Prediction of Electronic Transition Intensities

We now embark upon one of the more difficult of the concepts to be presented. We have already presented the types of poles possible without defining their nature. There are a variety of electronic transitions based upon the spacial configuration of the electrons involved. These interpolar interactions are responsible for transfer of electronic energy from site to site in the lattice. As shown below, there are dipole-dipole interactions, i.e.- dd as weU as dipole-quadrupole interactions, i.e.- dq . There are even quadrupole-quadrupole transitions. I.e. qq . 

Perhaps the easiest way to visualize this is to imagine a p-electron and its electronic density lobes in space, as shown in the following  

but the transition intensities will vaiy according to the type of pole interaction involved. Einstein (1903) was interested in this problem and defined many of the terms we use today. 

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