Showing papers on "Fourier transform spectroscopy published in 1988"
TL;DR: In this article, the infrared and microwave spectra are consistent with T-shaped CO2 complexes as shown originally by Steed, Dixon, and Klemperer for Ar-CO2.
Abstract: Sub‐Doppler infrared spectra of Ne–CO2, Ar–CO2, and Kr–CO2 have been recorded near 3613 and 3715 cm−1, in the region of the 2ν02+ν3/ν1+ν3 Fermi diad of CO2, using an optothermal molecular‐beam color‐center laser spectrometer. In addition, pulsed‐nozzle Fourier‐transform microwave spectra are reported for the ground vibrational states of the complexes. The infrared and microwave spectra are consistent with T‐shaped complexes as shown originally by Steed, Dixon, and Klemperer for Ar–CO2.1 The infrared band origins for the Ar and Kr complexes are red shifted, from that of free CO2, by 1.09 and 0.95 cm−1 for Ar–CO2 and by 1.97 and 1.76 cm−1 for 84Kr–CO2. For Ne–CO2, blue shifts of 0.15 and 0.19 cm−1 are observed. The lower Fermi components are free of perturbations, whereas the upper components of Ar–CO2 and Kr–CO2 are perturbed. For Ar–CO2 the perturbation is strong, shifting the positions of the observed Q‐branch lines of the Ka =1←0 subband by as much as 500 MHz.
112 citations
TL;DR: A structural model based on antiparallel beta-strands in the secondary structure of human complement component factor H in H2O and 2H2O buffers is proposed and discussed.
Abstract: Fourier transform infrared spectroscopy was used to investigate the secondary structure of human complement component factor H in H2O and 2H2O buffers. The spectra show a broad amide I band which after second-derivative calculations is shown to be composed of three components at 1645, 1663, and 1685 cm-1 in H2O and at 1638, 1661, and 1680 cm-1 in 2H2O. The frequencies of these components are consistent with the existence of an extensive antiparallel beta-strand secondary structure. The exchange properties of the amide protons of factor H as measured in 2H2O buffers are rapid and lead to an estimate of NH proton nonexchange that is comparable with those for small globular proteins. Human factor H is constructed from a linear sequence of 20 short consensus repeats with a mean of 61 residues in each one. To investigate the secondary structure further, secondary structure predictions were carried out on the basis of an alignment scheme for 101 sequences for these repeats as found in human factor H and 12 other proteins. These predictions were averaged in order to improve the reliability of the calculations. Both the Robson and the Chou-Fasman methods indicate significant beta-structural contents. Residues 21-51 in the 61-residue repeat show a clear prediction of four strands of beta-structure and four beta-turns. A structural model based on antiparallel beta-strands in the secondary structure is proposed and discussed.(ABSTRACT TRUNCATED AT 250 WORDS)
103 citations
TL;DR: In this article, the authors describe a pulsed two-dimensional Fourier transform ESR experiment and demonstrate its applicabilty for the double resonance of motionally narrowed nitroxides.
Abstract: We describe our pulsed two‐dimensional Fourier transform ESR experiment and demonstrate its applicabilty for the double resonance of motionally narrowed nitroxides. Multiple pulse irradiation of the entire nitroxide spectrum enables the correlation of two precessional periods, allowing observation of cross correlations between hyperfine lines introduced by magnetization transfer in the case of a three‐pulse experiment (2D ELDOR), or coherence transfer in the case of a two‐pulse experiment (COSY). Cross correlations are revealed by the presence of cross peaks which connect the autocorrelation lines appearing along the diagonal ω1=ω2. The amplitudes of these cross peaks are determined by the rates of magnetization transfer in the 2D ELDOR experiment. The density operator theory for the experiment is outlined and applied to the determination of Heisenberg exchange (HE) rates in 2,2,6,6‐tetramethyl‐4‐piperidone‐N‐oxyl‐d15 (PD‐tempone) dissolved in toluene‐d8. The quantitative accuracy of this experiment is established by comparison with the HE rate measured from the dependence of the spin echo T2 on nitroxide concentration.
