Grating instruments

Optical emission spectroscopy by grating instruments by prism instruments by Quantometers 200,000 10,000 60... 

Fixed optic, concave grating instruments (spectrograph type)... 

Evaluate the degree of carbon chain branching by approximately assessing the methyl.methylene ratio from the relative intensity of the absorption bands in the saturated C—H region below 3000 cm-1. This may necessitate re-recording the spectrum on a grating instrument to obtain better resolution. 

No discussion has been devoted to the recent use of Fourier transform spectrometers rather than dispersion instruments. The ease with which the spectral data can be manipulated and background subtracted make the FT methods particularly useful for studies of surface species, particularly during catalytic reaction. Recently there has been a surge of interest in the coupling of computer subtraction techniques to conventional grating instruments. For many IR surface studies, where only limited frequency range is required, this... 

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. 

As early as 1954, Jacquinot pointed out that interferometers have a considerably higher optical conductance than prism or grating spectrometers. In order to quantify this relation we use Eqs. 3.1-33 and 3.1-39 and add G or / as a superscript to designate the spectral optical conductance of grating instruments and interferometers, respectively ... 

A comparison of grating instruments and interferometers is not complete without discussing the so-called multiplex advantage and some other consequences of the geometry of the instruments. This is discussed in Sec. 3.5.2. 

The technique using p-s modulation has received different names depending on the kind of IR instrument used. Thus for grating instruments it was called PMIRRAS (polarization modulation infrared reflection-absorption spectroscopy) [6]. For FT spectrometers the name FTIRRAS [8] was suggested. However this name was later used also in connection with Fourier transform spectra applying the potential difference approach. 

From Inorganic Chemistry, 2, 151 (1963) reprinted by permission, t The spectra in Nujol were obtained with an Infracord with NaCl optics. The spectra in CC1< and CS2 were obtained with a Perkin-Elmer Model 421 grating instrument. 

The single grating instrument depicted in Figure 8.3 is very common in optical spectroscopy (1), but its application to Raman is relatively recent because of inadequate stray light rejection. The introduction of effective laser rejection filters (Section 8.2.5) removed this limitation and single spectrographs became attractive. They are simpler and more efficient than double or triple systems and usually much more compact. Variations of the classical Czerny-Turner... 

It is no coincidence, then, that several companies specializing in NIR equipment should spring up in nearby communities of Maryland over the years [12]. In fairness, Dickey-John produced the first commercial NIR filter instrument, and Technicon (now Bran + Leubbe) the first commercial scanning (grating) instrument. Available instruments and the principles of operation of each type are covered in a later chapter. However, before looking at the hardware, it is necessary to understand the theory. 

Still the workhorse of the analytical lab, grating instruments may be somewhat slow for modern process applications. Since most classical equations have been generated on grating instruments, there is a wealth of information available for the grating user. The better instruments are quite low in noise and have excellent reproducibility. 

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