Rayleigh and Raman scatter

Figure 12.2 The relationships between IR absorption, Rayleigh, and Raman scattering.

Fig. 14.—Vibrational-energy Levels Rayleigh and Raman Scattering.

The optical measurements presented in the previous chapters can be used to either characterize local, microstractural properties or as probes of bulk responses to orientation processes. In either case, it is normally desirable to make the connection between experimental observables and their molecular or microstractural origins. The particular molecular properties that are probed will naturally depend on the physical interaction between the light and the material. This chapter explores molecular models and theories that describe these interactions and identifies the properties of complex materials that can be extracted from measurements of optical anisotropies. The presentation begins with a discussion of molecular models that are applied to polymeric materials. Using these models, optical phenomena such as birefringence, dichroism, and Rayleigh and Raman scattering are predicted. Models appropriate for particulate systems are also developed. 

Cheung CK, Jones DR, Wang CH. Single particle reorientation and pair correlations of methyl iodide solutions studied by depolarized Rayleigh and Raman scattering. J Chem Phys 1976 64 3567-3572. 

Fluorescence is generally more sensitive to environmental factors than absorbance measurements. Signal intensity may be affected by pH, temperature, quenching, interfering substances, solvent, or interference from Rayleigh and Raman scattering. Many fluorescent species contain ionisable groups whose fluorescent properties are sensitive to pH. In some cases only one of the ionised species may be fluorescent. An example is the barbiturates which only fluoresce at elevated pH in the di-anionic form. The relationship of fluorescence intensity with pH should always be examined as part of the development of the method. 

Figure 6 Energy transfer diagram illustrating Rayleigh and Raman scattering (top), and Raman spectra for CCfr excited at room (298 K) and hqnid-N2 (77 K) temperatures by Ar+ ion laser radiation of Xq = 488.0 nm or vo = 20 492 cm (bottom). The number above the peaks is the Raman shift, Av = vq — Wc cm. Since the fraction of molecules occupying excited states depends on the Boltzmann factor (kT = 207 cm at 298 K), the intensities of anti-Stokes bands fall off rapidly with decreasing temperature (kT = 54 cm at 77 K) and increasing vibrational frequency Vk...

Yu Z, Brus LE (2001) Rayleigh and Raman scattering from individual carbon nanotube bundles. J Phys Chem B 105(6) 1123-1134... 

G. C. Tabisz. Collision Induced Rayleigh and Raman Scattering. In R. F. Barrow, D. A. Long, and J. Sheridan (eds.) Specialist Periodical Report—Molecular Spectroscopy VI, Chemical Society, London, 1979, pp. 136-173. 

The first SMS experiments in 1989 utilized either of two powerful doublemodulation FM absorption techniques, laser frequency-modulation with Stark secondary modulation (FM-Stark) or frequency-modulation with ultrasonic strain secondary modulation (FM-US) [3,26]. The secondary modulation was required in order to remove the effects of residual amplitude modulation produced by the imperfect phase modulator. In contrast to fluorescence methods, Rayleigh and Raman scattering were unimportant. Figure 2.3B (specifically trace d) shows examples of the optical absorption spectrum from a single molecule of pentacene in p-terphenyl using the FM-Stark method. 

Time-resolved fluorimetry is also useful for the elimination of interferences from stray light caused by Rayleigh and Raman scatter. The latter phenomena occur on a time scale of because they have... 

Placzek, G. Rayleigh and Raman scattering, in Handbuch der Radiologie, Vol. 6, Part 2, (ed. Marx, E.) p. 205, Leipzig, Akademische Verlagsgesellschaft 1934... 

Systems involving two centers with fixed mutual orientation have been shown to exhibit other circular differential effects with a similar linear dependence on the separation. Examples include circular differential Rayleigh and Raman scattering (Barron and Buckingham 1974 Andrews and Thirunamachandran 1978), optical rotation (Barron 1975) and two-photon circular dichroism in which only one chromophore is excited (Andrews 1976). As might be expected, on performing subsequent rotational averages for the case where A and B are randomly oriented, the odd-j terms in the rate equations vanish and consequently no circular dichroism is displayed. 

Time-resolved fluorimetry is also useful for the elimination of interferences from stray light due to Rayleigh and Raman scatter. The latter phenomena occur on a time scale of l(r14-l(T13 s and, as they have a much shorter duration than lamp or laser pulses, the light associated with them can be eliminated from the signal that ultimately reaches the detector. Time-correlated single-photon counting is superior in its ability to resolve multiple fluorescence from the same solution. 

The relationship between second harmonic generation (SHG) and hyper-Raman scattering is similar to the relation between Rayleigh and Raman scatterings, in the case of two-photon... 

Long, M.B., Multi-Dimensional Imaging in Combusting Flows by Lorenz-Mie, Rayleigh and Raman Scattering, Instrumentation for Flows with Combustion (Taylor, A.M.P.K., ed.), Academic Press, 468-508 (1993). 

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