Showing papers on "Infrared spectroscopy published in 1979"

Band limits and the vibrational spectra of tetrahedral glasses

Abstract: The primary features of the Raman and infrared spectra of $A{X}_{2}$ tetrahedral glasses are associated with the edges of the vibrational bands calculated by Sen and Thorpe. The dominant Raman peak is assigned to a singular matrix element rather than a peak in the density of vibrational states. Simple expressions are developed which yield useful values of the vibrational force constants and intertetrahedral angles for vitreous Si${\mathrm{O}}_{2}$, Ge${\mathrm{O}}_{2}$, and Be${\mathrm{F}}_{2}$.

Infrared spectra of chemisorbed CO on Rh

Abstract: The infrared spectrum of CO chemisorbed on alumina‐supported Rh atoms has been investigated. In agreement with previous work, three types of adsorbed species have been clearly distinguished on the basis of their C–O stretching frequencies. Species I, assigned as Rh(CO)2, is formed only with Rh atoms which are isolated from each other. Species II, assigned as Rh–CO, and III, assigned as Rh2CO, are formed on Rh clusters having two or more Rh atoms. CO‐species II and III undergo interactions with neighbor CO species causing an increase in wave number as coverage increases. Based on infrared intensity measurements for species I, the OC–Rh–CO angle is ∼90°. Chemisorbed 13CO yields the expected infrared spectrum on Rh, and rapid isotopic exchange between 13CO(ads) and 12CO(g) is observed which cannot be explained by the observed rate of desorption of CO from the supported Rh surface.

Vibrational spectroscopy of cation‐site interactions in phosphate glasses

Abstract: Thirty different binary metal oxide glasses having the metaphosphate composition have been prepared containing cations from the following groups: alkali metals, alkaline earths, transition metals, and lanthanide and actinide metals. Far infrared absorption assigned to the cation vibration in its oxygen cage has been measured for these glasses. Empirical ionic models are proposed correlating the absorption maximum with the cation mass, charge, and ionic radius. Discrepancies between the observed and predicted vibrational frequency indicate a more covalent interaction between the metal cation and the glass network. Raman intensities and vibrational frequencies of the network metaphosphate vibrations have been obtained and provide additional evidence about the cation–site interaction.

Vibrational spectroscopy of molecular constituents of one‐dimensional organic conductors. Tetrathiofulvalene (TTF), TTF+, and (TTF+)2 dimer

Abstract: An extensive vibrational assignment of TTF and TTF‐d4 is achieved, improving the previously reported one through the use of polarized infrared spectra of single crystals of the monoclinic form. Infrared spectra of the monoclinic and triclinic forms are compared and the different crystal field effects discussed. Powder Raman and infrared spectra of (TTF)Br1.0 and (TTF‐d4)Br1.0, Raman depolarization ratios and infrared spectra of (TTF)ClO4 and (TTF‐d4)ClO4 solutions are reported. The assignment of the ag, b1u, b2u, and b3u fundamental modes of (TTF)+ and (TTF‐d4)+ radicals allows the identification of most of the relevant frequency shifts following the ionization of the TTF structure. The possible use of the ionization shifts for the study of the electronic charge distribution in the conducting TTF systems is considered. The parallel investigation of the concentration effects on the visible and infrared absorption spectra of TTF+ in solution let us to identify anomalous infrared absorptions associated with ...

An infrared study of phase-III poly(vinylidene fluoride)

Abstract: Infrared spectra representative of crystalline regions of cast films of phase‐III poly(vinylidene fluoride) (PVF2) have been obtained by absorbance subtraction techniques using a FT‐IR instrument. The spectra contain more bands than previously reported and are not consistent with current models for the crystal structure. Several possible models and their relationship to the corresponding crystalline spectra of phase II and phase I are discussed.

Infrared spectroscopy of ferrihydrite: evidence for the presence of structural hydroxyl groups

Abstract: IR spectroscopy has shown that adsorbed water is almost completely removed from ferrihydrite by evacuation at room temperature. Absorption bands at 3615 and 3430 cm- 1 appearing thereafter are interpreted as arising from OH groups located respectively at the surface and deeper in the structure. These groups are readily converted to OD on treatment with D20 vapour and this has allowed the OH deformation vibration to be identified at 800 cm- I. It is proposed that OH groups in ferrihydrite are about half as numerous as those in akagan+ite (fl-FeOOH) and that they may occur in environments similar to those in this mineral. The formula for ferrihydrite proposed by earlier workers, 5 Fe203.9H20, should thus be amended to Fe203.2 FeOOH.2.6H20 in order to indicate the presence of structural OH groups. A re-appraisal of the ferrihydrite structure appears desirable. Naturally occurring ferric hydroxide gel has been studied by Chukhrov et al. (1971, 1972, 1973) using X-ray diffraction (XRD) and infrared (IR) spectroscopy. They proposed the name ferrihydrite and concluded that it had a defect-hematite structure, as proposed earlier by Towe & Bradley (1967) for a synthetic specimen. This structure was sustained by the failure of the latter authors to detect absorption bands assignable to deformation vibrations of structural OH groups in IR spectra. Schwertmann & Fischer (1973) arrived at a similar conclusion from IR spectra of naturally occurring ferric hydroxides. Chukh- rov et al. (1971) further stated that the presence of OH groups was precluded by the typical bonding between Fe octahedra in this type of structure. Thus on the basis of characteriza- tion by XRD, DTA and IR spectroscopy, ferrihydrite was accepted as a distinct mineral species of formula 5Fe203.9H20, containing no structural OH groups (Fleischer et al., 1975). The IR results quoted by these authors are central to the elucidation of the structure of ferrihydrite, but the procedures employed all involved the use of K Br pressed disks. It is suggested that this may not have been the most appropriate technique, and in this study, the spectrum of a synthetic ferrihydrite is re-examined using a film technique in conjunction with D20 exchange.