92 citations
TL;DR: In this paper, a Fourier transform infrared interferometer was used to study the multilayer spectra of CO physisorbed onto well defined NaCl(100) surfaces.
Abstract: Vibrational spectra of CO physisorbed onto well defined NaCl(100) surfaces were studied using a Fourier transform infrared interferometer. Structures of CO starting from the monolayer to multilayers were explored. At 31.5 K and a CO pressure of 1×10−6 mbar only the monolayer is formed. Polarization measurements confirm our earlier study that the monolayer CO molecules are aligned perpendicular to the NaCl(100) surface. Increasing the CO pressure to 7×10−6 mbar produces multilayer adsorption. The multilayer spectra closely resemble that of α‐CO absorption previously reported. The near perfect match of crystal structures and lattice constants of α‐CO and NaCl is reasoned to force the epitaxial growth of single crystal multilayers in our experiments. At 22 K the monolayer absorption is at 2155.01 cm−1 with a bandwidth (FWHH) of 0.26 cm−1. The two prominent features in the multilayer spectra at 22 K are assigned to the longitudinal optical (LO) mode at 2142.54 cm−1 and the transverse optical (TO) mode at 2138...
81 citations
TL;DR: In this article, the nu3 transitions of N3 radicals produced by HN3-Cl reactions in a multipass cell (effective path length 100 m) were investigated experimentally using a Fourier-transform spectrometer with maximum resolution 0.004/cm.
Abstract: The nu3 transitions of N3 radicals produced by HN3-Cl reactions in a multipass cell (effective path length 100 m) are investigated experimentally using a Fourier-transform spectrometer with maximum resolution 0.004/cm. A total of 176 rotation-vibration lines are listed in a table and used, in combination with published data on 240 optical lines (Douglas and Jones, 1965), to determine the nu3 molecular constants. The lower-than-expected value of the nu3 fundamental frequency (1644.6784/cm) is attributed to the vibronic interaction discussed by Kawaguchi et al. (1981).
65 citations
TL;DR: In this article, the Kitt Peak Fourier transform spectrometer was used to record the infrared emission spectrum of the Rydberg molecule XeH in a hollow cathode discharge of 2·2 torr H2 and 0·1 torr Xe.
Abstract: The infrared emission spectrum of the Rydberg molecule XeH was recorded with the Kitt Peak Fourier transform spectrometer. XeH was made in a hollow cathode discharge of 2·2 torr H2 and 0·1 torr Xe. The 0-0 bands of the C 2Π-B 2Σ+ and the D 2Σ+-C 2Π transitions were observed near 3250 cm−1 and 4420 cm−1, respectively. A rotational analysis provides spectroscopic constants for these states.
62 citations
62 citations
TL;DR: In this paper, the weak rotational spectrum of styrene has been measured by pulsed microwave Fourier transform (MWFT) spectroscopy and the assignments of the spectrum have been confirmed with radiofrequency-microwave double-resonance experiments associated with the MWFT technique.
61 citations
TL;DR: Air-broadened and N(2)-broadened halfwidth and pressure shift coefficients of 294 transitions in the nu(4) and nu(2) bands of (12)CH(4), measured from laboratory absorption spectra recorded at room temperature with the Fourier transform spectrometer in the McMath solar telescope facility of the National Solar Observatory.
Abstract: Air-broadened and N2-broadened halfwidth and pressure shift coefficients of 294 transitions in the nu4 and nu2 bands of C-12H4 have been measured from laboratory absorption spectra recorded at room temperature with the Fourier transform spectrometer in the McMath solar telescope facility of the National Solar Observatory. Total pressures of up to 551 Torr were employed with absorption paths of 5-150 cm, CH4 volume mixing ratios of 2.6 percent or less, and resolutions of 0.005 and 0.01/cm. A nonlinear least-squares spectral fitting technique has been utilized in the analysis of the twenty-five measured spectra. Lines up to J double-prime = 18 in the nu4 band and J double-prime = 15 in the nu2 band have been analyzed.
59 citations
TL;DR: In this paper, the feasibility of coupling a laser microprobe sampling system with a Fourier transform mass spectrometer (FTMS) for surface characterization is reported, and an integrated circuit chip demonstrates capabilities for focusing the laser on a selected spot on a sample surface.
