Fourier conventional spectroscopy

High quality IR spectra of different carbon surfaces were obtained by photo-thermal beam deflection spectroscopy (IR-PBDS) [123,124]. This technique was developed with the intention of providing an IR technique that could be used to study the surface properties of materials that are difficult or impossible to examine by conventional means. Recently, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been successfully applied to study the effect of different pretreatments on the surface functional groups of carbon materials [101,125-128]. Several studies aiming to improve the characterization of the carbon electrode surface and the electrode-electrolyte interface have been carried out using various in situ IR techniques [14,128-132]. The development of in situ spec-troelectrochemical methods has made it possible to detect changes in the surface oxides in electrolyte solutions during electrochemical actions. 

It is admitted that spectroscopy in the far-infrared suffers from the lack of more powerful sources and more sensitive detectors 2 ). Here Fourier transform spectroscopy has some advantages over conventional spectroscopy, e.g. with a grating instrument, and will probably be the most used method until coherent tunable laser sources take over. 

For this reason, the reviewer proposes to introduce the reader to Fourier transform spectroscopy in the hope that he will make use of it. The basic physical principles of spectroscopy and the theory and practice of Fourier transform spectroscopy are described. Its advantages and disadvantages are discussed relative to spectroscopic problems and always with reference to the grating spectrometer as representing conventional spectroscopy. 

Fig. 31. Two superimposed spectra of the rotation-vibration band of CO2 at about 6500 cm t obtained from Venus by means of Fourier transform spectroscopy (ledt) and corresponding portion of the spectrum obtained by means of conventional spectroscopy (right). For comparison, a spectrum is shown which was obtained by conventional spectroscopy in a laboratory. Data taken from Ref.

Conventional spectroscopy can be termed domain spectroscopy in that radiant power data are recorded as a function of frequency or the inversely related wavelength. In conirasl, time-domain spectroscopy. which can be achieved by the Fourier transform, is concerned with changes in radiant power w-iih time. Figure 7-41 illustrates Ihe difference. 

In conventional spectroscopy, measurements are carried out in the frequency domain. The intensity of radiation is recorded in dependence on the frequency or reciprocal wavelength. Some analytical methods, such as Fourier transform infrared (FT-IR) or pulsed nuclear magnetic resonance (NMR) spectroscopies, provide the information in the time domain. There, the opposite transformation into the frequency domain is of interest. 

The advantage of using Fourier transform spectroscopy is that data are acquired very much faster than via conventional, continuous wave, methods. This means a better signal-to-noise ratio can be achieved for an identical amount of compound in the same period of time. The increase in speed is 50-fold. 

Compared with conventional spectroscopy using dispersing spectrometers, Fourier spectroscopy has some definite advantages [4.17,18] ... 

To summarize, twenty years ago it was well established that Fourier transform spectrometers possessed a great advantage in sensitivity over more conventional spectrometers, but that the practice of Fourier transform spectroscopy was severely restricted because of the need for powerful computers to generate the spectral result and because the optical devices were very sensitive to perturbations. 

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