Vibrational spectra and carbon–hydrogen stretching mode assignments for a series of n‐alkyl carboxylic acids

Abstract: The Raman and infrared spectra for the C4, C8, C12, and C16 carboxylic acid series were obtained at liquid nitrogen temperatures, in the 2900 cm−1 spectral region and were compared to spectra for selected branched and straight chain alkane systems. For hexadecanoic acid‐d3 the Fermi resonance interaction between the CD3 symmetric stretching mode and the overtone level of the CD3 asymmetric deformation vibration was examined as a function of physical state. In this example of a negative Fermi resonance perturbation, in which the lower frequency overtone component is more intense than the higher frequency fundamental, the coupling increases as the system passes from either the matrix isolated species or solution phase to the polycrystalline state. The spectra of the carboxylic acid series, as well as the spectra of 2,2,4‐trimethyl pentane and n‐octane, suggest that in the 2900 cm−1 region an analogous Fermi resonance coupling exists between the CH3 symmetric stretching vibration at ∼2938 cm−1 and the 2871 cm−1 overtone transition of the CH3 asymmetric deformation. Unfortunately, the 2930–2940 cm−1 region for the solid systems is further complicated by transitions attributed to crystal interactions. Although the Fermi interaction for the methyl group has been recognized in the simpler halomethane system, for example, it has not been previously discussed in the more general context of significantly larger branched and straight chain molecules. Comparisons of the carboxylic acid spectra in the 2900 cm−1 region have also led to assignments for the α‐CH2 (adjacent to the carbonyl group) and the ω‐CH2 (adjacent to the methyl group) C–H stretching modes.

Synthetic allophane and imogolite

Abstract: Summary In order to prepare allophane and imogolite in the laboratory, solutions containing l–2× 10–3 M orthosilicic acid and 4–0.5 × 10–3 M A1C13 (SiO2/Al2O3 molar ratio; 0.5, 1.0, 2.0, 4.0 and 8.0) were heated at 95–100°C for 113 hours after addition of NaOH (NaOH/Al molar ratio; 1.0, 2.0, 2.8 and 3.0). Boehmite was found in the precipitates from all solutions with initial SiO2/Al2O3 ratios of 0.5. Imogolite was found with allophane II in the products from solutions with SiO2/Al2O3 ratios of 1.0 or greater and with NaOH/Al ratios of 2.8 or less (final pH 5.0), whereas allophane I was found in the precipitates from solutions with the same SiO2/Al2O3 ratios but with the NaOH/Al ratio of 3.0 (final pH = 5.0–6.3). The mode of formation, chemical composition, infrared spectra, electron micrographs, electron diffraction patterns and differential thermal analysis curves of synthetic imogolite and allophanes (I and II) were compared with those of their natural counterparts.

Spectral evidence for SO2 frost or adsorbate on Io's surface

Abstract: The infrared reflection spectrum of Io matches that from an SO2 frost grown in the laboratory.

Vibronic intensity enhancement in the infrared spectra of heavily doped (CH)x and (CD)x

Abstract: Fourier Transform IR transmission spectroscopy has been utilized to elucidate the nature of the polymer–dopant interaction in doped (CH)x. Significant changes in the IR spectrum occur after doping and several intense bands at 1385, 1295, and 832 cm−1 have been observed and their shifts studied upon deuteration. The origin of these intense features can be attributed to a vibronic activation and enhancement of the totally symmetric Raman active Ag modes in the IR spectrum.