Abstract: The feasibility is reported of coupling a laser microprobe sampling system with a Fourier transform mass spectrometer (FTMS) for surface characterization. Analysis of an integrated circuit chip demonstrates capabilities for focusing the laser on a selected spot on a sample surface. Analysis of a model glass sample for which high resolution is required to separate metal ions from metal oxide ions emphasizes the advantages of coupling such a sampling system to an FTMS instrument.
55 citations
TL;DR: In this article, double modulation Fourier transform infrared reflection absorption spectroscopy was employed for the in situ analysis of low-temperature plasma enhanced chemical vapor deposition formed SiO2 films deposited on HgCdTe, silicon, and aluminum substrates.
Abstract: The sensitivity and selectivity of double modulation Fourier transform infrared reflection absorption spectroscopy for absorbing species on a reflecting surface has been employed for the in situ analysis of low‐temperature plasma enhanced chemical vapor deposition formed SiO2 films deposited on HgCdTe, silicon, and aluminum substrates. An oblique angle of incidence of ∼55° was chosen to yield maximum sensitivity for the longitudinal optical (LO) phonon mode of SiO2 on Si. The peak frequency and shape of the LO mode absorption band varied with the quality of the SiO2 films thus providing a means of in situ assessment of reaction conditions at any stage of film growth. This diagnostic technique can be readily applied to the in situ analysis of dielectric thin films formed under a variety of reaction conditions.
TL;DR: More than 8000 completely resolved rotational lines in Cs2 have been measured with the techniques of Fourier transform spectroscopy, Doppler-free polarization, and optical optical double resonance.
Abstract: More than 8000 completely resolved rotational lines in the E 1Σ+u →X 1Σ+g, E 1Σ+g →(2)1Σ+g, E 1Σ+u →(1)1Πg, E 1Σ+u →(3)1Σ+g, D 1Σ+u →(2)1Σ+g, C 1Σu →X 1Σ+g, and D 1Σ+u →X 1Σ+g transitions of Cs2 have been accurately measured with the techniques of Fourier transform spectroscopy, Doppler‐free polarization spectroscopy, and optical optical double resonance. The wave numbers of all these rotational lines were determined with an accuracy of 1 to 5×10−3 cm−1. A thorough and simultaneous analysis of all the measured data yields molecular constants, potential energy curves, and dissociation energies for six different excited electronic states of the Cs2 molecule.
TL;DR: In this article, the response of half-integral spin I>1 nuclei in anisotropic systems to the quadrupolar echo (QE) pulse sequence (π/2)x−τ−(π/ 2)y is investigated, with particular emphasis on the effects of quadrupol relaxation.
Abstract: The response, in the frequency domain, of half‐integral spin I>1 nuclei in anisotropic systems to the quadrupolar echo (QE) pulse sequence (π/2)x−τ−(π/2)y is investigated, with particular emphasis on the effects of quadrupolar relaxation. Using a state multipole formalism, we derive the frequency spectra produced by one‐ or two‐dimensional Fourier transformation. Powder samples as well as uniformly and partially oriented samples are considered. The 2D QE experiment produces, in the F1 dimension (Fourier transformation with respect to τ), spectra which provide information about the static quadrupole coupling even if only the central line in the QE spectrum (obtained by Fourier transformation of the induction signal after the echo) is detected. For partially oriented and (incompletely dephased) powder samples, the F1 spectra allow the motional spectral densities to be determined with little or no effect of the inhomogeneous quadrupole coupling, which severely complicates the analysis of conventional (single...
TL;DR: A sensitive thermoluminescence emission spectrometer based on Fourier transform spectroscopy is described, sufficiently sensitive to record thermolUMinescence spectra of dosimeter phosphors and minerals for thermolumscence dating at levels corresponding to those found during actual use as radiation monitors or in dating.
Abstract: A sensitive thermoluminescence (TL) emission spectrometer based on Fourier transform spectroscopy is described. It employs a modified scanning Twyman-Green interferometer with photomultiplier detection in a photon-counting mode. The etendue is 180π mm2, and it covers the 350–600-nm wavelength range. The output can be displayed either as a 3-D isometric plot of intensity vs temperature and wavelength, as a contour diagram, or as a conventional TL glow curve of intensity vs temperature. It is sufficiently sensitive to record thermoluminescence spectra of dosimeter phosphors and minerals for thermoluminescence dating at levels corresponding to those found during actual use as radiation monitors or in dating. Examples of actual spectra are given.
