Showing papers on "Infrared spectroscopy published in 1995"

Fundamentals of Fourier Transform Infrared Spectroscopy

Abstract: Introduction to Infrared Spectroscopy Terms and Definitions The Properties of Light What Is an Infrared Spectrum? What Are Infrared Spectra Used For? The Advantages and Disadvantages of Infrared Spectroscopy The Advantages and Disadvantages of FTIR The Advantages of FTIRs The Disadvantage of FTIR FTIR: The Rest of the Story How an FTIR Works Interferometers and Interferograms How Many Scans Should Be Used? How an Interferogram Becomes a Spectrum Scanning Advice Instrumental Resolution What Determines Resolution in an FTIR Scan? What Resolution Should Be Used? FTIR Trading Rules FTIR Hardware Interferometers Infrared Sources Beamsplitters Infrared Detectors The Laser Testing Instrument Quality and Troubleshooting Proper Use of Spectral Processing The Rules of Spectral Processing Spectral Subtraction Subtraction Artifacts Baseline Correction Smoothing Spectral Derivatives Deconvolution Guidance, Precautions, and Limitations Spectral Library Searching The Search Process Interpreting Library Search Results Analysis of Mixtures: Subtract and Search Again Preparing Samples Properly Transmission Sampling Overview Windows, Cells, and Materials for Transmission Analysis Transmission Analysis of Solids and Powders KBr Pellets Mulls Transmission Analysis of Polymers The Cast Film Method The Heat and Pressure Method Transmission Analysis of Liquids Capillary Thin Films Sealed Liquid Cells Transmission Analysis of Gases and Vapors Reflectance Analysis Different Types of Reflectance Advantages and Disadvantages of Reflectance Sampling Specular Reflectance Diffuse Reflectance (DRIFTS) Abrasive Sampling Attenuated Total Reflectance (ATR) Depth of Penetration Applications of ATR Liquids Semi-Solids Polymers Powders ATR: Advantages and Disadvantages FTIR Sample Preparation: Overview and Recommendations Quantitative Infrared Spectroscopy Terms and Definitions Beer's Law Calibration and Prediction with Beer's Law Calibration Prediction An Experimental Protocol for Single Component Analyses Measuring Absorbances Properly Peak Areas versus Peak Heights Dealing with Overlapped Peaks Avoiding Experimental Errors Infrared Microscopy Hyphenated Infrared Techniques Infrared Microscopy Instrumentation Sample Preparation Applications Infrared Mapping and Imaging Glossary Index

Sum-frequency vibrational spectroscopy of the solid/liquid interface

Abstract: Sum-frequency spectroscopy (SFS) is a non-linear optical technique that yields vibrational spectra of molecules at interfaces. A brief summary of the theoretical background to SFS is provided and the origin of its unusual selection rules is explained. The application of SFS to the study of organic molecules at the solid/liquid interface is reviewed. Areas covered include liquid structure at solid surfaces, electrochemistry and the adsorption of surfactants at the solid/water interface.

Infrared and Raman spectroscopy : methods and applications

Abstract: Early history of vibrational spectroscopy general survey of vibrational spectroscopy tools for infrared and Raman spectroscopy vibrational spectroscopy of different classes and states of compounds evaluation procedures special techniques and applications (Part contents)

The conformational analysis of peptides using Fourier transform IR spectroscopy.

Abstract: Fourier transform infrared spectroscopy (FTIR) can be used for conformational analysis of peptides in a wide range of environments. Measurements can be performed in aqueous solution, organic solvents, detergent micelles as well as in phospholipid membranes. Information on the secondary structure of peptides can be derived from the analysis of the strong amide I band. Orientation of secondary structural elements within a lipid bilayer matrix can be determined by means of polarized attenuated total reflectance-FTIR spectroscopy. Hydrogen-deuterium exchange can be monitored by the analysis of the amide II band. This review gives some example of peptide systems studied by FTIR spectroscopy. Studies on alamethicin and alpha-aminoisobutyric acid containing peptides have shown that FTIR spectroscopy is a sensitive tool for identifying 3(10)-helical structures. Changes in the structure of the magainins upon interaction with charged lipids were detected using FTIR spectroscopy. Tachyplesin is an example of a beta-sheet containing membrane active peptide. Polarized ir spectroscopy reveals that the antiparallel beta-sheet structures of tachyplesin are oriented parallel to the membrane surface. Synthesis of peptides corresponding to functionally/structurally important regions of large proteins is becoming increasingly popular. FTIR spectroscopy has been used to analyze the structure of synthetic peptides corresponding to the ion-selective pore of the voltage-gated potassium channel. In biomembrane systems these peptides adopt a highly helical structure. Under conditions, where these peptides are aggregated the presence of some intermolecular beta-sheet structure can also be detected.

