Infrared spectra of cyclohexane-1,3-dione derivatives in the region of 1750–1550 cm−1

Russian Chemical Bulletin -     

Infrared spectra of triacetylene in the 4000-220 cm−1 region: Absolute band intensity and implications for the atmosphere of Titan

The gas phase infrared spectra of triacetylene were studied at room temperature in the 4000-220 cm⁻¹ wavenumber region. The absolute intensity of all the bands of noticeable strength were experimentally determined and the associated uncertainties were systematically estimated. The data obtained were then used for studying the detectability of C₆H₂ in Titan's atmosphere by means of infrared spectroscopy. The upper limit of mean stratospheric abundance derived from the already available Titan IR spectra (a fraction of ppb) is in agreement with the photochemical model estimates.     

Infrared spectra of pyridinium salts in solution—I. The region of middle frequencies

Infrared spectra of h₅- and d₅-pyridinium salts Py⁺H ⋯ A⁻ (A⁻= SbCl⁻₆, ClO⁻₄, BF⁻₄, J⁻, Br⁻, Cl⁻) and their N-deuterated analogues have been measured in organic aprotic solvents in the region of 1650-400 cm⁻¹ and assignments proposed for internal fundamental modes of the pyridinium ions. Notable differences of in-plane δ_NH and out-of plane γ_NH deformation mode frequencies in i.r. spectra of the salts in solution and in solid state have been established. In particular, the γ_NH mode frequencies in solution are 40–80 cm⁻¹ higher than those in solid state. In the series of the salts studied the γ_NH mode frequencies change from 903 to 1080 cm⁻¹ depending upon the H-bonding strength. A strong vibrational coupling γ_NH↔-ν₅ (γ_CH) has been shown to occur in h₅-pyridinium salts and a γ_ND↔v_10b (γ_CH) coupling in their N-deuterated analogues. Isotopic shifts and changes of the bandwidths of the v₁₄, v_19b and v_8b internal modes show that these modes are strongly mixed with the in-plane deformation mode δ_NH in h₅- and d₅-pyridinium salts.     

Raman and infrared spectra of GdTb (MoO4)3 single crystal in the region 250–1000 cm−1

Polarized Raman spectra (single crystal) at 300 K and infrared spectra (powder) at 300 and 85 K in the region 250–1000 cm⁻¹ of a binary molybdate of gadolinium and terbium have been recorded. Based on C_2ν symmetry, group theoretical analysis has been carried out and vibrational assignment is proposed. The observed symmetric stretching frequencies of the MoO²⁻₄ ion points to the absence of resonance vibrational interaction in this system.     

Low-frequency (20–400 cm−1) vibrational spectra of N-methylacetamide in the liquid state

Low-frequency Raman spectra (20–400 cm⁻¹) of liquid N-methylacetamide were studied. The experimental data were directly transformed into the R(v) representation. This spectrum was compared with the far infrared spectrum. Temperatures from 30 to 165 °C were investigated. A low-frequency band around 100 cm⁻¹ is assigned to a mode involving atoms in intermolecular hydrogen bonds. This assignment is qualitatively supported by the observed spectrum of Nd-methylacetamide.     

ATR-FT-IR spectroscopy in the region of 550–230 cm−1 for identification of inorganic pigments

A comprehensive study of ATR-FT-IR spectra of 40 inorganic pigments of different colours widely used in historical paintings has been carried out in the low wave number spectral range (550–230 cm^?1). The infrared spectra were recorded from mixtures of pigment and linseed oil. It is demonstrated that this spectral range – essentially devoid of absorption peaks of the common binder materials – can be well used for identification of inorganic pigments in paint samples thereby markedly extending the possibilities of pigment identification/confirmation by ATR-IR spectroscopy into the realm of pigments having no absorptions in the mid-IR region. In some cases the method can be used alone for pigment identification and in many cases it provides useful additional evidence for pigment identification using other instrumental techniques (electron microprobe analysis, XRF, optical microscopy). Together with earlier work this study provides a comprehensive overview of the pigment identification possibilities using ATR-FT-IR as well as a collection of reference spectra and is expected to be a useful reference for conservation practitioners.     

