Time-resolved infrared spectromete

In 2005, Towrie et al. [30] developed another time-resolved infrared spectrometer capable of performing femtosecond to microsecond time-resolution measurements, by adding to their spectrometer described in Ref [29] a sub-nanosecond Q-switch Nd YV04 laser (wavelength 1064 nm, pulse width 0.6 ns). The pulses generated by this laser were electronically synchronized with the probe pulses with about 0.3 ns jitter, and the harmonics of pulses from this laser were used as the pump pulses. 

Figure 20.8 Explanatory schematic illustration of the femtosecond time-resolved infrared spectrometer reported in Ref [32].

Yuzawa T, Kate C, George M W and Hamaguchi H O 1994 Nanosecond time-resolved infrared spectroscopy with a dispersive scanning spectrometer Appl. Spectrosc. 48 684-90... 

Related experiments have recently been carried out in Xe (sc) and Kr (sc) with a time-resolved infrared (TRIR) spectrometer . In this system, reaction is initiated with a laser as before, but spectra are measured one frequency at a time with a continuous diode laser as the IR source. This apparatus, which has a time resolution of ca. 10 s, has been used to observe the complete set of M(CO)5Ng complexes (M = Cr, Mo, W Ng = Kr, Xe) and has provided tentative evidence for W(CO)sAr in Ar (sc). The measurements are carried out with a small pressure of added CO chosen such that the complexes have lifetimes from 100 ns to 2 qs. The rate constants for reaction with CO increase as follows Xe < Kr < Ar W < Mo Cr. The IR spectra are supplemented by UV/visible spectra of Cr(CO)sNg, which are in satisfactory agreement with matrix spectra. 

Another method, which allows the structural characterization and elucidation of the reactivity of transient species using infrared spectroscopy, is to observe them in real time, using fast time-resolved infrared (TRIR) spectroscopy. In this section we shall focus on the application of fast (submillisecond) and ultrafast (subnanosecond) TRIR spectroscopy to coordination compounds, and describe experiments that cannot be performed using conventional infrared spectrometers. 

An alternative technique for time-resolved infrared measurements on a rapidscanning FT-IR spectrometer that not only overcomes the limitations of stroboscopic spectroscopy described in Section 19.3 but under certain circumstances appears to have better time resolution than measurements made on a step-scan interferometer has been developed by Masutani et al. [22-25]. In this technique, the sample perturbation is not timed to coincide with the scanning and data acquisition of the spectrometer, (i.e., the two are asynchronous). The basic instrument used for asynchronous time-resolved FT-IR spectrometry is a standard rapid-scanning FT-IR spectrometer to which is added a boxcar integrator and some timing circuitry. The instrumental setup is shown in Figure 19.8. 

For microsecond to nanosecond time-resolved infrared absorption measurements, three types of spectroscopic methods have been developed (i) a method using an infrared laser, (ii) a method using a dispersive spectrometer, and (iii) a method using an FT-IR spectrometer. The time resolution of each of these is limited to the fastest time-response capability of the detector used. 

Figure 203 Time-resolved Infrared difference spectra of photoexcited PYP (photoactive yellow protein) measured using a step-scan FT-IR spectrometer [141. Time is indicated on a common logarithmic scale after 50 ns from photoexcitation. AAbsorbance, absorbance difference a.u., absorbance unit. (Source Reprinted by permission from Macmillan Publishers Ltd Nature Structural and Molecular Biology [14]. Copyright 2001.)...

Towrie, M., Gabrielsson, A., Matousek, R, Parker, A.W., Rodriguez, A.M.B. and Vlcek, Jr., A. (2005) A high-sensitivity femtosecond to microsecond time-resolved infrared vibrational spectrometer. Appl. Spectrosc., 59,467-473. 

Time-resolved Fourier transform infrared spectroscopy has been used surprisingly little considering the nuadter of commercial spectrometers that are currently in laboratories and the applicability of this technique to the difficult tine regime from a few is to a few hundred is. One problem with time-resolved Fourier transform spectroscopy and possibly one reason that it has not been more widely used is the stringent reproducibility requirement of the repetitive event in order to avoid artifacts in the spectra( ). When changes occur in the eiaissirr source over the course of a... 

Fourier transform infrared spectroscopy spectrometers can cover wide spectral ranges with a single scan in a relatively short scan time, thereby permitting the possibility of kinetic time-resolved measurements. 

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. 

All these advantages explain why today most infrared experiments on biological samples are performed with FT-IR spectrometers. Partial exceptions are time-resolved studies, and the specied techniques employed there are discussed elsewhere in this volume (see [19]). Apart from the book already mentioned on FT-IR spectroscopy in which a special chapter is dedicated to biochemical and biomedical applications including instrumental and sampling aspects, several other useful guides for both the general application of infrared spectroscopy and the more specialized field of biomedical infrared spectroscopy have appeared. " ... 

Hashimoto, M. Yuzawa, T. Kato, C. Iwata, K. Hamaguchi, H.-O. Fast Time-resolved Mid-infrared Spectroscopy using Grating Spectrometers. In Handbook of Vibrational Spectroscopy, Chalmers, J. M., Griffiths, P. R, Eds. Wiley Chichester, UK, 2002 Vol. 1, pp 666-676. 

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