The Raman spectrum of brookite, TiO2 (Pbca, Z = 8)

Abstract: The Raman microprobe spectra of natural brookite crystals from Switzerland and Brazil and a synthetic brookite powder exhibit a characteristic intense band at 153 cm−1. In contrast, anatase has a band of similar intensity at 144 cm−1 and rutile lacks a strong band in this region. Polarization experiments with the Brazilian crystal permit 17 out of a predicted 36 vibrational bands to be readily assigned as A1g (127, 154, 194, 247, 412, 640 cm−1), B1g (133, 159, 215, 320, 415, 502 cm−1), B2g (366, 395, 463, 584 cm−1) and B3g (452 cm−1). Eight weaker bands and component sub-bands resolved at 172, 287, 545, 618 cm−1, 254, 329, 476 cm−1 and 497 cm−1 are tentatively assigned to B3g, B2g and A1g modes respectively. Traces of Si and Fe in the Brazilian crystal and Si, Fe, Al and S in the Swiss sample are indicated by spot electron microprobe analysis. Electron spin resonance spectra suggest small amounts of Fe3+ are substituting for Ti4+ in the structure. Concomitant protonation of oxygens to maintain charge balance yields OH groups which give rise to three sharp, low-intensity absorption bands near 3360, 3380 and 3404 cm−1 in the infrared spectra. X-ray photoelectron spectroscopy shows that surface-bound OH/H2O species exist in both crystals but no detectable Ti3+.

Quantitative analysis of trace OH in garnet and pyroxenes

Abstract: To calibrate infrared (IR) spectroscopy for quantitative analysis of trace structural OH in specific minerals, we have determined concentrations of H in pure separates of mantle derived pyrope garnet (56 ± 6 ppm H_2O by weight), augite (268 ± 8, ppm H_2O, and enstatite (217 ± 11 ppm H_2O) by manometry after heating the samples and extracting H_2 gas under vacuum. IR spectroscopy confirmed the presence of intrinsic OH in these samples prior to extraction and indicated between 86 and 100% removal of H during the extraction procedure. The integral specific absorption coefficients of 1.39 ± 0.14(lσ),7.09 ± 0.32, and 15.6 ± 0.94 /(ppm H_2O.cm^2) for pyrope, augite, and enstatite, respectively, allow precise spectroscopic determination of the OH content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million. Uncertainties in accuracy depend on mineral composition and characteristics of the OH absorption spectrum and are estimated to range between ± 10 and ± 50%.

A simple IR spectroscopic method for determining fictive temperature of silica glasses

Abstract: Infrared spectroscopy was used to determine fictive temperature of silica glasses. Positions of both the fundamental structural band at ∼ 1122 cm−1 monitored in infrared (IR) reflection mode and an overtone of this band at ∼ 2260 cm−1 monitored in IR transmission mode were found to be directly correlated with the glass fictive temperature. At any particular fictive temperature, the equilibrium structural band positions were found to be independent of the impurity content, such as hydroxyl, in different types of silica glass. From band shifts, the average SiOSi bond angle was computed to decrease by about 1.3° when the fictive temperature increased from 950 to 1400°C. Using this method, fictive temperatures of various as-received silica glasses were determined.

Luminescence quenching by OH groups in highly Er-doped phosphate glasses

Abstract: Highly (up to 4 mol% Er2O3) Er-doped phosphate bulk glasses have been prepared by common glass-melting techniques. Afterwards, a heat treatment was performed on the as-melted samples. The photoluminescence lifetime of Er ions for the 4I132–4I152 transition increases substantially, typically from 3 ms up to 7 ms for a sample doped with 2 mol% Er2O3, due to the heat treatment. The increase of the lifetime is ascribed to a decrease in concentration of hydroxyl groups incorporated in the glass, which is confirmed by IR absorption spectroscopic measurements. The photoluminescence peak intensity also increases because of drying by a factor of 3 to 7 depending on glass composition. Based on electric dipole-dipole interaction theory, the luminescence concentration quenching mechanism by hydroxyl groups is modelled. The model predicts that more than half of the hydroxyl groups in the glass is coupled to Er ions. The influence of the glass structure and role of Al3+ on the Er3+ luminescence is studied by infrared spectroscopy.

