Showing papers on "Fourier transform spectroscopy published in 2000"

Spectral measurement of absorption by spectroscopic frequency-domain optical coherence tomography.

Abstract: A new method of measurement that essentially combines Fourier-domain optical coherence tomography with spectroscopy is introduced. By use of a windowed Fourier transform it is possible to obtain, in addition to the object structure, spectroscopic information such as the absorption properties of materials. The feasibility of this new method for performing depth-resolved spectroscopy is demonstrated with a glass filter plate. The results are compared with theoretically calculated spectra by use of the well-known spectral characteristics of the light source and the filter plate.

Organic Spectroscopy: Principles And Applications

Abstract: General Introduction to Electromagnetic Spectrum and Molecular Spectroscopy Infrared Spectroscopy Ultraviolet Spectroscopy Nuclear Magnetic Resonance Spectroscopy Mass Spectrometry Optical Rotatory Dispersion and Circular Dichroism.

Metal−Support Interactions in Co/Al2O3 Catalysts: A Comparative Study on Reactivity of Support

Abstract: Co/Al2O3 catalysts have been prepared with conventional impregnation and sol−gel methods to vary the chemical reactivity of the alumina support. The material system has been investigated with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance Fourier transform spectroscopy (DRIFT), Brunauer−Emmett−Teller (BET) method, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) (with thermogravimetric analysis (TGA) and differential thermal analysis (DTA)), and gas chromotography (GC) for the catalytic oxidation of CO. It had been found that the reactivity of the support changes the surface structure and chemical composition of catalysts significantly. When the metal−support interaction is weak, Co3O4 is a predominant surface phase (which is interfaced by a “cobalt surface phase”). With an increase in support reactivity, CoO and CoAl2O4 are found to be present on the surface. The cobalt content on the surface decreases upon the increase in suppor...

Vibrational Spectroscopy Evidence for the Dual Nature of Water Sorbed into Epoxy Resins

Abstract: The physical interactions occurring between absorbed water molecules and the network of a tetrafunctional epoxy resin were studied by mid-infrared (MIR) and near-infrared (NIR) Fourier transform spectroscopy. The spectrum of the sorbed water molecules was isolated in both frequency ranges and the assignments of the various components of the spectrum were proposed accordingly. The results of the vibrational analysis reaffirm the existence of two populations of penetrant molecules, a mobile variety residing within microvoids and those strongly bound to the polymeric network through hydrogen bonding interactions. A comparative analysis of the NIR spectra makes it also possible to deduce the most likely structures of these adducts and their stoichiometry. Finally a method was identified for the quantitative estimation of the bound water responsible for the plasticization of the matrix.

Fourier transform infrared study of the pressure and laser induced polymerization of solid acetylene

Abstract: The polymerization of solid acetylene under pressure has been studied by Fourier transform infrared (FTIR) spectroscopy. Controlled laser irradiation cycles and the employment of infrared sensors to measure the sample pressure, allowed to separate the photochemical and the pressure effect on the injection and on the evolution of the reaction. The careful assignment of all the spectral features and analysis of their relative intensities and frequencies gave evidence to the specific effect of pressure and laser irradiation on the reaction products. Pressure induces an ordered growth of trans-polyenic species, while irradiation produces the opening of the double bonds and a consequent branching of the chains. Constant pressure measurements allowed to obtain precise information on the kinetics of the reaction. A monodimensional growth geometry, involving the molecules on the bc plane, agrees with the parameters extracted by the kinetic curves. Comparison between experiments at different temperatures suggests ...

