Monochromator Resolution

The infrared spectra were recorded with a Grubb-Parson single-beam grating spectrometer provided with a GS 4-type monochromator (resolution... 

Figure 21-3 A portion of the emission spectrum of a steel hollow-cathode lamp, showing lines from gaseous Fe, Ni.and Cr atoms and weak lines from Cr and Fe+ ions. The monochromator resolution is 0.001 nm, which is comparable to the true linewidths.

For second row transition metals, the corresponding Is 4d transition requires very high energies. Low monochromator resolution and short core-hole lifetimes hinder the ability to detect this transition in many cases. Other options to obtain information for these metals rely on intensity estimations of the 2p 4d (allowed) transitions at the f Cn.iii) edges. Another promising approach, mentioned in... 

Figure 5. Dispersed fluorescence spectrum and fluorescence decay resulting from excitation of jet-cooled anthracene to S, + 766 cm 1 (122). The fluorescence spectrum was obtained with 1.6 A monochromator resolution (sR). An arrow marks the excitation wavelength. The decay corresponds to detection of the vj = 390 cm 1 band in the spectrum with R — 3.2 A.

Figure 41. Measured fluorescence decays of the 1750 cm-1 (h-type) band in the v,b = 1420cm"1 spectrum of jet-cooled anthracene as a function of carrier gas parameters. Decays were measured under identical conditions except for carrier gas. For each decay x = 6 mm, the monochromator resolution R = 3.2 A, and the laser bandwidth BW cs 2 cm"1.

Any recording spectrophotometer or spectralline photometer is suitable for oxygen consumption measurements if meets three important requirements (1) high monochromator resolution (2) sensitivity and (3) stability. Since hemoglobin derivatives have rather narrow absorption bands in the visible spectrum, a perfect calibration of the monochromator is necessary. Spectral-line photometers using low-pressure mercury lamps in conjunction with appropriate interference filters are well suited for utilization of the Hb02 method, as there are three different filters for the... 

Due to the rather stringent requirements placed on the monochromator, a double or triple monocln-omator is typically employed. Because the vibrational frequencies are only several hundred to several thousand cm and the linewidths are only tens of cm it is necessary to use a monochromator with reasonably high resolution. In addition to linewidth issues, it is necessary to suppress the very intense Rayleigh scattering. If a high resolution spectrum is not needed, however, then it is possible to use narrow-band interference filters to block the excitation line, and a low resolution monocln-omator to collect the spectrum. In fact, this is the approach taken with Fourier transfonn Raman spectrometers. 

Effect of the monochromator s slit width on noise and resolution for the ultraviolet absorption spectrum of benzene. The slit width increases from spectrum (a) to spectrum (d) with effective bandpasses of 0.25 nm, 1.0 nm, 2.0 nm, and 4.0 nm. 

Infrared instruments using a monochromator for wavelength selection are constructed using double-beam optics similar to that shown in Figure 10.26. Doublebeam optics are preferred over single-beam optics because the sources and detectors for infrared radiation are less stable than that for UV/Vis radiation. In addition, it is easier to correct for the absorption of infrared radiation by atmospheric CO2 and 1420 vapor when using double-beam optics. Resolutions of 1-3 cm are typical for most instruments. 

A monochromator is useful not only for removing unwanted lines from the X-ray source but also for narrowing the otherwise broad lines. For example, each of the MgXa and AlXa doublets is unresolved and about 1 cY wide at half-intensity. A monochromator can reduce this to about 0.2 cY This reduction of the line width is very important because in an XPS specttum, unlike an ultraviolet photoelectron specttum, the resolution is limited by the line width of the ionizing radiation. Unfortunately, even after line narrowing to 0.2 cY... 

There also will be improvements in instrumentadon and software to decrease data acquisidon time. Changes can be made to improve lateral spatial resolution. For example, if the probe monochromator is replaced by a tunable dye laser spadal resolutions down to about 10 pm can be achieved. 

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