Infrared absorption by the B nitrogen aggregate in diamond

Abstract: Two approaches have been adopted in attempting to determine the strength of the one-phonon infrared absorption by the B nitrogen aggregate in diamond. On the one hand, we have heat treated purely type IaA specimens with known infrared absorption strengths (and thus also known nitrogen concentrations) to bring about partial aggregation of the A centres to B centres, monitoring changes in the strengths of the A, and resultant B, one-phonon components by decomposition of the ensuing infrared spectra. Secondly, we have made direct chemical assays of nitrogen in diamonds that show dominant B absorption features. This approach is complicated because diamonds in which the B aggregate is the only point defect also contain extended defects that may or may not involve nitrogen. These defects may or may not, in turn, contribute to absorption in the one-phonon region. Nevertheless, the nitrogen concentrations have been measured for two distinct groups of diamonds that both uncritically might at first glance ...

Sex- and age-related composition of 10 617 calculi analyzed by infrared spectroscopy.

Abstract: A series of 10 617 calculi were analyzed by stereomicroscopy and infrared spectroscopy. This first study of French calculi was compared with large series in the literature. That the frequency of pure calculi was the lowest ever observed can be related to the methodology routinely used in our laboratory, which includes microsampling. We described more than 70 components among the 10 617 calculi. The overall sex ratio male to female patients was high (2.27) and increased over the period 1981-1993. Calcium oxalate was the most frequent component (86.48%), followed by calcium phosphate (79.75%) and purines (18.64%). We found a low occurrence of "infection" stones. The sex ratio was related to stone composition and differed according to the main component. For instance, calcium oxalate dihydrate (COD) was more frequent in men than in women, with a sex ratio of 4.97 versus 2.57 for calcium oxalate monohydrate (COM). On the contrary, calcium phosphate was more frequent in female patients (sex ratio 0.72 versus overall ratio). The high frequency of COD calculi (23.17%) suggests that hypercalciuria is particularly frequent in French patients susceptible to stone formation. For each main component, a specific profile was observed in relation to the sex and age of the patients with stones.

Coordination of Adsorbed Boron: A FTIR Spectroscopic Study

Abstract: We studied B adsorption on amorphous aluminum and iron hydroxides, allophane, and kaolinite as a function of pH and initial B concentration. Boron adsorption lowered the point of zero charge of all four adsorbents, implying specific adsorption (inner-sphere complexation) of B. We provided novel information on the coordination of B adsorbed at mineral-water interfaces by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The ATR-FTIR spectra of interfacial B species were influenced by pH and mineral type. Strong trigonal B and weak tetrahedral B bands of the asymmetric stretching mode were observed on the difference spectra at pH 7 for amorphous iron hydroxide, whereas both strong trigonal and tetrahedral B bands were found at pH 10. A strong IR band of asymmetric stretching of tetrahedral B shifted to higher frequencies in am-Fe(OH) 3 paste at both pH's relative to that of boric acid solution at pH 11. Trigonal B asymmetric stretching bands shifted to higher frequencies on the difference spectra for am-Al(OH) 3 and allophane at both pH's compared to that of boric acid solution at pH 7. Polymerization of B on mineral surfaces is shown to be possible. The results provide spectroscopic evidence that both B(OH) 3 and B(OH) 4 - are adsorbed via a ligand exchange mechanism.

New Sol-Gel Attenuated Total-Reflection Infrared Spectroscopic Method for Analysis of Adsorption at Metal-Oxide Surfaces in Aqueous-Solutions - Chelation of TiO2, ZrO2, and Al2O3 Surfaces by Catechol, 8-Quinolinol, and Acetylacetone

Abstract: A new sol-gel method has been used to study, by in situ internal reflection infrared spectroscopy, the adsorption of coordinating ligands onto metal oxide surfaces from dilute aqueous solutions. Good sensitivity has been achieved in spectra obtained from a single internal reflection for catechol, 8-quinolinol, and acetylacetone adsorbed to TiO 2 , ZrO 2 , and Al 2 O 3 gel layers. The spectra indicate that the adsorbates bind to surface metal ions as bidentate ligands and that more than one ligand may be bound to some surface metal ions.

Molecular Gradients of .omega.-Substituted Alkanethiols on Gold: Preparation and Characterization

