Showing papers on "Infrared spectroscopy published in 1993"
TL;DR: In this article, the integrated molar extinction coefficients for infrared absorption bands of pyridine adsorbed on acid sites in Si/Al-based catalysts were determined for infrared spectra of five zeolites and two amorphous silica-aluminas.
2,429 citations
1,460 citations
804 citations
TL;DR: In this article, low-energy electron diffraction and reflection-absorption infrared spectroscopy were used to study the monolayers formed by the adsorption of n−alkane thiols [HS(CH2)mCH3] on both (111) and (100) singlecrystal gold substrates.
Abstract: Low‐energy electron diffraction and reflection‐absorption infrared spectroscopy were used to study the monolayers formed by the adsorption of n‐alkane thiols [HS(CH2)mCH3] on both (111) and (100) single‐crystal gold substrates. Samples were prepared by dosing either from solution (m=15, 17, 18, and 21) or in ultrahigh vacuum (m=0–9). On Au(111), ordered surface structures are obtained which can be indexed as (n√3×√3)R30°, where n varies from 1 to 6. On Au(100), the adsorption of short chain thiols leads to the formation of a c(2×2) overlayer while the longer chain homologs show additional diffraction spot splittings. It is also found that chain length influences both the character of the diffraction seen and perturbs the reactive sticking probability of molecules dosed in UHV. Infrared studies reveal that the polymethylene chains of the monolayers formed on Au(100) are comprised of nearly all‐trans conformations and are less canted than the comparable structures formed on Au(111). A simple model is propos...
439 citations
TL;DR: In this paper, a complete description of the first-order Raman and Brillouin spectra of single-crystal aluminum nitride is provided, and the frequency has been measured and the symmetry identified of each of the Raman active zone-center optic modes, and five independent elastic constants have been measured.
Abstract: A complete description of the first-order Raman and Brillouin spectra of single-crystal aluminum nitride is provided. The frequency has been measured and the symmetry identified of each of the Raman-active zone-center optic modes, and the five independent elastic constants have been measured. The widths of the principal Raman modes increase with increasing oxygen content up to a critical value of approximately 1 at. %, after which they are constant. This behavior supports the hypothesis of a change in the nature of the oxygen defect at that concentration.
388 citations
TL;DR: In this article, the authors investigated the infrared transmission spectra of molecules adsorbed on silver island films evaporated on CaF2 and showed that only the vibrational modes which give dipole changes perpendicular to the metal surface are infrared active.
Abstract: Infrared transmission spectra of molecules adsorbed on silver island films evaporated on CaF2 have been investigated. The spectra are remarkably simple compared with those of the molecules in the solid state (KBr pellets). Only the vibrational modes which give dipole changes perpendicular to the metal surface are infrared active. In addition, their intensities are about 200 times larger than those of the free molecule. These results can be fully accounted for if the electric field which excites the surface molecule is perpendicular to the local surface of the metal islands and is stronger than the incident electric field. The origin of the absorption enhancement and the surface selection rule is discussed theoretically by using a classical electromagnetic model.
367 citations
TL;DR: In this paper, a large-pore Ti-containing zeolite, which is active for hydrocarbon oxidation at mild conditions, has been obtained by direct synthesis using IR spectroscopy, XRD, thermal analysis, XPS, EXAFS-XANES, and DRS-UV techniques.
Abstract: A large-pore Ti-containing zeolite, which is active for hydrocarbon oxidation at mild conditions, has been obtained by direct synthesis. This is isomorphous with zeolite β, and the crucial effect of alkali metal cations on the product has been described. By means of IR spectroscopy, XRD, thermal analysis, XPS, EXAFS-XANES, and DRS-UV techniques, it has been shown that the synthesis carried out without alkali metal cations leads to zeolite β with Ti located in the framework positions. The results allow us to propose a model which explains the varying Ti coordination for as-made and calcined samples, hydrated and dehydrated. The model is consistent with the literature data on TS-1 and TS-2 structures
340 citations
TL;DR: In this paper, the authors modeled the family of interstellar IR emission bands at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 microns by calculating the fluorescence from a size distribution of interstellar polycyclic aromatic hydrocarbons embedded in the radiation field of a hot star.
