Rapid-scan

The principle of the rapid scan mode is simple after taking a reference spectrum of the sample in its ground state, one activates the reaction (e.g., by a laser flash) and obtains an interferogram in a much shorter time than the half life time of the reaction (e.g., the photocycle). 

The velocity of the scanner V ax and the desired spectral resolution A determine the scan duration At and thereby the time resolution  

State of the art spectrometers today yield typically a time resolution of 7 ms at 4 cm spectral resolution. As we have shown, Fourier transformation makes it possible to even resolve processes whose half life times are of the order of the scan time (Gerwert et al., 1990). If the half life of the observed process is shorter than the duration of the scan, then the intensity of the interferogram is convoluted by the absorption change due to the chemical reaction in the sample. Thus, the absorption changes during the bacteriorhodopsin photocycle can be described by sums of exponentials. This leads to 

Significant improvements of state of the art spectrometers yielding increased scanner velocity are unlikely to occur. This has practical reasons, e.g., the acceleration at the turning points is already on the order of several g. Without a radical change of design, rapid scan time resolution is limited to the millisecond range. 

Fourier transformation produces a time-dependent series of difference spectra. The absorbance changes at a specific wavenumber are simply obtained by reordering the data in dependence of time. Examples are discussed in section 6.6.3. 

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In wide sectors of industry there is a growing need of inspection methods which go without liquid coupling media. The excitation of bulk and surface waves by means of air-coupled ultrasonic probes is therefore an attractive tool for NDE. This is tme e.g. for the rapid scanning of large composite structures in the aerospace industry [1]. In other cases, the use of liquid couplants is prohibitive like the thickness measurement of powder layers. 

Diffey W M and Beck W F 1997 Rapid-scanning interferometer for ultrafast pump-probe spectroscopy with phase-sensitive detection Rev. Sci. Instrum. 3296-300... 

Slow scanning (i) of the mass spectrum over a GC peak for substance A gives spectrum (a), but rapid scanning (ii) gives spectrum (b), which is much closer to the true spectrum (c). 

Rapid-Scan Corrosion Behavior Diagram (CBD) Basically, all the same equipment used in the conductance of an ASTM G5 slow-scan polarization study is used for rapid-scan CBDs (that is, a standard test cell, potentiostat, voltmeters, log converters, X-Y recorders, and electronic potential scanning devices). The differences... 

The measurement range is dependent on the instrument but can cover the range -50 to +500 °C. The accuracy is not as high as the best contact thermometers. One reason for this is that the emissivity of the surface has an effect on the measurement result, and an emissivity correction is necessary for most instruments. The positive features are noncontact measurement and very fast dynamics, which enable a rapid scan of surface temperatures from a distance this is convenient when carrying out, for example, thermal comfort measurements. 

Quantitative HPLC analysis was carried out on a Spectraphysics 8720 chromatography system, a rapid scan detector by Barspec on a Zorbax ODS column with acetonitrile water 75/25 as the eluent. 

Experimental limitations initially limited the types of molecular systems that could be studied by TRIR spectroscopy. The main obstacles were the lack of readily tunable intense IR sources and sensitive fast IR detectors. Early TRIR work focused on gas phase studies because long pathlengths and/or multipass cells could be used without interference from solvent IR bands. Pimentel and co-workers first developed a rapid scan dispersive IR spectrometer (using a carbon arc broadband IR source) with time and spectral resolution on the order of 10 ps and 1 cm , respectively, and reported the gas phase IR spectra of a number of fundamental organic intermediates (e.g., CH3, CD3, and Cp2). Subsequent gas phase approaches with improved time and spectral resolution took advantage of pulsed IR sources. 

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 mass spectrometers providing unit resolution are routinely used as chroaatographic detectors. Ion separation is accomplished using either a magnetic sector, quadrupole filter or ion trap device. Ions can also be separated by time-of-flight or ion cyclotron resonance mass analyzers but these devices are not widely used with chromatograidiic inlets and will not be discussed here [20]. 

Retzik, M. and Froehlich, P., Extending the capability of luminescence spectroscopy with a rapid-scanning fluorescence spectrophotometer, Am. Lab., March, 68, 1992. 

Generally, measurement of absorption spectra of the colored form of spirobenzopyran is very difficult using normal spectrophotometry, as the colored form is thermally unstable. The absorption spectra of the colored form of 6,8-dinitro-BIPS 7, which is exceptionally stable in DMSO even at 23°C, are shown in Figure 1.4. Generally, it is possible to obtain a reasonable absorption spectrum of the colored form by the use of a rapid scanning spectrophotometer. 

Sufficiently rapid scanning capability (100 ms per scanning unit)... 

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