Inelastic Raman scattering

Suppose that a combination tone involves a single excitation of modes of 11 and 11 symmetry. Then, since 

Consider a reduction in symmetry until all representations are reduced to 1 -D IRs. Then the character in any class can only be 1. Consequently, Qk is invariant under all the operators of the point group and so belongs to f, which correlates with the totally symmetric representation of the point symmetry group of the molecule. Therefore 7t2 Qk2 is invariant under any of the operators of the point group of the molecule. k 

In inelastic Raman scattering a photon loses (or gains) one quantum of rotational or vibrational energy to (or from) the molecule. The process involves the electric field of the radiation inducing an electric dipole in the molecule and so depends on the polarizability tensor of the molecule. (A (second-order) tensor is a physical quantity with nine components.) The induced electric dipole D is proportional to the electric field E  

Example 9.3-1 Determine the number of bands to be expected in the Raman spectrum of a planar ML3 molecule. 

From the character table for D3h, components of the polarizability form bases for the IRs A/, E, and E . From eq. (9.1.4) the normal coordinates form bases for the representations A/, 2E, and A2 . Therefore the Raman active modes are A/ and 2E, and there are three Raman bands, with two coincidences. (A coincidence means that a Raman band and an infra-red band have the same frequency.) 

---

As previously mentioned, the evanescent wave could interact with the optically rare medium not only by being absorbed but also by being scattered either elastically (Rayleigh Scattering) or inelastically (Raman Scattering). Because it is not within the scope of this paper to review the complete history and theory of Raman scattering, further information is indicated in Ref. 

Intensity of inelastically (Raman) scattered photons (i) as a function of the wavenumber separation (Raman shift) from the elastically (Rayleigh) scattered photons and (ii) as a function of the exciting radiation wavelengths (three-dimensional spectrum). 

Raman spectroscopy relies on inelastic (Raman) scattering of monochromatic light from a laser in the visible, near infrared, or near ultraviolet range. Raman spectroscopic techniques have historically failed to separate different black resins. SpectraCode [79]... 

In addition to ordinary inelastic Raman scattering, two additional resonance enhancement forms of Raman spectroscopy have proven useful for the study of polymers UV resonance Raman spectroscopy and surface-enhanced Raman spectroscopy. These two resonance techniques use conventional instrumentation but exhibit useful enhancement effects. 

---