TL;DR: It is pointed out that the factorization approximation for the relaxation function holds rigorously in the accumulated photon echo and the Fourier cosine transform of the heterodyne-detected echo signal provides the hole-burning spectrum.
Abstract: Fourier-transform spectroscopy using the technique of femtosecond accumulated photon echo with incoherent light has been performed in dye-doped polymers. Several types of interference effect or quantum beat between the zero-phonon line and other spectral components including the phonon sideband, the vibronic lines, and the photoproduct state have been observed. Based on the density matrix incorporating the transition-frequency modulation, it is pointed out that the factorization approximation for the relaxation function holds rigorously in the accumulated photon echo. We also clarified that the Fourier cosine transform of the heterodyne-detected echo signal provides the hole-burning spectrum.
TL;DR: In this article, the ν 2 fundamental band of NH 2 has been observed at high resolution (0.0045 cm −1 ) using a Fourier transform infrared spectrometer and a fast-flow multiple-traversal absorption cell.
TL;DR: In this paper, a newly built infrared spectrometer is used for vibrational studies at the electrochemical interface, which is achieved by using a slow scan speed (∼6 μm) s−1 for the Michelson interferometer.
Abstract: We report on a newly built infrared spectrometer to be used for vibrational studies at the electrochemical interface. The usual way to select the weak interface absorption consists in changing the electrode potential and measuring the associated change in absorption. However, up to now it was difficult to benefit from both the advantages of using a lock‐in detection and Fourier transform spectroscopy. Our apparatus allows simultaneous use of these two techniques. This is achieved by using a slow scan speed (∼6 μm s−1) for the Michelson interferometer. The electrode potential may be modulated at a frequency as low as 100 Hz. The ultimate sensitivity of our apparatus corresponds to a relative change of transmitted light intensity of ΔI/I∼10−6, for a measuring time of 45 min, in the 800–4200 cm−1 range, with a resolution of 25 cm−1. Our ultimate resolution capability is 0.5 cm−1. Data are presented that have been obtained on the n‐Si/acetonitrile interface using an attenuated total reflection geometry, which...
TL;DR: In this article, a large number of spin-rovibronic levels of the upper electronic state of NH2 have been excited with a single mode rhodamine 6G dye laser.
Abstract: A large number of spin-rovibronic levels of the upper electronic state of NH2 have been excited with a single mode rhodamine 6G dye laser. Fluorescence spectra were obtained over a wide spectral range (12 000-3700 cm-1) using a Fourier transform spectrometer. Levels of the bending vibration were observed from ν″2 = 4 up to 10, showing the reordering of the K-structure at the barrier to linearity; their observed energies are in good agreement with the predictions of Jungen, Hallin and Merer [16, 17], Duxbury and Dixon [19] and Peric, Peyerimhoff and Buenker [20]. Numerous vibrational levels involving nv 1 and 2v 3 were also detected and approximate anharmonic parameters have been deduced. Local perturbations are observed and discussed; the interpretations proposed by Jungen et al. [18] for some of these in the A 2 A 1 state are experimentally confirmed.
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01 Jan 1988
TL;DR: In this paper, the authors introduce the data processing and sources of error for FTIR spectroscopy and present a new perspective of vibrational spectroscopic analysis in material science.
Abstract: Introduction to data processing and sources of error, R.W.Hannah GC/IR - a technique come of age, D.W.Vildrine polarization modulation FTIR spectroscopy, L.A.Nafie solid sampling techniques, J.M.Chalmers and M.W.Mackenzie rheo-optical FTIR spectroscopy of macromolecules, H.W.Siesler new perspectives of vibrational spectroscopy in material science, G.Zerbi FTIR studies of catalyst systems under realistic processing conditions, P.C.M. van Woerkom.
