Polarization (waves) - Polarization in Nature, Science, and Technology - Chemistry

Chemistry

Polarization is principally of importance in chemistry due to circular dichroism and "optical rotation" (circular birefringence) exhibited by optically active (chiral) molecules. It may be measured using polarimetry.

The term "polarization" may also refer to the through-bond (inductive or resonant effect) or through-space influence of a nearby functional group on the electronic properties (e.g., dipole moment) of a covalent bond or atom. This concept is based on the formation of an electric dipole within a molecule, which is related to polarization of electromagnetic waves in infrared spectroscopy. Molecules will absorb infrared light if the frequency of the bond vibration is resonant with (identical to) the incident light frequency, where the molecular vibration at hand produces a change in the dipole moment of the molecule. In some nonlinear optical processes, the direction of an oscillating dipole will dictate the polarization of the emitted electromagnetic radiation, as in vibrational sum frequency generation spectroscopy or similar processes.

Polarized light does interact with anisotropic materials, which is the basis for birefringence. This is usually seen in crystalline materials and is especially useful in geology (see above). The polarized light is "double refracted", as the refractive index is different for horizontally and vertically polarized light in these materials. This is to say, the polarizability of anisotropic materials is not equivalent in all directions. This anisotropy causes changes in the polarization of the incident beam, and is easily observable using cross-polar microscopy or polarimetry. The optical rotation of chiral compounds (as opposed to achiral compounds that form anisotropic crystals), is derived from circular birefringence. Like linear birefringence described above, circular birefringence is the "double refraction" of circular polarized light.

Read more about this topic:  Polarization (waves), Polarization in Nature, Science, and Technology

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