Estimation of the contribution of absorption bands for overtones and composite frequencies in IR spectra of olefins and heteroatomic organic compounds

Intensities of fundamental, overtone, and composite absorption bands for 11 olefins, 17 nitrogen- and oxygen-containing organic compounds, and 12 sulfur-containing organic compounds are calculated in the anharmonic approximation. The first and second derivatives of the electric dipole moment of a molecule were calculated by the quantum-chemical ab initio MP2/6-31G(1d) approach. It is shown that, for the studied compounds, the average contribution of overtones and composite frequencies to absorption in the region from 100 to 4000 cm⁻¹ is of about 10%. The major contribution (on the average 80%) of overtones and composite frequencies falls in the regions (mainly from 1600 to 2800 cm⁻¹) where fundamental transitions are rarely observed. The calculations well describe the centers and intensities of the fundamental, overtone, and composite absorption bands and can be used for the standard-free spectrochemical determination of the compounds of interest by their overtone spectra.     

Estimation of absorption band contribution for overtones and combined frequencies in the fingerprint region for alkanes, nitriles, amines, and nitroalkanes

In the anharmonic approximation the intensities of fundamental, overtone, and combined absorption bands are calculated in the range from 100 cm^-1 to 4000 cm^-1 for a series of alkanes, nitriles, amines, and nitroalkanes. The first and second derivatives of the molecular dipole moment are calculated by quantum chemical methods in the ab initio approximation using the MP2/6-31G(1d) basis set. Overtones and combined frequencies are found to make a significant contribution (5–20%) to the total absorption. The spectral distribution of this contribution depends on the molecular structure. For nitriles and amines significant absorption of the overtones and combined frequencies is observed in the same regions where fundamental absorption bands characteristic of these compounds are located.     

An application of near-infrared and mid-infrared spectroscopy to the study of selected tellurite minerals: xocomecatlite,tlapallite and rodalquilarite

Near-infrared and mid-infrared spectra of three tellurite minerals have been investigated. The structures and spectral properties of copper bearing xocomecatlite and tlapallite are compared with an iron bearing rodalquilarite mineral. Two prominent bands observed at 9,855 and 9,015 cm⁻¹ are assigned to ²B_1g → ²B_2g and ²B_1g → ²A_1g transitions of Cu²⁺ ion in xocomecatlite. The cause of spectral distortion is the result of many cations of Ca, Pb, Cu and Zn in the tlapallite mineral structure. Rodalquilarite is characterised by ferric ion absorption in the range 12,300–8,800 cm⁻¹. Three water vibrational overtones are observed in xocomecatlite at 7,140, 7,075 and 6,935 cm⁻¹ whereas in tlapallite bands are shifted to lower wavenumbers at 7,135, 7,080 and 6,830 cm⁻¹. The complexity of rodalquilarite spectrum increases with the number of overlapping bands in the near-infrared. The observation of intense absorption feature near 7,200 cm⁻¹ confirms hydrogen bonding water molecules in xocomecatlite. Weak bands observed near 6,375 and 6,130 cm⁻¹ in tellurites are attributed to the hydrogen bonding between (TeO₃)²⁻ and H₂O. A number of overlapping bands at low wave numbers 4,800–4,000 cm⁻¹ are caused by combinational modes of tellurite ion. (TeO₃)²⁻ stretching vibrations are characterised by three main absorptions at ~1,070, 780 and 665 cm⁻¹. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of the nature of ions on the position of the absorption bands of water OH bonds in diffuse reflection spectra in the near-infrared region

The effect of the nature of anions and cations on the position of the absorption bands of free and crystallization water in inorganic salts in the near-infrared region (7400–4000 cm⁻¹) was systematically studied. It was shown experimentally that the shift of the absorption bands of free water to the high-frequency region is 100 cm⁻¹ in the region of 6900 and 62.1 cm⁻¹ in the region of 5160 cm⁻¹. It was concluded that the results on the shift of the water absorption bands in moisture-containing solid-state compounds with respect to those of pure liquid water can serve for a qualitative estimate of the bond energy of water with the substance under study and can be used to choose the wavelength for measuring the humidity of these objects and those more complicated in composition by means of near-infrared spectroscopy.     

Structure of NR<Subscript>4</Subscript>BR-H<Subscript>2</Subscript>O and CoBr<Subscript>2</Subscript>-NR<Subscript>4</Subscript>BR-H<Subscript>2</Subscript>O solutions according to electronic and IR spectroscopy data

Absorption spectra of NR₄Br-H₂O and CoBr₂-NR₄Br-H₂O (R = Et, Bu) aqueous solutions were measured within the range of 1000–25000 cm⁻¹, and the influence of tetraalkylammonium cations on the equilibrium between cobalt octahedral and tetrahedral complexes was revealed. The specificity of hydration interactions in solutions under study in various concentration ranges and resulting from them difference in spectral characteristics were analyzed. Variously directed changes in positions of bands in the region of stretching vibrations, a composite frequency of 5200 cm⁻¹, and the first water overtone occurring due to the concentration variation were found.     

