Showing papers on "Infrared spectroscopy published in 1994"

Introductory Raman spectroscopy

Abstract: Part 1 Basic Theory.- Historical Background of Raman Spectroscopy Energy Units and Molecular Spectra Vibration of a Diatomic Molecule Origin of Raman Spectra Factors Determining Vibrational Frequencies Vibrations of Polyatomic Molecules Selection Rules for Infrared and Raman Spectra Raman Versus infrared Spectroscopy Depolarisation Ratios The Concept of Symmetry Point Symmetry Elements The Character Table Classification of Nominal Vibrations by Symmetry Point Group Selection Rules Resonance Raman Spectra Space Group Symmetry Normal Vibrations in a Crystal Selection Rules for Solids (Factor Group) Polarised Raman Spectra of Single Crystals Normal Co-ordinate Analysis Band Assignments and Isotopic Shifts. Part 2 Instrumentation and Experimental Techniques: Major Components Excitation Sources Sample Illumination and Scattered Light Collection Monochromator or Spectograph Detection System Instrument Calibration Sampling Techniques Depolarisation Ratios Raman Difference Spectroscopy. Part 3 Special Techniques: Nonlinear Raman Spectroscopy Time-Resolved (IR2) Spectroscopy Matrix Isolation Raman Spectroscopy High Pressure Raman Spectroscopy Surface Enhanced Raman Spectroscopy Raman Spectroelectrochemistry Raman Microscopy FT-Raman Spectroscopy New Raman Techniques. Part 4 Applications: Applications to Structural Chemistry Applications to Biochemistry, Biology, and Medicine Solid State Application of Raman Spectroscopy Industrial Applications Appendices Chapter References Subject Index.

Size-Specific Infrared Spectra of Benzene-(H2O)n Clusters (n = 1 through 7): Evidence for Noncyclic (H2O)n Structures

Abstract: Resonant ion-dip infrared spectroscopy has been used to record size-specific infrared spectra of C(6)H(6)-(H(2)O)n clusters with n = 1 through 7 in the O-H stretch region. The O-H stretch spectra show a dramatic dependence on cluster size. For the n = 3 to 5 clusters, the transitions can be divided into three types-attributable to free, pi hydrogen-bonded, and single donor water-water O-H stretches-consistent with a C(6)H(6)-(H(2)O)n structure in which benzene is on the surface of a cyclic (H(2)O)n cluster. In n = 6 and 7 clusters, the spectra show distinct new transitions in the 3500 to 3600 wave number region. After comparison of these results with the predictions of ab initio calculations on (H(2)O)n clusters, these new transitions have been assigned to double donor O-H stretches associated with the formation of a more compact, noncyclic structure beginning with (H(2)O)(6). This is the same size cluster for which ab initio calculations predict that a changeover to noncyclic (H(2)O)n structures will occur.

Infrared Spectroscopic Analyses on the Nature of Water in Montmorillonite

Abstract: Interlayer cations and moisture content greatly influence the molecular vibrations of H20 in montmoriUonite as shown through reflectance spectroscopy in the infrared. The absorptions due to H~O have been studied in montmorillonites exchanged with H, Na, Ca, Mg and Fe 3+ interlayer cations under variable moisture environments. Band assignments have been made for absorptions in the 3 ~tm region due to structural OH vibrations, symmetric and asymmetric 1-120 stretching vibrations and the H20 bending overtone. Changes in the energies of the absorptions due to H20 stretching vibrations were observed as the samples were dehydrated by reducing the atmospheric pressure. Absorptions near 3620 cm -1 and 3550 cm -1 have been assigned to water bound directly to cations (inner sphere) and surface- bonded H20 and absorptions near 3450 cm -1 and 3350 cm ~ have been assigned to additional adsorbed water molecules. Band assignments have been made for combination bands in the near-infrared as well. Absorptions near 1.41 ~m and 1.91/zm are assigned to bound H20 combination bands, while the shoulders near 1.46 izm and 1.97 ~*m are assigned to combinations of additional H20 molecules adsorbed in the interlayer regions and along grain surfaces.

