Electric quadrupole radiation angular distribution

It is apparent that the angular distribution of electric quadrupole radiation is generally a rather complicated function of 0,<(> but a simple example will serve to illustrate the main features. We consider an oscillating spheroidal charge distribution. In this case the off-diagonal elements of the electric quadrupole moment tensor vanish because of the symmetry of the system. If the z-axis is taken as the axis of symmetry we have = Q22 since the tensor is... 

They quanta may carry away different angular momenta (L). IfL= 1,2,3,... the radiations are called dipole, quadrupole, octupole, etc., respectively. Gamma radiation with L = 0 does not exist because the electromagnetic waves have transversal nature (the photons have spin 1). Each multipolarity 2 is characterized by a specific angular distribution. The radiation may be electric or magnetic, depending on the term of the electromagnetic interaction that is responsible for the particular transition. 

The general expressions for the fields produced by an electric quadrupole source are of rather complicated form. However, we are mainly interested in the fields in the wave zone since this will enable us to discuss the angular distribution and total power radiated. When using B = curl A we therefore retain only the term which varies as 1/r. The magnetic field is found to have the following form ... 

For characterizing a dipolar molecule in its electronic ground state, few methods are more instructive than pulsed-nozzle Fourier-trans-form microwave spectroscopy (32). As illustrated schematically in Fig. 5, a short pulse of microwave radiation directed at the gas pulse excites a rotational transition in the species of interest subsequently the rotationally excited molecules reemit radiation, which is detected. This technique provides a remarkably sensitive probe for transients, the properties of which can be specified with all the precision and detail peculiar to rotational spectroscopy only microseconds after their production. In relation to a weakly bound adduct A --B formed by two molecular reagents A and B, for example, we may draw on the rotational spectrum to determine such salient molecular properties as symmetry, radial and angular geometry, the intermolecular stretching force constant and internal dynamics, the electric charge distribution, and the electric dipole and quadrupole moments of A -B (see Table I). 

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