Abstract: We have modeled the family of interstellar IR emission bands at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 microns by calculating the fluorescence from a size distribution of interstellar polycyclic aromatic hydrocarbons (PAHs) embedded in the radiation field of a hot star. It is found that the various emission bands are dominated by distinctly different PAHs, from molecules with much less than about 80 C atoms for the 3.3 micron feature, to molecules with 10 exp 2-10 exp 5 C atoms for the emission in the IRAS 12 and 25 micron bands. We quantitatively describe the influence on the emergent spectrum of various PAH properties such as the molecular structure, the amount of dehydrogenation, the intrinsic strength of the IR active modes, and the size distribution. Comparing our model results to the emission spectrum from the Orion Bar region, we conclude that interstellar PAHs are likely fully, or almost fully, hydrogenated. Moreover, it is found that the intrinsic strengths of the 6.2 and 7.7 micron C-C stretching modes, and the 8.6 micron C-H in-plane bending mode are 2-6 times larger than measured for neutral PAHs in the laboratory.
297 citations
TL;DR: In this article, long-slit optical and near-IR spectroscopy was performed for the bright NW and faint SE components of the oxygen-poor H II galaxy I Zw 18, yielding physical conditions and O, N, S and He abundances for these components.
Abstract: Long-slit optical and near-IR spectroscopy are presented for the bright NW and faint SE components of the oxygen-poor H II galaxy I Zw 18, yielding physical conditions and O, N, S, and He abundances for these components. All of the elemental abundances for the two components of I Zw 18 are equal (within errors), thereby placing constraints on evolutionary theories for this system.
277 citations
TL;DR: In this article, the current use of electrical and optical methods to study the semiconducting properties of SiC was reviewed. And the authors treated Hall measurements, deep-level transient spectroscopy, infrared absorption and luminescence.
Abstract: We review the currentuse of electrical and optical methods to study the semiconducting properties of SiC. More specifically we treat Hall measurements, deep-level transient spectroscopy, infrared absorption and luminescence. Some very recent results, not yet available in the literature, on donor and acceptor levels in 3C-SiC, 4H-SiC and 6H-SiC are discussed.
268 citations
TL;DR: In this paper, a systematic investigation of the IR and Raman spectra of pure and Al-, B-, Ti- and Fe-substituted silicalites in the SiO stretching region (1500-700 cm-1) is presented.
Abstract: A systematic investigation of the IR and Raman spectra of pure and Al-, B-, Ti- and Fe-substituted silicalites in the SiO stretching region (1500–700 cm–1) is presented. As well as the characteristic stretching modes of the skeleton, silicalites containing hydroxylated nests show also broad bands at ca. 960 cm–1(IR) and at ca. 976 cm–1(Raman), associated with O3Si—OH group modes, with prevailing Si—OH stretching character. The replacement of Si with heavier elements (like Ti or Fe) causes the appearance of new IR- and Raman-active modes (i) at 960 cm–1(IR and Raman) and at 1127 cm–1(Raman) in Ti silicalite; (ii) at 1015 cm–1(IR) and at 1020 cm–1(Raman) in Fe silicalite. Neither the Raman nor the IR spectra of the skeletal modes are substantially modified by the introduction of Al (ZSM5). The presence of boron induces the appearance in the IR spectra of a complex absorption at 1380 cm–1 and at 960–930 cm–1, which corresponds to the absorptions at 1417 and 976 cm–1 in the Raman spectra. The assignment of the absorptions associated with heteroatoms and hydroxylated nests is discussed in detail.
TL;DR: The atomic layer epitaxy (ALE) reactions of TiCl 4 at 175 and 450 o C with silica preheated at 200-820 o C, were studied by nuclear magnetic resonance and Fourier transform infrared spectroscopy, while etching experiments with sulfuric acid were carried out to determine the amount of amorphous titanium species as mentioned in this paper.
Abstract: The atomic layer epitaxy (ALE) reactions, i.e., the saturating gas-solid reactions of TiCl 4 at 175 and 450 o C with silica preheated at 200-820 o C, were studied by nuclear magnetic resonance and Fourier transform infrared spectroscopy, while etching experiments with sulfuric acid were carried out to determine the amount of amorphous titanium species. At 175 o C TiCl 4 reacted directly with the OH groups of silica either monofunctionally or bifunctionally depending on the preheat temperature of silica
TL;DR: In this article, the authors presented complete mid-infrared monolayer spectra perfectly extracted from the strong water vapor bands using the polarization-modulated IRRAS method, which is not sensitive to the isotropic absorptions of the sample environment.
