Showing papers on "Fourier transform spectroscopy published in 1992"

Fourier Transform Infrared Spectroscopy

Abstract: Typically, lignins are characterized by IR spectroscopy in the solid state. The examination of lignins in solution has long been a domain of UV and NMR spectroscopy. However, with the advent of the FTIR technique, the IR spectra of liquid samples now can be readily obtained. The need to measure IR spectra in solution exists when there is not enough time to isolate lignin from solution as, for example, is the case when spent pulping liquors have to be analyzed rapidly during a pulping process for process control. This section describes briefly the common liquid sampling accessories and applications of solution state FTIR spectroscopy to lignins. For more details on FTIR spectroscopy, the reader is referred to Chapter 4.1.

Luminescence and structural study of porous silicon films

Abstract: The luminescence properties of 3 μm thick, strongly emitting, and highly porous silicon films were studied using a combination of photoluminescence, transmission electron microscopy, and Fourier transform infrared spectroscopy. Transmission electron micrographs indicate that these samples have structures of predominantly 6–7 nm size clusters (instead of the postulated columns). In the as‐prepared films, there is a significant concentration of Si—H bonds which is gradually replaced by Si—O bonds during prolonged aging in air. Upon optical excitation these films exhibit strong visible emission peaking at ≊690 nm. The excitation edge is shown to be emission wavelength dependent, revealing the inhomogeneous nature of both the initially photoexcited and luminescing species. The photoluminescence decay profiles observed are highly nonexponential and decrease with increasing emission energy. The 1/e times observed typically range from 1 to 50 μs. The correlation of the spectral and structural information suggest...

Characterization of diamondlike carbon by infrared spectroscopy

Abstract: Comparison of Fourier transform infrared (FTIR) absorption spectroscopy, high resolution 13C nuclear magnetic resonance spectroscopy, and hydrogen evaluation by forward recoil elastic scattering (FRES) measurements shows that FTIR cannot be used to determine the carbon hybridization or total hydrogen content of diamondlike carbon films (DLC). FTIR absorption reflects only the optically active hydrogen in the DLC and, using it together with FRES, it can provide an estimate of the unbound hydrogen contained in the films. The fraction of unbound hydrogen can reach values of up to ∼50%.

Remote Sensing by Fourier Transform Spectrometry

Abstract: The Basic Principles of Fourier Transform Spectrometry The Ideal Fourier Transform Spectrometer The Physics and Chemistry of Remote Sensing Real Fourier Transform Spectrometers Case Studies of Remote Sensing Fourier Transform Spectrometers Remote Sensing Environments General Observations and Conclusions Appendix Bibliography and References Index.

Time‐resolved Fourier transform spectroscopy with 0.25 cm−1 spectral and <10−7 s time resolution in the visible region

Abstract: The development of a new time‐resolved Fourier transform spectrometer that is capable of 0.25 cm−1 spectral resolution and better than 10−7 s temporal resolution in the visible is reported. The time‐resolved capability of the spectrometer is achieved by coupling a step‐scan interferometer to a transient digitizer/laser system. The operation of the spectrometer is described in detail, and scattered light and laser‐induced fluorescence spectra from an I2 gas cell are presented to demonstrate the temporal and spectral resolution of the spectrometer.

Fourier transform infrared spectroscopy of the BH3 ν3 band

Abstract: The gas‐phase infrared spectrum of the BH3 ν3 band was observed in the 2600 cm−1 region by a Fourier transform infrared spectrometer. The borane molecule was produced with a discharge in a B2H6 and He mixture. The spectral pattern was consistent with the D3h structure of borane. The observed spectrum between 2450–2730 cm−1 was analyzed to determine band origins, rotational constants, and centrifugal distortion constants. The ν3 band origins of 11BH3 and 10BH3 were 2601.5743(15) and 2615.7935(21) cm−1, respectively, with one standard deviation in parentheses. The B–H bond length was determined for the first time experimentally to be r0=1.190 01(1) A from the ground state rotational constant B0.

