Radiation, electromagnetic polarized

Optical activity is the ability of a compound to rotate the plane of polarized light. This property arises from an interaction of the electromagnetic radiation of polarized light with the unsymmetric electric fields generated by the electrons in a chiral molecule. The rotation observed will clearly depend on the number of molecules exerting their effect, i.e. it depends upon the concentration. Observed rotations are thus converted into specific rotations that are a characteristic of the compound according to the formula below. 

An electric or magnetic current or potential of alternating polarity will create radiating electromagnetic fields (EMFs). The frequency of alternation is a chief characteristic, and EMF is generated across an enormous range of frequencies. This frequency spectrum is shown in Fig. 22.5, with several common identifiers noted for certain bands. 

Some crystals polarize radiation electromagnetic waves transmitted through the crystal have electric field vectors that aU he in the same plane. What property of these crystals permits this ... 

If a beam of unpolarized electromagnetic radiation is transmitted in the z direction, the amplitudes of the components of the sinusoidally varying electric field in the x and y planes are identical. When the beam is passed through a polarizer, the component of the electric field in one plane is transmitted, as described in more detail in Chapter 12. For unoriented samples such as all gases and liquids and isotropic solids, the absorbance of all bands in the spectrum is independent of the orientation of the polarizer. If the molecules in a certain sample are preferentially oriented in a given direction, however, the component of the dynamic dipole moment derivative of each vibrational mode, d i./dQ, in the direction that the radiation is polarized will change as the polarizer is rotated. 

See also Chiroptical Spectroscopy, General Theory Electromagnetic Radiation Fluorescence Polarization and Anisotropy IR Spectroscopy, Theory Linear Dichroism, Applications Rayleigh Scattering and Raman Spectroscopy, Theory Symmetry in Spectroscopy, Effects of. 

In order to describe the second-order nonlinear response from the interface of two centrosynnnetric media, the material system may be divided into tlnee regions the interface and the two bulk media. The interface is defined to be the transitional zone where the material properties—such as the electronic structure or molecular orientation of adsorbates—or the electromagnetic fields differ appreciably from the two bulk media. For most systems, this region occurs over a length scale of only a few Angstroms. With respect to the optical radiation, we can thus treat the nonlinearity of the interface as localized to a sheet of polarization. Fonnally, we can describe this sheet by a nonlinear dipole moment per unit area, -P ", which is related to a second-order bulk polarization by hy P - lx, y,r) = y. Flere z is the surface nonnal direction, and the... 

Non-polarized electromagnetic radiation, of course, comprises two perpendicular polarizations, which can change both in amplipide and in phase with respect to each other. If the two polarizations are in phase with each other, the resultant is just another linearly polarized beam, with the resultant polarization direction given by a simple vector addition of the... 

Plane-polarized electromagnetic radiation showing the electric field, the magnetic field, and the direction of propagation. 

Electric field component of plane-polarized electromagnetic radiation. 

In the previous section we defined several characteristic properties of electromagnetic radiation, including its energy, velocity, amplitude, frequency, phase angle, polarization, and direction of propagation. Spectroscopy is possible only if the photon s interaction with the sample leads to a change in one or more of these characteristic properties. 

In the second broad class of spectroscopy, the electromagnetic radiation undergoes a change in amplitude, phase angle, polarization, or direction of propagation as a result of its refraction, reflection, scattering, diffraction, or dispersion by the sample. Several representative spectroscopic techniques are listed in Table 10.2. 

The plane of polarization is conventionally taken to be the plane containing the direction of E and that of propagation in Figure 2.1 this is the xy plane. The reason for this choice is that interaction of electromagnetic radiation with matter is more commonly through the electric component. 

Figure 2.1 Plane-polarized electromagnetic radiation travelling along the x axis Ey is the electric component is the magnetic component...

Concluding this section, two interesting variants of the STM should be addressed. The spin-polarized STM (SPSTM), which works with a ferromagnetic tip, can be used to probe surface magnetism with high resolution [5.47, 5.48]. Other modifications of the STM involve electromagnetic radiation, whereby two basic concepts can... 

So far we have only considered scalar interference, however, the vector nature of electromagnetic radiation can give rise to polarization interference... 

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