Rayleigh line broadening

In the case of solutions, concentration fluctuations only contribute to the central elastic part of the scattering spectrum. However, the Brownian movement of solute molecules creates weak frequency displacements that broaden the central peak. This phenomenon is called Rayleigh line broadening or quasielastic scattering [26-28]. This section deals with elastic scattering only. 

Rayleigh line-broadening methods have been applied increasingly to highly swollen gel systems although there is much less agreement about the interpretation... 

The ratio of the intensity of anti-Stokes and Stokes lines is primarily determined by the Boltzmann population of the excited vibrational states. For mid-IR frequencies this fractional population is very low (seIO-4 at 2000cm-1). As a result, Raman spectra are usually taken from the Stokes side of the Rayleigh line as these are generally very much more intense and are not broadened by emissions from hot states. 

In the region where intramolecular fluctuations are unimportant, polydispersity broadens the Rayleigh line and the broadening can be used to characterize the extent of the polydispersity. Burchard et have discussed the theory and... 

The DLS technique involves measurement of the Doppler broadening of the Rayleigh-scattered light as a result of Brownian motion (translational diffusion) of the particles. This thermal motion causes time fluctuations in the scattering intensity and a broadening of the Rayleigh line. The Rayleigh line has a Lorentzian line shape. In macromolecular solutions, concentration... 

Figure 26 shows the dispersion curve of the Kr monolayer obtained from a large number of spectra like those in Fig. 25. The hybridization splitting around the crossing with the substrate Rayleigh wave (solid line) is clearly observed. Also the predicted tiny frequency upshift close to the T point due to the coupling to the substrate vibrations is seen. The observed linewidth broadening is also shown in Fig. 26. As a measure of the broadening, the quantity Ae = [( ) — with dE the FWHM of the major loss feature...

Fig, 26. Experimental dispersion curve of the Kr monolayer and measured line width broadening As of the Kr creation phonon peaks. The solid line in the dispersion plot is the clean Pt(lll) Rayleigh phonon dispersion curve and the dashed line the longitudinal phonon bulk band edge of the Pt(l 11) substrate, both in the r Mn azimuth which is coincident with the r Kk, azimuth. 

The lines labeled A and B are ESR scattering from the and P3/2 states, respectively, and lines C and D are TPS to the P3/2 and P% final states, respectively (see Fig. 2). The line labeled R corresponds to Rayleigh scattering. Also indicated in the figure are the positions of the Dj and D2 atomic resonances. Not shown in Fig. 3 are the observed Rayleigh-scattered peaks, which were always present, often with a pronounced asymmetric broadening, which we tentatively ascribe to self-phase modulation. 

Figure 6.25 Linewidth broadening of the Cu(lll) surface hole state as a function of binding energy, Pe e + Pe ph (solid line), Pe-ph (dotted line), the Rayleigh mode contribution to Pe-ph (dashed line), and photoemission data (diamonds). Adapted from Ref. [67].

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