Fourier transform infrared wavenumber resolution

Fourier transform infrared (FTIR) spectra were measured using a Dlgilab FTS-14 spectrometer with the Real Time Disk Operating System (RDOS). The samples were scanned 256 times at a resolution of one point every four wavenumbers with double precision. 

Fourier transform infrared spectra of Csl pellets of the AI13- and GaAli2-sulfate and selenate salts and of the deuterated Al -sulfate salt were run on a Mattson Galaxy 4030 spectrometer at a resolution of 2 wavenumbers. 

The essential problem of the dispersive spectrometer lies with its monochromator. This contains narrow slits at the entrance and exit which limit the wavenumber range of the radiation reaching the detector to one resolution width. Samples for which a very quick measurement is needed, for example, in the eluant from a chromatography column, cannot be studied with instruments of low sensitivity because they cannot scan at speed. However, these limitations may be overcome through the use of a Fourier-transform infrared spectrometer. 

Fourier transform infrared spectroscopy (FT-IR) analysis of dried and annealed powders were carried out in an Impact 400, Nicolet spectrometer in the wavenumber range 400-4000 cmi at resolution of 4 cmi for studying the chemical groups. For this analysis, KBr pellets were pressed to hold the samples to be analyzed. 

Fourier Transform infrared system at four wavenumber resolution in double beam operation. Standard double precision computer software were used to present data properly scale expanded in absorbance form. 

Fourier transform infrared-attenuated total reflectance (FTIR, ATR-FTIR, Nicolet 8700, USA) spectroscopy was used to analyze the chemical structures of the specimens. All spectra were collected with 4 cm wavenumber resolution after 64 continuous scans at a wavelength range of 4000—600 cm ... 

Sample characterization. Fourier-transform infrared (FTIR) spectroscopy in ATR mode was used to monitor the geopolymerization. FTIR spectra were obtained using a ThermoFisher Scientific Nicolet 380 infrared spectrometer. The IR spectra were gathered over a wavenumber range of 400 to 4000 cm with a resolution of 4 cm To follow the evolution of the involved bonds in time, a software was used to acquire a spectrum every 10 min for 13 hours. The atmospheric CO2 contribution was removed with a straight line between 2400 and 2280 cm To allow comparisons of spectra, they were corrected using baseline and normalized. 

An infrared spectrum is a plot of percent radiation absorbed versus the frequency of the incident radiation given in wavenumbers (cm ) or in wave length ( xm). A variation of this method, diffuse reflectance spectroscopy, is used for samples with poor transmittance, e.g. cubic hematite crystals. Increased resolution and sensitivity as well as more rapid collection of data is provided by Fourier-transform-IR (FTIR), which averages a large number of spectra. Another IR technique makes use of attenuated total reflectance FTIR (ATR-FTIR) often using a cylindrical internal reflectance cell (CIR) (e.g. Tejedor-Tejedor Anderson, 1986). ATR enables wet systems and adsorbing species to be studied in situ. 

As mentioned in the introduction, a major advantage that Fourier transform spectroscopy has over laser spectroscopy is that it is straightforward to record the entire spectrum of a species at once. Diode lasers in the infrared are not continuously tunable and have mode gaps which can only be filled by switching diodes. Many ultraviolet lasers are not continuously tunable either. Tunable difference frequency methods and diode lasers involve much longer scan times than are necessary with a Fourier transform device. For example, the Bomem DA3.002 can scan a bandwidth of 100 or more wavenumbers in the mid-IR at a resolution of 0.005 cm-1 in less than 3 minutes. A diode laser which scans in 20 MHz steps may require more than a day to scan the same spectral region. 

Since FT-IR spectrometry is based on the interference of waves of light (or radiation), first an account of this phenomenon is briefly given, before explaining the Fourier transform method by which an infrared spectrum is obtained from a measured interferogram. Some characteristics of FT-IR spectrometry, namely, wavenumber resolution, measurable wavenumber region, and accurate determination of wavenumbers are discussed. To facilitate the understanding of the description, which inevitably requires some mathematical formulations, many illustrations are provided. 

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