Carbon monoxide adlayer structures on platinum (111) electrodes: A synergy between in‐situ scanning tunneling microscopy and infrared spectroscopy

Abstract: The spatial structure of compressed carbon monoxide adlayers on Pt(111) in aqueous acidic solution has been explored by means of in‐situ scanning tunneling microscopy (STM) along with infrared reflection–absorption spectroscopy (IRAS). Besides offering a detailed structural picture of this electrochemical interface in comparison with the well‐studied Pt(111)/CO system in ultrahigh vacuum (uhv) environments, the real‐space structural information provided by STM allows an assessment of the obfuscating influence of dynamic dipole coupling upon IRAS binding‐site assignments. In turn, the latter data provide an important crosscheck on the validity of binding‐site assignments deduced from the STM images. Emphasis is placed on the structures formed from near‐saturated CO solutions, encouraged by the electrode potential‐induced adlayer phase transition at ca. 0 V vs SCE observed previously under these conditions by IRAS. At potentials below 0 V, a hexagonal close‐packed (2×2)–3CO adlayer is observed, with a CO co...

Progress toward Understanding Zeolite .beta. Acidity: An IR and 27Al NMR Spectroscopic Study

Abstract: Zeolite β was prepared with different Si/Al atios by a hydrothermal method and dealuminated by leaching with dilute HCl. Samples of β from the various stages of H-β synthesis, and after leaching, were characterized by X-ray diffraction and IR and 27 Al MAS-NMR (MAS=magic angle spinning) spectroscopies. All the samples exhibited both Lewis and Bronsted acidities. The types of OH groups present, and also their distribution, are greatly affected by sample treatment. Five types of hydroxyl IR absorptions were found: those from strongly acidic bridging hydroxyl groups (3605 cm -1 ), OH groups bonded to extralattice aluminum (3660-3680 cm -1 ), internal SiOH at framework defects (3730 cm -1 ), and terminal SiOH groups (3745 cm -1 ) and a «very high frequency» (VHF) absorption (3782 cm -1 )

Blue emission in porous silicon: Oxygen-related photoluminescence

Abstract: A blue-photoluminescence (PL) band, centered at 2.6 eV, was observed in thermally and chemically oxidized light-emitting porous silicon layers with an efficiency that can exceed 0.1%. The PL decay is found to be independent of excitation intensity and detection wavelength, and to be nonexponential with a characteristic time of \ensuremath{\sim}1 nsec. A correlation between the intensity of the blue PL and the intensity of the infrared absorption related to bonded oxygen has been established. These results are examined in relation to the possible mechanisms for the blue-PL band.

Molecular structures and normal vibrations of trifluoromethane sulfonate (CF3SO3-) and its lithium ion pairs and aggregates

Abstract: The molecular structures, harmonic vibrational frequencies, infrared absorption intensities, internal force constants, and electronic charges of the trifluoromethanesulfonate (triflate) anion, its lithium ion pairs, and several aggregates have been studied using the ab initio self-consistent field Hartree-Fock method with 3-21+G * , 6-31+G augmented with polarization functions (d type orbitals) on the sulfur atom, and 6-31+G * basis sets. The calculated frequency shifts of the υ s (SO 3 ), υ s (CF 3 ), δ s ,(CF 3 ), and υ(CS) modes and the splitting widths of the υ as (SO 3 ) modes in lithium triflate ion pairs and aggregates are compared with those observed in IR and Raman spectra of lithium triflate dissolved in some polar, aprotic solvents

Investigation of the Structure of Microporous Ti-Si Mixed Oxides by X-ray, UV Reflectance, FT-Raman, and FT-IR Spectroscopies