Origin of the doublet at 1360 and 1340 cm−1 in the Raman spectra of tryptophan and related compounds

Raman spectra of indole, skatole, tryptophan and its derivatives including C₄-monodeuterated tryptophan were studied with special attention to the origin of the band around 1350 cm⁻¹. The band is observed as a doublet or triplet depending on the compound and solvent, which was ascribed to Fermi resonance between one fundamental and one or two combination bands of the out-of-plane bending vibrations. Removal of the interaction is seen for C₄D-tryptophan and some solutions of skatole. The assignments of the component vibrations were made based on the shifts in frequencies upon C₄-deuteration. In tryptophan derivatives the doublet (or triplet) peaks exhibit steep changes in relative intensity at the pK_a points of the dissociable groups, which is ascribed as arising from slight frequency shifts of a pK_a-sensitive component vibration. Relations between the relative intensity and environment of indole were obtained and their possible applicability to the analyses of Raman spectra of proteins is suggested.     

ATR-FT-IR spectral collection of conservation materials in the extended region of 4000-80 cm–1

In this paper, a spectral collection of over 150 ATR-FT-IR spectra of materials related to cultural heritage and conservation science has been presented that have been measured in the extended region of 4000-80 cm^–1 (mid-IR and far-IR region). The applicability of the spectra and, in particular, the extended spectral range, for investigation of art-related materials is demonstrated on a case study. This collection of ATRFT-IR reference spectra is freely available online (http://tera.chem.ut.ee/IR_spectra/) and is meant to be a useful tool for researchers in the field of conservation and materials science.     

X-ray absorption signatures of hydrogen-bond structure in water–alcohol solutions

Despite fundamental importance, the experimental characterization of the hydrogen bond network, particularly in multicomponent protic solutions, remains a challenge. Although recent work has experimentally validated that the oxygen K-edge X-ray absorption spectra is sensitive to local hydrogen bond patterns in pure water and aqueous alcohol solutions, the generality of this observation is unknown—as is the sensitivity to the electronic structure of the alcohol cosolvent. In this work, we investigate the electronic structure of water solvated alcohol model geometries using energy specific time-dependent density functional theory to calculate oxygen K-edge X-ray excitations. We find that the geometry of dangling hydrogen bonds in pure water is the main contributor to the pre-edge feature seen in the X-ray absorption spectra, agreeing with previous experimental and theoretical work. We then extend this result to solvated alcohol systems and observe a similar phenomenon, yet importantly, the increase of electron donation from alkyl chains to the alcohol OH group directly correlates to the strength of the core excitation on the dangling hydrogen bond model geometry. This trend arises from a stronger transition dipole moment due to electron localization on the OH group.     

K–edge X–ray absorption spectra of argon in sputtered aluminum films

We have measured K–edge X–ray absorption spectra of argon in sputtered aluminum films at a synchrotron radiation facility (the Photon Factory). We found that the energy and shape of white line change when the film is annealed at 500 °C and the spectrum becomes resembling that of argon implanted in silicon. From the analyses of the X–ray absorption spectra and TEM observation we concluded that argon exists as very small atom clusters with a diameter less than 1 nm or exist as isolated atoms in the as–sputtered aluminum film, and that the size of the clusters become as big as 10 nm diameter when the film is heated.     

The i.r. rotation—vibration spectrum of CH3F in the region of 3000 cm−1

The i.r. spectrum of CH₃F has been remeasured with a resolution of about 0.04 cm⁻¹ from 2800 cm⁻¹ to 3160 cm⁻¹. There are four important vibrational transitions that contribute to the spectrum in this region and these have been identified as the two CH-stretching fundamentals, ν₁ and ν₄, the overtone of the E-type CH-deformation mode, 2ν₅, and the combination of the AI and E-type CH-deformation modes, ν₂ + ν₅. The spectrum shows evidence of a number of strong perturbations and we believe that we have identified a Fermi resonance between the states |υ₁ = > and |υ₅ = 2, l₅ = 0>, another Fermi resonance between the states |υ₄ = 1, l₄ = ± 1>; and |υ₂ = 1, υ₅ = 1, l₅ = ±1>; and Coriolis interactions between |υ₅ = 2, l₅, = 0> and |υ₂ = 1, υ₅ = 1, l₅ = ±1> and between |υ₁ = 1> and |υ₄ = 1, l₄ = ±1>. About 600 rotation-vibration transitions have been assigned and many of these have been analyzed to obtain effective rotational constants. The interpretation of the effective rotational constants is complicated by the strong perturbations but we believe that we have been able to estimate some of the unperturbed molecular parameters.     