Line-shape distortions in misaligned cube corner interferometers

Abstract: Line-shape distortions caused by the misalignment of the moving cube mirror in Fourier transform spectrometers have been described. A method of studying and correcting these distortions is presented. By using this method we can estimate the accuracy of the line position, which is especially important in high-resolution Fourier transform spectroscopy. The method is verified in simulations, and in practice it has been used to align the Oulu Fourier transform spectrometer.

Multichannel Fourier-transform infrared spectrometer

Abstract: A compact Fourier-transform IR spectrometer without a moving mechanism was developed. The spectrometer consists of a shearing interferometer for forming a spatially distributed interferogram and an IR array detector for observing the interferogram. The shearing interferometer of the developed system is a birefringent interferometer with a Savert plate; the IR array detector is a PtSi Schottky- barrier detector with 4096 elements. The optics and the system configuration are described in detail, and the experimental results of the IR absorption spectra of polystyrene and polyethylene terephthalate film are shown. The developed optics is as small as 20 × 6 cm ϕ in size. The spectral resolution of the prototype system is ~ 27.6 cm−1 between 5000 and 2000 cm−1. The methods and their possibilities of resolution improvement are also described.

Polymer coated silver halide infrared fibers as sensing devices for chlorinated hydrocarbons in water

Abstract: Fiberoptic evanescent wave spectroscopy (FEWS) based on AgClBr fibers and a Fourier transform infrared (FTIR) spectrometer was used for the first time to measure chlorinated hydrocarbons (CH) in water. A minimum detection limit lower than 10 mg/l was achieved by coating the fiber with low density polyethylene (LDPE), which shows reversible enrichment of CH. The response of the sensor to CH diffusion through the polymer layer was analyzed theoretically and the results were found to be in good agreement with the experiments.

Calibration of a Fourier transform spectrometer using three blackbody sources

Abstract: A procedure to calibrate a Fourier transform spectrometer is presented. Blackbody sources of three different temperatures are used to eliminate errors in the calibration that result from the limited accuracy of the temperature measurement of the calibration sources. With three spectra of blackbodies it is possible to assume that the temperatures are unknown variables as are the parameters of the functions that describe the spectrometer. A nonlinear Gaussian balancing calculation is used to determine these unknown variables and to minimize the influence of noise. A comparison between the results obtained with this method and a conventional calibration procedure is presented.

[9] Fourier resolution enhancement of infrared spectral data

Abstract: Publisher Summary This chapter presents a critical discussion of the computational methods of Fourier resolution enhancement (band narrowing) and their role in the analysis of the infrared absorption spectra of proteins. This type of numerical data processing does not affect the instrumental resolution but changes the shape of the infrared bands and, by reducing their width, allows a better visual separation (that is, resolution) of individual component bands. One area of biology in which infrared spectroscopy has become particularly useful is the structural analysis of proteins and, in particular, the determination of the secondary structure of soluble and membrane-bound proteins. There are two common methods of resolution enhancement via band narrowing that use the Fourier transform: Fourier self-deconvolution (FSD) and Fourier derivation (FD). The chapter discusses a number of practical considerations in the application of the numerical computer methods for band narrowing. The Fourier resolution enhancement in applications may be employed to advantage on any data set that satisfies two criteria: (1) high S/N ratio and (2) composite bands with intrinsic widths that are large as compared to the instrumental resolution.

Fourier transform emission spectroscopy of ScN

Abstract: The near‐infrared electronic emission spectrum of ScN has been observed in the 1.6–1.8 μm spectral region using a Fourier transform spectrometer. The three bands with origins at 5820.0944(5), 6051.2858(20), and 6266.1290(13) cm−1 have been assigned as the 0‐0, 1‐1, and 2‐2 bands of the A 1Σ+−X 1Σ+ electronic transition. The principal equilibrium molecular constants for the ground state obtained from a fit of the observed lines are B‘e=0.554 609(17) cm−1, r‘e=1.687 23(3) A and the corresponding values for the excited state are B’e=0.549 277(17) cm−1, re=1.695 40(3) A. Although ScN is a well‐known refractory solid, our work is the first observation of the gas‐phase ScN molecule.