A new direct Fourier transform infrared analysis of free fatty acids in edible oils using spectral reconstitution

A new transmission-based Fourier transform infrared (FTIR) spectroscopic method for the direct determination of free fatty acids (FFA) in edible oils has been developed using the developed spectral reconstitution (SR) technique. Conventional neat-oil and SR calibrations were devised by spiking hexanoic acid into FFA-free canola oil and measuring the response to added FFA at 1,712 cm⁻¹ referenced to a baseline at 1,600 cm⁻¹(1,712 cm⁻¹/1,600 cm⁻¹). To compensate for the known oil dependency of such calibration equations resulting from variation of the triacylglycerol ester (C═O) absorption with differences in oil saponification number (SN), a correction equation was devised by recording the spectra of blends of two FFA-free oils (canola and coconut) differing substantially in SN and correlating the intensity of the ester (C═O) absorption at the FFA measurement location with the intensity of the first overtone of this vibration, measured at 3,471 cm⁻¹/3,427 cm⁻¹. Further examination of the spectra of the oil blends by generalized 2D correlation spectroscopy revealed an additional strong correlation with an absorption in the near-infrared (NIR) combination band region, which led to the development of a second correction equation based on the absorbance at 4,258 cm⁻¹/4,235 cm⁻¹. The NIR-based correction equation yielded superior results and was shown to completely eliminate biases due to variations in oil SN, thereby making a single FFA calibration generally applicable to oils, regardless of SN. FTIR methodology incorporating this correction equation and employing the SR technique has been automated.     

Vibrational spectra and thermodynamic functions of allyl acetate

Raman spectrum of allyl acetate molecule has been photographed in liquid phase using 4358 ? line of mercury arc as the exciting line. Infrared absorption spectrum of the molecule has been recorded in liquid phase in the frequency range 200–4000 cm⁻¹. Both the spectra have been analysed to identify the fundamental frequencies. AssumingC _s symmetry, the observed fundamental frequencies have been assigned to various modes of vibration and compared with the frequencies of allyl halides and acetic acid. On the basis of present assignments of fundamental vibrational frequencies and assumed approximate structural parameters of the molecule, thermodynamic functions have been computed.     

IR spectroscopic investigation of structural hydroxyl groups in W−Si heteropolycompound supported on Al2O3

Structural hydroxyl and deuteroxyl groups within the K₄[SiW₁₂O₄₀]/Al₂O₃ and K₆[SiW₁₁PdO₃₉]/Al₂O₃ systems were studied by diffuse-reflectance FTIR spectroscopy in a spectral range of fundamental stretching vibrations, first overtones, and combination bands of stretching and bending vibrations. For hydroxyl groups, the region of combination vibrations is the most informative. The calculated frequencies of bending vibrations of hydroxyl groups (865 and 730 cm⁻¹) are characteristic of acidic OH groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2017–2020, October, 1999.     

Infrared characteristic bands of highly dispersed silica

Summary Infrared studies were carried out for several silica modifications. On powdering bulk silica in air, new bands were observed to appear at 3400 cm⁻¹ and 950 cm⁻¹ irrespective of its inner crystallographic structure. In addition to the bands observed for bulk silica, bands were observed for silica gel at the following frequencies: 3400, 1650, 1120, 950, and 870 cm⁻¹. Assignment of these band was made by using a deuteration technique and by preparing a transparent film of silica gel on a rock salt plate from tetramethoxy-silane and water vapor. The band at 3400 cm⁻¹ is νOH of silanol or sorbed water; 1650 cm⁻¹, δOH of sorbed water; 1120 cm⁻¹, δOH of silanol; 950 cm⁻¹,ν SiO of slanol; 870 cm⁻¹, νSiOSi of bridged ≡SiOSi≡ link on the surface.

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Zusammenfassung Es wurden Infrarot-Untersuchungen an verschiedenen Silica-Modifikationen ausgeführt. Wenn man festes Silica an Luft pulvert, werden neue Banden bei 3400 cm⁻¹ und 950 cm⁻¹ unabh?ngig von der inneren Kristallstruktur beobachtet. Zus?tzlich zu diesen Banden ergeben sich weitere in Silica-Gel bei den Frequenzen 3400, 1650, 1120, 950 und 870 cm⁻¹. Die Zuordnung dieser Banden lie? sich mit Deuterierungs-methode und durch Herstellung transparenter Filme von Silica-Gel auf Steinsalzplatten aus Tetramethoxysilan und Wasserdampf erreichen. Die Bande bei 3400 cm⁻¹ entspricht dem νOH von Silanol oder sorbiertem Wasser. 1650 cm⁻¹ dem δOH von sorbiertem Wasser, 1120 cm⁻¹ dem δOH von Silanol, 950 cm⁻¹ den δSiO vom Silanol, 870 cm⁻¹ dem νSiOSi der Brückenbindung an der Oberfl?che.