Abstract: A series of high surface area, microporous, Ti-Si mixed oxides having a wide range of elemental compositions was prepared by a sol-gel method. Since the materials were noncrystalline, X-ray absorption spectroscopy at the Ti K edge was used to probe the first-shell coordination environment around Ti. Incorporation of Si into the mixed oxide shortened the average Ti-O bond distance derived from EXAFS and disrupted the normal octahedral coordination of pure titania. The shortest Ti-O bond distance was 1.82 [angstrom] and was attributed to Ti primarily residing in tetrahedral sites, which was also indicated by a significant pre-edge peak present in Ti K edge XANES. Shifts in the UV absorption edges for the mixed oxides were attributed to titania domain sizes decreasing with increasing Si content in accord with the well-known quantum size effect. The smallest domain size was estimated as less than 1 nm for a sample with a Ti:Si atomic ratio of 1:8. Lattice vibrations in the materials were probed with FT-Raman and FT-IR absorption spectroscopies, and the results were consistent with a shortening of the Ti-O bond and the formation of Ti-O-Si linkages in the mixed oxides. In situ experiments showed that adsorbed water profoundly affects the localmore » environment around surface Ti atoms. 44 refs., 11 figs., 3 tabs.« less

Dimensions of luminescent oxidized and porous silicon structures

Abstract: X-ray absorption measurements from H-passivated porous Si and from oxidized Si nanocrystals, combined with electron microscopy, ir absorption, \ensuremath{\alpha} recoil, and luminescence emission data, provide a consistent structural picture of the species responsible for the visible luminescence observed in these samples. The mass-weighted average structures in por-Si are particles, not wires, with dimensions significantly smaller than previously reported or proposed.

Highly efficient heterogeneous photooxidation of 2-propanol to acetone with amorphous manganese oxide catalysts

Abstract: Amorphous manganese oxides, potassium oxalatomanganate complexes, and crystalline tunnel structure manganese oxides (hollandite, todorokite, pyrolusite) have been prepared and used as photocatalysts for the oxidation of 2-propanol to acetone. Amorphous mixed valent manganese oxides, a new class of photocatalytic materials, were the most active catalysts studied at room temperature under visible light illumination. High activities correlate with higher oxidation state manganese (Mn[sup 3+], Mn[sup 4+]) oxides, large surface oxygen concentrations, and the presence of hydroxyl groups on surfaces of these catalysts. BET (surface area analysis), XRD (X-ray diffraction), EDX (energy dispersive X-ray analysis), SEM (scanning electron microscopy), XPS (X-ray photoelectron spectroscopy), and FTIR (Fourier transform infrared) data support these correlations. A mechanism for these photooxidation flow reactions involving manganese oxide catalysts has been proposed. Photochemical and characterization data suggest that the design of active photocatalysts may rely on preparation of mixed valent amorphous oxides that release oxygen more readily than crystalline materials. Conversions as high as 8% and 100% selectivity to acetone have been realized with such systems. 45 refs., 9 figs., 1 tab.

Monitoring the oxidation of edible oils by fourier transform infrared spectroscopy.

Abstract: Edible fats and oils in their neat form are ideal candidates for Fourier transform infrared (FTIR) analysis, in either the attenuated total reflectance or the transmission mode. FTIR spectroscopy provides a simple and rapid means of following complex changes that take place as lipids oxidize. Safflower and cottonseed oils were oxidized under various conditions, and their spectral changes were recorded and interpreted. The critical absorption bands associated with common oxidation end products were identified by relating them to those of spectroscopically representative reference compounds. The power and utilty of FTIR spectroscopy to follow oxidative changes was demonstrated through the use of “real-time oxidation plots.” A quantitative approach is proposed in which standards are used that are spectroscopically representative of oxidative end products and by which the oxidative state of an oil can be defined in terms of percent hydroperoxides, percent alcohols and total carbonyl content. By using either relative absorption as a basis or calibrating on representative standards, FTIR analysis provides a rapid means of evaluating the oxidative state of an oil or of monitoring changes in oils undergoing thermal stress.

IR and Raman spectroscopic studies of the interaction of trehalose with hen egg white lysozyme

Abstract: Infrared and Fourier transform Raman spectra are reported for dried mixtures of trehalose and lysozyme. The Raman spectra show effects on the protein amide I band and some sugar bands that are not present when the components are dried separately. Comparison of ir spectra with those published previously show significant differences. It is concluded that these arise because of differences in the extent of drying of the moisture, and that, contrary to some claims, vibrational spectroscopy does not so far show any clear evidence of specific trehalose/protein interactions and that results may be interpreted in terms of entrapment of water within the mixture. © 1994 John Wiley & Sons, Inc.

