Absorption spectroscopy, lead compounds electronic transitions

Core-level spectroscopies are the appropriate tools to study the electronic distribution around free atoms and the changes induced in this distribution on condensation or on the formation of compounds involving other elements. These spectroscopies are also very useful to track the formation of clusters which finally coalesce to form well-defined solid phases. For the R, X-ray absorption spectroscopy is very useful because of the simplicity of the final multiplet structure, as the transitions obey dipole selection rules. Generally, two types of transitions are observed one in which the 4f electron participates in the transition and another in which it remains as a spectator. In the former case, a transition of a d electron to the empty f shell is involved. This leads to the formation of the nd 4f - d 4f + ( = 3,4) multiplets which are in fact finger prints of the R atom configurations. In the same way, the transitions from p levels scan the empty sd states of the conduction band. 

In normal Raman spectroscopy a sample is placed in a (monochromatic) laser beam and the very weak scattered light of lower frequency is studied. In such a study the colour of the laser light is usually chosen to be away from any absorption band of the sample because such a choice reduces the risk that the focused laser beam will destroy the sample by heating it. In the resonance Raman effect the laser beam colour is deliberately chosen to coincide with an absorption band—an electronic transition—of the sample. Whilst this may lead to the destruction of the sample, for favourable cases it leads to Raman scattering which is much stronger than normal. This, in turn, means that the laser power can be reduced, improving the chances of sample survival. The spectra obtained from compounds showing such a resonance Raman effect are both simpler and more complicated than normal Raman spectra. They are simpler because, often, only totally symmetric vibrational modes are seen. The reason for this is that if the electronic... 

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