Showing papers on "Fourier transform spectroscopy published in 1985"

Fourier transform ion cyclotron resonance mass spectrometry

Abstract: As for Fourier transform infrared (FT-IR) interferometry and nuclear magnetic resonance (NMR) spectroscopy, the introduction of pulsed Fourier transform techniques revolutionized ion cyclotron resonance mass spectrometry: increased speed (factor of 10,000), increased sensitivity (factor of 100), increased mass resolution (factor of 10,000—an improvement not shared by the introduction of FT techniques to IR or NMR spectroscopy), increased mass range (factor of 500), and automated operation. FT-ICR mass spectrometry is the most versatile technique for unscrambling and quantifying ion-molecule reaction kinetics and equilibria in the absence of solvent (i.e., the gas phase). In addition, FT-ICR MS has the following analytically important features: speed (∼1 second per spectrum); ultrahigh mass resolution and ultrahigh mass accuracy for analysis of mixtures and polymers; attomole sensitivity; MS n with one spectrometer, including two-dimensional FT/FT-ICR/MS; positive and/or negative ions; multiple ion sources (especially MALDI and electrospray); biomolecular molecular weight and sequencing; LC/MS; and single-molecule detection up to 10 8 Dalton. Here, some basic features and recent developments of FT-ICR mass spectrometry are reviewed, with applications ranging from crude oil to molecular biology.

Description of the absorption spectrum of iodine recorded by means of Fourier Transform Spectroscopy : the (B-X) system

Abstract: An in extenso analysis of the (B-X) I2 iodine absorption spectrum recorded by means of Fourier Transform Spectroscopy is presented. It is shown that the 100 000 recorded transitions covering the 11 000-20 040 cm-1 range and published in several Atlases may be recalculated by means of only 46 constants : 45 are Dunham coefficients describing the vibrational and rotational constants of both X state (up to v" = 19) and B state (up to v' = 80, situated only at 1.6 cm-1 from the dissociation limit of the B state), and one empirical scaling factor which takes account of neglected centrifugal constants higher than Mv. The overall standard error between computed and measured wavenumbers is equal to 0.002 cm -1 in agreement with the differences of numerous independent absolute wavenumbers and the computed ones.

Structure and dynamics of the excited CH–chromophore in (CF3)3CH

Abstract: The absorption spectra of gaseous (CF3) 3CH (1,1,1,3,3,3‐hexafluoro, 2‐trifluoromethyl propane) were recorded in the IR between 800 and 12 000 cm−1 by high resolution interferometric Fourier transform techniques and in the visible from 12 000 to 17 000 cm−1 by laser photoacoustic spectroscopy. Instead of single bands in the CH overtone region, complex multiplet structures were observed. Thirty‐nine bands were assigned as arising from the interacting CH‐stretching and CH‐bending manifolds, which account for most of the absorption in the overtone region. The results can be understood quantitatively with an effective, tridiagonal many‐level Fermi resonance Hamiltonian. Close agreement is obtained for the positions and intensities of the observed spectral features using only seven spectroscopic parameters. The experimental and theoretical results are summarized in Tables II, III, and IV. The Hamiltonian can be used to calculate and understand the time‐dependent redistribution of vibrational energy between the...

Millimeter-wave dielectric measurement of materials

Abstract: It is no longer necessary to use extrapolated microwave dielectric values when designing millimeter-wave components and systems. Very recently, highly accurate millimeter-wave (5- to 1/2-mm) data on complex dielectric permittivity and loss tangent have become available to engineers for a variety of materials such as common ceramics, semiconductors, crystalline, and glass materials. One quasi-optical measurement method has proved to be most accurate and reproducible, namely, dispersive Fourier transform spectroscopy (DFTS) applied to a polarizing interferometer. The openresonator method and the Mach-Zehnder-IMPATT spectrometer will also be described and compared. The fact that the dielectric loss increases with frequency in the millimeter, unlike the microwave, is an important feature of these data. Reliable measurements also reveal that the methods of preparation of nominally identical specimens can change the dielectric losses by a factor of three.