Aircraft (ER-2) laser infrared absorption spectrometer (ALIAS) for in-situ stratospheric measurements of HCI, N(2)O, CH(4), NO(2), and HNO(3).

Abstract: The Aircraft Laser Infrared Absorption Spectrometer (ALIAS) instrument is a high-resolution (0.0003 cm-(1)) scanning tunable-diode-laser spectrometer designed, tested, and flown more than 30 times on the National Aeronautics and Space Administration's high-altitude ER-2 aircraft in the Airborne Arctic Stratospheric Expedition of 1991-1992. Using long-path infrared laser absorption spectroscopy to detect optical absorptions as small as 10-(5), ALIAS provides fast, continuous in-situ measurements of key atmospheric gases, with gas detection sensitivities of tens of parts in 10(12). With four lasers and detectors in a single liquid-nitrogen Dewar, simultaneous measurements of HCI, NO(2), HNO(3), CH(4), and N(2)O are made using laser sources at 3.4-8 µm, injected into a 1-m-long, 80-pass Herriott cell.

IR spectra and structure of V2O5GeO2Bi2O3 glasses

Abstract: This paper reports a study of the structure V2O5GeO2Bi2O3 glasses by IR spectroscopy to obtain information about the competitive role of each of V2O5, GeO2 and Bi2O3 in the formation of the glass network. The amorphous samples were obtained by the twin-roller technique. Bi2O3 leads to transformation of the layered and chain vanadate structure and depolymerization of three-dimensional germanate lattice. The bismuthate complexes can be viewed as deformed BiO6 groups. It is established that with a decrease in the V2O5 content VO4 groups are formed. GeO4 structural unit with different degrees of polymerization arer present in the network in the entire concentration range.

An In-Situ ATR-FTIR Study: The Surface Coordination of Salicylic Acid on Aluminum and Iron(III) Oxides

Abstract: Information on the bonding of organic ligands to hydrous metal oxide surfaces, necessary to gain insight into the mechanisms of surface reactivity, was extracted using attenuated total reflection-Fourier transform infrared spectroscopy. Various ligands were investigated in-situ on the surface of δ-Al 2 O 3 in water. Keeping the study of structure with respect to surface reactivity in the foreground, we report here specifically on the model ligand salicylate, which we also examined on the surfaces of other oxides, including corundum, hematite, lepidocrocite, and goethite. Because the direct ligand-metal bond vibrations absorb in the same region as the metal-oxygen vibrations in the bulk oxide, evidence of bonding was obtained by observing changes in the spectrum of the ligand itself

Secondary Structure Estimation of Proteins Using the Amide III Region of Fourier Transform Infrared Spectroscopy: Application to Analyze Calcium-Binding-Induced Structural Changes in Calsequestrin

Abstract: A Fourier transform infrared spectroscopic method has been developed to analyze protein secondary structure by employing the amide III spectral region (1350-1200 cm-1) Benefits of using the amide III region have been shown to be substantial The interference from the water vibration (~ 1640 cm-1) in the amide I region can be avoided when one is using the amide III band; furthermore, the amide III region also presents a more characterized spectral feature which provides easily resolved and better defined bands for quantitative analysis Estimates of secondary structure are accomplished with the use of Fourier self-deconvolution, second derivatization, and curve-fitting on original protein spectra The secondary structure frequency windows (α-helix, 1328-1289 cm-1; unordered, 1288-1256 cm-1; and β-sheets, 1255-1224 cm-1) have been obtained, and estimates of secondary structural contents are consistent with X-ray crystallography data for model proteins and parallel results obtained with the use of the amide I region We have further applied the analysis to the structural change of calsequestrin upon Ca2+ binding Treatment of calsequestrin with 1 mM Ca2+ results in the formation of crystalline aggregates accompanied by a 10% increase in α-helical structure, which is consistent with previous results obtained by Raman spectroscopy Thus the amide III region of protein IR spectra appears to be a valuable tool in estimating individual protein secondary structural contents

