Grating dispersion

Until a few years ago dispersive (grating or prism) instruments were used to acquire infrared spectra. These instruments were relatively slow and insensitive, which made recording spectral information on-the-fly frmi chromatograpbic instruments all but impossible except under conditions which severely compromised the performance of the chi tograph. This... 

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). 

Different types of IR instruments are available dispersive grating spectrophotometers, FT instruments, and nondispersive photometers. Until the 1980s, and the... 

There are three classes of instruments for the measurement of VCD. The first is based on a dispersive grating monochromator as the source of wavelength discrimination. This was the first kind of VCD instrument to be built and this design was used in the discovery of VCD in 1974 [1]. The early versions of these instruments have been described in detail [3,4,44-47], The low-frequency limit was initially 1900 cm"l, the cut-off of the InSb detector. Using a PbSnTe detector the low-frequency limit was extended to 1550 cm l [46], and subsequently using HgCdTe detectors the limit was lowered to 1250 cm l[48] and then 900 cm l [49], and finally using a Si As detector it was lowered to 650 cm l [50]. 

IR Spectroscopy. Samples for IR spectroscopy were prepared by pressing 100-mg KBr pellets containing 1 mg of sample. Samples were run both on a Perkin-Elmer model 167 dispersive (grating) instrument and on a Perkin-Elmer model 1750 Fourier transform diffractometer-model 7300 laboratory computer system. Only the latter instrument afforded the resolution needed to identify the skeletal frequencies of isopropyl groups. 

Most spectral information is obtained if a dispersive grating (polychro-mator) disperses the probe light on a linear diode array, such that an entire spectrum can be measured at once. A second diode array should then be used to record the reference beam (an example is given in Fig. 5 ). Pulse compression is needed in both the pump and probe beams to compensate for group velocity dispersion (GVD) in the entire setup. 

Until the early 1980s, most IR spectrometer systems were double-beam dispersive grating spectrometers, similar in operation to the double-beam system for UV/VIS spectroscopy described in Chapter 2. These instruments have been replaced almost entirely by FTIR spectrometers because of the advantages in speed, signal-to-noise ratio, and precision in determining spectral frequency that can be obtained from a modern multiplex instrument. There are NIR instruments that are part of double-beam dispersive UV /VIS/NIR systems, but many NIR instruments are stand-alone grating instruments. 

Figure 10 Diagram of the echelle spectrograph developed by Pelletier [133] SI, entrance slit LI, collimating lens Ml, mirror CD, cross-disperser (grating) EG, echelle grating L2, focusing lens FP, spectrograph focal plane. (Adapted with permission from Ref. 133.)...

Average linear dispersion, grating centered at 514 nm 1.8 cm" /pixel (0.6 cm /pixel)... 

Mazzacurati V., Montagna M., PiUa 0., Viliani G., Ruocco G., Signorelli G. Vibrational dynamics and Raman scattering in fractals A numerical study. Phys. Rev. B 1992 45 2126-2137 Mazzacurati V., Benassi P., Ruocco G. A new class of multiple dispersion grating spectrometers. J. Phys. E Sci. Instrum. 1988 21 798-804... 

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