TL;DR: In this article, the C 2 H radical is produced by flowing C 2H 2 through a radiofrequency discharge and the resulting emission is recorded in the mid-infrared with a high-resolution Fourier transform spectrophotometer.
TL;DR: In this article, two-dimensional correlation techniques were applied to microwave Fourier transform (MWFT) spectroscopy, and experiments were performed on 1-chloro-1fluoroethene in order to show common energy levels within the 35Cl hyperfine structure.
TL;DR: In this article, the rotational spectra of 1,2- and 1,3-benzene-d2 have been measured over the 8-18 GHz range with a pulsed microwave Fourier transform spectrometer.
TL;DR: In this article, the infrared intersubband absorption in modulation-doped MOVPE-grown AlxGa1−xAs/GaAs single-quantum wells has been studied by Fourier transform infrared spectroscopy.
Abstract: Infrared intersubband absorption in modulation‐doped MOVPE‐grown AlxGa1−xAs/GaAs single‐quantum wells have been studied by Fourier transform infrared spectroscopy. High signal to noise ratio was obtained by utilizing the multiple internal reflection (MIR) technique and a quantitative model of the absorption for this geometry was developed. Overlapping from multiphonon absorption was eliminated by using radiation polarized in two orthogonal directions and taking the difference between the resulting spectra, only one of them exhibiting the intersubband peak. The absorption wavelengths and intensities were fitted to theoretical expressions and the dimensions of the quantum wells were compared with independent determinations by photoluminescence, double crystal x‐ray diffraction, and Hall‐effect measurements. A narrow linewidth of about 6 meV was measured, corresponding to a 0.1‐ps lifetime of electrons in the excited state.
TL;DR: An automatic low-pressure packing unit with control of packing time and pressure to prepare powder samples for diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was designed in this paper.
Abstract: An automatic, low‐pressure packing unit has been designed with control of packing time and pressure to prepare powder samples for diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This unit also provides a polished packing surface that ensures constant measurement height of the sample in the spectrometer. Use of this unit coupled with sample rotation during measurement and control of particle size and size distribution, provides excellent precision in obtaining DRIFTS spectra. For example, repackings by a single person or by several untrained people gave coefficients of variation from 0.8% to 2.3% for each digital spectral value for a coal sample and from 1.3% to 3.7% for thymol blue, a sharp spectral featured organic, rather than the 15%–30% normally found for repackings of the same sample. Thus representative DRIFTS spectra can be obtained quickly and efficiently from a powder sample with a single spectrum using this low‐pressure, mechanical packing device, control of particle parameters, and sample rotation as opposed to previous efforts requiring the repacking of several samples and averaging of the spectra.
TL;DR: In this paper, a rotational analysis of the ground state of the diatomic molecule RbCs was carried out using the combined techniques of laser-induced fluorescence (LIF) and Fourier transform spectroscopy (FTS).
TL;DR: In this paper, Fourier transform Raman spectroscopy has been performed with an inexpensive bench-top FT-IR spectrometer optimized for the near-infrared using a continuous-wave Nd: YAG laser with an output at 1.064 μm.
Abstract: Fourier transform Raman spectroscopy has been performed with an inexpensive bench-top FT-IR spectrometer optimized for the near-infrared. The laser excitation source was from a continuous-wave Nd: YAG laser with an output at 1.064 μm. Spectra from solid samples, ground as powders, have been obtained. Many of these are well known to fluoresce in the visible region and are thus intrinsically difficult to study by the Raman method. The FT-Raman method is described, and improvements in the technique are considered.
TL;DR: In this paper, a Fourier transform (FT) spectrometer was configured to measure near-infrared (near-IR) transmission spectra using 80 meters of a 206-μm optical fiber.
Abstract: A Fourier transform (FT) spectrometer was configured to measure near-infrared (near-IR) transmission spectra using 80 meters of a 206-μm optical fiber. The single-beam signal-to-noise ratio (S/N) was evaluated for the remote-sensing spectrometer for both Ge and InSb detectors. The instrumental performance was compared with that of the conventional FT spectrometer. The optical attenuation of several different fibers was measured and their possible use as transmission sensors was evaluated. Some advantages and implications of combining an FT spectrometer with optical-fiber sensor measurements are discussed.