Germanium quantum dots: Optical properties and synthesis

Abstract: Three different size distributions of Ge quantum dots (>~200, 110, and 60 A) have been synthesized via the ultrasonic mediated reduction of mixtures of chlorogermanes and organochlorogermanes (or organochlorosilanes) by a colloidal sodium/potassium alloy in heptane, followed by annealing in a sealed pressure vessel at 270 °C. The quantum dots are characterized by transmission electron microscopy, x-ray powder diffraction, x-ray photoemission, infrared spectroscopy, and Raman spectroscopy. Colloidal suspensions of these quantum dots were prepared and their extinction spectra are measured with ultraviolet/visible (UV/Vis) and near infrared (IR) spectroscopy, in the regime from 0.6 to 5 eV. The optical spectra are correlated with a Mie theory extinction calculation utilizing bulk optical constants. This leads to an assignment of three optical features to the E(1), E(0'), and E(2) direct band gap transitions. The E(0') transitions exhibit a strong size dependence. The near IR spectra of the largest dots is dominated by E(0) direct gap absorptions. For the smallest dots the near IR spectrum is dominated by the Gamma25-->L indirect transitions.

Properties of carbon nitride films with composition ratio C/N=0.5–3.0 prepared by the ion and vapor deposition method

Abstract: Carbon nitride films with the composition ratio CR(C/N)=0.5–3.0 were prepared by the ion and vapor deposition method, where carbon was evaporated on various substrates while being simultaneously bombarded with 0.5–10.0 keV nitrogen ions. The properties of the films were studied by x‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FT‐IR), ultraviolet transmission spectroscopy, x‐ray diffraction, and hardness measurements. The films formed at energies lower than 0.8 keV and CR(C/N)=0.6–0.7 on tungsten carbide showed the highest Knoop harness of 6400 kgf/mm2 on films with 1 μm thickness and a maximum optical band gap of 2.7 eV. X‐ray diffraction measurements demonstrated that all films have an amorphous structure. The XPS and FT‐IR studies indicated that the peak newly observed at 286.3 eV in the C‐1s1/2 XPS spectra arises from triple bonding C≡N.

Low Dielectric Constant Interlayer Using Fluorine-Doped Silicon Oxide

Abstract: A new interlayer dielectric film using fluorine-doped silicon oxide (SiOF) for multilevel interconnection of very large scale integration (VLSI) has been fabricated The film is deposited by a simple technique, which is hexafluoroethane ( C2F6) addition to conventional tetraethoxysilane (TEOS)-based plasma-enhanced chemical vapor deposition (PE-CVD) Si–F bond formation in the film is detected by chemical bonding structural studies using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) Low dielectric constants caused by Si–F bond formation and good gap-filling ability due to in situ etching by C2F6 plasma are obtained Therefore, SiOF film has very high applicability as an interlayer dielectric film for advanced VLSI devices

Infrared spectroscopy of polycyclic aromatic hydrocarbon cations. 1. Matrix-isolated naphthalene and perdeuterated naphthalene.

Abstract: Ionized polycyclic aromatic hydrocarbons (PAHs) are thought to constitute an important component of the interstellar medium. Despite this fact, the infrared spectroscopic properties of ionized PAHs are almost unknown. The results we present here derive from our ongoing spectroscopic study of matrix isolated PAH ions and include the spectra of the naphthalene cation, C10H8(+), and its fully deuterated analog, C10D8(+), between 4000 and 200/cm. Ions are generated by in situ Lyman-alpha photoionization of the neutral precursor. Bands of the C10H8(+) ion are observed at 1525.7, 1518.8, 1400.9, 1218.0, 1216.9, 1214.9, 1023.2, and 758.7/cm. Positions and relative intensities of these bands agree well with those in the available literature. The 758.7/cm band has not previously been reported. C10D8(+) ion bands appear at 1466.2, 1463.8, 1379.4, 1373.8, 1077.3, 1075.4, and 1063.1/cm. Compared to the analogous modes in the neutral molecule, the intensities of the cation's CC modes are enhanced by an order of magnitude, while CH modes are depressed by this same factor. Integrated absorption intensities are calculated for the strongest bands of C10H8 and for the observed bands of C10H8(+). Absolute intensities derived for the naphthalene cation differ from earlier experimental results by a factor of approximately 50, and from theoretical predictions by a factor of approximately 300. Reasons for these discrepancies and from the astronomical implications of PAH cation spectra are discussed.