Infrared study of magnesium–nickel hydroxide solid solutions

The IR spectra of the co-precipitated solid solutions Mg_xNi_1−x(OH)₂ were studied in the 4000–40 cm⁻¹ region. The spectra as a whole resemble those of Mg(OH)₂ and β-Ni(OH)₂, while certain differences are noted when compared with the spectra of the mechanically mixed samples Mg(OH)₂+β-Ni(OH)₂. Such a behavior may imply formations of mono-phase solid solutions which have a brucite-like crystal structure. The composition-dependent band shifts were observed for the fundamentals and this tendency is discussed in terms of polarization of the OH bond and partial covalency of the MO bonds. The gradual changes in band position of Mg_xNi_1−x(OH)₂ (1.00≥x≥0.00) were used to assign the IR active lattice modes of the solid solutions and to review the assignment of β-Ni(OH)₂.     

Evolution of thermal disorder in the absorption and Raman spectra of all-trans-β-carotene

The temperature-dependent visible absorption and resonant Raman spectra of all-trans-β-carotene extremely diluted in dimethyl sulfoxide are investigated to clarify the effects of temperature on conjugated polyenes. The visible absorption and Raman spectra are found to blueshift with increasing temperature. The blueshift in polyenes is attributed to the decrease in the liquid density and the concomitant decrease in the refractive index by the Lorentz–Lorenz relation. We demonstrate that visible absorption is reproduced well by simple Franck–Condon analysis using a single Huang–Rhys factor over a temperature range. The analysis reveals features of temperature dependence in terms of important spectral parameters, such as line width, Raman scattering cross section and Huang–Rhys factor.     

The study of the speciation of uranyl–sulphate complexes by UV–Vis absorption spectra decomposition

Uranyl–sulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical significance. The spectra of UO₂(NO₃)₂ + Na₂SO₄ solutions of different Φ _S = [SO₄²⁻]/[U(VI)] ratio at pH = 2 were recorded for this purpose. As the presence of uranyl-nitrate complexes should be expected under these experimental conditions, the spectra of UO₂(NO₃)₂ + NaNO₃ solutions with different Φ _N = [NO₃⁻]/[U(VI)] ratio at pH = 2 were also measured. The effects of Φ _S and Φ _N ratios value were most pronounced in wavelength interval 380–500 nm. Therefore, these parts of experimental overall spectra were used for deconvolution into the spectra of individual species by the method proposed. It enabled to calculate stability constants of anticipated species at zero ionic strength. The Specific Ion Interaction Theory (SIT) was used for this purpose. Stability constants of UO₂SO₄, UO₂(SO₄)₂²⁻, UO₂NO₃ ⁺ and UO₂(NO₃)₂ coincided well with published data, but those for UO₂(SO₄)₃⁴⁻ and UO₂(NO₃)₃⁻ were significantly lower.     

Raman spectrum of carbonates MIICO3 in the 1100-1000cm −1 region: observation of the ν1, mode of the isotopic (C16O182O)2− ion

The Raman spectrum of a series of carbonates M^IICO₃ with aragonite or calcite structure has been reinvestigated in the 1100-1000 cm⁻¹ region, corresponding to the totally symmetric stretch (ν₁) of the (CO₃)²⁻ anion. Besides the very strong peak corresponding to the ν₁ mode of the (C¹⁶O₃)²⁻ ion, nearly all spectra exhibit a very weak satellite peak whose frequency agrees well with the calculated ν₁ frequency of the isotopic ion (C¹⁶O¹⁸₂O)⁻². Small deviations from the theoretical values are qualitatively discussed on the basis of vibrational couplings between near-neighbour anions.     

The photoacoustic spectra of substituted benzenes in the near infrared region—I

The photoacoustic spectra of three benzonitriles, five acetophenones and three benylbromides were recorded using the commercial EDT OAS 400 photoacoustic spectrometer in the near i.r. region, i.e. 3850–10000 cm⁻¹ (2.6−1.0 μm). A combined study of the mid and far i.r. absorption spectra with the near i.r. PAS spectra led to a provisional assignment of the observed PAS peaks as combinations of fundamentals and overtone bands.