Spectral sharpening

Finlayson GD, Drew MS and Funt BV 1994b Spectral sharpening sensor transformations for improved color constancy. Journal of the Optical Society of America A 11(4), 1553-1563. 

Inspection of the spectral shapes in Fig. 4 indicates that the linewidth of the six-line component due to the inner radical becomes sharpened with t2. This spectral sharpening is interpreted as being due to the dependence of the relaxation rate on the resonance frequency the relaxation is slower for the radicals at or near the peak of spectral lines than that for the radicals at the spectral tail because of the angular dependence of the hyperfine coupling. 

An example of the enhanced resolution is presented in Figure 64, where the Au L3-edge XANES of a gold foil is shown both in the normal transmission mode and in the FIERFD mode (Safonova et al., 2006). This spectral sharpening was used to determine the actual adsorption site of CO on a small alumina-supported platinum cluster (Safonova et al., 2006). The measured spectra are shown in Figure 65. Clearly, the features in the XANES spectra recorded by the use of HERFD are richer than what is determined by using total fluorescence detection. 

Biomolecular spectroscopy on frozen samples at cryogenic temperatures has the distinct disadvantage that the biomolecules are in a state that is not particularly physiological. Recall that EPR spectroscopy is done at low temperatures to sharpen-up spectra by slowing down relaxation, to increase amplitude by increasing Boltzmann population differences, and to decrease diamagnetic absorption of microwaves by changing from water to ice. Certain S = 1/2 systems, notably radicals and a few mononuclear metal ions, have sufficiently slow relaxation, and sufficiently limited spectral anisotropy to allow their EPR detection in the liquid phase at ambient temperatures, be it in aqueous samples of reduced size. 

Significant improvements in the appearance of the NMR spectrum of molten globule states are, however, observed upon addition of small amounts of trifluoroethanol (TFE), less than 10 vol%. Amide proton exchange rates are reduced and resonances are sharpened although the chemical shift dispersion is also decreased [51]. The net result is an increased resolution that simphfies considerably the spectral assignment. The increased spectral resolution is in fact due to the fact that the peptides become more denatured rather than more structured and that, in order to obtain more structural information about the folded state, the peptide is partially unfolded ... 

While the ESR signal decay showed only a decrease in intensity when A1 was used as the substrate, the complex spectrum observed when PE was used as the substrate continued to ehange its pattern. A decrease the spectral intensity and sharpening of the eentral ESR line were observed (Fig. 6.13). In addition air exposure (7 days) of the coated fibers resulted in a inajor change where only toe eentral line was observed. Similar signals were also observed du 4 P... 

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