Study of hydracids trapped in monatomic matrices. I. Near infrared spectra and aggregate structures

Abstract: The infrared spectra of H35Cl, D35Cl, HBr, DBr and their mixtures in solid argon and krypton in the range 10–30 K are presented. Studies have been made over a wide concentration range, for matrix/hydracid ratio from 1000 to 20 which, together with annealing experiments and H/D isotopic dilutions, allow a complete discussion of polymeric species spectra. In the monomer region, Q features are clearly identified at low M/R ratio and assigned to lattice distortion effects on isolated molecules. A new assignment for dimer bands is proposed, in which the two molecules are not equivalent and characterized by different values of force constants and moment derivatives. The trimer is found cyclic, a configuration already mentioned, the three molecules being equivalent and oriented along the sides of an equilateral triangle. After annealing, a new polymeric species associated with a strong band at lower frequency appears and is identified, in the light of H/D mixture spectra, as a cyclic planar tetramer. From accurate frequency measurements one concludes that the H/D isotopic substitution slightly changes the hydracid force constant, a DX molecule acting as a stronger perturber than a HX one on any partner belonging to the same aggregate. At last the analysis of mixed H35Cl–HBr and HCl–HI spectra enables a comparison between the perturbing power of these three molecules, the decreasing electron donor power being in the order HI, HBr, HCl.

The 4-8 micron spectrum of the infrared source W33 A

Abstract: The spectrum of the highly obscured infrared source W33 A from 4.5 to 8 microns is measured in order to investigate the intervening cold, dense interstellar material. Spectrophotometry at a relative spectral resolution of about 0.015 by an airborne filter-wheel infrared spectrometer reveals strong absorption features at 4.61, 5.99 and 6.78 microns. The absorption at 4.61 microns is attributed primarily to the fundamental vibration-rotation band of CO at a column density (at least 10 to the 19th/sq cm) which is 10% of the carbon inferred from silicate abundances. The strengths and line widths of the absorption agt 5.99 and 6.78 microns are interpreted as evidence of absorption in the resonance bands of carbonyl, carbon-carbon double, methyl and methylene bonds of hydrocarbons associated with interstellar dust.

Theory of High Frequency Differential Interferometry: Application to the Measurement of Infrared Circular and Linear Dichroism via Fourier Transform Spectroscopy

Abstract: A general method for the direct measurement of differential absorption intensities using a Fourier transform infrared spectrometer is described. The differential intensities must be higher in frequency than the interferogram frequencies and may arise from a periodic variation of the absorption strength of the sample, or by dichroic response of the sample to alternate states of polarization of the infrared beam. Specific expressions are presented for the measurement of circular and linear dichroism. These expressions represent an extension of the Grosjean-Legrand polarization modulation technique to Fourier transform interferometry.

Solute‐solvent interaction and its effect on the vibronic and vibrational structure of pyrene spectra

Abstract: — The enhancement of weakly allowed electronic and vibrational transitions of pyrene in polar solvents at room temperature has been studied by optical and infrared techniques. We previously reported the formation of molecular complexes between pyrene and alcohols by monitoring the changes in the fundamental stretching vibrational band of the —OH group of alcohols in the presence of pyrene. The infrared spectrum of pyrene in the region 1575–1700cm-1 has been found in the present work to undergo changes in polar solvents, consistent with complex formation, with the appearance of new bands at wavenumbers where symmetry-forbidden transitions exist. The enhancement of weak bands in the electronic spectra is attributed to the reduction in the symmetry of the pyrene molecule brought about by complex formation. Further support for this interpretation is provided by the finding that I-methylpyrene, which has reduced symmetry, shows the enhancement in the electronic spectra and the appearance of new bands in the infrared spectra even in inert solvents. The anomalous behavior of aromatic solvents is discussed.

Interaction of hydrazine with copper(II) chloride in acidic solutions. Formation, spectral and magnetic properties, and structures of copper(II), copper(I), and mixed-valence species

Abstract: : The reaction of hydrazine with copper(II) chloride in acidic aqueous solution has been shown to produce at least four distinct complexes. Hydrazine behaves as a reducing agent, leading to the white, diamagnetic copper(I) complex (N2H4)CuCl and the black paramagnetic mixed-valence copper(I,I,II) complex (N2H5)2Cu2Cl6. Blue and green copper(II) complexes (N2H5)2CuCl4 2H2O and (N2H5) CuCl3 are also formed. Infrared spectra establish the presence of coordinated hydrazinium ions in the blue, green, and black compounds. Structures are proposed for all of these materials based on spectroscopic and magnetic measurements.

Monolayer Studies of Chiral and Racemic 12-Hydroxyoctadecanoic Acids

Abstract: The monolayer properties of chiral and racemic 12-hydroxyoctadecanoic acids (12HOA) have been studied. Both acids showed, in each pressure-area isotherm, a pressure plateau. This was interpreted as a two-dimensional phase transition region: from the expanded monolayer composed of bent chain molecules with both the hydroxyl and carboxyl groups attached to the water surface, to the condensed monolayer composed of straight chain molecules oriented steeply to the water surface. It was suggested by measuring infrared spectra of the collapsed films and the built-up films that the condensed monolayer involves intermolecular hydrogen bonds. Differences between (R)- and dl-12HOA were found in the plateau pressure and its temperature dependence leading to the transition energy. These results were attributed to the formation of a recemic molecular compound during condensation of monolayers of dl-12HOA, prior to collapse, followed by a different manner of hydrogen bonding. Electron microscope observation gave strong ...