notes06-07-page245 - The light loses energy to the material...

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Among these functions are x , y, and z. So we can see immediately that the IR active modes of any molecule having this point group will be A 1 ,B 1 , and B 2 . The A 2 mode is IR forbidden and any vibrations having this symmetry will not appear in the IR spectrum (or it may appear as a very weak line). From before we know the modes of water have A 1 , and B 1 symmetry and hence are all IR active and appear in the IR spectrum 34.2. Raman Spectroscopy Raman spectroscopy is somewhat di f erent than IR spectroscopy in that vibra- tional frequencies are measured by way of inelastic scattering of high frequency (usually visible) light.
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Unformatted text preview: The light loses energy to the material in an amount equal to the vibrational energy of the molecules is the sample. This lose of energy shows up in the scattered light as a new down shifted frequency from that of the original input light frequency. Unlike IR absorption which is based on the electric dipole, Raman scattering is based on the polarizability of the molecule Roughly speaking the polarizability of a molecule determines how the electron density is distorted through interaction with an electromagnetic fi eld. 233...
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