Rapid-scan FTIR spectroscopy

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. ... 

Examples Using Rapid Scan FTIR Spectroscopy... 

In one of the first attempts to apply rapid-scanning FTIR spectroscopy to the dynamic study of deformation phenomena in polymers isotactic polypropylene has been investigated by this technique... 

Karpowicz, R.J. and Brill, T.B. (1984) In Situ Characterization of the Melt Phase of RDX and HMX by Rapid-Scan FTIR Spectroscopy Combustion and Flame 55, 317-325. 

Oyumi, Y., Brill, T.B., Rheingold, A.L. and Lowe-Ma, C. (1985) Thermal Decomposition of Energetic Materials 2. The Thermolysis of N0o and C10i Salts of the Pentaerythrityltetrammonium Ion, C(CH2NHo)4, by Rapid-Scan FTIR Spectroscopy. The Crystal Structure of [C(CH2NH3)4](N03)i . Journal of Physical Chemistry 89, 2309-2315. 

Brill, T.B. and Russell, T.P. ( 1988) Characterization of the Thermal Degradation of Selected Energetic Materials and Mixtures by Rapid-Scan FTIR Spectroscopy Air Force Armament Laboratory, Technical Report 88-85, 1-44. 

Rapid-scan FTIR spectroscopy was used to follow the conversion of (4) to the bidentate product (5) as shown in Scheme l/ At 25°C in methylcyc-lohexane the rate constant k has the following values Cr, 6 x 10 s Mo, 2 X 10 s W, 6 X 10 s . The long alkyl side chains on N-N were present for solubility reasons and do not seem to affect the rate of CO loss from (4) since 4,4 -Me2-2,2 -bipy reacts at approximately the same rate. The reactivity order Mo W = Cr is the normal one for substitutions in this triad, but the absolute rate constants are much larger than usually observed for CO dissociation. This is no doubt due to the promixity of a dangling nitrogen in (4) and its assistance in CO loss via an interchange process. 

The advent of rapid-scanning FTIR systems has tremendously expanded the application of vibrational spectroscopy in the field of rheo-optics and will certainly stimulate further progress in this research area. A similar developm t can presently be observed for X-ray diffraction since the availability of synchrotron... 

Ori ally ai lied jH edominantly as an analytical tool in the field of polymer characterization infrared spectroscopy has bem increasingly utilized in the last decades for the ducidation of the diysical structure of polymers. However, with the advent of rapid-scanning FTIR instruments and the development of the iheo-optical FTIR technique infrared spectro py has been launched into a completely new ex of polymer ph ical applications. 

To emphasize the importance of coworker contributions, the history of our work in this area can be traced. Fast Thermolysis/FTIR Spectroscopy originated in our proposal to the Aerospace Sciences Directorate of the Air Force Office of Scientific Research in the Spring of 1982. At that time the Nicolet 60SX FTIR spectrometer, the first truly rapid-scanning FTIR spectrometer, was about to be introduced, and was needed to make the program viable. 

In thermolysis FTIR the sample (typically 200 /ug) is loaded onto a quartz boat, which is inserted straight into a platinum coil filament. With the beam focused several mm above the filament surface, the IR-active gas products from the fast heated sample can be detected in near real-time. Fast thermolysis/FTIR spectroscopy combines rapid-scan FTIR (20 scans/s) with pyrolysis of a material and realtime measurement of the gas spectra [376]. Temperature, mass changes and spectral data of IR active gases are thus measured simultaneously as a function of time during the rapid heating phase. High-resolution vapour phase libraries are used for identification. 

IR and Raman spectroscopies are both tools that may be useful for monitoring polymerisation rates and cure mechanisms, particularly sequential time-lapse measurements of functional group concentrations at predefined intervals when utilising multichannel Raman or rapid-scan FTIR or FT-Raman detection. 

CIR-FTIR spectroscopy provides a direct technique for studying in situ hydrous metal oxide surfaces and molecules adsorbed on these surfaces (37). By itself, FTIR spectrometry is a well established technique which offers numerous advantages over dispersive (grating) IR spectrometry (1) improved accuracy in frequency measurements through the use of a HeNe laser (2) simultaneous frequency viewing (3) rapid, repetitive scanning which allows many spectra to be collected in a small time interval (4) miriimal thermal effects from IR beam and (5) no detection of sample IR emissions (38). 

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. 

FTIR spectroscopy to a particular pesticide, the methods have general applications to numerous compounds. Most of these utilize the high sensitivity of FTIR, and the data manipulation capability of the system. In several of the gas evolution studies, spectra were acquired at less than one-minute intervals. While this is not really "rapid scanning," the high resolution required for vapor phase spectra would not have been possible with a normal dispersive instrument. Several other techniques using FTIR show promise in the area of pesticide analysis. 

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. 

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... 

Thus, this paper gives tantalising glimpses of the possible applications of in-situ rapid-scan time-resolved FTIR spectroscopy. Unlike the digital time-resolved technique, the rapid-scan method does not require reaction reversibility and may thus have wider application. The technique does have its limitations, however. 

Some new developments of two-dimensional spectroscopy are discussed. As a specific example, two-dimensional correlation analysis of a polymer laminate film using several different spectroscopic techniques is presented. The versatility of this technique was developed using depth-profiling photoacoustic spectroscopy, mid-and near-IR dynamic rheooptical developments, and spectroscopic imaging microscopy. Spatial and temporal variations of near-IR spectra are effectively analysed by the two-dimensional correlation technique. Step-scanning FTIR spectrometers provide an opportunity to obtain desired spectral information often difficult to obtain by the conventional rapid-scanning technique. 12 refs. 

Successful concepts for "reaction-modulated" IR difference spectroscopy use the multiplex advantage of FTIR spectroscopy or the availability of high-intensity laser IR sources. A kinetic photometer using tunable IR diode lasers as sources for the mid-infrared has been developed in our laboratory and will be described elsewhere [6]. It covers the time-domain from approx. 500 nsec to some seconds. A second approach is time-resolved FTIR spectroscopy using a rapid-scanning interferometer, several scans can be recorded per second and the time-domain of slow reactions thus be covered [7]. The following schemes illustrate both concepts ... 

In routine FTIR spectroscopy the spectrometer is operated in continuous scan mode. In this mode of operation, the moving mirror is scanned at a constant velocity, v (cms ), with the light beam path difference at any time, t being given hy 6 = 2 1 (cm). An internal HeNe laser beam is also passed through the interferometer and, since it is essentially monochromatic (I5,798cm ), it is used to accurately calibrate the positions of Mm for data sampling. Continuous scan FTIR is most commonly used to monitor stable samples, but can also be used in rapid-scan mode to monitor time-dependent processes on timescales down to ca. 20 ms. 

---