Time-resolved Fourier transform infrared spectroscopy of optically pumped carbon monoxide

Abstract: The paper discusses measurements of vibration-to-vibration (V–V) energy transfer rates for CO–CO using time-resolved step-scan Fourier transform infrared spectroscopy of optically pumped carbon monoxide. In the experiments, time evolution of all vibrational states of carbon monoxide excited by a CO laser and populated by V–V processes (up to v∼40) is monitored simultaneously. The V–V rates are inferred from these data using a kinetic model that incorporates spatial power distribution of the focused laser beam, transport processes, and multi-quantum V–V processes. Although the model predictions agree well with the time-dependent step-scan relaxation data, there is variance between the model predictions and the up-pumping data, however. Comparison of calculations using two different sets of V–V rates with experimental spectra showed that the use of the semi-empirical V–V rates of DeLeon and Rich provides better agreement with experiment. It is also shown that the multi-quantum V–V rates among high vibrational quantum numbers, calculated by Cacciatore and Billing, are substantially overpredicted. The results provide some new insight into nonequilibrium vibrational kinetics, and also demonstrate the capabilities of the step-scan Fourier transform spectroscopy for time-resolved studies of molecular energy transfer processes and validation of theoretical rate models.

High resolution Fourier transform spectroscopy of jet-cooled molecules

Abstract: The spectroscopic literature reporting on the coupling between Fourier transform spectrometers and supersonic jet expansions is reviewed. Particular attention is devoted to high resolution infrared absorption experiments. Short and much longer introductions are provided on Fourier transform spectrometers and jets, respectively, with emphasis on the problems raised by coupling the two techniques. Details of the optical designs reported in the literature are considered. The literature on all the molecules studied is tabulated. Some of the spectroscopic results are highlighted, in particular those obtained at Universite Libre de Bruxelles.

Pulsed spectrometer for nuclear quadrupole resonance for remote detection of nitrogen in explosives

Abstract: We describe a pulsed spectrometer for detection of nuclear quadrupole resonance on the nuclei of nitrogen N-14 with fast Fourier transform. The use of a multipulse sequence, four channel system for data registration and processing permits detection of the nuclear quadrupole resonance (NQR) signal in the presence of strong interference and the piezo effect. Using this spectrometer we registered the NQR signal from an explosive sample of 150 g (92% RDX) at a distance of 22 cm, and the time of detection was 81 s.

Vibrational properties of ultrathin PTCDA films on Ag(110)

Abstract: We have investigated 3,4,9,10-perylene-tetracarboxylic acid-dianhydride (PTCDA) films on the Ag(110) surface by High-resolution electron energy loss (HREEL) and Fourier transform infrared (FTIR) spectroscopy. X-ray photoemission spectroscopy, low-energy electron diffraction (LEED), and quadrupole mass spectroscopy were used to control thickness, composition, and order of the vacuum-sublimated PTCDA films. Taking advantage of the high surface sensitivity of HREELS, it is possible to clearly distinguish molecules in direct binding contact to the surface from those being in a PTCDA environment, because the spectra show differential peak shifts of the vibrational lines for the former molecules. To aid the interpretation of the spectra, discrete Fourier transform calculations of the vibrational frequencies of the free molecule were carried out. The results are in good agreement with the experimental values for the molecules in the multilayer and allow the identification of most of the experimental modes, if experimental information from off-specular HREELS measurements is taken into account. By the comparison of the calculated frequency spectrum with FTIR data it is possible to extract the effects of the intermolecular interaction on the vibrational spectra.

Temperature and pressure dependence of linewidths and integrated absorption intensities for the O2(a1Δg-X3Σg-) transition

Abstract: The electric-dipole forbidden a1Δg − X3 (0,0) band of gas-phase O2 has been studied in absorption at wavelengths around 1.27 μm using Fourier transform spectroscopy and a long-path absorption cell. Experiments were conducted at temperatures of 294, 243, and 200 K and at pressures in the range 140−750 Torr. Both pure O2 and a mixture of 21% O2/79% N2 were studied, and line widths, integrated line intensities, and integrated absorption intensities (AIs) for the (0,0) vibrational band were measured. Integrated AIs were found to be independent of temperature, pressure, and gas composition, and the recommended value for the vibrational band from the current study is Sint = 3.210(15) × 10-24 cm molecule-1 (1σ error) for pure 16O2, corresponding to an Einstein A-coefficient of A = 2.256(10) × 10-4 s-1. The effect of including other oxygen isotopomers is to increase the integrated AI value for this origin band to Sint = 3.226(15) × 10-24 cm molecule-1. Widths of individual spectroscopic lines decrease with increa...