Density functional study of nitrogen oxides

Abstract: Equilibrium geometries, bond dissociation energies, dipole moments, harmonic vibrational frequencies, and infrared intensities were calculated for a set of ten neutral nitrogen oxides (NO, NO2, NO3, N2O, sym N2O2, asym N2O3, sym N2O3, sym N2O4, asym N2O4, and N2O5) by applying one local and two gradient‐corrected nonlocal functionals in a Gaussian‐type‐orbital density functional method. Comparison with available experimental data shows that, except for the bond dissociation energies, the local functional gives very accurate molecular properties. Nonlocal functionals considerably improve the bond dissociation energies, but the results still overestimate the experimental values by about 10 kcal/mol on average. For the other properties, the results obtained with nonlocal functionals are not necessarily superior to those calculated with the local functional. The properties of two molecules (sym N2O3 and asym N2O4) are predicted for the first time and several reassignments are proposed in the vibrational spect...

The determination of peroxide value by Fourier transform infrared spectroscopy.

Abstract: A rapid method for the quantitative determination of peroxide value (PV) of vegetable oils by Fourier transform infrared (FTIR) transmission spectroscopy is described. Calibration standards were prepared by the addition oft-butyl hydroperoxide to a series of vegetable oils, along with random amounts of oleic acid and water. Additional standards were derived through the addition of mono- and diglyceride spectral contributions, as well as zero PV spectra obtained from deuterated oils. A partial least squares (PLS) calibration model for the prediction of PV was developed based on the spectral range 3750–3150 cm−1. Validation of the method was carried out by comparing the PV of a series of vegetable oils predicted by the PLS model to the values obtained by the American Oil Chemists Society iodometric method. The reproducibility of the FTIR method [coefficient of variation (CV)=5%)] was found to be better than that of the chemical method (CV =9%), although its accuracy was limited by the reproducibility of the chemical method. The method, as structured, makes use of a 1-mm CaF2 flow cell to allow rapid sample handling by aspiration. The spectrometer was preprogrammed in Visual Basic to guide the operator in performing the analysis so that no knowledge of FTIR spectroscopy is required to implement the method. The method would be suitable for PV determinations in the edible oil industry and takes an average of three minutes per sample.

Evaluation of a series of tyrosine-derived polycarbonates as degradable biomaterials.

Abstract: A series of four polycarbonates derived from the ethyl, butyl, hexyl, and octyl esters of desaminotyrosyl-tyrosine was prepared by condensation polymerization. The resulting polymers had weight average molecular weights ranging from 120,000-450,000, and their chemical structure was confirmed by elemental analysis, nuclear magnetic resonance, and Fourier transform infrared spectroscopy. The polycarbonates were evaluated as degradable biomaterials. Their surface properties were determined by electron spectroscopy for chemical analysis, attenuated total reflectance-Fourier transformed infrared spectroscopy, and contact angle measurement. The degree of surface hydrophobicity was related to the length of the alkyl ester pendent chain. The tensile properties were dependent on the chemical structure of the polymers: For thin, solvent cast film specimens, the tensile modulus varied from 1.2-1.6 GPa, and the strength at break from 60-220 MPa. The degradation of polymeric films was followed in vitro by measuring changes in mechanical strength for up to 40 weeks, and the decrease in molecular weight and changes in surface chemistry for up to 80 weeks. The length of the pendent chain affected the degradation behavior and strength retention; the polymers with short pendent chains were more readily hydrolyzable. For sterilization, ethylene oxide treatment was less destructive, as judged by molecular weight retention, than gamma-irradiation. Spin-cast films of all tested polycarbonates were not cytotoxic toward cultured rat lung fibroblasts. The cell response was influenced by the chemical structure of the polymer. The least hydrophobic polycarbonate (having a short ethyl ester pendent chain) was a more stimulating substrate for cell growth than the more hydrophobic polymers (carrying longer alkyl ester pendent chains).