Rapid-scan infrared spectroscopy

Reaction was produced by flash photolysis of chlorine-formic acid mixtures and the rate was followed by rapid-scan infrared spectroscopy. 

Because it is widely recognized that a significant amount of reactivity takes places rapidly during sorption processes, it has become necessary to employ new experimental techniques that can adequately measure these processes with high temporal sensitivity. Techniques such as rapid-scan infrared spectroscopy and quick-EXAFS have shown great promise in the early stages of their development and application in our field. It will be over the next decade(s) that these... 

Results of a comprehensive study of the absolute spectral radiance of the infrared emissions from methane—air expins have been reported (Ref 44). The spectral growth of these expanding flames was recorded with a time resolution of one msec in the spectral range 1.7— 5.0 microns. Time resolved spectra were obtained as a function of stoichiometry, nitrogen dilution and Halon dilution. Similar data are also available for coal dust-air explns. Additional applications of rapid scan IR spectroscopy are discussed in Ref 50. In this work, flare spectra (Mk45, LUU-2B and LUU-2B/B) in the 1.7-4.7 and 9—14 micron regions were studied. The Mk-45 and LUU-2B/B showed similar spectral character with Na and C02 emissions superimposed on a gray body continuum, while LUU-2B flares demonstrated variable emittance properties... 

In recent years, infrared spectroscopy has been enhanced by the possibility of applying Fourier transform techniques to it. This improved spectroscopic technique, known as Fourier transform infrared spectroscopy (FTIR), is of much greater sensitivity than conventional dispersive IR spectroscopy (Skoog West, 1980). Moreover, use of the Fourier transform technique enables spectra to be recorded extremely rapidly, with scan times of only 0-2 s. Thus it is possible to record spectra of AB cements as they set. By comparison, conventional dispersive IR spectroscopy requires long scan times for each spectrum, and hence is essentially restricted to examining fully-set cements. 

P 26] Time-resolved FTIR spectroscopy was performed by operation of an infrared spectrometer in the rapid scan acquisition mode (see Figure 1.59) [110]. The effective time span between subsequent spectra was 65 ms. Further gains in time resolution can be achieved when setting the spectral resolution lower (here 8 cm4) or by using the step-scan instead of rapid-scan mode. 

The challenge now is to perform time-resolved experiments and thus, to benefit from the huge potentialities of infrared spectroscopy to identify reaction mechanisms induced by irradiation. For example, in the LINAC-FTIR coupling, the Rapid Scan system of the spectrometer can be used with a resolution of 100 to 10 ms, and for reactions much faster it could be possible to use the Step Scan system. 

To investigate the kinetics that control the rate of network connection of a highly cross-linked photopolymer system, Lovell et al. (2001) utilized rapid scan near-infrared (NIR) spectroscopy to study the polymerization of a dimethylacrylate dental resin. The research exploited the Thermo Electron rapid-scan capabilities to analyze the system with a time resolution of ss 30 ms. This was sufficiently faster than traditional techniques, which required data collection at the 2-second time scale and would thus miss the reaction of interest that reacts to... 

Figure 3.13. (d) Time-resolved attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectra collected during arsenic (As) oxidation on random stacked bimessite (RSB). Peaks represent the oxidation product, arsenate, adsorbed at the RSB surface. (Z ) As oxidation kinetic data collected on RSB (O) on hexagonal bimessite (H-Bi) ( ) during a batch experiment. Inset shows the peak height versus time plot for the spectra seen in the top panel, illustrating the higher time resolution achievable with rapid-scan ATR-FUR spectroscopy. (From Borda and Sparks, unpublished data, 2006.)... 

Infrared spectra are represented in terms of a plot of percentage transmittance versus wavenumber (cm-1). In its most common form, infrared spectroscopy makes use of Fourier transformation, a procedure for interconverting frequency functions and time or distance functions. Fourier-transform IR (FTIR) spectroscopy allows the rapid scanning of spectra, with great sensitivity, coupled with... 

Rapid-scanning spectroscopy (RSS) is a method in which a selected portion of the ultraviolet, visible, or near-infrared spectrum is scanned on a time scale ranging from several sec to a few /isec. The applications of this technique to systems in which short-lived transient species exist or large reaction rates are encountered are numerous... 

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