Photodiode array Fourier transform spectrometer with improved dynamic range.

Abstract: An unconventional Fourier transform spectrometer is described which does not require mechanical scanning. The instrument uses a photodiode array as detector and incorporates features whereby the systematic background noise associated with this type of device may be compensated for to give good quality interferograms. Sample spectra are presented to demonstrate the performance of the instrument.

FTIR matrix isolation study of carbon‐13 substituted SiC2

Abstract: The products from vaporizing silicon carbide at 2900 K and quenching in argon at 8 K have been studied using Fourier transform infrared spectroscopy. Under the assumption of various possible geometries, calculations based on two vibrations observed at 1741.1 and 824.4 cm−1 were made to predict frequencies for SiC2 singly and doubly substituted with carbon‐13. Comparison with the spectra observed on isotopic substitution shows conclusively that these vibrations belong to SiC2, and that the molecule is cyclic (i.e., possesses C2v symmetry) in the ground state. This geometry is in agreement with recent results from a rotational analysis of the band system at 500 nm. Force constants derived in the present study suggest that the silicon atom is singly bonded to two doubly bonded carbon atoms.

The Fourier transform infrared spectrum of methyleneimine in the 10 μm region

Abstract: The infrared spectrum of methyleneimine, CH2NH, has been observed in the gas phase with a resolution of 0.0048 cm−1 using the National Optical Observatory solar Fourier transform spectrometer. The CH2NH was produced by the pyrolysis of CH3NH2 at ∼1000 °C. Vibrational band origins and rotational constants have been determined for the ν7, ν8, and ν9 bands. These were analyzed as a set of three states strongly coupled by Coriolis interaction. More than 2500 transitions were assigned, of which many are ‘‘forbidden’’ transitions, such as qQ branches, induced in the ν9 band by the strong Coriolis interaction between ν7 and ν9. Owing to the high precision of the data, and the high J values of many of the observed transitions, it was necessary to include many of the high order interaction constants in order to achieve a quantitative fit.

The electron storage ring as a source of infrared radiation

Abstract: The characteristics of synchrotron radiation in the infrared region have been investigated at the Berlin electron storage ring BESSY using Fourier spectroscopy. In accordance with calculation, it was found that BESSY at 100 mA beam current delivers higher fluxes than a conventional source only in the spectral region below 30 cm−1, provided the interferometer is the throughput-limiting element. If, however, the throughput is limited by small sample size or, if the experiment requires a large f-number, the high brightness of synchrotron radiation could already yield flux advantages at several hundred wavenumbers. The possible application in one particular experiment - infrared reflection-absorption spectroscopy of adsorbed molecules on metal single crystal surfaces - is discussed. In the course of the investigations described here, it was also established that the short light pulses of the synchrotron radiation (∼ 100 ps) do not adversely affect the resolution in Fourier transform spectroscopy.

Rovibrational analysis of ν3 HCN‐‐‐HF using Fourier transform infrared spectroscopy

Abstract: The gas phase rovibrational spectrum of the ν3 band arising from the C≡N stretching vibration in the hydrogen bonded heterodimer HCN‐‐‐HF has been observed at 0.004 cm−1 instrumental resolution using a Fourier transform infrared spectrophotometer. Analysis of the spectrum gave the following molecular parameters (in cm−1): ν3=2120.935(12), α3=+5.06(19)×10−4, B’=0.119 283(19), D’J=2.30(7)×10−7. Excited state amplitude lifetimes of observed transitions are demonstrated to be 5.6(4)×10−10 s.

Chemical, Biological and Industrial Applications of Infrared Spectroscopy

Abstract: Structural and Dynamical Properties of Membrane Assemblies by Vibrational Spectroscopy Biological FT-IR: Industrial and Academic Applications Applications of Infrared Spectroscopy to the Solution of Problems in the Petroleum Industry Miscellaneous FT-IR: From TRS to PAS Applications of Vibrational Spectroscopy to the Solution of Problems in the Petroleum Industry Unconventional Applications of FT-IR Spectrometry to the Study of Surfaces The Importance of Group Frequencies in Practical Analysis Infrared and Raman Spectroscopy of Polymers Vibrational Spectroscopy in the Data Processing Industry - Selected Applications Applications of Fourier Transform Spectroscopy to Monitor Chemical Reactions.

