Light scattering inelastic. Raman effect

Cyvin, S. J., Rauch, J. E. and Decius, J. C. (1965) Theory of hyper-Raman effects (nonlinear inelastic light scattering) selection rules and depolarization ratios for the second-order polarizability. 

Inelastic scattering of light due to the excitation of vibrations had already been predicted in 1923 [37] and was confirmed experimentally a few years later by Raman [38], Because at that time the Raman effect was much easier to measure than infrared absorption, Raman spectroscopy dominated the field of molecular structure determination until commercial infrared spectrometers became available in the 1940s [10]. 

Inelastic photon scattering processes are also possible. In 1928, the Indian scientist C. V. Raman (who won the Nobel Prize in 1930) demonstrated a type of inelastic scattering that had already been predicted by A. Smekal in 1923. This type of scattering gave rise to a new type of spectroscopy, Raman spectroscopy, in which the light is inelastically scattered by a substance. This effect is in some ways similar to the Compton effect, which occurs as a result of the inelastic scattering of electromagnetic radiation by free electrons. 

Infrared and Raman spectroscopy are related by the fact that both permit the detection of bond vibrations. Like IR spectroscopy, the spectral bands are reported in cnT1. An important difference is that the wavelength and intensity of inelastically scattered light is measured in the Raman spectroscopic method. The Raman effect causes the scattered radiation to shift according to the energies of molecular vibrations. Although Raman spectroscopy involves a physical principle different from that in IR spectroscopy, the two techniques are complementary. 

Raman spectroscopy is based upon the Raman effect in which light, usually of visible wavelengths and chosen to be monochromatic, interacts with a sample to give rise to a small fraction of inelastically scattered radiation (of shifted frequencies). In... 

Fig. 8.12 The Raman effect. Monochromatic light of frequency vQ is scattered by a sample, either without losing energy (Rayleigh band) or inelastically, in which a vibration is excited (Stokes band), or a vibra-tionally excited mode in the sample is de-excited (anti-Stokes band). The spectrum is that of the light scattered by the sample. The energy level diagrams illustrate that the scattering process occurs via highly unstable states of high energy.

Table II Space- and Time-Resolved Measurements from Inelastic Light Scattering. All methods are suitable for nonequilibrium conditions. Here, RS refers to Raman scattering, CARS to coherent anti-Stokes Raman spectroscopy, and RIKES to Raman-induced Kerr effect.

The Raman technique is often applied for single crystals studies. The Raman effect occurs when a beam of monochromatic light with frequency o, passes through a crystal leading to inelastic scattering by the phonons of the crystal with frequency shifts coph of... 

The interactions of electromagnetic radiation with the vibrations of a molecule, either by absorption in the infrared region or by the inelastic scattering of visible light (Raman effect), occur with the classical normal vibrations of the system (Pauling and Wilson, 1935). The goal of our spectroscopic analysis is to show how the frequencies of these normal modes depend upon the three-dimensional structure of the molecule. We will therefore review briefly in this section the nature of the normalmode calculation more detailed treatments can be found in a number of references (Herzberg, 1945 Wilson etal., 1955 Woodward, 1972 Cali-fano, 1976). We will then discuss the component parts that go into such calculations. 

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