Vibrational spectroscopy of a transient species through time-resolved Fourier transform infrared emission spectroscopy: The vinyl radical

Abstract: An approach for detecting the vibrational spectrum of transient species is demonstrated on the vinyl radical. Photodissociation of carefully chosen precursors at selected photolysis wavelengths produce highly vibrationally excited radicals. Infrared (IR) emission from these radicals is then measured by time-resolved Fourier transform spectroscopy with nanosecond time resolution. All nine vibrational bands of the vinyl radical, generated from four different precursors, are obtained and reported here for the first time.

Characterization and application of dichroic filters in the 0.1-3-THz region

Abstract: Low-loss dichroic filters, a subgroup of frequency-selective components, have been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3 THz and with Fourier transform spectroscopy. The two data sets are fully consistent. The time-domain spectrometer is used to investigate the phase velocity behavior of dichroic filters. The dichroic filters have various applications in frequency mixing, multiplying, and diplexing experiments. In a novel application, cascaded filters were used to limit the terahertz pulse bandwidth and to monitor molecular transitions of atmospheric water vapor in a selected frequency band.

Dispersion-insensitive measurement of thickness and group refractive index by low-coherence interferometry

Abstract: We describe a low-coherence interferometric technique for simultaneous measurement of geometric thickness and group refractive index of highly dispersive samples. The technique is immune to the dispersion-induced asymmetry of the interferograms, thus overcoming limitations associated with some other low-coherence approaches to this simultaneous measurement. We use the experimental configuration of a tandem interferometer, with the samples to be characterized placed in an air gap in one arm of the measurement interferometer. Unambiguous, dispersion-insensitive measurements of critical group-delay imbalances in the measurement interferometer are determined from the optical frequency dependence of interferogram phases, by means of dispersive Fourier transform spectrometry. Sample thickness and group refractive index are calculated from these group delays. A thickness measurement precision of 0.2 µm and group index measurement accuracy of 5 parts in 105 across a wavelength range of 150 nm have been achieved for BK7 and fused-silica glass samples in the thickness range 2000 to 6000 µm.

Near‐infrared absorption cross sections and integrated absorption intensities of molecular oxygen (O2, O2‐O2, and O2‐N2)

Abstract: Near-infrared absorption cross sections and integrated absorption intensities of gas phase oxygen and nitrogen mixtures have been determined from laboratory measurements using a coolable multipass gas cell and Fourier transform spectroscopy. Spectra were recorded at instrument resolutions of 0.5 and 0.05 cm−1, between 2200–12,500 cm−1 (between 4.5 and 0.8 μm). Monomer and binary cross sections of the a1 Δg ← χ3 Σg− (0,0) and (1,0) bands and underlying continuum absorptions of oxygen centered near 7,850 and 9,400 cm−1 (1.27 and 1.06 μm) were determined for mixtures of 21%, 50%, and 75% oxygen in nitrogen, from measurements at a total pressure of 100 kPa (1000 mbar) and temperatures of 200, 230, and 294 K. Where possible, comparisons are made between the results obtained from this work and those of previous studies.

Effect of Temperature and Concentration on Self-Association of Octan-1-ol Studied by Two-Dimensional Fourier Transform Near-Infrared Correlation Spectroscopy

Abstract: Temperature- and concentration-dependent variations in self-association of octan-1-ol were studied by two-dimensional (2D) Fourier transform near-infrared (NIR) correlation spectroscopy. The obtained results suggest a similar mechanism of the thermal dissociation of hydrogen-bonded species for octan-1-ol and other straight chain alcohols (butan-1-ol, decan-1-ol). However, the extent of self-association in neat butan-1-ol seems higher than that for longer chain alcohols (octan-1-ol, decan-1-ol) under the same experimental conditions. At low and moderate concentrations of octan-1-ol in CCl4 the dimers are open, while in the pure liquid alcohol one can find some cyclic dimers. In both phases the cyclic aggregates dominate and the amount of the linear species is negligible. The population of the free OH groups increases with temperature, reaching 13% at 80 °C, and this increase occurs faster at elevated temperatures. The synchronous peak near 6600 cm-1 is shown to be a part of the broad polymer band, whereas ...

