters of a distinctive structural nature with respect to those encountered in frozen aqueous mixtures.     

The FTIR spectra of substituted tetraoxa[8]circulenes and their assignments based on DFT calculations

The FTIR spectrum of symmetrical derivative of the tetraoxa[8]circulene, named para-dinaphthyleno-2,3,10,11-tetraundecyldiphenylenotetrafuran (p-2B2N4R, R = n-C₁₁H₂₃) has been recorded and interpreted using density functional theory (DFT) calculations for the model compounds p-2B2N4R (R = H, C₂H₅). The unsubstituted tetraoxa[8]circulene, namely para-dinaphthylenodiphenylenotetrafuran (p-2B2N) and para-dinaphthyleno-2,3,10,11-tetraethyldiphenylenotetrafuran (p-2B2N4R, R = C₂H₅) belong to the D_2h and D₂ symmetry point groups, respectively. The equilibrium molecular geometry, harmonic vibrational frequencies and infrared intensities have been calculated utilizing the DFT/B3LYP method with the 6–31G(d) basis set using the symmetry constraints. Comparison of the calculated vibrational spectra with the experimental data provides a reliable assignment of the observed bands in the FTIR spectra. The results of quantum-chemical calculations provide a complete interpretation of vibrational modes based on a good agreement with all details of the experimental spectra.     

Structural,vibrational and thermodynamics propertiesof Zn-based semiconductors

We have preformed first-principle calculations for the structural, vibrational and thermodynamic properties of the IIB–VIA Zn-based semiconductor compounds ZnX (X = O, S, Se, Te). The phonon dispersion curves along several high-symmetry lines at the Brillouin zone together with the corresponding phonon density of states are calculated using density-functional perturbation theory. The calculated phonon frequencies at the Γ, X, and L points of the Brillouin zone show good agreement with the experimental values and other calculations. The thermodynamics properties including the phonon contribution to the Helmholtz free energy ΔF, the phonon contribution to the internal energy ΔE, the entropy S, and the constant-volume specific heat C_V are determined within the harmonic approximation based on the calculated phonon dispersion relations. If 298 K is taken as a reference temperature, the difference values of H ? H₂₉₈ have been also calculated and compared with the available experimental data.     

Molecular and vibrational structure of the extracellular bacterial signal compound N-butyryl-homoserine lactone (C4-HSL)

The molecular and vibrational structure of the title compound (C4-HSL) was studied by experimental and theoretical methods. The infrared (IR) absorption spectrum was measured in the solid state and in CCl₄ suspension. The observed absorption bands were compared with transitions obtained with B3LYP/cc-pVTZ density functional theory (DFT) calculations. Two stable molecular conformations were predicted, corresponding to an endo- and an exo-conformer with similar energies. Intermolecular amide–amide hydrogen bonding in the crystal state was approximated by a simple cluster model, leading to excellent agreement with the observed solid state IR spectrum. Due to the low solubility of C4-HSL in common solvents for IR spectroscopy, such as CS₂ and CCl₄, a liquid solution spectrum of pure, monomeric C4-HSL was not obtained. However, absorbance peaks observed in oversaturated CCl₄ solution could be assigned to distinct contributions from suspended micro-crystalline aggregates and dissolved monomeric species. The key vibrational bands of the monomeric form of C4-HSL are reported here for the first time: 3425 cm^?1 [ν(N–H)], 1784 cm^?1 [ν(CO), lactone], 1688 cm^?1 [amide I], and 1494 cm^?1 [amide II] (CCl₄).     

The state energy and the displacements of the potential minima of the 2Ag− state in all-trans-β-carotene as determined by fluorescence spectroscopy

The fluorescence spectrum of all-trans-β-carotene was recorded at 170 K. The 1B_u⁺ → 1A_g⁻ fluorescence exhibited clear vibrational structures constituting a mirror image with those of the 1B_u⁺ ← 1A_g⁻ absorption, and the deconvolution of the entire spectrum identified the 2A_g⁻(0) → 1A_g⁻(0) transition at 14 500 cm⁻¹. The displacements of the 1B_u⁺ and 2A_g⁻ potential minima along ν₁ and ν₂ (the CC stretching and C–C stretching normal coordinates, respectively) were determined to be 1.2 and 0.9, and 1.6 and 1.5, respectively. Thus, much larger potential displacements in the 2A_g⁻ state than in the 1Bu⁺ state have been shown.     

