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.     

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.     

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.     

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 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.     

Ab initio simulation of the photoelectron spectra of HCO− and DCO−

Large scale, vibrational CI calculations using a global ab initio potential energy surface are used to calculate multidimensional Franck-Condon overlaps from the ground vibrational state of HCO⁻ and DCO⁻ to all final bound and several quasibound vibrational states of HCO and DCO. The resulting Franck-Condon spectra are compared with recent experimental photoelectron spectra of HCO⁻ and DCO⁻.     

Infrared and Raman spectra of N-methyl-N′-alkylureas

The i.r. and Raman spectra of solid CH₃NHCONH(CH₂)nCH₃ (n = 0–15), MUR′, are presented. The vibrational assignment is proposed on the basis of the spectral comparison and the results of the normal coordinate analysis for some short chain molecules. MUR′ are concluded to be in the extended trans form including the methylurea part. Analysis of methylene band progressions based on the transfer matrix theory, in which the end group effect is taken into account, proves that the force field for the n-alkyl chain of MUR′ agrees with that for n-alkanes within the limit of experimental error.     

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.     

Infrared and Raman spectra in the region below 1800 cm−1 of some amino acid chelates of the type cis-[(NH3)2Pt(amac)](NO3), where amacthe anions of glycine,l-alanine,l-aminobutyric acid,l-valine and l-norvaline

The IR and Raman spectra of a series of complexes of the general formula cis-[(NH₃)₂Pt(amac)](NO₃), where amac = the chelated anions, glycinate (gly), l-alaninate (ala), l-2-aminobutyrate (2-aba), l-valinate (val) and l-norvalinate (nval) have been recorded in the 1800-250 cm⁻¹ (IR) and 1800-100 cm⁻¹ (Raman) regions. Several characteristic bands have been identified or empirically assigned, based mainly on deuteration experiments and previous similar studies. The difference in ν^a_COO − ν^s_COO for the carboxylate group increases with increasing length of the aliphatic side chain of the amino acids, i.e. gly < ala < 2-aba < val < nval, indicative of the more covalent character of the PtO bond, the stability of the corresponding chelates being the opposite. If the tentative assignment of the νPtO bond made is correct, the above suggestion is confirmed by the variation of this frequency, which decreases in the above order.     

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.     

A spectroscopic investigation of the carrageenans and agar in the 1500-100 cm−1 spectral range

Fourier transform infrared (FTIR) and Raman spectra in the 1600-100 cm⁻¹ range have been employed in a structural analysis of biopolymers of the polygalactane type. In spite of the complexity of the spectra in this region, precise assignments have been made, first on the basis of previously calculated frequencies of the basic unit (d-galactose) and secondly by comparing the spectra of kappa-, iota-, and lambda-carrageenans, as well as agar and appropriate disaccharides. The results of this work provide confirmation of previous assignments of IR absorptions at 930, 820, 805 and 845 cm ⁻¹ and the interpretation of several other bands, notably those due to bending vibrations of the glycosidic linkages and those between 1040 and 1010 cm⁻¹. The latter are associated with the OSO symmetrical stretch. Assignments are also presented for the 700-100 cm⁻¹ region, on which there are no previous reports. The present analysis may provide a basis for further studies of the conformational changes accompanying gelation, a process which is different from one polygalactane to another.     

Vibrational spectra of ICl2− and IBr2− ions in aminopyridinium trihalides

IR and Raman spectra for iodine dichlorides and iodine dibromides of 2-, 3- and 4-aminopyridines (2AP, 3AP and 4AP) in solids have been measured, together with those for pyridine (Py). Raman spectra in methanol solutions have also been obtained.Although each AP molecule has two nitrogen atoms each having a lone pair of electrons, it is found that protonation occurs at the ring nitrogen atom. It is concluded that two configurations for ICl₂⁻ ion, symmetric and asymmetric, coexist in solids as well as in solution. For IBr₂⁻, two configurations coexist in solids, while only asymmetric configuration exists in solution.     

Infrared polarized spectra of hexamethylbenzene above and below the λ point at 116 K

The i.r. spectrum of hexamethylbenzene (HMB) has been investigated above and below the λ point between phase II (stability range 383-116 K) and phase III (below 116 K) in order (i) to get information on the molecular and/or crystal modifications involved in the phase transition and (ii) to assign i.r. absorptions. Spectra of randomly oriented samples and of single crystals having ab and bc as predominant faces were taken at different temperatures. In phase II the number of bands and their polarizations clearly indicate that the benzene like modes feel a potential of symmetry higher than that of the site, whilst the band broadness of the absorptions due to methyl stretchings and bendings does not allow any indication on “peripheral” potential. Changes occurring in the spectrum of the low temperature phase should indicate a more ordered situation in which the molecular symmetry is D_3d or S₆.     

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.     

Laser ionization spectra and electronic structure of Kn and NaKn−1 clusters

Photoionization of small K_n and NaK_n−1 clusters with n ⩽ 34 has been achieved in a crossed laser-molecular-beam experiment. The relative ion peak intensities in mass spectra reveal fragmentation effects which are wavelength-dependent. The vertical ionization profiles in the threshold region give some insight into the electronic structure.     

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.