Abstract: This study devoted to the FT-IR spectroscopy of monolayers spread at the air/water interface is, to our knowledge, the first report presenting complete mid-infrared monolayer spectra perfectly extracted from the strong water vapor bands. This has been possible with the use of the polarization-modulated IRRAS method, which is not sensitive to the isotropic absorptions of the sample environment. On the basis of theoretical modeling and experiments, the best angle of incidence has been found near 76° for detection of intraplane as well as out-of-plane oriented monolayer absorptions. With the use of such experimental conditions, on the normalized difference (covered vs. uncovered water) PM-IRRAS spectra, monolayer vibrational bands come out upward or downward, depending on the orientation of their transition moment with respect to the interface. Application to the study of deuterated arachidic acid and arachidate monolayers allows observation of the vibrational modes of the polar head groups interacting with the liquid water molecules and provides some evidence of their symmetrical anchoring. The virbrational modes of the liquid water subphase contribute to these difference spectra as broad dips that certainly contain information on a possible restructuring of the water molecules at the interface.
TL;DR: In this paper, Fourier transform infra-red (FTi.r.) spectroscopy was used for real-time monitoring of the molecular changes occurring during the thermo-oxidative degradation of polybenzimidazole material.
TL;DR: The formation of Si-O-defect groups due to the incorporation of Ti in the framework of zeolites is evidenced by means of solid-state tetraethylammonium (TEA) cation exchange; a new assignment for the infrared (IR) band in both β-Ti and TS-1 is presented as discussed by the authors.
Abstract: The formation of Si–O–defect groups due to the incorporation of Ti in the framework of zeolites is evidenced by means of solid-state tetraethylammonium (TEA) cation exchange; a new assignment for the infrared (IR) band in both β-Ti and TS-1 is presented.
TL;DR: It is estimated that about 1% of the organics found in the coma of Comet Halley could have been produced by thermal formaldehyde reactions taking place in the nucleus.
TL;DR: In this article, the metallofullerene LaC 82 has been isolated for the first time from the carbon soot using two-step liquid chromatographic method, and it was well identified as a stable molecule classified to a novel family of fullerene cage molecules.
TL;DR: In this paper, the electrolyte anion (dopant) used for the preparation of these films heavily influences the π-conjugated system of the polymer backbone, and CF 3 SO 3 was found to be the best dopant and to cause the least structural disorder or furan ring opening.
Abstract: Polyfuran films have been synthesized by electropolymerization of terfuran and investigated as a function of film preparation conditions in both the doped and undoped state. These Films have been characterized by infrared spectroscopy, scanning electron microscopy, optical absorption, X-ray photoelectron spectroscopy, dc conductivity, and electron spin resonance measurements. The electrolyte anion (dopant) used for the preparation of these films heavily influences the π-conjugated system of the polymer backbone. Structural disorder and doping level depends on the nature of the electrolyte anion. CF 3 SO 3 - was found to be the best dopant and to cause the least structural disorder or furan ring opening
TL;DR: In this article, the authors compare reported compositions of a C:H films in a ternary phase diagram and conclude from the comparison of NMR and infrared data that infrared analysis does not provide a quantitative measure of the sp3/sp2 ratio.
Abstract: We compare reported compositions of a‐C:H films in a ternary phase diagram. It is assumed that the films comprised three phases: sp3 hybridized carbon, sp2 hybridized carbon and hydrogen. The data are found to split into two well‐separated groups. This separation depends on the method used to measure the sp3/sp2 ratio. We conclude from the comparison of NMR and infrared data that infrared analysis does not provide a quantitative measure of the sp3/sp2 ratio.
TL;DR: In this article, a unique correlation was established between the characteristic absorption pattern in the OH stretching region and the experimental conditions applied in the course of the production and of the pretreatment procedure on the other.
TL;DR: In this paper, the effects of carbonation on the solidification/stabilization (S/S) of zinc using Portland cement Type V (OPC) has been investigated by X-ray photoelectron spectroscopy (XPS) and FTIR.
