Rayleigh peaks

The scan of a fluorescence emission spectrum should routinely include the region of the Rayleigh peak (see Fig. B3.6.1). This provides a built-in indicator of turbidity of the buffer and protein solutions. The height of the peak for the protein solution should not differ greatly from that obtained for the solvent from the equivalent buffer blank scan it will increase markedly if there is dust or aggregate in the solution. 

In real fluids, low-frequency light-scattering reveals a central Rayleigh peak, due to heat diffusion, and two symmetrically displaced Brillouin peaks, due to sound waves, such that... 

Figure 2 Measurement of scattered light at 90° The excitation radiation for the Raman experiment must be monochromatic. Scattering of UV or visible photons produces an intense Rayleigh peak and weaker Raman peaks, displaced from the Rayleigh by. These arise because of energy transfer from the incident photon hvo to the molecule, which is raised to an excited vibrational level. The readout signal is proportional to the flux of the scattered light (7sc), which is directly related to the fourth power of the scattered frequency (vsc), irradiance of the source ( 0), and the concentration of scattering molecules...

Raman diffusion is observed at a wavelength that is higher than the excitation wavelength. The diffused photons have quantum energy inferior to that of the excitation photons. Therefore, the intensity of the Raman peak is lower than that of the Rayleigh peak. Raman can perturb the emission spectrum and thus one should subtract the Raman from the emission spectrum. 

An example of a pure rotational Raman spectrum, including the Stokes and anti-Stokes branches, is shown in Figure 8.2 for the case of N2 note that the line intensity of the Rayleigh peak at Fl is off the scale, as expected. Note also that the... 

In these lectures we will present the theory of atomic scattering focusing in particular on the atom surface potential. This potential is separated in an attractive part of the Van der Waals type and in a repulsive part related to the surface charge which is approximate as a superposition of atomic charges. The lateral Fourier trasform of this potential, which enters in the cross sections, has a gaussian form which is essential in order to explain the falling off of the Rayleigh peaks at the zone boundary. 

For a molecule with a three-fold or higher symmetry axis, only [Oolbody non-zero and eqs. ( 29) and (3.31) simplify considerably. Note that the term in cr in eq. (3.31) has no time dependence it Fourier transform is a delta function at zero frequency which corresponds to Rayleigh scattering. Of course, the Rayleigh peak does have a finite width however, it is due to... 

Figure 1. A schematic diagram showing the relative positions of Rayleigh and Brillouin scattering peaks. The incident light has frequency cOq the Brillouin frequency shift is cOg. The widths of the Brillouin and Rayleigh peaks (Tg and Tp.) are also shown.

From the discussion given in earlier chapters, we note that in liquid crystals, the main scattering is due to collective or correlated orientational fluctuations. These, of course, are much slower processes than individual molecular motions. The spectrum from these correlated or collective orientational fluctuations is therefore very sharp and is embedded in the central Rayleigh peak region. 

Here, we briefly summarize the results for the dynamic structure factor. The dynamic sfiucture factor exhibits three peaks, a central Rayleigh peak caused by the thermal diffusion, and two symmetrically placed Brillouin peaks caused by sound. The width of the central peak is determined by the thermal diflfusivity, Dj, while that of the two Brillouin peaks is related to the sound attenuation coefficient, r. For the SRD algorithm [57],... 

One novel feature of the simulations (13) was the presence of a central Rayleigh peak for the smallest wave vector = (2ir/a) (1/8,0,0) studied at high temperatures in the system of 20U8 particles. The width of this peak is governed by the thermal diffusivity and provides a crude estimate of the thermal conductivity since the specific heat is known from other calculations. 

Figure 10. The full cttrves are the MD SfQ.m) data for longitudinal phonons propagating in the basal plane of hep fi-Ni. The dashed dot curve shows the center of mass spectrum. The remnant of the Rayleigh peak is to be noted for...

---