Resonant Raman Scattering RRS

Higher-order effects in photon scattering are small in general, but cross sections may be strongly enhanced in the vicinity of resonances. The tunability of monochromatized synchrotron radiation makes it possible to 

Here k, El denote the binding energies of the K and L shells, respectively. 

The author thanks Professor H. Kleinpoppen and Professor H. O. Lutz for numerous discussions which stimulated his interest in synchrotron-based experiments. Special thanks go to Dr. G. Materlik, who made valuable comments on the manuscript. The manuscript was completed in March 1985. 

in Synchrotron Radiation, Techniques and Applications (edited by C. Kunz), Springer, Berlin (1979), pp. 1-23. 

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Figure Bl.3.5. Four WMEL diagrams for fiilly resonant Raman scattering (RRS). Diagrams (a) and (b) both have doorway stage rr(A.j2 ) (Figure B 1.3.4(a)), in which a vibrational coherence is created in the ground electronic state, g. For the window event in (a), field 1 promotes the bra from the ground electronic state, g, to...

The considerably more selective method is resonance Raman scattering (RRS). The selectivity of the method is due to the fact that the spectra display only vibrations associated with the electronic excitation of the chromophore being studied. After irradiation of the substance with monochromatic light of frequency v0 in its absorption band, in the scattering light narrow RRS bands are observed with frequencies shitted relative to v0. The origin of these bands is ascribed to the electronic transition from the excited level to the first vibrational level of the ground state. 

Conjugated chain vibrations are selectively enhanced. If side groups are attached to the chain, their vibrational Raman lines will not be enhanced. Thus simple resonance Raman scattering (RRS) spectra are often obtained, free of interference from the medium. 

As is well known, there is a qualitative and quantitative difference between normal Raman scattering (NRS) and resonance Raman scattering (RRS) for molecules in the bulk. The most prominent feature is the intense scattering in the resonance case, as compared to the scattering of a molecule not in resonance. In fact, the signals are so strong that extremely small quantities can be detected in the RRS case, even without the help of SERS (e.g., see Ref. 212). 

The normal Raman scattering (NRS) regime is defined by the condition hfi>L (E — Ej). Resonance Raman scattering (RRS) is defined by the condition hoL (Ee — Ej). In RRS the value of dcr/dQ corresponding to the by resonance enhanced value of can be 10 to 10 times greater than in the corresponding NRS case. 

Raman scattering cross sections of typical adsorbates are low, therefore two fundamental techniques were elaborated to enhance them resonance Raman scattering (RRS) and surface-enhanced Raman scattering (SERS) [125-127]. 

In this paper, we present a comparative study of polyaromatics or polyheteroaromatics by means of Resonant Raman Scattering (RRS). Although a larger number of these compounds exhibit a very intense fluorescence, hiding, in some cases, the Raman signal, our capability to choose excitation lines from the near U.V. (X[Pg.375]

However, Raman spectrum shows weak signal intensity compared with conventional Rayleigh scattering and fluorescence, which is a widely used technique for molecular detection. Raman scattering cross-sections imply that the scattering intensities are between 10 and 10 cm/molecule (for comparison, the maximum fluorescence cross-section is 10 cm /molecule). Resonance Raman scattering (RRS) can increase the cross-section when a molecule is excited by a laser with a resonance frequency. However, RSS still has an insufficient... 

This article describes the elements of Raman spectrometers for routine analyses which are available commercially. Instruments designed only for special research are not covered. Only spectrometers for classical (linear) Raman scattering are mentioned, not those for observing resonance Raman scattering (RRS), surface-enhanced Raman scattering (SERS) and all nonlinear Raman techniques they are described elsewhere in this Encyclopedia. 

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