Ft‐ir spectroscopy as a tool for the study of biological and chemical treatments of barley straw

Abstract: Diffuse reflectance Fourier transform infrared (FT-IR) spectroscopy has been used to characterise the changes in barley straw when subjected to biological and chemical treatments. The untreated and treated straws were also analysed by traditional analytical techniques for neutral sugar residues and lignin. A comparison between the spectroscopic data and the chemical analyses showed that FT-IR spectroscopy was a quick and non-destructive analytical technique which could be used to assess the efficacy of treatments applied to annual plants.

Nuclear magnetic resonance Fourier transform spectroscopy

Abstract: Theworld of the nuclear spins is a true paradise for theoretical and experimental physicists. It supplies, for example, most simple test systems for demonstrating the basic concepts of quantum mechanics and quantum statistics, and numerous textbook-like examples have emerged. On the other hand, the ease in handling nuclear spin systems predestines them for the testing of novel experimental concepts. Indeed, the universal procedures of coherent spectroscopy have been developed predominantly within nuclear magnetic resonance (NMR) and have found widespread application in a variety of other fields.

Vibrational spectra of penta‐atomic silicon–carbon clusters. I. Linear SiC4 in Ar at 10 K

Abstract: A Fourier transform infrared (FTIR) study has resulted in the first identification of a fundamental vibration of SiC4, the ν1, C■C stretching mode at 20801 cm−1 SiC4 was produced by trapping in Ar at 10 K the products of the vacuum ultraviolet (VUV) photolysis of silane (SiH4) and 1,3‐butadiene (C4H6) or the products from the evaporation of a mixture of Si and C powder The vibrational assignment is confirmed by 13C ‐isotopic data for 20 isotopomers, which is in excellent agreement with the predictions of ab initio calculations

Infrared ellipsometer for the study of surfaces, thin films, and superlattices.

Abstract: An automatic infrared ellipsometer for the study of surface and interface phenomena has been constructed. The system is based on a Fourier transform spectrometer that we equipped with an ellipsometer unit. Polarizers and analyzers are of the ion-etched wire-grid type. Their rotation is governed by means of a computer-controlled stepping-motor system. A discussion of calibration procedures for the infrared range is given, and special attention is given to the problem of selecting the best measurement strategy. The polarization state of the reflected beam is determined by measuring the intensity at 72 regularly spaced polarizer/analyzer settings. It is found that the effects of interferometric polarization, beam wandering, and detector dichroism cannot be neglected. However, these error sources have been eliminated by analyzing the zeroth, second, and fourth harmonic components of the azimuthally recorded intensity. Both the multiplex advantage of Fourier transform spectroscopy and the phase sensitivity of ellipsometry are combined in this instrument. Measurements on superconducting films, superlattices, and doped GaAs films are reported.

Structural phenomena related to associative and dissociative adsorption of water on Ni(110)

Abstract: The adsorption of water on Ni(110) has been studied by thermal desorption spectroscopy (TDS), work function (ΔΦ), Fourier transform infrared reflection–absorption spectroscopy (FTIR‐RAS), low energy electron diffraction (LEED), and electron‐stimulated desorption ion angular distribution (ESDIAD). The major findings of this study are the following: (1) Water molecules in the chemisorbed c(2×2) half‐monolayer do not cluster and the plane of the molecules is highly inclined to the surface normal; (2) no ESDIAD evidence of oriented water dimers is observed at 130 K and no FTIR activity is observed following adsorption at 80 K until multilayers are populated; (3) water has been measured to partially dissociate at a minimum temperature of 205±2 K; (4)the binding energy of water to the Ni(110) surface is increased by H‐bonding to adsorbed hydroxyls (produced by the partial dissociation) in a linear OH(ad)/H2O complex with planar symmetry in the [001] direction. This bonding results in a higher temperature desorp...

Fourier transform resonance Raman spectroscopy of phytochrome.

