Dispersive spectrometer, time-resolved

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... 

Time Resolution. Time-resolved studies of surface species are of considerable interest in the field of catalysis since they offer a means for investigating the kinetics of adsorption and surface reaction and for distinguishing between species active and inactive in catalysis (32, 33, 34). Dispersive spectrometers can be used for this purpose (33, 35) but are restricted to the observation of either a single frequency or a narrow range of frequencies, unless the dynamics of the observed phenomenon are very slow compared to the time required for the acquisition of a spectrum. FT spectroscopy allows these limitations to be surmounted and opens up the possibility of recording complete spectra very rapidly. 

Time resolved hole burning spectra were measured by means of a femtosecond transient absorption spectrometer system. A second harmonics of a mode locked cw Nd + YAG laser (Quantronix, 82MHz) was used for a pumping source. A synchronously pumped rhodamine 6G dye laser with a saturable absorber dye jet (DODCl/DQOCI) and dispersion compensating prisms in the cavity was used. The output of the dye laser (lOOfs fwhm, 600pJ/pulse) was... 

To obtain IR spectra on a time scale of nanoseconds, the sample cell in conventional spectrometers is usually excited by an Nd YAG laser. Flow cells with a pathlength of at least 0.1 mm must be used for photoreactive samples and the pulse repetition frequency is then limited to 1 Hz. In step scan FTIR spectroscopy,211 the time evolution is collected at single points of the interferogram, which is then reconstructed point-by-point and subsequently transformed to time-resolved IR spectra. Alternatively, dispersive instruments equipped with a strong IR source can be used.212 The time resolution of both methods is about 50 ns. FTIR instruments provide a triggerable fast-scan mode to collect a complete spectrum within a few milliseconds.213... 

TR in potential modulation experiments is limited to 10 -10 s by the response of the thin-layer cell and, in the case of ATR, to 10 s by the response of the electrochemical equipment, especially the potentiostat (0.5-10 p,s) [478] and the A/D converter [473] used. The first millisecond time-resolved IR spectra of an ultrathin film at the electrode-electrolyte interface were also measured with a dispersive spectrometer by repetitive measurements of IR absorption at fixed wavenumbers and conversion of the data into TR spectra [623]. The disadvantage of this technique was long collection times (on the order of a few tens of hours). 

In order to obtain the spectrum of the emitted field, the probe pulse is frequency resolved by a spectrometer after it has passed the sample (see, e.g. Ref. 54). Because the PP signal is measured as the time-integrated energy rate (cf. Eq. (7)), the corresponding spectrum may be considered as stationary, although it inherently depends on the delay time At. Contrary to the case of time-resolved fluorescence (see next Section), the effects of the spectrometer therefore need not to be considered in the theoretical description, and we may define the dispersed PP signal as the intensity of the Fourier transform of the total emitted field (6), 3uelding °di... 

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. 

Time-Resolved Measurements Using a Dispersive Infrared Spectrometer... 

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