Spectroscopic and Ab Initio Investigation of the νOH Overtone Excitation in Trans-Formic Acid

Abstract: Fourier transform spectroscopy and intracavity laser absorption spectroscopy are used to record the absorption spectrum of formic acid at high spectral resolution, in the ranges of the 2νOH (6968.258 cm−1) and 4νOH (13 284.075 cm−1) vibrational bands of the trans-rotamer, respectively. Numerous perturbations combined with a large line density limit the extent to which the vibration–rotation analysis is performed. Some 689 lines are assigned in the first overtone band and related vibration–rotation constants are determined. Only the band origin and upper state principal A-rotational constant are determined for the n=4 overtone band, because of much higher spectral density. Interpolation, helped by literature data, provides all missing principal rotational constants in the nOH series, for n=1 to 4. All major vibration–rotation parameters appear to evolve very smoothly along the series. This trend is fully supported by ab initio calculations performed at the MP2/cc-pVTZ level of theory and based on an effect...

Factors Affecting the Performance of Bench-Top Raman Spectrometers. Part I: Instrumental Effects

Abstract: D uring the last decade, Raman spectroscopy has become more popular than at any other time in its 70-year history. Several factors have contributed to this explosive increase in usage. Sample preparation for Raman spectrometry has always been easy, but when visible lasers were used to excite the Raman spectrum, the majority of samples gave rise to such high ̄ uorescence that the Raman spectrum was dominated by the shot noise associated with the ̄ uorescence. The accessibility to longer wavelength lasers, such as the 785

High-information time-resolved Fourier transform spectroscopy at work.

Abstract: The first instrumental setup, to our knowledge, that is capable of recording in a few hours the time-resolved Fourier transform (TRFT) interferograms of gas-phase spectra that cover several thousands of inverse centimeters with spectral- and time-resolution limits that are equal, at best, to 2.5 × 10-3 cm-1 and 2 ns, respectively, is reported. It was developed on the stepping-mode Connes-type interferometer of the Laboratoire de Photophysique Moleculaire Universite de Paris Sud. Also, for the first time, to our knowledge, these high-resolution TRFT spectra, illustrated with the Doppler-limited emission spectra of the N2 transitions (B–A) and (B′–B) between 5500 and 11 000 cm-1 and of the atomic Ar lines between 1800 and 4000 cm-1, are recorded in the infrared spectral range. To obtain identical results that have the same signal-to-noise ratio, we should have increased the recording time of our unique previous high-information TRFT spectra by approximately 50,000. In other words, one hour is now long enough to obtain what would previously have required six years to record.

Monitoring a recombinant Pichia pastoris fed batch process using Fourier transform mid-infrared spectroscopy (FT-MIRS)

Abstract: The use of Fourier transform mid-infrared spectroscopy (FT-MIRS) to predict the concentrations of key analytes in fed-batch cultivations of an industrial strain of Pichia pastoris in a chemical complex medium was investigated. Models for glycerol, methanol (substrates), and product (an heterologous protein) were built, and evaluated. The use of a multi-bounce attenuated total reflectance (HATR) accessory aided spectral acquisition in optically dense samples. Generally, all models were robust and performed well on external validation, using data from processes not present in the original modelling exercise. Substrate models lacked the complexity of some previous IR models, and the models performed adequately even at low analyte concentration (<1 g l−1). Thus, simultaneous, rapid monitoring of low concentrations of multiple analytes in a complex bioprocess matrix with little or no sample pre-treatment is achievable using ATR FT-MIRS.