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Raman spectroscopy of polymers
Chapter 5
Raman spectroscopy of polymers
In the previous chapters, IR spectroscopy of polymers was discussed. In this chapter, a complementary technique that also measures the vibrational energy levels, Raman spectroscopy, will be examined. As discussed in Chapter 2, there is a fundamental difference in the IR and Raman techniques. IR spectroscopy depends on a change in the permanent dipole moment of the chemical bond or molecule with the vibrational normal mode in order to produce absorption. Raman spectroscopy, on the other hand, depends on a change in the induced dipole moment or polarization to produce Raman scattering. This difference in the physical nature of the selection rules may seem minor, but it plays a major role in the manner in which the two vibrational techniques are used for the study of polymers.
The nature of Raman scattering spectroscopy In the first paragraph of the paper by C.V. Raman and K.S. Krishnan [1] in which they introduce this technique, they state If we assume that the X-ray scattering of the 'unmodified' type observed by Professor Compton corresponds to the normal or average state of the atoms and molecules, while the 'modified' scattering of altered wavelength corresponds to their fluctuations from that state, it would follow that we should expect also in the case of ordinary light two types of scattering, one determined by the normal optical properties of the atoms or molecules, and another representing the effect of their fluctuations from their normal state. It accordingly becomes necessary to test whether this is actually the case... The results of these tests led to the following statement later in the paper: Some sixty different common liquids have been examined in this way, and every one of them showed the effect in greater or less degree. Thus, the technique we now call the Raman effect was first observed.
Raman spectroscopy of polymers
In the previous chapters, IR spectroscopy of polymers was discussed. In this chapter, a complementary technique that also measures the vibrational energy levels, Raman spectroscopy, will be examined. As discussed in Chapter 2, there is a fundamental difference in the IR and Raman techniques. IR spectroscopy depends on a change in the permanent dipole moment of the chemical bond or molecule with the vibrational normal mode in order to produce absorption. Raman spectroscopy, on the other hand, depends on a change in the induced dipole moment or polarization to produce Raman scattering. This difference in the physical nature of the selection rules may seem minor, but it plays a major role in the manner in which the two vibrational techniques are used for the study of polymers.
The nature of Raman scattering spectroscopy In the first paragraph of the paper by C.V. Raman and K.S. Krishnan [1] in which they introduce this technique, they state If we assume that the X-ray scattering of the 'unmodified' type observed by Professor Compton corresponds to the normal or average state of the atoms and molecules, while the 'modified' scattering of altered wavelength corresponds to their fluctuations from that state, it would follow that we should expect also in the case of ordinary light two types of scattering, one determined by the normal optical properties of the atoms or molecules, and another representing the effect of their fluctuations from their normal state. It accordingly becomes necessary to test whether this is actually the case... The results of these tests led to the following statement later in the paper: Some sixty different common liquids have been examined in this way, and every one of them showed the effect in greater or less degree. Thus, the technique we now call the Raman effect was first observed.