Detection modes rapid-scanning

Since modern FTIR spectrometers can operate in a rapid scan mode with approximately 50 ms time resolution, TRIR experiments in the millisecond time regime are readily available. Recent advances in ultra-rapid scanning FTIR spectroscopy have improved the obtainable time resolution to 5 ms. Alternatively, experiments can be performed at time resolutions on the order of 1-10 ms with the planar array IR technique, which utilizes a spectrograph for wavelength dispersion and an IR focal plane detector for simultaneous detection of multiple wavelengths. ... 

Rapid-scanning Spectrophotometers. These en loy multi-channel detectors. The most commonly encountered detector of diis t e is tlie linear photodiode array. The reversed-optics mode is employed, so that radiation is passed throu tiie sample or reference cell, tiien dispersed by a dif action grating polychiomator integrated intensity of radiation incident on it which is determined by tiie spectial dispersion photo ode ratio. If, for example, a 200-nm txmdwidtii of radiation were dispersed across 256 photodiodes, tiie nominal resolution per photodiode woitid be 0.78 nm. 

Such FPA detector setups were first used by the group of Lauterbach for the parallel characterization of solid samples and the product gas stream from catalytic reactors [18,19]. These authors also changed the mode of operation from the previously used step-scan mode to the rapid scan mode which made it possible to even record transient processes [20,21]. The group of Lauterbach was also the first to apply FPA IR spectroscopy to a problem from zeolite science, even if it was only in form of a feasibility study. They investigated the adsorption of CO on Cu-ZSM-5 and on Pt/Si02 in order to prove that it would be possible to detect the absorption bands of adsorbed species [19J. Since experiments were carried out at room temperature, bands for CO on the Cu-ZSM-5 would be expected to have very low intensity, and indeed, no spectra for CO on this solid were shown. The band of CO on the noble metal, on the other hand, could clearly be detected without problems, and a signal-to-noise ratio not much different from that obtained for a conventional experiment. 

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