Optical spectra data fitting

Because of the technological importance of ions as active elements in solid-state lasers, optical spectra of lanthanides in sites of low symmetry have been studied extensively. For these sites, the constraints imposed by group theory are weak, and selection rules are often nonexistent (such is the case with Kramers ions in C2 symmetry, for example). Thus, it becomes difficult to unravel the optical spectrum unambiguously. Even if this has been done, it is not straightforward to fit the data with a crystal-field Hamiltonian. The parameter space is large (14 crystal-field parameters in C2 symmetry) and several minima may exist that are indistinguishable from one another insofar as the quality of the fit is concerned. 

The bulk of applications of RRS to electrochemistry have been undertaken by Van Duyne and his co-workers and have been connected with the study of electrogenerated cation and anion radicals. This work is discussed in a review by Van Duyne [34]. Whilst no kinetic determination have been made using RRS, the capability is obviously there as it has been shown that transient data can be obtained on a ms timescale, although with all the systems studied the data fitted a model of simple diffusion control. The great advantage of Raman transients over optical transients in the UV-visible region of the spectrum is that peaks in a Raman spectrum are usually very narrow and therefore interference from other species in solution is unlikely. 

Fig. 4. The reflectivity (a) and the optical conductivity (b) in the p direction are similar to the ones along the a directions (Fig. 3). However, the absence of data above 4 eV changes the high energy spectrum of the optical conductivity. These changes are not relevant for the low frequency spectral range. The Maxwell-Garnett (MG) fit is also displayed as well as the intrinsic reflectivity and conductivity calculated from the fit (see Table 2 for the parameters).

CO-stretching mode. Only the Ai conformer (center arrow) is clearly discemable. The Ao peak is indicated by the arrow on the right, and the A3 peak is indicated by the arrow on the left. The spectrum has a background (solvent + protein) optical density of 1. (B) Example of myoglobin-CO VES data and fit. The dots are the square root of the experimental vibrational echo intensities at zero pulse delay with the laser wavelength varied. See text for details of the calculation. 

Dust is responsible for interstellar polarization and polarization in dust circumstellar envelopes and stars embedded in dark nebulae. As a rale, the wavelength dependence in these cases has a maximum whose position depends on the size and matter of particles. The wavelength dependence of interstellar polarization in optics is well represented by the relation p(A,)/pmax=exp[-Kln (Xmax/ )], where K is accepted equal to 1.15 and Xmax is the wavelength of the maximum of polarization p iax (Serkowski et al. [4]).For this dependence the term the Serkowski law was estab hshed. Soon after pubhcation of this dependence it was found that the factor K depends on the location of the maximum of the degree of polarization in the spectrum. However, three modifications of the Serkowski law have been proposed to better fit observed data Wilking et al. [5], Whittet et al. [6], and Martin et al. [7]. 

Fic. 18. Composite optical absorption spectrum for a-Si H determined from optical transmission, pbotoacoustic deflection, and photoconductivity measurements. The linear fits to the data indicate exponential absorption lges with characteristic widths of 48 and 60 meV. [Reprinted with permission from Solid State Communications, C. B. Roxlo, B. Abeles, C. R. Wronski, G. D. Cody, and T. Tiedje, Comment on the optical absorption edge in a-Si H, Copyright 1983, Pergamon Press, Ltd.]... 

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