Oscillating electric dipole

The oscillating electric dipole density, P (the polarization), that is induced by the total incident electric field,... 

When monochromatic radiation falls on a molecular sample in the gas phase, and is not absorbed by it, the oscillating electric field E (see Equation 2.1) of the radiation induces in the molecule an electric dipole which is related to E by the polarizability... 

These are polarized along the z, x andy axes, respectively, since they involve and This means that when, for example, a — Aj transition occurs an oscillating electric dipole is set up along the x axis. 

In the context of discussion of the Raman effect, Equation (5.43) relates the oscillating electric field E of the incident radiation, the induced electric dipole fi and the polarizability a by... 

Fig. 1. An incident electromagnetic field of intensity, having an associated electric field, U, induces dipole oscillation in the absorbers. The transmitted...

The first term in the brackets represents a static electric field in the material and the second term represents a dipole oscillating at 2co, tvdce the frequency of the incident light. This is a process knovm as SHG. 

To obtain a clear understanding of electrodynamic bonding, start with the field of a static electric dipole. Then, let the dipole oscillate so it emits electromagnetic waves (photons). Consider what happens when the emitted field envelopes another dipole (London, 1937). Finally, determine the factors that convert neutral molecules into dipoles (that is, their polarizabilities). 

When the oscillating electric held of an incident light ray interacts with a molecule, a small oscillating dipole moment is induced in the molecule as a consequence of its polarisability, a. Polarisability itself is a measure of the change in the dipole moment of a molecule induced by an electric held, and in the simplest case, where the electric held E and induced dipole moment p are in the same direction ... 

The exciting radiation, usually laser light, may be of any wavelength. Interaction is not by absorption and only requires the presence of polarizable molecules. The oscillating electric field of the incident radiation E = E0 cos 27xut induces a dipole moment... 

A molecule must have a permanent dipole moment to be micro-wave active. As it rotates, the changing dipole moment interacts with the oscillating electric field of the electromagnetic radiation, resulting in absorption or emission of energy. This requirement means that homonuclear molecules such as H2 are microwave inactive, but heteronuclear molecules such as SO3, S02, NO and, of course, H20 are active. 

Due to the oscillahng nature of the local electric held, Eioc, an oscillating electric dipole moment p = —er is indnced. Taking into account that p = aEioc, a being the atomic polarizability (a relahon that holds for not very high local electric helds), and using Equation (4.13), we obtain ... 

Hyper)polarizabilities are defined as the coefficients in the Taylor series expansion of the dipole moment - or the energy - in the presence of static and/or oscillating electric fields ... 

The first term in eq. [21] is the contribution of the intrinsic rotational strengths if oscillators a and/or b are themselves chiral. The second term is the coupled oscillator contribution due to the intrinsic moments and the third term is the coupled oscillator contribution due to the geometric arrangement of the two electric dipole oscillators. The latter two contributions give rise to a conservative bisignate couplet in the observed spectrum, if the coupled modes are sufficiently separated in frequency such that the positive and negative contributions do not cancel. 

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