Raman spectra of Sr3(PO4)2 and Ba3(PO4)2 orthophosphates at various temperatures

The Raman spectra for Sr₃(PO₄)₂ and Ba₃(PO₄)₂ were investigated in the temperature range from 80 to 1623 K at atmospheric pressure. An unexpected melting of each sample was observed around 1573–1583 K in this study. In the temperature range from 80 to 1323 K, the Raman wavenumbers of all observed bands for Sr₃(PO₄)₂ and Ba₃(PO₄)₂ continuously decrease with increasing temperature. A quantitative analysis on the wavenumbers of Raman bands for both samples reveals that the ν₃ antisymmetric stretching vibrations show the strongest temperature dependence and the ν₂ symmetric bending vibration displays the weakest temperature dependence. The effects of cations on Raman bands are discussed. The reason for the unexpected melting of both samples is mainly attributed to the significant contribution from excess surface energy and the grain-boundary energy that has apparently lowered the melting points of the small samples, i.e., Gibbs–Thomson effect.     

High-resolution infrared analysis of seven fundamental bands of gaseous isothiazole between 750 and 1500 cm−1

The gas phase IR spectrum of isothiazole, C₃H₃NS, between 550 and 1700 cm⁻¹ was recorded with a resolution of ca. 0.003 cm⁻¹. The rotational structure of seven fundamental bands in the region 750–1500 cm⁻¹ has been assigned and analysed by the Watson Hamiltonian model. A number of local resonances in the bands have been identified and explained qualitatively in terms of Coriolis interactions. For each band upper state spectroscopic constants, including band center, rotational constants, and quartic centrifugal distortion constants are given. From observed crossings due to resonances we locate the weak bands ν₉(A′) and ν₁₃(A′) at 1041.9(2) and 642.0(3) cm⁻¹, respectively. The anharmonic frequencies have been determined using a cc-pVTZ basis set, at the MP2 and B3LYP levels; the two theoretical methods give very similar results for rotational constants, anharmonic band center frequencies and distortion constants, and many of these are in good agreement with experiment.     

An infrared study on Langmuir–Blodgett films of 14,15-bis(hydroxyimino)-13-thiaoctacosane

The Langmuir–Blodgett (LB) films of 14,15-bis(hydroxyimino)-13-thiaoctacosane (TOC) on aluminium plated substrates were investigated using Fourier transform infrared (FTIR), grazing angle (GAIR) and horizontal attenuated total reflectance (HATR) techniques. The LB films of TOC can be transferred onto the solid substrate successfully. The molecular structure of LB films was analysis by comparing the GAIR and HTAR spectra. The intense bands at 2848 and 2918 cm⁻¹ are assigned to symmetric ν_s(CH₂) and asymmetric ν_a(CH₂) stretching vibrations of methylene groups. These peaks suggest that the alkyl chains in TOC are nearly in all-trans conformational state. The presence in the infrared spectra of several bands due to the methylene wagging and twisting modes and of the splitting of the bands due to the methylene scissoring mode at 1467 and 1459 cm⁻¹ and the CH₂ rocking mode at 720 and 731 cm⁻¹ also indicates that in films of TOC alkyl chains are in the all-trans conformation and packed in either an orthorhombic or a monoclinic structure with an orthorhombic subcell containing two mutually orthogonal molecules. Another conclusion presented in this paper that the alkyl chain tilt, which is the angle between the axis, which bisects the C–C bonds and the surface normal, was quite large by comparing the GAIR and HATR spectra.     

Infrared and Raman spectra of magnesium ammonium phosphate hexahydrate (struvite) and its isomorphous analogues. IX: Spectra of protiated and partially deuterated cubic magnesium caesium phosphate hexahydrate