Abstract: The Pr and Pfr forms of phytochrome in H2O and D2O have been studied by Fourier transform resonance Raman spectroscopy with near-infrared excitation (1064 nm). It is demonstrated that this technique is a powerful method for analyzing the chromophore structures of photosensitive pigments. The high spectral quality allows discussion of vibrational assignments based on an empirical approach using previously published data obtained from model compounds. The reduction in intensity of a high-frequency band assigned to the ring-C/D methine bridge vibration is an indication for the non-coplanarity of the ring D in Pfr. The high intensity of a C-H out-of-plane vibration also supports this hypothesis. In Pr, a broad peak at approximately 1100 cm-1 is assigned to an out-of-plane vibration of a strongly hydrogen-bonded pyrrole C=NH+ group. It is missing in Pfr, suggesting deprotonation of the corresponding ring during the transformation from Pr to Pfr.

Fourier‐transform infrared observation of the ν4 stretching mode of C5 in Ar at 10 K

Abstract: The vibrational spectrum of the C5 carbon cluster produced by trapping the products of the vacuum‐ultraviolet photolysis of 2‐methyl‐1,3‐butadiene, or the high‐temperature evaporation of graphite in Ar at ∼10 K, has been analyzed by Fourier‐transform spectroscopy and has resulted in the identification for the first time of the second infrared‐active stretching mode, ν4(σu), at 1446.6 cm−1. The assignment is supported by extensive 13C isotopic data, and is in good agreement with the results of ab initio calculations.

Spectroscopic quantitative analysis of blood glucose by Fourier transform infrared spectroscopy with an attenuated total reflection prism.

Abstract: As an alternative way of long-term glycemic monitoring, the glucose measurement by analyzing Fourier transform infrared absorbance spectra with an attenuated total reflection prism has been developed. In glucose aqueous solution, glucose has characteristic absorptions at the wave numbers of 1033 and 1080 cm-1 and the absorption intensities are proportional to glucose concentrations. In serum and whole blood samples, however, red blood cell corpuscles, serum albumin and serum gamma-globulin interfere with the absorbance spectra of glucose and shift the base line upward significantly. Therefore, to eliminate these interferences in serum and whole blood samples, the feasibility of the calibration curves obtained by using difference absorbance spectra with those of fasting samples was studied. As a result, highly significant correlations between glucose concentrations estimated by Fourier transform infrared spectroscopic method and those measured by glucose oxidase method were obtained (r = 0.981 and 0.989 for serum and whole blood samples, respectively). From these experiments, it was concluded that by infrared spectroscopy glucose concentrations in the serum and whole blood samples could be measured quantitatively or monitored if the base line drifts and interferences were subtracted.

Fourier transform spectroscopy and spectrometer

Abstract: A Fourier transform spectrometer for conducting Fourier transform spectroscopy. The spectrometer has a light source emitting light to a sample via a rapid scan interferometer. The transmittance of the sample varies when stimulated. A stimulus generator gives a stimulus to the sample at regular intervals of τ asynchronously with a reference signal produced for the interferometer. A delay circuit produces a trigger delayed with respect to each stimulation to control a gate circuit. Radiation emanating from the sample is detected by a detector. The output signal from this detector is gated onto a band-pass filter after a given delay Δτ with respect to each stimulation by the gate circuit. The gate circuit produces a digital interferogram. The band-pass filter passes only those frequency components which satisfy the condition: m/2τ

Determination of Sugars and Organic-acids in Fruit Juices By Ft Mid-ir Investigation of Dry Extract

Abstract: In an extension of the approach adopted by Meurens et al. for dispersive NIR spectroscopy, the principle of using dry extracts has been applied to FT-IR spectroscopy, to make use of three advantages: the rapidity of Fourier transform spectroscopy, the solvent elimination, and the better peak resolution in the mid-IR region. However, sampling appears more difficult in mid-IR than in NIR spectroscopy. The feasibility of quantitative analysis has, in a first step, been tested on synthetic samples before application to natural fruit juices. The performance of our dry extract method is reported in terms of spectroscopy as well as of multicomponent quantitative analysis of sugars and organic acids in fruit juices.