TL;DR: Raman and infrared spectroscopic studies and conductivity and viscosity measurements of propylene carbonate (PC) doped with various concentrations of lithium perchlorate are reported in this paper.
Abstract: Raman and infrared spectroscopic studies and conductivity and viscosity measurements of propylene carbonate (PC) doped with various concentrations of lithium perchlorate are reported. The assignment of the vibrational modes was supplemented by AM1 normal coordinate analysis. Both Raman and infrared spectra showed band splitting in the fundamental vibrational frequencies of PC and perchlorate anion. Spectral curve fitting within the totally symmetric perchlorate band shape showed contributions of free ion, solvent-shared ion pairs, and contact ion pairs. Strong Li + -PC interaction was observed for the PC ring deformation band at 112 cm -1 . Ion pairing as deduced by spectroscopic techniques provided a rationale to account for conductivity and viscosity data
TL;DR: In this article, the authors developed a method for the determination of free fatty acids (FFA) in fats and oils based on both transmission and attenuated total reflectance approaches, covering an analytical range of 0.2-8% FFA.
Abstract: Rapid direct and indirect Fourier transform infrared (FTIR) spectroscopic methods were developed for the determination of free fatty acids (FFA) in fats and oils based on both transmission and attenuated total reflectance approaches, covering an analytical range of 0.2–8% FFA. Calibration curves were prepared by adding oleic acid to the oil chosen for analysis and measuring the C=O band @ 1711 cm–1 after ratioing the sample spectrum against that of the same oil free of fatty acids. For fats and oils that may have undergone significant thermal stress or extensive oxidation, an indirect method was developed in which 1% KOH/methanol is used to extract the FFAs and convert them to their potassium salts. The carboxylate anion absorbs @ 1570 cm–1, well away from interfering absorptions of carbonyl-containing oxidation end products that are commonly present in oxidized oils. Both approaches gave results comparable in precision and accuracy to that of the American Oil Chemists’ Society reference titration method. Through macroprogramming, the FFA analysis procedure was completely automated, making it suitable for routine quality control applications. As such, the method requires no knowledge of FTIR spectroscopy on the part of the operator, and an analysis takes less than 2 min.
TL;DR: Raman, infrared transmission, and photoluminescence measurements of the two classes of materials are compared and a possible mechanism for the efficient luminescence in porous Si is discussed in light of the similarities between siloxene and porous Si.
Abstract: Using Raman and infrared transmission spectroscopy, the vibrational properties of siloxene (${\mathrm{Si}}_{6}$${\mathrm{O}}_{3}$${\mathrm{H}}_{6}$) and its derivatives are investigated and interpreted in terms of various structural modifications of siloxene which have been proposed in the past. On the basis of experimental and theoretical investigations siloxene is found to be a mixture of ${\mathrm{Si}}_{6}$ rings and/or linear Si chains interconnected by oxygen, and Si planes terminated by H and OH. The influence of thermal annealing, chemical treatment, and laser irradiation on the structure of siloxene is discussed in terms of the corresponding changes of the vibrational spectra and the x-ray-diffraction patterns. The vibrational properties of siloxene are very similar to those of electrochemically anodized porous Si. Raman, infrared transmission, and photoluminescence measurements of the two classes of materials are compared and a possible mechanism for the efficient luminescence in porous Si is discussed in light of the similarities between siloxene and porous Si.
TL;DR: In this paper, the mid-infrared reflectance spectra of a number of mineral mixtures (including quartz-microcline, quartz-hornblende, microcline-albite and albite-augite) were measured using an interferometer spectrometer with a 4/cm resolution.
TL;DR: In this article, the OD and CN stretching vibrations of HDO and CD 3 CN molecules have been used as probes of the structural environments of water and acetonitrile in infrared spectroscopy.
Abstract: Mixtures of water and acetonitrile in the full concentration range have been studied by infrared spectroscopy. OD and CN stretching vibrations of HDO and CD 3 CN molecules have been used as probes of the structural environments. Acetonitrile molecules which are unaffected by water molecules are found for a broad concentration range (0.1≤xH 2 O≤0.8), showing that a preferential solvation occurs. The strong tendency for self-association of water molecules is evident from the occurrence of a broad OD stretching band. Chains of water molecules linked by hydrogen bonds are suggested to be formed rather than spherical clusters