Infrared and Raman spectra of cubic magnesium caesium phosphate hexahydrate, MgCsPO₄·6H₂O (cF100), and its partially deuterated analogues were analyzed and compared to the previously studied spectra of the hexagonal analogue, MgCsPO₄·6H₂O (hP50). The vibrational spectra of the cubic and hexagonal dimorphic analogues are similar, especially in the regions of HOH stretching and bending vibrations. In the difference IR spectrum of the slightly deuterated analogue (<5% D), one distinctive band appears at 2260 cm⁻¹ with a small shoulder at around 2170 cm⁻¹, but only one band is expected in the region of the OD stretchings of isotopically isolated HDO molecules. The small weak band could possibly result from second-order transitions (a combination of HDO bending and some libration of the same species) rather than statistical disorder of the water molecules. By comparing the IR spectra in the region of external vibrations of water molecules of the protiated compound recorded at RT (room temperature) and at LNT (liquid nitrogen temperature) and those in the series of the partially deuterated analogues, it can be stated with certainty that the bands at 924 and 817 cm⁻¹ result from librations of water molecules, rocking and wagging respectively. And the band at 429 cm⁻¹ can be safely attributed to a stretching Mg–O_w mode. In the ν₃(PO₄) and ν₄(PO₄) region in the infrared spectra, one band in each is observed, at 995 and 559 cm⁻¹, respectively. In the region of the ν₁ modes, in the Raman spectrum of the protiated compound, one very intense band was observed at 930 cm⁻¹ which is only insignificantly shifted to 929 cm⁻¹ in the spectrum of the perdeuterated compound. The band at 379 cm⁻¹ in the Raman spectrum could be assigned to the ν₂(PO₄) modes. With respect to the phosphate ion vibrations, the comparison between the two polymorphic forms of MgCsPO₄·6H₂O and their deuterated compounds shows that ν₁(PO₄) and ν₃(PO₄) appear at lower wavenumbers in the cubic phase than in the hexagonal phase. These data are in full agreement with the lower repulsion potential at the cubic lattice sites compared with that for the hexagonal lattice sites.     

HF and DFT studies and vibrational spectra of 1,2-bis(2-pyridyl)ethylene and its zinc (II) halide complexes

Ab initio restricted Hartree–Fock and density function theory calculations using BLYP, B3LYP and B3PW91 functionals were carried out to study molecular structure and vibrational spectrum of 1,2-bis(2-pyridyl)ethylene (which is abbreviated as bpe). Comparison of calculated and experimental results indicates the density functional B3LYP and BLYP/6-311G* methods are more accurate in predicting fundamental vibrational frequencies than the scaled other approaches. On the basis of calculated results, assignment of fundamental vibrational modes of bpe was proposed. Complexes of the type Zn(bpe)X₂ [where X = Cl, Br, I] have been studied in the 4000–400 cm⁻¹ region, and assignments of all the observed bands were made. The analysis of the infrared spectra indicates that there is some structure-spectra correlations.     

Vibrational spectra and structure of methoxysilanes and products of their hydrolysis

Equilibrium geometries and force fields for the series of molecules (MeO)_nSiMe_4−n(I), (OH)_nSiMe_4−n(II), and (MeO)_nSi(OH)_4−n(III) with n = 1–4 are obtained at the DFT/B3LYP level of theory with 6-31G^* and aug-cc-pVDZ basis sets in order to predict the structural parameters and vibrational spectra of these molecules, the larger part of which was not characterized experimentally. The performance of these theoretical methods was assessed on the existing spectral data for series I. The B3LYP/aug-cc-pVDZ method, firstly applied to this class of molecules, demonstrates a fair agreement with experimental vibrational frequencies even without empirical scaling. For molecules of series II and III vibrational spectra are predicted in order to supply spectral data for monitoring the sol–gel processes at the hydrolysis stage. The hyperconjugative strengthening of SiO bonds with the number of oxygen atoms coordinated to silicon leads to the growth of their frequencies, but the larger increase of νSiO (due to kinematic factors) occurs at the SiOMe/SiOH substitution. The predicted distinctive feature of series II and III is the appearance of bands with high IR intensity in the 1000–900 cm⁻¹ spectral region that increase their frequencies with n. In series III it is accompanied with the steady increase of the ν_sSiO₄ frequency in the 700–600 cm⁻¹ range.     

Raman spectroscopy of a sulfur dioxide visual sensor: The origin of the two colors in the solid sample

The vibrational spectroscopic characterization of a sulfur dioxide visual sensor was carried out using a Raman microscope system. It was observed the formation of two distinct complexes, that were characterized by the position and relative intensities of the bands assigned to the symmetric stretching, ν_s(SO₂), of the linked SO₂ molecules. In fact, in the yellowish orange complex, that corresponds to the 1:1 stoichiometry, only one band is observed, assigned to ν_s(SO₂) at ca. 1080 cm^?1 and, in the deep red complex, that corresponds to the 1:2 complex, at ca. 1070 and 1090 cm^?1 are observed. The variation of the relative intensities of the bands assigned to ν_s(SO₂) present in the Ni(II)·SO₂ complex, in different points of the sample, shows clearly the requirement of the Raman microscope in the vibrational characterization of this kind of molecular sensor.