Rayleigh scatter

Figure Bl.2.2. Schematic representation of the polarizability of a diatomic molecule as a fimction of vibrational coordinate. Because the polarizability changes during vibration, Raman scatter will occur in addition to Rayleigh scattering.

The first temi results in Rayleigh scattering which is at the same frequency as the exciting radiation. The second temi describes Raman scattering. There will be scattered light at (Vq - and (Vq -i- v ), that is at sum and difference frequencies of the excitation field and the vibrational frequency. Since a. x is about a factor of 10 smaller than a, it is necessary to have a very efficient method for dispersing the scattered light. 

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. 

Dadap J I, Shan J, Eisenthal K B and Heinz T F 1999 Second-harmonic Rayleigh scattering from a sphere of centrosymmetric material Phys. Rev. Lett. 83 4045-8... 

Perhaps the best known and most used optical spectroscopy which relies on the use of lasers is Raman spectroscopy. Because Raman spectroscopy is based on the inelastic scattering of photons, the signals are usually weak, and are often masked by fluorescence and/or Rayleigh scattering processes. The interest in usmg Raman for the vibrational characterization of surfaces arises from the fact that the teclmique can be used in situ under non-vacuum enviromnents, and also because it follows selection rules that complement those of IR spectroscopy. 

Goldanskii V I and Krupyanskii Y F 1989 Protein and protein-bound water dynamics studied by Rayleigh scattering of Mdssbauer radiation (RSMR) Q. Rev. Biophys. 22 39-92... 

TR measurements for correspondingly increased rejection of Rayleigh scattering. The addition of each grating typically introduces a throughput efficiency factor of roughly 30%, however, so that the overall efficiency of a... 

Distribution of radiation for (a) Rayleigh scattering and (b) large-particle scattering. 

Thus Rg is a constant in any particular experiment where Rayleigh scattering is obtained, since the entire angular dependence of the light intensity is correctly contained in the 1 + cos 6 term. 

If experimental values of Rg are observed to be independent of 0, then Rayleigh scattering is established and Eq. (10.60) can be applied to the data with confidence. 

The Rayleigh scattering theory which culminates in Eq. (10.60) as its most pertinent form for our purposes is based on the explicit assumption that interference effects are absent. The objective of the present section is to correct the Rayleigh theory to allow for interference effects. There are several assumptions-limitations that are implied by our approach ... 

For Rayleigh scattering, 5j - 6, = 0-there are no phase differences-and each of the cosine terms in Eq. (10.71) equals unity. In this case, which corresponds to i Rayleigh Ee right-hand side of Eq. (10.71) equals E n, and we can write... 

Draw a plot in polar coordinates of the scattering envelope in the xy plane. How would the envelope of a Rayleigh scatterer compare with this plot By interpolation, evaluate 145, iiss, and z. Use Fig. 10.13 to estimate the value of rrms to which this dissymmetry ratio corresponds if X (in toluene) is 364 nm. What are some practical and theoretical objections to this procedure for estimating rrms ... 

All three terms in this equation represent scattering of the radiation. The first term corresponds to Rayleigh scattering of unchanged wavenumber v, and the second and third terms correspond to anti-Stokes and Stokes Raman scattering, with wavenumbers of (v + 2v () and (v — 2v () respectively. 

The resulting spectmm is illustrated in Figure 5.15, and Figure 5.16 shows in detail the processes involved in the first Stokes and anti-Stokes transitions and in the Rayleigh scattering. 

Figure 5.16 Raman and Rayleigh scattering processes involving virtual states Fq and Fj...

The mechanism for Stokes and anti-Stokes vibrational Raman transitions is analogous to that for rotational transitions, illustrated in Figure 5.16. As shown in Figure 6.3, intense monochromatic radiation may take the molecule from the u = 0 state to a virtual state Vq. Then it may return to u = 0 in a Rayleigh scattering process or to u = 1 in a Stokes Raman transition. Alternatively, it may go from the v = state to the virtual state Fj and return to V = (Rayleigh) or to u = 0 (Raman anti-Stokes). Flowever, in many molecules at normal... 

Rawwool Raybestos g-Ray detectors Ray diagram Rayleigh number Rayleigh scatter Rayleigh scattering... 

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