Measurements of (12)CH4 nu4 band halfwidths using a tunable diode laser system and a Fourier transform spectrometer.

Abstract: Air-broadened and N2-broadened halfwidths at room temperature for twenty-five transitions in the nu-4 fundamental band of (C-12)H4 have been determined from IR absorption spectra recorded with a tunable diode laser spectrometer. Two tunable diode lasers operating in the 1250-1380-kayser region were used to obtain these data. Air-broadened halfwidths for twenty of these lines were also determined from additional spectra recorded at 0.01-kayser resolution with the Fourier transform spectrometer in the McMath solar telescope complex on Kitt Peak. The air-broadened halfwidths obtained from these two techniques are very consistent with agreement better than 3 percent in most cases.

High resolution infrared spectrum of methyleneimine, CH2NH,in the 3 μm region

Abstract: The infrared spectrum of the short‐lived methyleneimine, CH2NH, was obtained in the gas phase with a resolution of about 0.01 cm−1 from 2800 to 3200 cm−1, using the Kitt Peak National Observatory Solar Fourier Transform Spectrometer. The ν2 band and the high order Coriolis coupled ν3 and 2ν5 bands have been analyzed rotationally. Several hundred transitions have been fitted and accurate band origins and rotational constants have been determined for each of the bands.

Growth and characterisation of Pb1-xEuxTe

Abstract: Pb1-xEuxTe single-crystalline epitaxial films were prepared by a modified hot-wall technique. The structural properties were checked by X-ray diffractometry and microprobe analysis. Single-phase material with up to 5% Eu content was produced. Transport properties were investigated between 5 and 300K yielding electron concentrations and mobilities comparable with those of PbTe epitaxial layers. The direct energy gap and its dependence on Eu content as well as on temperature were determined by optical absorptance and reflectance measurements using Fourier transform spectroscopy. This technique also yielded the phonon and free-carrier contributions to the dielectric function in the far-infrared region. Intraband magneto-optical experiments were carried out in Faraday and Voigt geometries in order to obtain information on the effective masses and their anisotropies. For the interpretation of these reflectance and transmittance data as a function of frequency and magnetic field, a Drude model calculation for this many-valley system was performed. For the Voigt geometry in particular, the dielectric tensor and the appropriate complex refractive indices for the ordinary and extraordinary modes are treated in detail. The Shubnikov-de Haas data reveal that the L valleys are not occupied by the carriers equally. Magneto-optical studies between 5 and 50K confirm these findings. Possible sources for the carrier repopulation and its change with temperature are discussed.

Fourier transform time of flight mass spectrometer

Abstract: A time of flight mass spectrometer includes means for gating the flow of ions from the source to the detector with a modulation function, the frequency of which is swept. The detected ion current is obtained as a function of the ion current modulation frequency to derive an ion mass interferogram output in the frequency domain. The interferogram output is Fourier transformed from the frequency domain to the time domain to obtain a time of flight mass spectrum output in the time domain. The Fourier transform time of flight mass spectrometer provides increased duty cycle and signal-to-noise ratio for a given scan time.

Optical method for resolution enhancement in photodiode array Fourier transform spectroscopy.

Abstract: In this paper, we propose a method for optically improving the resolving power of the photodiode array Fourier transform spectrometer [ T. Okamoto S. Kawata S. Minami , Appl. Opt.23, 269 ( 1984)] rather than using mathematical superresolution techniques. The spatial frequency of the interferogram is modulated by the dispersing element added to the triangular common path interferometer so that the spectral resolution is enhanced in the effective spectral range. Since the modification of the method is only the addition of the dispersing optical element to the original optical setup, the advantages of the simple, stable, and easy optical alignment and the large optical throughput with the photodiode array Fourier transform spectroscopy are maintained. Experimental results demonstrate the resolution enhancement by the proposed method with the emission spectra of a low pressure mercury lamp and a cadmium lamp.