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The authors wish to express their thanks to Dr.Y. Miura, a chief of this Laboratory, for his encouragement in the course of this study, to Dr.I. Teraoka, a researcher of this Laboratory, for the preparation of sample and to Dr.R. Soda of the National Institute of Industrial Health, for his valuable discussions.     

S1←S0 vibronic spectrum and structure of fluoral in the S1 state

The vibronic absorption spectrum of fluoral vapor was studied in the region of the S₁←S₀ electronic transition (313–360 nm). The origin O₀ ⁰⁺) of the transition (29419 cm⁻¹) and a number of fundamental frequencies in the S₀ and S₁ states were determined. The character of intensity distribution in the spectral bands indicates that the electronic excitation leads to significant change of the CF₃ group orientation relative to the molecular frame. Moreover, it was found that the carbonyl fragment of the molecule in the S₁ state has pyramidal structure (in contrast, the carbonyl fragment of the fluoral molecule in the S₀ state is planar). The experimental torsion and inversion energy levels were used for the calculation of internal rotation and inversion potential functions of fluoral molecule in the S₁ state. The potential barriers to internal rotation and inversion were found to be 1270 cm⁻¹ (15.2 kJ mol⁻¹) and 550 cm⁻¹ (6.6 kJ mol⁻¹), respectively. The conformational changes caused by S₁←S₀ electronic excitation in the fluoral molecule are similar to those observed in acetaldehyde and biacetyl molecules and differ from the conformational behavior of hexafluorobiacetyl molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 294–299, February, 1998.     

Photoelectron spectroscopy of the trimethylenemethane negative ion

The photoelectron spectrum of the trimethylenemethane (TMM) negative ion is described. The electron affinity of TMM is found from the spectrum to be 0. 431±0.006 eV, and the energy difference between the [(X)\tilde]³ A￠₂\tilde X^3 A'_2 ³A′₂ and [(b)\tilde]¹ A₁\tilde b^1 A_1 ¹A₁ states of TMM is determined to be 16.1±0.2 kcal/mol. The energy difference between the lowest energy triplet and singlet states is estimated to be 13–16 kcal/mol. The enthalpy of formation of TMM is measured to be 70±3 kcal/mol, and the C-H bond enthalpy in 2-methylallyl radical is 90±2 kcal/mol. Previously unobserved vibrational frequencies of 425, 915, and 1310 cm⁻¹ are found for the triplet state of TMM, whereas a frequency of 325 cm⁻¹ is found for the singlet state. In addition, an overtone peak is observed for the triplet state at 1455 cm⁻¹, and both states contain peaks that are assigned to bands arising from excited vibrational levels of the ion.     

MIR and NIR spectroscopy of sol–gel hydrotalcites with various trivalent cations

Three different hydrotalcites were synthesized from magnesium ethoxide, and aluminium, gallium and indium acetylacetonate, using the sol–gel technique. The colloid suspensions initially obtained were gelled and separated by centrifugation. XRD diffraction patterns confirmed that all solids thus obtained possessed a hydrotalcite structure. The resulting hydrotalcites were characterized by mid-infrared (MIR) and near-infrared (NIR) spectroscopies. The two types of spectra were found not to depend on the synthetic medium or trivalent metal used and were thus quite similar. The MIR spectra for the three solids included a strong band at 3500–3000 cm⁻¹ due to stretching vibrations of the different types of O–H groups in them. The signal at about 1370 cm⁻¹ observed for all solids indicates that the sole interlayer anion present was carbonate. The NIR spectra exhibited the bands for the first and second overtone of the O–H stretching vibration in addition to various combination bands.     

Intramolecular donor-acceptor interaction in stilbene and styrene π-complexes with tricarbonylchromium. Observation in the IR spectra

The IR spectra of complexes derived from conjugated arylalkenes and tricarbonylchromium, namely (stilbene)tricarbonylchromium and (styrene)tricarbonylchromium, displayed three absorption bands instead of two expected in the region of carbonyl stretching vibrations (1800–2000 cm⁻¹). Additional absorption bands also appeared in the region corresponding to metal-π-fragment stretching vibrations (250–400 cm⁻¹). These findings indicated additional interaction involving the central metal atom, carbonyl ligands, and aromatic π-system. Such interaction increases mobility of the tricarbonylchromium fragment which may become capable of readily migrating from one π-fragment to another under certain conditions.     

Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited (<Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript>) electronic state

The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited (S ₁) electronic state. The ν_00trans = 25861 cm⁻¹ values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state (S ₁) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v′) transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ν_00trans trans origin allowed the table to be extended to high quantum numbers v′. The torsional vibration frequencies up to v′ = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited (S ₁) electronic state.     

Raman Combinations and Stretching Overtones from Water, Heavy Water, and NaCl in Water at Shifts to ca. 7000 cm−1

Photographic Raman spectra were obtained at shifts to ca. 7000 cm^–1 for pure water and for a saturated aqueous solution of NaCl using argon ion laser excitation. Raman spectra were also obtained photoelectrically for H₂O and D₂O between ca. 2500 and ca. 7000 cm^–1 using 248-nm excimer laser excitation and boxcar detection. Overtone and combination assignments are presented for H₂O and D₂O. The first IR OH-stretching overtone from water occurs 215 cm^–1 above the first Raman OH-stretching overtone because the IR overtones are dominated by asymmetric stretching. The second OH-stretching Raman overtone from water is estimated to occur near 10,020 ± 20 cm^–1, with 9950 cm^–1 as a lower limit.     

Solvent effects on the absorption spectrum of the perylene-SbCl<Subscript>5</Subscript> complex

The perylene-SbCl₅ complex is characterized by two absorption maxima, whose positions depend on the nature of the solvent. The maximum in the region of 19×10⁻³ cm⁻¹ corresponds to the perylene cationic form and depends on the medium polarity, while another, in the region of 14×10⁻³ cm⁻¹, corresponding to the perylene-SbCl₅ complex, is governed primarily by the ability of the solvent to the electrophilic solvation. However, the quantitative generalization of the data on the frequencies of absorption maxima is only possible using multiparameter equations that take into account various properties of the solvents.     

Infrared spectra of cyclic ethers and their derivatives

Data for the characteristic bands of cyclic ethers are reviewed. The infrared spectra of a number of 2-mono- and 2, 5-di-substituted derivatives of tetrahydrofuran are investigated. Absorption bands at about 900 cm⁻¹ are related to pulsation vibrations, and those at about 1200 cm⁻¹ to antisymmetric skeletal vibrations, of the tetrahydrofuran ring. It is shown that to confirm the presence of a tetrahydrofuran ring in a molecule, it is necessary to take into account not only the band of valence antisymmetric vibrations of the group C-O-C (ν _C-O-C ^as 1075 cm⁻¹), but also bands due to ring pulsation vibrations (ring symmetric valence vibrations ν _sk ^s ∼ 900 cm¹).     

Crystal structure of N-phenyl-N′-isopropylp-phenylenediamine

We have previously reported the results of studies of the hydrogen bond nature in N-phenyl-N′-isopropyl-p-phenylenediamine by a quantum chemistry method and FTIR spectroscopy [1–3]. It is shown that the IR spectrum of N-phenyl-N′-isopropyl-p-phenylenediamine has IR bands in the vNH absorption region at 3380 cm⁻¹ and 3400 cm⁻¹ corresponding to the NH groups involved in hydrogen bonding.     

IR matrix isolation spectra of some perfluoro organic-free radicals Part 1. C2F5

The pentafluoro ethyl radical has been prepared by the pyrolysis of C₂F₅I in a platinum effusion tube at ?650°C and isolated in an argon matrix. By elimination of absorption bands attributable to known fluorine compounds and from relative intensity measurements on the remaining bands, twenty frequencies were assigned C₂F₅ in the spectral range 4000–200 cm^?1. Fourteen of these frequencies were assigned as fundamentals of C₂F₅, with C_s symmetry, and the remainder to combination or overtone modes of the radical.     

UV/Vis Spectral Study of the Self-aggregation of Pinacyanol Chloride in Ethanol–Water Solutions

The concentration dependent self-aggregation of 1,1′-diethyl-2,2′-carbocyanine chloride (pinacyanol chloride dye) in 7.5% (v/v) ethanol + 92.5% water solution in the range of 10⁻⁶–10⁻³ mol⋅dm⁻³ has been investigated by quantitative UV/vis and derivative spectroscopy. Bands with maxima at 601, 546, 522, and 507 nm could be attributed, respectively, to the monomer, a sandwich-type dimer, a vibronic overtone of the dimer, and a higher aggregate, most probably a stacked trimeric form of the dye. Using the PeakFit program, the overlapping bands were separated and analyzed for all concentrations studied. From the spectral fitting routine, extinction coefficients of 192,000, 156,000, and 282,000 cm⁻¹⋅mol⁻¹⋅dm³ were determined for the monomer, dimer and trimer respectively.