Abstract: A general methodology capable of generating a molecular, chemical concentration gradient on a solid substrate in one surface dimension is presented. Although the method can be extended to more than one surface dimension, and to a variety of molecule/substrate systems, we have chosen to demonstrate it by utilizing thiols on gold as the model system. The gradients are prepared by cross-diffusing ω-substituted alkanethiols, HS(CH 2 ) n X (X = OH, CO 2 CH 3 , COOH, and CD 3 , n = 10-19), with or without fully deuterated chains, and simple n-alkanethiols, HS(CH 2 ) m Y (Y = CH 3 , m = 9-17), toward each other from opposite ends of a polysaccharide matrix deposited on top of a gold substrate. The so-prepared gradients are characterized by a number of techniques, including ellipsometry, contact angle measurements, and infrared reflection absorption spectroscopy (IRAS). The observed ellipsometric thicknesses and the limiting contact angles of the gradient assemblies agree very well with the values obtained from the corresponding single component and mixed self-assembled monolayers. The infrared data furthermore suggest that the entire gradient is composed ofwell-organized and densely packed all-trans hydrocarbon chains for thiols with chain length >10. The lateral dimensions of the gradient regions vary between 4 and 8 mm for the combination diffusion pairs employed in this study. The upper and lower values account for diffusion pairs with long and short hydrocarbon chains, respectively. It must be stressed, however, that the infrared and ellipsometric techniques only can provide information about the molecular organization on the macroscopic scale because of the relatively large spot size (1 mm) used in the experiments. Scanning probe microscopy must be employed to further investigate the mechanism of gradient formation, the molecular concentration profile, and mixing behavior on the microscopic (molecular) scale. We believe, however, that the large number of chemical and structural combinations attainable with the present approach can be used to address a broad range of surface physics/chemistry problems in material science and generate novel and unique model organic architectures. We discuss briefly the potential applications ofthese novel gradients in areas of relevance to molecular recognition and biosensing.

Self-emission noninvasive infrared spectrophotometer

Abstract: A method and apparatus for monitoring glucose, ethyl alcohol and other blood constituents in a noninvasive manner. The measurements are made by monitoring infrared absorption of the desired blood constituent in the long infrared wavelength range where the blood constituent has a strong and distinguishable absorption spectrum. The long wavelength infrared energy emitted by the person as heat is monitored and the infrared absorption of particular constituents in the blood (such as glucose or blood alcohol) is measured by infrared detector (412) at characteristic infrared absorption wavelengths for those constituents. The measurements are preferably synchronized with systole and diastole of the cardiac cycle monitored by cardiac monitor (718) so that the signal contribution caused by veins and tissues (which do not pulse) may be cancelled by microprocessor (418) when a ratio of the detected signals is taken. The concentration of the blood constituents is then determined in accordance with a polynomial equation.

A diamond anvil cell for IR microspectroscopy

Abstract: A large optical‐aperture membrane diamond anvil cell designed for infrared spectroscopy is described. The cell offers definite advantages compared to existing systems. Other possibilities concerning x‐ray diffraction analyses with the cells are mentioned.

Infrared-detectable groups sense changes in charge density on the nickel center in hydrogenase from chromatium vinosum

Abstract: Fourier transform infrared studies of nickel hydrogenase from Chromatium vinosum reveal the presence of a set of three absorption bands in the 2100-1900 cm-1 spectral region. These bands, which do not arise from carbon monoxide, have line widths and intensities rivaling those of a band arising from the carbon monoxide stretching frequency (v(CO)) in the Ni(II).CO species of this enzyme [Bagley, K. A., Van Garderen, C. J., Chen, M., Duin, E. C., Albracht, S. P. J., & Woodruff, W. H. (1994) Biochemistry 33, 9229-9236]. The positions of each of these three infrared absorption bands respond in a consistent way to changes in the formal redox state of the nickel center and to the photodissociation of hydrogen bound to the nickel. Up to eight different states of the nickel center have been produced, depending on the redox state and/or the activity state of the enzyme and the presence of carbon monoxide. In seven of these states, the three IR absorption bands in the set have unique frequency positions. It is concluded that the set is due to intrinsic, non-protein groups in the enzyme, whose identities are presently unknown, and that these groups are situated very close to the nickel center and sense the charge density at the Ni site.

The erbium‐impurity interaction and its effects on the 1.54 μm luminescence of Er3+ in crystalline silicon

Abstract: We have studied the effect of erbium‐impurity interactions on the 1.54 μm luminescence of Er3+ in crystalline Si. Float‐zone and Czochralski‐grown (100) oriented Si wafers were implanted with Er at a total dose of ∼1×1015/cm2. Some samples were also coimplanted with O, C, and F to realize uniform concentrations (up to 1020/cm3) of these impurities in the Er‐doped region. Samples were analyzed by photoluminescence spectroscopy (PL) and electron paramagnetic resonance (EPR). Deep‐level transient spectroscopy (DLTS) was also performed on p‐n diodes implanted with Er at a dose of 6×1011/cm2 and codoped with impurities at a constant concentration of 1×1018/cm3. It was found that impurity codoping reduces the temperature quenching of the PL yield and that this reduction is more marked when the impurity concentration is increased. An EPR spectrum of sharp, anisotropic, lines is obtained for the sample codoped with 1020 O/cm3 but no clear EPR signal is observed without this codoping. The spectrum for the magnetic...